Public Key Infrastrucure-thesis

International University of Africa

Faculty of computer studies

Chapter One

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Public key Infrastructure

by

Muhedin Abdullahi Mohammed

International University of Africa

1.1

Faculty of computer studies

Introduction Computers and use of the Internet have fostered new interest in

cryptography partly due to the new emphasis on personal privacy. Little is realized that in our efforts to make it easy for computers to share stuff, it would make it easy for other people to see all of our personal stuff, too. Perhaps you’ve discovered for yourself that it is far too easy for unknown persons to read your email, private documents, love letters, financial information, and so on. The Internet is truly the Global Village, a village where everyone can see what you do and hear what you say. The good news is that you can use cryptography to protect yourself from the eavesdroppers and Peeping Toms of the village. Not only can cryptography scramble your files, but it can also be used to prove who you are (and maybe who you aren’t!). Cryptography can be used to alert you if the contents of a file have been changed, attest to the identity of the person who sent you a message, keep online communications safe and secure, and, of course, hide important data. And the best news of all is that not every cryptographic solution is expensive, and you don’t need to be a rocket scientist to incorporate crypto solutions into your network. Because cryptography is usually associated with spies, secret messages, and clandestine meetings, you might have thought that cryptography stopped being used at the end of the Cold War. Believe it or not, its use is actually on the rise. We think that’s partially due to more awareness of personal identity theft and also because more is being written in the media about how data needs more protection that a common PC gives you. [1]

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Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

1.2

Faculty of computer studies

What is Cryptography? Everyone has secrets; some have more than others. When it becomes

necessary to transmit those secrets from one point to another, it's important to protect the information while it's in transit. Cryptography, which is the art of keeping messages secure, presents various methods for taking legible, readable data, and transforming it into unreadable data for the purpose of secure transmission, and then using a key to transform it back into readable data when it reaches its destination. [2] The best way to prevent the misuse of critical information is to convert into a form that is unintelligible to a person who gains unauthorized access to it. The Egyptians were among the first people to develop a technique that was used to disguise important information. This technique is called cryptography. Cryptography is an art of converting information into a secret code that can be interpreted only by a person who knows how to decode The process of distinguishing information into an unintelligible form is known as encryption. The information that needs to be distinguished is called plaintext. The encrypted information is called ciphertext. After the encrypted information reaches its destination it has to be converted into a plaintext so that the information is intelligible. The process of converting ciphertext into plaintext is known as decryption. Encryption and decryption require the use of some secret information, usually referred to as a key. Depending on the encryption mechanism used, the same key might be used for both encryption and decryption; in such a case the mechanism is known as secret key cryptography. While for other

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Public key Infrastructure

by

Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

mechanisms, the keys used for encryption and decryption might be different and that is known as public key cryptography [3]

Fig 1.1: process of cryptography [4]

Predating computers by thousands of years, cryptography has its roots in basic transposition ciphers, which assigns each letter of the alphabet a particular value. A simple example is to assign each letter a progressively higher number, where A=1, B=2, and so forth. Using this formula for example, the word "Islam", once encrypted, would read "9 19 12 1 13". The Secure Sockets Layer (SSL) is a common encryption protocol used in ecommerce. When you make a purchase over the Internet, this is the technology the merchant uses to make sure you can safely transmit your credit card information. Using this protocol, your computer and the online merchant's computer agree to create a type of private "tunnel" through the public Internet. This process is called the "handshake." When you see a URL in your Web browser that starts with "https" instead of "http", it is a secure connection that is using SSL. The goal of cryptography extends beyond merely making data unreadable, it also extends into user authentication that is, providing the recipient with assurance that the encrypted message originated from a trusted source. 4

Public key Infrastructure

by

Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

The study of cryptography is advancing steadily, and scientists are rapidly creating mechanisms that are more difficult to break. The most secure type of cryptography yet may be quantum cryptography, a method that has not yet been perfected, which instead of using a key, relies on the basic laws of physics, and the movement and orientation of photons to establish a connection that is absolutely secure and unbreakable. . [2]

Cryptography is the art of secret writing.

1.3 Types of Cryptography Cryptography has been implemented in many ways. During war times, messages were encoded in a number of ways. The methods ranged from writing hidden messages in musical score to the arrangement of the 52 cards in a pack so that their order of placement represents specific information. Now cryptography is used in information technology, it is also used in computations in different ways. There are several ways of classifying cryptographic algorithms. For purposes of this research, they will be categorized based on the number of keys that are employed for encryption and decryption, and further defined by their application and use. The three types of cryptography that will be discussed are:-[3] 1. Private (secret) Key Cryptography (SKC). 2. Public Key Cryptography (PKC). 5

Public key Infrastructure

by

Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

3. Hash functions.

1.3.1 Private Key Cryptography Most cryptography techniques are key based. A key is a mathematical value that is attached to plaintext. This key has a formula that encrypts or decrypts the information. With private key cryptography also known as secret key cryptography (SKC), a single key is used for both encryption and decryption. As shown in Figure 1.2, the sender uses the key to encrypt the plaintext and sends the ciphertext to the receiver. The receiver applies the same key to decrypt the message and recover the plaintext. Because a single key is used for both functions, secret key cryptography is also called symmetric encryption. With this form of cryptography, it is obvious that the key must be known to both the sender and the receiver; that, in fact, is the secret. The biggest difficulty with this approach, of course, is the distribution of the key. Secret key cryptography schemes are generally categorized as being either stream ciphers or block ciphers. Stream ciphers operate on a single bit at a time and implement some form of feedback mechanism so that the key is constantly changing. A block cipher is so-called because the scheme encrypts one block of data at a time using the same key on each block. In general, the same plaintext block will always encrypt to the same ciphertext when using the same key in a block cipher whereas the same plaintext will encrypt to different ciphertext in a stream cipher.

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Public key Infrastructure

by

Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

Stream ciphers come in several flavors but two are worth mentioning here. Self-synchronizing stream ciphers calculate each bit in the keystream as a function of the previous n bits in the keystream. It is termed "self-synchronizing" because the decryption process can stay synchronized with the encryption process merely by knowing how far into the n-bit keystream it is. One problem is error propagation; a garbled bit in transmission will result in n garbled bits at the receiving side. Synchronous stream ciphers generate the keystream in a fashion independent of the message stream but by using the same keystream generation function at sender and receiver. While stream ciphers do not propagate transmission errors, they are, by their nature, periodic so that the keystream will eventually repeat. Block ciphers can operate in one of several modes; the following four are the most important: 

Electronic Codebook (ECB) mode is the simplest, most obvious application: the secret key is used to encrypt the plaintext block to form a ciphertext block. Two identical plaintext blocks, then, will always generate the same ciphertext block. Although this is the most common mode of block ciphers, it is susceptible to a variety of brute-force attacks.



Cipher Block Chaining (CBC) mode adds a feedback mechanism to the encryption scheme. In CBC, the plaintext is exclusively-ORed (XORed) with the previous ciphertext block prior to encryption. In this mode, two identical blocks of plaintext never encrypt to the same ciphertext.



Cipher Feedback (CFB) mode is a block cipher implementation as a selfsynchronizing stream cipher. CFB mode allows data to be encrypted in units smaller than the block size, which might be useful in some applications such as encrypting interactive terminal input. If we were using 1-byte CFB mode, 7

Public key Infrastructure

by

Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

for example, each incoming character is placed into a shift register the same size as the block, encrypted, and the block transmitted. At the receiving side, the ciphertext is decrypted and the extra bits in the block (i.e., everything above and beyond the one byte) are discarded. 

Output Feedback (OFB) mode is a block cipher implementation conceptually similar to a synchronous stream cipher. OFB prevents the same plaintext block from generating the same ciphertext block by using an internal feedback mechanism that is independent of both the plaintext and ciphertext bitstreams.

Fig 1.2 Secret Key Cryptography

Secret key cryptography algorithms that are in use today include: 

Data Encryption Standard (DES): The most common SKC scheme used today, DES was designed by IBM in the 1970s and adopted by the National Bureau of Standards (NBS) [now the National Institute for Standards and Technology (NIST)] in 1977 for commercial and unclassified government applications. DES is a block-cipher employing a 56-bit key that operates on 64-bit blocks. DES has a complex set of rules and transformations that were designed specifically to yield fast hardware implementations and slow software implementations, although this latter point is becoming less 8

Public key Infrastructure

by

Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

significant today since the speed of computer processors is several orders of magnitude faster today than twenty years ago. 

Advanced Encryption Standard (AES): the Advanced Encryption Standard, became the official successor to DES in December 2001. AES uses an SKC scheme called Rijndael, a block cipher designed by Belgian cryptographers Joan Daemen and Vincent Rijmen. The algorithm can use a variable block length and key length; the latest specification allowed any combination of keys lengths of 128, 192, or 256 bits and blocks of length 128, 192, or 256 bits. NIST initially selected Rijndael in October 2000 and formal adoption as the AES standard came in December 2001.



Blowfish: A symmetric 64-bit block cipher invented by Bruce Schneier; optimized for 32-bit processors with large data caches, it is significantly faster than DES on a Pentium/PowerPC-class machine. Key lengths can vary from 32 to 448 bits in length. Blowfish, available freely and intended as a substitute for DES or IDEA, is in use in over 80 products.[5]

Private Key cryptography is very efficient in terms of processing speed and using minimal computing resources, but has two limiting security problems:o First, how can two individuals who are interacting for the first time over an insecure network (such as the Internet) exchange a symmetric key securely? If the individuals tried to transmit the symmetric key over the insecure network, intending to encrypt information with it in subsequent communications, an attacker could intercept it key while in transit and use it to intercept and decrypt the later messages that the individuals hoped to keep confidential. Alternatively, an attacker could perform processes of his own with the symmetric key to make it appear as if a message written by the

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Public key Infrastructure

by

Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

attacker had actually originated from the one of the individuals trying to communicate over the insecure network. o Second, since both the ―sender‖ and the ―receiver‖ of a message share the

same symmetric key, the authentication and integrity is not provable to a third party who does not also hold the key. Thus, while the authentication and integrity of a message may be sufficient between two trusted individuals, the sender could deny, or repudiate, the message. In general, symmetric cryptography cannot provide the additional security sever called non-repudiation. [3]

1.3.2 Public-Key Cryptography Public-key cryptography has been said to be the most significant new development in cryptography in the last 300-400 years. Modern PKC was first described publicly by Stanford University professor Martin Hellman and graduate student Whitfield Diffie in 1976. Their paper described a two-key crypto system in which two parties could engage in a secure communication over a non-secure communications channel without having to share a secret key. PKC depends upon the existence of so-called one-way functions, or mathematical functions that are easy to compute whereas their inverse function is relatively difficult to compute. Let us give you two simple examples: 1. Multiplication vs. factorization: Suppose we tell you that we have two numbers, 9 and 16, and that we want to calculate the product; it should take almost no time to calculate the product, 144. Suppose instead that we tell you that we have a number, 144, and we need you tell us which pair of integers we multiplied together to obtain that number. You will eventually 10

Public key Infrastructure

by

Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

come up with the solution but whereas calculating the product took milliseconds, factoring will take longer because you first need to find the 8 pair of integer factors and then determine which one is the correct pair. 2. Exponentiation vs. logarithms: Suppose we tell you that we want to take the number 3 to the 6th power; again, it is easy to calculate 3 6=729. But if we tell you that we have the number 729 and want you to tell us the two integers that we used, x and y so that logx 729 = y, it will take you longer to find all possible solutions and select the pair that we used. While the examples above are trivial, they do represent two of the functional pairs that are used with PKC; namely, the ease of multiplication and exponentiation versus the relative difficulty of factoring and calculating logarithms, respectively. The mathematical "trick" in PKC is to find a trap door in the one-way function so that the inverse calculation becomes easy given knowledge of some item of information. Generic PKC employs two keys that are mathematically related although knowledge of one key does not allow someone to easily determine the other key. One key is used to encrypt the plaintext and the other key is used to decrypt the ciphertext. The important point here is that it does not matter which key is applied first, but that both keys are required for the process to work (Figure 1.3). Because a pair of keys is required, this approach is also called asymmetric cryptography. In PKC, one of the keys is designated the public key and may be advertised as widely as the owner wants. The other key is designated the private key and is never revealed to another party. It is straight forward to send messages under this scheme. Suppose Ali wants to send Mohamed a message. Ali encrypts some information using Mohamed's public key; Mohamed decrypts the ciphertext using 11

Public key Infrastructure

by

Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

his private key. This method could be also used to prove who sent a message; Ali, for example, could encrypt some plaintext with his private key; when Mohamed decrypts using Ali's public key, he knows that Ali sent the message and Ali cannot deny having sent the message (non-repudiation).

Fig 1.3 Public Key Cryptography

Public-key cryptography algorithms that are in use today for key exchange or digital signatures include: 

RSA: The first, and still most common, PKC implementation, named for the three mathematicians who developed it — Ronald Rivest, Adi Shamir, and Leonard Adleman. RSA today is used in hundreds of software products and can be used for key exchange, digital signatures, or encryption of small blocks of data. RSA uses a variable size encryption block and a variable size key. The key-pair is derived from a very large number, n, that is the product of two prime numbers chosen according to special rules; these primes may be 100 or more digits in length each, yielding an n with roughly twice as many digits as the prime factors. The public key information includes n and a derivative of one of the factors of n; an attacker cannot determine the prime factors of n (and, therefore, the private key) from this information alone and that is what makes the RSA algorithm so secure. Some descriptions of PKC erroneously state that RSA's safety is due to the difficulty in factoring large prime numbers. In fact, large prime numbers, 12

Public key Infrastructure

by

Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

like small prime numbers, only have two factors! The ability for computers to factor large numbers, and therefore attack schemes such as RSA, is rapidly improving and systems today can find the prime factors of numbers with more than 200 digits. Nevertheless, if a large number is created from two prime factors that are roughly the same size, there is no known factorization algorithm that will solve the problem in a reasonable amount of time. Regardless, one presumed protection of RSA is that users can easily increase the key size to always stay ahead of the computer processing curve. As an aside, the patent for RSA expired in September 2000 which does not appear to have affected RSA's popularity one way or the other. 

Diffie-Hellman: After the RSA algorithm was published, Diffie and Hellman came up with their own algorithm. D-H is used for secret-key key exchange only, and not for authentication or digital signatures.



ElGamal: Designed by Taher Elgamal, a PKC system similar to DiffieHellman and used for key exchange.[5]

It is worth mentioning that there are some advantages and disadvantages For PKC over SKC among which are the following:o Increased security is one the most important advantages of public key cryptography over secret key cryptography. This is because public key cryptography uses both public key and private key for encryption. The private key is known only to the owner of the key and the public key is shared with authorized users. In secret key cryptography only the public key is used for encryption. This public key is sent over the network to be shared with the other users. While being transferred any intruder can track and misuse it. 13

Public key Infrastructure

by

Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

o Another advantage of public key cryptography is that it ensures nonrepudiation. This is possible because the owners use their private keys, which is only known to them, to encrypt information. Any information signed by that key is safe because no one other than the intended recipient knows about the private key therefore the sender can not deny sending the information. In the case of secret key cryptography the public key is not secret; therefore the sender can deny it sending the message. This is because the public key can be hacked and used by intruders for transactions. o One disadvantage of public key cryptography is that it is slower than the

secret key cryptography, this is because, in the public key cryptography the sender has to first obtain the intended receiver’s public key to send information .[3]

1.3.3 Hash functions Hash function is mathematical algorithm. There is no concept of keys in the hash functions. A hash function accepts information as data attaches a value to this information and sends it. The most important advantage of the hash function is that no one can tamper with the information that is transmitted this technique. This is because the hash function is one-way cryptography technique. A hash function is said to be one-way because even if the output of a hash function is known, it is impossible to determine the input that constitutes the original information. For example, if data X is encrypted using a hash function to generate a value, Y, it is impossible to recover the value of X if Y is known. Hash functions are used to create signatures. These signatures are used to authenticate users. A hash function is also used to protect passwords; specially UNIX systems apply the hash function to user’s password and store the hash value and not the 14

Public key Infrastructure

by

Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

password itself. To authenticate the user a password is requested and the response runs through a hash function to generate the hash value. If the user supplies the correct password and is authenticated, the resulting hash value is the same as the stored value. The hash function is irreversible, which implies that obtaining the hash value doesn’t reveal the password to an attacker. Hash functions can be used to generate signatures. Assume that both the sender and the recipient of some data share a public key then by combining the data message with the public key, and running it through hash function, a signature is generated in the form of a hash value. The data message is transmitted with the signature.The recipient combines the received message the public key to generate a hash value. If the hash value is identical with the hash value that was sent with data message, it implies that the data signatures are identical. In this way the authenticity of the message is verified.[3]

Fig 1.4 hash function [5]

Hash algorithms that are in common use today include: 

Message Digest (MD) algorithms: A series of byte-oriented algorithms that produce a 128-bit hash value from an arbitrary-length message. o

MD2: Designed for systems with limited memory, such as smart cards. 15

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa o

Faculty of computer studies

MD4: Developed by Rivest, similar to MD2 but designed specifically for fast processing in software.

o

MD5: Also developed by Rivest after potential weaknesses were reported in MD4; this scheme is similar to MD4 but is slower because more manipulation is made to the original data. MD5 has been implemented in a large number of products although several weaknesses in the algorithm were demonstrated by German cryptographer Hans Dobbertin in 1996.



Secure Hash Algorithm (SHA): Algorithm for NIST's Secure Hash Standard (SHS). SHA-1 produces a 160-bit hash value and describes five algorithms in the SHS: SHA-1 plus SHA-224, SHA-256, SHA-384, and SHA-512 which can produce hash values that are 224, 256, 384, or 512 bits in length, respectively Hash functions are sometimes misunderstood and some sources claim that

no two files can have the same hash value. This is, in fact, not correct. Consider a hash function that provides a 128-bit hash value. There are, obviously, 2128 possible hash values. But there are a lot more than 2128 possible files. Therefore, there have to be multiple files — in fact, there have to be an infinite number of files! — that can have the same 128-bit hash value. The difficulty is finding two files with the same hash! What is, indeed, very hard to do is to try to create a file that has a given hash value so as to force a hash value collision — which is the reason that hash functions are used extensively for information security and computer forensics applications. Alas, researchers in 2004 found that practical collision attacks could be launched on MD5, SHA-1, and other hash algorithms. At this time, there is no obvious successor to MD5 and 16

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

SHA-1 that could be put into use quickly; there are so many products using these hash functions that it could take many years to flush out all use of 128- and 160-bit hashes. . [5] PGP uses a cryptographically strong hash function on the plaintext the user is signing. This generates a fixed-length data item known as a message digest. (Again, any change to the information results in a totally different digest.) Then PGP uses the digest and the private key to create the ―signature.‖ PGP transmits the signature and the plaintext together. Upon receipt of the message, the recipient uses PGP to recompute the digest, thus verifying the signature. PGP can encrypt the plaintext or not; signing plaintext is useful if some of the recipients are not interested in or capable of verifying the signature. As long as a secure hash function is used, there is no way to take someone's signature from one document and attach it to another, or to alter a signed message in any way. The slightest change in a signed document will cause the digital signature verification process to fail. The figure below shows the process [4]

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Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

Fig 1.5 PGP uses Hash function [4]

1.4

Digital Cryptography Basics This section introduces a number of basic building blocks of modern digital

cryptography, describes what they can do for you, and explains how to compose them to produce useful and practical secure services. [6]

1.4.1 Message Digests Message digest functions convert sequences of bits, possibly quite long, called messages, into fixed-length binary "fingerprints" or message digests of the original sequences. See Figure 1.6. A message digest function has two goals: 

It should be computationally infeasible to find another message whose digest is the same as the digest of a given message. 18

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa 

Faculty of computer studies

It should be computationally infeasible to find two arbitrary messages whose digests are the same.

Fig 1.6 Message digest function

In the common case where an authentication method takes a large amount of computational effort and that effort is proportional to the number of bits being authenticated, you can secure a large document by authenticating its much smaller fixed-size message digest. A message digest function is not identical to a checksum. A checksum is usually quite simple and is designed to detect transmission errors or accidental changes. An adversary can deliberately circumvent the testing of a checksum by adjusting the message to leave the checksum unchanged. By comparison, a message digest is complex and is designed to defeat attempts by an adversary to change the message. First, consider a checksum calculated by simply adding all octets in a message and discarding the bits of the sum above the least significant eight bits. In most cases, an adversary could easily modify the message to become a different message with the same checksum. For example, inserting an octet with value V

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Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

into the message will have no effect on the checksum if you can also insert a second octet with value (256 - V) anywhere in the message. Next, consider a more complex function in which you take the product of the octets in the message, adding to each octet its position in the message, and the check octet is the middle eight bits of this product. For example, if the message consists of bytes with values

Then the check octet is the middle eight bits of

With this level of complexity, it is no longer quite so trivial for an adversary to figure out how to change the message without changing the check byte, although it can still be done. Cryptographically or computationally secure message digest functions are substantially more complex than this example, producing check quantities of at least 128 bits or 16 eight-bit bytes. They largely meet the following goals. Expressing the goals of message digests more formally, if the message digest is N bits, then 1. To find a second message with the same message digest as a given message, no method should require an expected effort significantly less than trying 2 N1

possible other messages;

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Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

2. To find two arbitrary messages with the same message digest, no method should require an expected effort significantly less than trying 2 N/2 messages, remembering all their digests, and looking for a match. Like other modern digital cryptographic functions, message digest functions are typically used and sometimes defined only for integer numbers of octets, rather than arbitrary numbers of bits [6]

1.4.2 Message Authentication Codes A message authentication code (MAC) function computes a MAC from a message and a secret key. If the originator and the receiver share knowledge of that secret key, the receiver can calculate the same function of the message and secret key and see if it matches the MAC accompanying the message. See figure 1.7.If the MAC matches, then you know, within the strength of the MAC function and key, that some program with possession of the secret produced the MAC. Of course, every program that can verify the MAC needs to know this secret. Thus all of them can create valid MACs even if they should only receive and verify these codes.

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Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

Fig 1.7 Message authentication codes

A simple MAC function might append the secret to the message, then calculate a message digest of the result and use it as the MAC. The message (without the secret) and MAC could then be sent to the recipient. The recipient would also append the secret (which the receiver needs to know as well) to the message and calculate the same message digest function. If the resulting digest matches the MAC, it validates the message. A difficulty with MAC authentication in a system with multiple originators and receivers is that you must choose between two strategies, both of which have problems: 1. Have a different secret for every pair of entities. This method is logistically difficult because the number of keys increases with the square of the number of entities and the keys must be securely distributed. If the system includes

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Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

E number of entities, you have E*(E – 1)/2 pairs. For example, for 100 entities, you have 4950 pairs. For 1000 entities, you have 499,500 pairs. 2. Share one secret among all the entities. This technique is relatively insecure. The more entities that have a secret, the more likely the secret is to be compromised due to loss, subversion, or betrayal. This technique also means the same secret will be used many times; the more exposures of the uses of a secret, the easier an adversary may find it to break that secret analytically. In addition, with this strategy any of the entities can forge messages from any of the other entities and a recipient will be unable to detect this fraud based on the MAC. As with message digest functions, if a strong MAC is N bits long, the difficulty of finding two messages with the same MAC is proportional to 2 N/2. You should pick N large enough for your application and then, to avoid the secret quantity being the weak point, use a secret quantity that is random and at least N/2 bits long. For example, if you need a 160-bit MAC, the secret key should be at least 80 random bits. [6]

1.4.3 Digital Signatures You can use public key authentication to produce "digital signatures" These

signatures

have

a

very

desirable

characteristic—namely,

it

is

computationally infeasible for anyone without the private key to produce a signature that will verify for a given message. Modern digital signatures consist of (1) a message and (2) a message digest of that message asymmetrically transformed under a private key of the signer. See Figure 1.8

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Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

Fig 1.8 Digital signature

A typical implementation of digital signature involves a message-digest, a private key for encrypting the message digest, and a public-key for decrypting the message digest. The digital signature procedure is as follows:  The sender. The software used by the sender computes; using a standard algorithm, a ―message digest‖ from the message. The message digest is unique to the original message in that only the original, unmodified message could have produced the message digest. The sender then encrypts the message digest with his private key, yielding an encrypted message digest. 24

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

He sends the message and the encrypted message digest to a recipient. The two parts together form the digitally signed message.  The recipient. The recipient decrypts the received message digest with the signer’s public key. The recipient then computes a message digest from the received message using the same algorithm as the signer. He then compares the decrypted received message digest to the computed message digest. If the two are the same, he accepts the message.The recipient knows that the signer has sent the message because only the sender’s public key will work. However, it still remains that a particular public key be unquestionably associated with a particular individual or organization.[6]

1.5

Cryptanalysis Cryptanalysis is the study of methods for obtaining the meaning of

encrypted information, without access to the secret information which is normally required to do so. Typically, this involves finding the secret key. In non-technical language, this is the practice of code-breaking or cracking the code, although these phrases also have a specialized technical meaning. Even though the goal has been the same, the methods and techniques of cryptanalysis have changed drastically through the history of cryptography, adapting to increasing cryptographic complexity, ranging from the pen-and-paper methods of the past, through machines like Enigma in World War II, to the computer-based schemes of the present. The results of cryptanalysis have also changed it is no longer possible to have unlimited success in code breaking, and there is a hierarchical classification of what constitutes a rare practical attack. In the mid-1970s, a new class of cryptography was introduced: asymmetric cryptography. Methods for breaking these cryptosystems are typically radically 25

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

different from before, and usually involve solving carefully-constructed problems in pure mathematics, the best-known being integer factorization. [7]

1.5.1 Classical cryptanalysis Although the actual word "cryptanalysis" is relatively recent methods for breaking codes and ciphers are much older. The first known recorded explanation of cryptanalysis was given 9th century by Arabian polymath Abu Yusuf Yaqub ibn Ishaq al-Sabbah Al-Kindi in A Manuscript on Deciphering Cryptographic Messages. This treatise includes a description of the method of frequency analysis. Frequency analysis is the basic tool for breaking most classical ciphers. In natural languages, certain letters of the alphabet appear more frequently than others; in English, "E" is likely to be the most common letter in any sample of plaintext. Similarly, the digraph "TH" is the most likely pair of letters in English, and so on. Frequency analysis relies on a cipher failing to hide these statistics. For example, in a simple substitution cipher (where each letter is simply replaced with another), the most frequent letter in the ciphertext would be a likely candidate for "E". In practice, frequency analysis relies as much on linguistic knowledge as it does on statistics, but as ciphers became more complex, mathematics became more important in cryptanalysis.[7]

1.5.2 Modern cryptanalysis Even though computation was used to great effect in cryptanalysis in World War II, it also made possible new methods of cryptography orders of magnitude more complex than ever before. Taken as a whole, modern cryptography has 26

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

become much more impervious to cryptanalysis than the pen-and-paper systems of the past, and now seems to have the upper hand against pure cryptanalysis. In industry, ciphers are not free from flaws: for example, the A5/1, A5/2 and CMEA algorithms, used in mobile phone technology, can all be broken in hours, minutes or even in real-time using widely-available computing equipment. [7]

1.6 Key Concepts A key is a value that works with a cryptographic algorithm to produce a specific ciphertext. Keys are basically really, really, really big numbers. Key size is measured in bits; the number representing a 1024-bit key is darn huge. In public key cryptography, the bigger the key, the more secure the ciphertext. However, public key size and conventional cryptography’s secret key size are totally unrelated. A conventional 80-bit key has the equivalent strength of a 1024-bit public key. A conventional 128-bit key is equivalent to a 3000-bit public key. Again, the bigger the key, the more secure, but the algorithms used for each type of cryptography are very different and thus comparison is like that of apples to oranges. While the public and private keys are mathematically related, it’s very difficult to derive the private key given only the public key; however, deriving the private key is always possible given enough time and computing power. This makes it very important to pick keys of the right size; large enough to be secure, but small enough to be applied fairly quickly. Additionally, you need to consider who might be trying to read your files, how determined they are, how much time they have, and what their resources might be. Larger keys will be cryptographically secure for a longer period of time. If what you want to encrypt needs to be hidden for many years, you might want to use a very large key. Of 27

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

course, who knows how long it will take to determine your key using tomorrow’s faster, more efficient computers? There was a time when a 56-bit symmetric key was considered extremely safe. Keys are stored in encrypted form. PGP stores the keys in two files on your hard disk; one for public keys and one for private keys. These files are called keyrings. As you use PGP, you will typically add the public keys of your recipients to your public keyring. Your private keys are stored on your private keyring. If you lose your private keyring, you will be unable to decrypt any information encrypted to keys on that ring . [4]

1.6.1 Key management In cryptography, key management includes all of the provisions made in a cryptosystem design, in cryptographic protocols in that design, in user procedures, and so on, which are related to generation, exchange, storage, safeguarding, use, vetting, and replacement of keys. There is a distinction between key management, which concerns keys at the users' level (i.e., passed between systems or users or both), and key scheduling which is usually taken to apply to the handling of key material within the operation of a cipher. Appropriate and successful key management is critical to the secure use of every crypto system without exception. It is, in actual practice, the most difficult aspect of cryptography generally, for it involves system policy, user training, organizational and departmental interactions in many cases, coordination between end users, etc. Many of these concerns are not limited to cryptographic engineering and so are outside a strictly cryptographic brief, though of critical importance. As a result, some aspects of key management fall between two stools as the cryptographers 28

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

may assume this or that aspect is the responsibility of the using department or upper management or some such, while said department or upper management regard it all as being outside their concerns because 'technical', and so within the purview of the cryptographers.[7]

1.6.2 Key Distribution For symmetric encryption to work, the two parties to an exchange must share the same key, and that key must be protected from access by others. Furthermore, frequent key changes are usually desirable to limit the amount of data compromised if an attacker learns the key. Therefore, the strength of any cryptographic system rests with the key distribution technique, a term that refers to the means of delivering a key to two parties who wish to exchange data, without allowing others to see the key. For two parties A and B, key distribution can be achieved in a number of ways, as follows: 1. A can select a key and physically deliver it to B. 2. A third party can select the key and physically deliver it to A and B. 3. If A and B have previously and recently used a key, one party can transmit the new key to the other, encrypted using the old key. 4. If A and B each has an encrypted connection to a third party C, C can deliver a key on the encrypted links to A and B. Options 1 and 2 call for manual delivery of a key. For link encryption, this is a reasonable requirement, because each link encryption device is going to be exchanging data only with its partner on the other end of the link. However, for end-to-end encryption, manual delivery is awkward. In a distributed system, any given host or terminal may need to engage in exchanges with many other hosts and 29

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

terminals over time. Thus, each device needs a number of keys supplied dynamically. The problem is especially difficult in a wide area distributed system. Option 3 is a possibility for either link encryption or end-to-end encryption, but if an attacker ever succeeds in gaining access to one key, then all subsequent keys will be revealed. Furthermore, the initial distribution of potentially millions of keys must still be made. For end-to-end encryption, some variation on option 4 has been widely adopted. In this scheme, a key distribution center is responsible for distributing keys to pairs of users (hosts, processes, applications) as needed. Each user must share a unique key with the key distribution center for purposes of key distribution. For asymmetric key distribution or public key distribution several techniques have been proposed for it. Virtually all these proposals can be grouped into the following general schemes: 

Public announcement



Publicly available directory



Public-key authority



Public- certificates In public announcement of PKs, the point of public-key encryption is that

the public key is public. Thus, if there is some broadly accepted public-key algorithm, such as RSA, any participant can send his or her public key to any other participant or broadcast the key to the community at large. For example, because of the growing popularity of PGP (pretty good privacy), which makes use of RSA, many PGP users have adopted the practice of appending their public key to messages that they send to public forums, such as USENET newsgroups and 30

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

Internet mailing lists. Although this approach is convenient, it has a major weakness. Anyone can forge such a public announcement. That is, some user could pretend to be user A and send a public key to another participant or broadcast such a public key. Until such time as user A discovers the forgery and alerts other participants, the forger is able to read all encrypted messages intended for A and can use the forged keys for authentication. A greater degree of security can be achieved by maintaining a publicly available dynamic directory of public keys. Maintenance and distribution of the public directory would have to be the responsibility of some trusted entity or organization. The authority maintains a directory with a {name, public key} entry for each participant. Stronger security for public-key distribution can be achieved by providing tighter control over the distribution of public keys from the directory. The scenario of this is attractive, yet it has some drawbacks. The public-key authority could be somewhat of a bottleneck in the system, for a user must appeal to the authority for a public key for every other user that it wishes to contact. As before, the directory of names and public keys maintained by the authority is vulnerable to tampering. An alternative approach, first suggested by Kohnfelder is to use certificates that can be used by participants to exchange keys without contacting a public-key authority, in a way that is as reliable as if the keys were obtained directly from a public-key authority. In essence, a certificate consists of a public key plus an identifier of the key owner, with the whole block signed by a trusted third party. Typically, the third party is a certificate authority, such as a government agency or a financial institution that is trusted by the user community. A user can present his or her public key to the authority in a secure manner, and obtain a certificate. The 31

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

user can then publish the certificate. Anyone needed this user's public key can obtain the certificate and verify that it is valid by way of the attached trusted signature. A participant can also convey its key information to another by transmitting its certificate. Other participants can verify that the certificate was created by the authority.[10]

1.6.3 Key Protection A good passphrase is one method of protecting your keys, but almost as important is the need to store your keys in a non-obvious location. If you are on a network with a full PKI (Public Key Infrastructure) system, there’s probably not much you can do about that as the system administrators will have set up key servers, back-up keys, and recovery keys (if they’re good, that is!). But what do you do if you’re using your own system? There are four good, safe methods of keeping your keys safe: 1. Don’t save your keys on your desktop computer. 2. If you must store your keys on your desktop computer, see if you can change the name of the folder or locate the keys in a different directory. Always save copies of your keys to a removable drive such as a USB keychain drive, CD, or floppy disk or even a flash. 3. Keep the USB drive, CD, floppy or the flash with your keys on your person. 4. If you cannot keep your key storage media on you, put it in a safe place such

as a safe, a bank safe-deposit box, or a locking cabinet.[1]

32

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International University of Africa

Faculty of computer studies

Chapter Two

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Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

2.1 Introduction One of the big motivators behind public key cryptography is that there is some hope for securely exchanging encryption keys in an insecure medium. However, that is not as easy as it sounds. If used in a naïve manner, the basic public key methods for communication are susceptible to a man-in-the-middle attack, in which the two parties end up talking to an attacker who relays messages, instead of to each other. `

Man-in-the-middle attacks are possible because public key cryptography in

and of itself provides no means of establishing trust. PKI provides the means to establish trust by binding public keys and identities together in a way that gives reasonable assurance that we are communicating securely with the expected entity. Using public key cryptography, we can be sure that if we encrypt data with a public key, only someone with the corresponding private key can decrypt it. If we simply exchange public keys over an insecure medium, there is no easy way to be sure that the public keys we receive belong to the people we think they do. In other words, traditional public key cryptography does not establish trust between entities. That is where PKI comes in. The basic idea behind public key infrastructure is to introduce a trusted third party to the mix. The idea is that we somehow acquire the public key of the trusted third party over a secure medium. In addition, each entity registers its public key with that trusted party, along with information about that entity. Basically, the trusted party is expected to ensure that the public key really does belong to the registrant and all of the associated data is accurate. If the authority approves, certificate is certified, which is a piece of data containing our public key along 34

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

with other identifying information. Once our certificate has been signed, we can hand that certificate to anyone, and as long as that person has securely obtained the authority's public key, he can take our certificate and validate it by checking the authority's signature. [13] Complex

business

systems,

e-commerce

and

automated

business

transactions require robust and rigorous security measures. Companies using the Internet environment as a platform to conduct business have a better probability of success if they accommodate the needs of security-conscious clientele. Today’s Internet clientele demand stringent security protocols to protect their interests, privacy, communication, value exchange, and information assets .[9]

2.2

What does the e-commerce mean? A company that performs any online activity is generally considered an e-

commerce company. Online activity means any business operation conducted over a network 24 hours a day and 7 days a week all year round. Under this definition, all kinds of business activities on the Web such as 

buying, selling, and trading



service provision



banking



entertainment

are characterized as e-commerce or e-business. Although e-commerce is a relatively new term even from our computer dictionary, it was widely used by many big corporations decades ago. In particular, the banking industry used Electronic Funds Transfer (EFT) to transfer money between accounts and/or banks 35

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

long before the creation of the Internet. Also, many big companies and government organizations use the so-called Electronic Data Interchange (EDI) sharing information among divisions and/or departments. Business over a small network environment has become very active only since the easy availability of databases and computers. Before the advent of the Internet, e-commerce or any online business was expensive. Usually some dedicated underground wiring or channels using microwave technologies were involved to provide a direct link among the dedicated organizations. The physical link and data transmission format were usually proprietary and therefore established an essential secure environment for the business activity. These kinds of business still exist and are active today. In fact, many people consider this kind of e-commerce as business over a secure channel or network. The Internet opened the flood gates for affordable networking. Twenty-four hours a day and 7 days a week, connecting people all over the globe is no longer a problem. All of a sudden, we have a global economy reaching every corner of the world. For example, a luxury home or house auction in South Africa can instantly attract hundreds of buyers from Europe and North America. All buying, selling, and other transactions can be completed within minutes. It is believed that total Internet money transactions will be more than a trillion dollas by that time. This is the power of bringing people and business together. On the other hand, with the same network type and data transmission protocol, e-commerce on the Internet operates in an insecure environment. In general, from a security point of view, the Internet is a place where anybody can be everybody. Again, all of a sudden, online fraud occurs everywhere. 36

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

For example, if someone has ordered some goods from your Web site on the Internet, do you trust his or her identity? Do you trust his or her credit card number? Even if you can get the money from the credit card company, how do you know you are not charging someone else illegally? In fact, online security is a big issue for us all, not just businesses. In order to provide a secure business transaction in an insecure network or environment, a number of technologies are introduced. In particular the Public-Key Infrastructure (PKI) with digital keys, certificates, the Certification Authority (CA), and the Secure Sockets Layer (SSL) are introduced in some detail. [8]

2.3 Certificates Certificates contain a wealth of information that can be used to tie the public key inside the certificate to an entity, either an individual or an organization. Certificates have the name of the entity, called the distinguished name in the PKI world. Server-side certificates also usually contain the fully qualified domain name of the server. They have an expiration date, which means we will have to go back and get a new certificate periodically. A digital certificate contains information about the person or organization to whom it was issued (the subject) as well as information about the organization that issued the certificate (the issuer). The issuer signs the certificate with its private key, and the certificate may contain all of the information necessary to validate that signature, including its public key. However, such information should not actually be used to validate the signature on the certificate. After all, anyone could create a key pair to use in signing, place it in the certificate, and claim it is from the issuer.

37

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

Certificates also have a serial number that is unique, at least across all certificates from a given issuer. The serial number can be used to identify a certificate quickly. The basic idea here is that the issuer signs the certificate with its private key, so anyone who has securely obtained the issuer's public key will be able to validate the authenticity of the entire certificate. The entity to whom the certificate was issued cannot change data in it, such as the expiration date. If he or she tries, the signature will not check out. Clearly, the issuer is vouching that the information in the certificate is correct when it signs. If we trust the issuer's validation of the core information, we should be able to trust its signature. Once a certificate has been issued, it is generally put into production. The entity with the certificate gives it to parties that wish to communicate. Other people can validate the certificate by checking the signature, assuming that they have securely obtained the public key of the issuer. They can encrypt data to the public key found in the certificate, and only the entity to which the certificate was issued should have the corresponding private key needed to decrypt the data. The issuer does not even have a copy of the private key. Generally, the subject generates a key pair (a public key and an associated private key) and bundles the public key along with a bunch of information into a certificate-signing request. The certification authority (often called simply a CA) or its designate authenticates the data, perhaps requiring interaction from the subject. Then, when it is confident enough, the CA will create the final certificate, sign it, and give it back to the subject. Each Digital Certificate contains the following information: the figure 2.1 below show an example of a certificate. 38

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

Fig 2.1 Digital Certificate [1]

Managing Digital Certificates and the associated keys requires policies and procedures to deal with issuance, storage, recovery, modification, and so on. That, in a nutshell, is really what the infrastructure in Public Key Infrastructure is all about. Almost anyone can set up a server to issue Digital Certificates and keys, but it takes a whole lot more to effectively build and manage a system that can handle the complexities and the traffic load without completely falling apart. [13]

39

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

2.4 PKI Components Different components comprise a PKI. A PKI is a framework of people, processes, policies, protocols, hardware, and software used to generate, manage, store, deploy, and revoke public key certificates. The following outlines the typical components in a PKI used in an e-commerce environment. Note that although the security and integrity of the physical infrastructure is important to the successful implementation of a PKI, that subject is beyond the scope of this research [9]

2.4.1 Certificate Authority (CA) A Certification Authority (CA) is an organization or company that issues certificates. By its very nature, a CA has a huge responsibility to ensure that the certificates it issues are legitimate. That is, the CA must ensure beyond all reasonable doubt that every certificate it issues contains a public key that was issued by the party that claims to have issued it. It must be able to produce acceptable proof for any certificate that it issues on demand. Otherwise, how can the CA itself be trusted? A CA must be trusted, and so for that trust to be extended, its certificate containing its public key must be widely distributed. For public CAs, their certificates are generally published so that anyone can obtain them. More commonly, the software that makes use of them, such as a web browser, is shipped containing them. There are two basic types of CAs. A private CA has the responsibility of issuing certificates only for members of its own organization, and is likewise trusted only by members of its own organization. A public CA, such as VeriSign or Thawte, has the responsibility of issuing certificates for any member of the 40

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

public, and must be trusted by the public. The burden of proof varies depending on the type of CA that has issued a certificate and the type of certificate that is issued. A private CA is often ideal for use in a corporate setting. For example, a company could set up its own CA for email, using S/MIME as the standard for encrypting and authenticating email messages. The company's CA would issue certificates to each employee, and each employee would configure their S/MIMEcapable email clients to recognize the company's CA as being trusted. For a private CA, verifying the identity of a subject is often a reasonably simple and straightforward matter. When used in a corporate environment, for example, employees are known, and their identities can be easily identified using information obtained from the company's human resources department. In such a scenario, the human resources department is said to be acting as a Registration Authority (RA). A public CA commonly issues certificates for public web sites requiring encryption and/or authentication, often for e-commerce in which customer information must be transmitted securely to place an order. For such operations, it's essential that the customers transmit their information to the site that is supposed to be receiving it without worrying about someone else obtaining the information. For a public CA, verifying the identity of a subject is considerably more difficult than it is for a private CA. The information required from the subject to prove its identity to the CA varies depending on whether the subject is an individual or a business. For an individual, the proof required could be as simple as a photocopy of a government-issued ID, such a driver's license or passport. For a business or other organization, similar government documentation proving your right to use the name will also likely be required. It's important to note that most public CAs provide their services to make money, and not to simply benefit the public. They still have a responsibility to 41

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

verify a subject's identity, but not actually guarantee anything—the liability is too great to provide an absolute guarantee. Certainly, it is in the CA's best interests to verify a subject's identity to the best of its ability, however. If a CA gains the reputation of issuing certificates to anyone who asks (and pays them enough money), they're not going to remain in business for very long because nobody will trust them. [14]

We can think of a Certificate Authority (CA) as the king. He is the ultimate authority and a figure of great trust. He is in charge of making identity papers for all his subjects. He signs these papers and stamps them with the Royal Stamp. Along with the identity papers he lists what responsibilities and privileges the bearer has. Because the king has issued and signed these papers, all subjects of the PKI kingdom trust these papers. In order to set up a working PKI, we have to go to the king of the PKI kingdom and ask for one of these identity papers. This identity paper identifies us to the PKI kingdom and also spells out what tasks we are allowed to do. When the king is satisfied that our identity has been verified, he signs that paper for us. By magic, two keys have appeared in our pockets that are linked to the identity paper. The king keeps a copy of the paper for future reference. This paper is our Digital Certificate. One more thing: The king doesn’t really give out Digital Certificates out of the goodness of his heart. He doesn’t have this huge altruistic streak that makes him want to make online transactions more secure. No, this is a business to him and, like all businesses, he charges for his services. And he charges a lot. So, if we

42

Public key Infrastructure

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International University of Africa

Faculty of computer studies

need a lot of certificates from the king (CA), it could get very expensive! So in the real world, this all translates as follows: 

Our request is sent to a Certificate Authority like Entrust, Verisign, GeoTrust, Baltimore, Thawte, and so on. The request includes verifiable personal information about us like a driver’s license number or a passport number.



The CA issues us a Digital Certificate after we have completed the application. During the application process, our computer has generated both the public and private keys that are linked to the Digital Certificate.



In order to get our certificate signed by the CA, we send in notarized paperwork to the CA’s office. After they verify our identity, they sign the certificate. This is called a root signed certificate.



Now we can use that certificate to encrypt and/or digitally sign e-mail and to encrypt and/or digitally sign documents.[1]

2.4.2 Certificate Revocation Most certificates are given a lifespan when created, but there are times that you might want to revoke a certificate to keep it from being used. For example, a person might lose his keys or change positions within the company, or an ecommerce site using SSL may merge with another company. In these situations, and many more, a certificate should be revoked. But, this is much easier said than done. Do you remember the days when merchants had little booklets of bad credit card numbers? (Yes, much simpler and more trusting days.) A certificate revocation is 43

Public key Infrastructure

by

Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

much like that. It uses a Certificate Revocation List (CRL) which is a list of certificate serial numbers signed by the CA. When someone attempts to validate the certificate, the CA can look up the serial number to see if it is good and form a response. However, this is yet another job that CAs find very time consuming and it slows down the process of issuing certificates and the other jobs that a CA is responsible for. The usual answer is to put the CRL on an LDAP server. This, though, brings up other problems. How often should the CRL server send updates to the CA? Should it even send them to the CA or should the authentication process work some other way? Ideally persons, applications, and other computers ought to be able to query the CRL via the LDAP which then queries the CA. These are some of the issues you’ll have to contend with when you are dealing with Digital Certificates. It’s not a hard job when you have a limited number of certificates, but when the numbers of certificates reaches into the tens of thousands, it becomes quite a large task. There is something you can do to reduce the burden of updating CRLs — and this is something you can do when certificates are initially issued. There is a field in the certificate in which you can set an expiration date. When that date comes around, the certificate automatically becomes unusable for new transactions. Of course, you’d still have the job of issuing a new certificate to replace the expired one (like getting a new credit card when your old one reaches its expiration date). Reissuing a new certificate in this case is a lot easier and less labor intensive than revoking one and updating the CRL. As we mentioned before, it’s not such a big deal when you are dealing with a limited number of certificates, but setting expiration dates should be standard procedure when you are dealing with large numbers of certificates [1] 44

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

2.4.3 Registration Authority (RA) Sometimes the PKI kingdom and the king are overwhelmed or tired of having to process all the certificate paperwork all of the time. It’s time then to delegate responsibility to someone else. Enter the Registration Authority (RA). It’s like the prince of the PKI kingdom and he can do things under the king’s authority. The prince is a lower-level authority than the king, and in many respects can be seen as subservient to the king. The king tells the prince what authority he has and what duties he can undertake. In most situations, the prince acts as a middleman between the person requesting a Digital Certificate and the king. That’s because the king can sometimes be overwhelmed with requests coming from many different entities and the prince can help take a load off. Often the prince will process applications for identity papers (Digital Certificates) and sometimes give temporary papers until he can verify the person’s identity and then he forwards the identity papers to the king for him to sign. If you have a small organization or a small e-commerce business, you probably won’t need an RA. As we indicated above, the RA is a type of support vehicle for a CA that gets overwhelmed with requests. You’ll most often find RA in large organizations that have many offices. Each office can have its own RA with the CA located at the headquarters building. The RAs can store up their requests for signed Digital Certificates and then forward them to the CA to handle all in one batch. An RA has its own digital signature (which identifies it as an RA) that is issued by the CA and gives the RA authority and permission to issue Digital Certificates. The RA’s Digital Certificate is signed by the CA to show that it is authentic. When an RA issues certificates, it creates a chain of records indicating the issuance and signing process. Not so amazingly, this downward delegation is 45

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

called chaining certificates. If you were to examine the details of a Digital Certificate issued by an RA, you would see a hierarchical relationship and the certificates at the top of the hierarchy signify a higher level of trust and authority than those at the bottom of the hierarchy [1]

Fig 2.2 PKI Architecture [10]

2.5 PKI Management Functions PKI identifies a number of management functions that potentially need to be supported by management protocols. These are indicated in Figure 2.2 and include the following: 46

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

 Registration: This is the process whereby a user first makes itself known to a CA (directly, or through an RA), prior to that CA issuing a certificate or certificates for that user. Registration begins the process of enrolling in a PKI. Registration usually involves some offline or online procedure for mutual authentication. Typically, the end entity is issued one or more shared secret keys used for subsequent authentication. 

Initialization: Before a client system can operate securely, it is necessary to install key materials that have the appropriate relationship with keys stored elsewhere in the infrastructure. For example, the client needs to be securely initialized with the public key and other assured information of the trusted CA(s), to be used in validating certificate paths.



Certification: This is the process in which a CA issues a certificate for a user's public key, and returns that certificate to the user's client system and/or posts that certificate in a repository.



Key pair recovery: Key pairs can be used to support digital signature creation and verification, encryption and decryption, or both. When a key pair is used for encryption/decryption, it is important to provide a mechanism to recover the necessary decryption keys when normal access to the keying material is no longer possible, otherwise it will not be possible to recover the encrypted data. Loss of access to the decryption key can result from forgotten passwords/PINs, corrupted disk drives, damage to hardware tokens, and so on. Key pair recovery allows end entities to restore their encryption/decryption key pair from an authorized key backup facility (typically, the CA that issued the End Entity's certificate).

47

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa 

Faculty of computer studies

Key pair update: All key pairs need to be updated regularly (i.e., replaced with a new key pair) and new certificates issued. Update is required when the certificate lifetime expires and as a result of certificate revocation.



Revocation request: An authorized person advises a CA of an abnormal situation requiring certificate revocation. Reasons for revocation include private key compromise, change in affiliation, and name change.



Cross certification: Two CAs exchange information used in establishing a cross-certificate. A cross-certificate is a certificate issued by one CA to another CA that contains a CA signature key used for issuing certificates.[10]

2.6 PKI Security Services The principle business objectives and risk management controls that can be implemented by a PKI are summarized in this section. An organization should only consider the implementation of a PKI if they have an actual business need for one or more of the security services described in the following sections. Note that these security services depend on the correct use of accepted certificate formats and signing protocols. Without adherence to accepted certificate formats and signing protocols, relying entities cannot determine the correctness of results from various operations.

2.6.1 Confidentiality Confidentiality means ensuring that the secrecy and privacy of data is provided with cryptographic encryption mechanisms. Customer personal information and legal or contractual data are prime examples of data that should be 48

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

kept secret by using confidentiality mechanisms. Encryption of data is possible by using either public (asymmetric), or secret (symmetric) cryptography. Since public key cryptography is not as efficient as secret key cryptography for data encipherment, it is normally used to encipher relatively small data objects such as secret

keys

used

by

symmetric-based

encryption

systems.

Symmetric

cryptographic systems are often incorporated into PKIs for bulk data encryption; thus, they are normally the actual mechanism used to provide confidentiality.

2.6.2 Integrity Integrity means ensuring that data cannot be corrupted or modified and transactions cannot be altered. Public key certificates and digital signature envelopes are good examples of information that must have an assurance of integrity. Often, the content of messages, emails, purchase transactions and contracts, and information that others rely on, also require the assurance of integrity. Integrity can be provided within a PKI by the use of either public (asymmetric), or secret (symmetric) cryptography. An example of secret key cryptography used for integrity is DES in Cipher Block Chaining mode where a Message Authentication Code (MAC) is generated. Note that in the PKI environment, using symmetric cryptographic systems for implementing integrity does not scale particularly well. Public key cryptography is typically used in conjunction with a hashing algorithm such as SHA-1 or MD5 to provide integrity. A well-designed PKI will use protocols that require the use of these algorithms to provide an efficient integrity mechanism. .

2.6.3 Authentication Authentication means verifying that the identity of entities is provided by the use of public key certificates and digital signature envelopes. Authentication in 49

Public key Infrastructure

by

Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

the e-commerce environment is performed very well by public key cryptographic systems incorporated into PKIs. In fact, the primary goal of authentication in a PKI is to support the remote and unambiguous authentication between entities unknown to each other, using public key certificates and CA trust hierarchies. Authentication in a PKI environment relies on the mathematical relationship between the public and private keys. Messages signed by one entity can be tested by any relying entity. The relying entity can be confident that only the owner of the private key originated the message, because only the owner has access to the private key. .

2.6.4 Non-Repudiation Non-repudiation means ensuring that data cannot be renounced or a transaction denied. This is provided through public key cryptography by digital signing. Non-repudiation is a critical security service of any e-commerce application where value exchanges, legal, or contractual obligations are negotiated. Non-repudiation is a by-product of using public key cryptography. When data is cryptographically signed using the private key of a key pair, anyone who has access to the public key of that pair can determine that only the owner of the key pair itself could have signed the data in question. For this reason, it is paramount that end entities secure and protect their private keys used for digitally signing data.[9]

50

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

2.7 Uses For PKI Systems The dream of PKI was to issue a Digital Certificate to everyone which they would store on a smart cart, electronic token, floppy disk, or similar device. When a person wanted to conduct a bank transaction, he/she would insert his/her certificate token into a reader and would be automatically identified. When he/she was finished with his/her banking, he/she could board a bus and place his/her token on the reader which would verify that he/she has a monthly transportation card. Then, when he/she got home, he/she could log on to his/her favorite online shopping site and run his/her token through the reader. That would give the shopping site his/her name, address, store account number, and credit card number. It is important to understand that a PKI is not by itself an authentication, authorization, auditing, privacy, or integrity mechanism. Rather, a PKI is an enabling infrastructure that supports these various business and technical needs. In particular, a PKI only allows for the identification of entities. For example, a PKI does not infer trust by itself, but requires the establishment of a trust base, on which the PKI can rely. This requirement means that the basis of trust must be established on a personal, business, or other level, before it can be accepted by the PKI. A real world example of this is, suppose you misplace your drivers license and are issued a temporary one which does not have your photograph. A temporary license without a picture does not allow a store clerk to determine if you are the owner of it. Therefore, you may not be able to write a check or use a credit card because your identification mechanism, the temporary license, is not acceptable. This indicates that the trust inferred by identification is a rather subjective matter.

51

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

Therefore, PKI is mainly used for secure transactions between companies or governmental agencies. An e-commerce Web site that uses SSL for encryption is a portion of PKI system. Encrypted e-mail is also another transaction that may be a part of a PKI system. Some companies or agencies may want all staff to digitally sign any documents they’ve created. Because a digital signature is derived from a Digital Certificate and its key, this is also part of a PKI system. There are so many possible scenarios and solutions it’s almost impossible to list them all. However, PKI in the workplace is usually tied to three things: 1. Identifying system users 2. Using Digital Certificates to describe access permissions 3. Using Digital Certificates to encrypt email and other data If you’re a small company and can’t afford an expensive PKI system; especially if you just want to do a few things, you’re much better off using PGP. PGP is a type of PKI solution without all the overhead. Instead of depending upon Certificate Authorities and key servers, you rely upon a circle of trusted colleagues and acquaintances to verify your identity and you use free public key servers to distribute your public keys. It works well for small organizations, but it can get really complicated for large ones. PKI can be used to indicate a company’s commitment to maintaining a secure infrastructure. Note that PKI is not used to replace any security policies or procedures, but it can be used to strengthen implementation. Because Digital Certificates can be used to control access to computers, networks, and documents, it can help keep unauthorized personnel out. If all documents are digitally signed by their creators, then you can also control the integrity of your data and also tie ultimate responsibility to the data’s creator. It’s

52

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International University of Africa

Faculty of computer studies

difficult for someone to say they didn’t write a particular memo if their digital signature is on it. [1]

2.8 PKI Protocols To achieve the basic security services mentioned above the public key infrastructure uses a number of protocols which include the following: SSL,TLS, IPsec for communication and transactional security  S/MIME and PGP for email security 

SET for value exchange[9]

2.8.1 Secure Socket Layer (SSL) The Transmission Control Protocol/Internet Protocol (TCP/IP) governs the transport and routing of data over the Internet. Other protocols, such as the HyperText Transport Protocol (HTTP), Lightweight Directory Access Protocol (LDAP), or Internet Messaging Access Protocol (IMAP), run "on top of" TCP/IP in the sense that they all use TCP/IP to support typical application tasks such as displaying web pages or running email servers.

Fig 2.3 Position of the SSL protocol 53

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

The SSL protocol runs above TCP/IP and below higher-level protocols such as HTTP or IMAP. It uses TCP/IP on behalf of the higher-level protocols, and in the process allows an SSL-enabled server to authenticate itself to an SSL-enabled client, allows the client to authenticate itself to the server, and allows both machines to establish an encrypted connection. These capabilities address fundamental concerns about communication over the Internet and other TCP/IP networks:  SSL server authentication allows a user to confirm a server's identity. SSL-enabled client software can use standard techniques of public-key cryptography to check that a server's certificate and public ID are valid and have been issued by a certificate authority (CA) listed in the client's list of trusted CAs. This confirmation might be important if the user, for example, is sending a credit card number over the network and wants to check the receiving server's identity.  SSL client authentication allows a server to confirm a user's identity. Using the same techniques as those used for server authentication, SSLenabled server software can check that a client's certificate and public ID are valid and have been issued by a certificate authority (CA) listed in the server's list of trusted CAs. This confirmation might be important if the server, for example, is a bank sending confidential financial information to a customer and wants to check the recipient's identity.  An encrypted SSL connection requires all information sent between a client and a server to be encrypted by the sending software and decrypted by the receiving software, thus providing a high degree of confidentiality. 54

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

Confidentiality is important for both parties to any private transaction. In addition, all data sent over an encrypted SSL connection is protected with a mechanism for detecting tampering--that is, for automatically determining whether the data has been altered in transit. The SSL protocol includes two sub-protocols: the SSL record protocol and the SSL handshake protocol. The SSL record protocol defines the format used to transmit data. The SSL handshake protocol involves using the SSL record protocol to exchange a series of messages between an SSL-enabled server and an SSLenabled client when they first establish an SSL connection. This exchange of messages is designed to facilitate the following actions:  Authenticate the server to the client.  Allow the client and server to select the cryptographic algorithms, or ciphers, that they both support.  Optionally authenticate the client to the server.  Use public-key encryption techniques to generate shared secrets. 

Establish an encrypted SSL connection.

2.8.2 Transport Layer Security (TLS) Transport Layer Security (TLS) and its predecessor, Secure Sockets Layer (SSL), are cryptographic protocols that provide secure communications on the Internet for such things as web browsing, e-mail, Internet faxing, instant messaging and other data transfers. There are slight differences between SSL and TLS, but the protocol remains substantially the same. The TLS protocol allows applications to communicate across a network in a way designed to prevent eavesdropping, tampering, and message forgery. TLS 55

Public key Infrastructure

by

Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

provides endpoint authentication and communications privacy over the Internet using cryptography. Typically, only the server is authenticated (i.e., its identity is ensured) while the client remains unauthenticated; this means that the end user (whether an individual or an application, such as a Web browser) can be sure with whom it is communicating. The next level of security—in which both ends of the "conversation" are sure with whom they are communicating—is known as mutual authentication. Mutual authentication requires public key infrastructure (PKI) deployment to clients unless TLS-PSK or TLS-SRP are used, which provide strong mutual authentication without needing to deploy a PKI. TLS involves three basic phases: 1. Peer negotiation for algorithm support 2. Key exchange and authentication 3. Symmetric cipher encryption and message authentication During the first phase, the client and server negotiate cipher suites, which determine the ciphers to be used, the key exchange and authentication algorithms, as well as the message authentication codes (MACs). The key exchange and authentication algorithms are typically public key algorithms, or as in TLS-PSK preshared keys could be used. The message authentication codes are made up from cryptographic hash functions using the HMAC construction

2.8.3 The IPsec Protocol IPsec protocols operate at the network layer, layer 3 of the OSI model. Other Internet securities protocols in widespread use, such as SSL, and TLS , operate from the transport layer up (OSI layers 4 - 7). This makes IPsec more flexible, as it 56

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

can be used for protecting layer 4 protocols, including both TCP and UDP, the most commonly used transport layer protocols. IPsec has an advantage over SSL and other methods that operate at higher layers: an application doesn't need to be designed to use IPsec, whereas the ability to use SSL or another higher-layer protocol must be incorporated into the design of an application. The IP security architecture uses the concept of a security association as the basis for building security functions into IP. A security association is simply the bundle of algorithms and parameters (such as keys) that is being used to encrypt and authenticate a particular flow in one direction. Therefore, in normal bidirectional traffic, the flows are secured by a pair of security associations. The actual choice of encryption and authentication algorithms (from a defined list) is left to the IPsec administrator. In order to decide what protection is to be provided for an outgoing packet, IPsec uses the security parameter index (SPI), an index to the security association database (SADB), along with the destination address in a packet header, which together uniquely identify a security association for that packet. A similar procedure is performed for an incoming packet, where IPsec gathers decryption and verification keys from the security association database. For multicast, a security association is provided for the group, and is duplicated across all authorized receivers of the group. There may be more than one security association for a group, using different SPIs, thereby allowing multiple levels and sets of security within a group. Indeed, each sender can have multiple security associations, allowing authentication, since a receiver can only know that someone knowing the keys sent the data. Note that the relevant standard does not describe how the association is chosen and duplicated across the group; it 57

Public key Infrastructure

by

Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

is assumed that a responsible party will have made the choice.IPsec was intended to provide either transport mode or tunnel mode. In transport mode, only the payload (the data you transfer) of the IP packet is encrypted and/or authenticated. The routing is intact, since the IP header is neither modified nor encrypted; however, when the authentication header is used, the IP addresses cannot be translated, as this will invalidate the hash value. The transport and application layers are always secured by hash, so they cannot be modified in any way (for example by translating the port numbers). Transport mode is used for host-to-host communications. In tunnel mode, the entire IP packet (data plus the message headers) is encrypted and/or authenticated. It must then be encapsulated into a new IP packet for routing to work. Tunnel mode is used for network-to-network communications (secure tunnels between routers, e.g. for VPNs) or host-to-network and host-tohost communications over the Internet. [11]

2.8.4 Pretty Good Privacy (PGP) PGP (short for Pretty Good Privacy), created by Philip Zimmermann, is the de facto standard program for secure e-mail and file encryption on the Internet. Its public-key cryptography system enables people who have never met to secure transmitted messages against unauthorized reading and to add digital signatures to messages to guarantee their authenticity. PGP uses a digital signature (a combination of hashing and public key encryption) to provide integrity, authentication and non-repudiation. It uses a combination of secret key and public key to provide privacy. In other words it uses 58

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

one hash function, on secret key and tow private-public key pairs. Fig 2.4 shows how PGP creates a secure email. The email message is hashed to create a digest. The digest is encrypted (signed) using A’s private key. The message and the digest are encrypted using the one time secret key created by A. The secret key is encrypted using B’s public key and sent together with the encrypted combination of message and digest. The second fig 2.4(B) shows how PGP uses hashing and combination of a three keys to extract the original message at the receiver site

Sender Site A

Fig 2.4(A)

PGP at the sender site

Receiver Site B

59

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Muhedin Abdullahi Mohammed

International University of Africa

Fig 2.4(B)

Faculty of computer studies

PGP at the receiver site

The combination of encrypted secret key and message plus digest is received. The encrypted secret key is first decrypted (using B’s private key) to get the one time secret key created by the sender. The secret key is then used to decrypt the combination of the message plus digest. After receiving the original message and the encrypted digest, the receiver separates the two. He/she applies the same hash function to the message to create a second digest. The receiver also decrypts the received digest using the public key of the sender. If the two digests are the same all three aspects of security (integrity, authentication and nonrepudiation) are preserved. [12]

2.8.5 Secure/Multipurpose Internet Mai Extension(S/MIME) The two most common solutions for encrypted e-mail are PGP (Pretty Good Privacy mentioned in the above article and S/MIME (Secure/Multipurpose Internet Mail Extension). MIME was created as a standard for transferring or transporting 60

Public key Infrastructure

by

Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

different types of files attached to e-mails, such as GIFs, JPEGs, DOC files, and so on. The S in S/MIME indicates a standard for incorporating secure encryption standards into the protocol. In a perfect world this would work perfectly; however, as is usually the case, the various vendors have taken to interpreting the standards to meet their own needs. S/MIME works, but different e-mail clients use it differently, and the results are not always fabulous. On the plus side, S/MIME is cheap and is included in most e-mail systems and e-mail clients such as Outlook. When problems with e-mail security raised their ugly heads, the vendors of e-mail programs realized that they would have to figure out a way for everyone to be able to send secure e-mail. That is, e-mail in some sort of coded or encrypted form. It only made sense that this new feature be standardized, so they created S/MIME — Secure Multipurpose Internet Mail Extensions. Standards being as they are, we don’t have to remind you that the assorted vendors have interpreted the standards to suit their needs. That means that S/MIME (or MIME, for that matter) doesn’t always work perfectly between different e-mail programs. But, it works well enough to at least give it a try. [1]

2.8.6 Secure electronic transaction(set) Secure Electronic Transactions (SET) is an open protocol which has the potential to emerge as a dominant force in the securing of electronic transactions. Jointly developed by Visa and MasterCard, in conjunction with leading computer vendors such as IBM, SET is an open standard for protecting the privacy, and ensuring the authenticity, of electronic transactions. This is critical to the success of electronic commerce over the Internet; without privacy, consumer protection cannot be guaranteed, and without authentication, neither the merchant nor the consumer can be sure that valid transactions are being made. 61

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

Secure Electronic Transactions (SET) relies on the science of cryptography – the art of encoding and decoding messages. Cryptography dates back many centuries – even in the time of Julius Caesar, encryption was used to preserve the secrecy of messages. Preserving the secrecy of transactions is no different, though stronger encryption algorithms are used, as well as significantly stronger encryption keys. Encryption advancements have come about through its application by the military, and by advances in computing power and mathematics. The SET protocol relies on two different encryption mechanisms, as well as an authentication mechanism. SET uses symmetric encryption, in the form of the aging Data Encryption Standard (DES), as well as asymmetric, or public-key, encryption to transmit session keys for DES transactions. Rather than offer the security and protection afforded by public-key cryptography, SET simply uses session keys (56 bits) which are transmitted asymmetrically – the remainder of the transaction uses symmetric encryption in the form of DES. This has disturbing connotations for a "secure" electronic transaction protocol – because public key cryptography is only used only to encrypt DES keys and for authentication, and not for the main body of the transaction. The computational cost of asymmetric encryption is cited as reason for using weak 56 bit DES, however other reasons such as export/import restrictions, and the perceived need by law enforcement and government agencies to access the plain-text of encrypted Secure electronic transactions will be an important part of electronic commerce in the future. Without such security, the interests of the merchant, the consumer, and the credit or economic institution cannot be served. Privacy of transactions, and authentication of all parties, is important for achieving the level of trust that will allow such transactions to flourish. However, it is important that 62

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

the encryption algorithms and key-sizes used, will be robust enough to prevent observation by hostile entities (either criminal or foreign powers). The ideal of the secure electronic transactions protocol (SET) is important for the success of electronic commerce. However, it remains to be seen whether the protocol will be widely used because of the weakness of the encryption that it uses . [11]

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International University of Africa

Faculty of computer studies

Chapter three

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Muhedin Abdullahi Mohammed

International University of Africa

3.1

Faculty of computer studies

What is SSL and how does it work? Before we first introduce the SSL, let us make an analogy between

communications between computers on the Internet and communications between people

over

the

telephone.

Without

SSL,

your

computer-to-computer

communications suffer from the same security problems from which your telephone communications suffer: Who are you talking to? In a phone conversation, how can you be sure that the person who picks up the phone at the other end is really the person you are trying to call (especially if you have never spoken to them before)? What if your phone call was intercepted or re-routed, or what if someone else is answering your call recipient's phone? There really is no way to be sure you have reached the right person, especially if they are trying to fool you. Eavesdropping? As you are aware of from watching TV or reading, it is very easy to tap phone lines: the police and spies do this all the time to covertly gather information. It is not easy to detect if your lines are tapped. The same applies with communications over the Internet -- how can you be sure that your communications are not being "tapped" and recorded? These results in two very real security issues for communications over the Internet: Knowing for sure that you are connecting to the right computers (i.e. those at your bank and not those at a hacker's or phisher's web site), and  . Knowing that your data is safe from prying eyes during transit to those computers. This is where SSL comes in. To solve these problems to a large degree, most Internet services support use of SSL as a mechanism for securing communications. SSL (Secure Sockets Layer) is the standard security technology for establishing an encrypted link between a web server and a browser. This link ensures that all data passed between the web server and browsers remain private and integral. SSL is an 65

Public key Infrastructure

by

Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

industry standard and is used by millions of websites in the protection of their online transactions with their customers. To be able to create an SSL connection a web server requires an SSL Certificate. When you choose to activate SSL on your web server you will be prompted to complete a number of questions about the identity of your website and your company. Your web server then creates two cryptographic keys - a Private Key and a Public Key. [11] The SSL protocol, which was developed by Netscape in 1994, allows clients (Web browsers, typically) and HTTP servers to communicate over a secure connection. It offers encryption, source authentication, and data integrity as means to protect information exchanged over insecure, public networks. There are several versions of SSL: SSL 2.0 has security weaknesses and is hardly used today; SSL 3.0 is universally supported; and finally the Transport Layer Security (TLS), which is an improvement on SSL 3.0, has been adopted as an Internet standard and is supported by almost all recent software. Encryption protects data from unauthorized use by converting it to an apparently meaningless form before transmission. The data is encrypted by one side (the client or the server), transmitted, decrypted by the other side, then processed. Source authentication is a method of verifying the data sender's identity. The first time a browser or other client attempts to communicate with a Web server over a secure connection, the server presents the client with a set of credentials in the form of a certificate. Certificates are issued and validated by trusted authorities known as certification authorities (CAs). A certificate represents the public-key identity of a person. It is a signed document that says: I certify that the public key in this document belongs to the entity named in this document. Signed (certificate 66

Public key Infrastructure

by

Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

authority). Well-known CAs include Verisign, Entrust, and Thawte. Note that the certificates used with SSL/TLS today are X.509 certificates. [15] In this way SSL is able to provide: •Privacy The connection is made private by encrypting the data to be exchanged between the client and the server. In other words, only they can decrypt it and make sense of the data. This allows for secure transfer of private information such as credit card numbers, passwords, secret contracts, etc. •Data integrity The SSL connection is reliable. The message transport includes a message integrity check based on a secure hash function. So there is practically no possibility of data corruption without detection. •Authenticity The client can authenticate the server and an authenticated server can authenticate the client (optionally). This means that the information is guaranteed to be exchanged only between the intended parties. The authentication mechanism is based on the exchange of digital certificates. •Non-repudiation

Digital signatures and certificates together imply non-repudiation. This establishes accountability of information about a particular event or action to its originating entity, and the communications between the parties can be proved later. 67

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

SSL is comprised of two protocols: the record protocol and the handshake protocol. The record protocol defines the way that messages, passed between the client and server, are encapsulated. At any point in time it has a set of cipher suite, which defines the parameters associated with it, known as a cryptographic methods being used.

3.2 Negotiable Encryption Among the features of SSL that have made it the de facto standard vehicle for secure e-commerce transactions is its support for negotiable encryption and authentication algorithms. The designers of SSL realized that not all parties will use the same client software and consequently not all clients will include any particular encryption algorithm. The same is true for servers. The client and server at the two ends of a connection negotiate the encryption and decryption algorithms (cipher suites) during their initial handshake. It may turn out that they do not have sufficient algorithms in common, in which case the connection attempt will fail. Note that while SSL allows both the client and the server to authenticate each other, typically only the server is authenticated in the SSL layer. Clients are customarily authenticated in the application layer, through the use of passwords sent over an SSL-protected channel. This pattern is common in banking, stock trading, and other secure Web applications. The SSL full handshake protocol is illustrated in Figure 3.1. It shows the sequences of messages exchanged during the SSL handshake.

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International University of Africa

Faculty of computer studies

Figure 3.1: SSL handshake protocol

These messages mean: 1. ClientHello: The client sends the server information such as SSL protocol version, session id, and cipher suites information such cryptographic algorithms and key sizes supported. 2. ServerHello: The server chooses the best cipher suite that both the client and server support and sends this information to the client. 3. Certificate: The server sends the client its certificate which contains the server's public key. While this message is optional, it is used when server authentication is required. In other words, it is used to confirm the server's identity to the client.

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International University of Africa

Faculty of computer studies

4. Certificate Request: This message is sent only if the server requires the client to authenticate itself. Most e-commerce applications do not require the client to authenticate itself. 5. Server Key Exchange: This message is sent if the certificate, which contains the server's public key, is not sufficient for key exchange. 6. ServerHelloDone: This message informs the client that the server finished the initial negotiation process. 7. Certificate: This message is sent only if the server requested the client to authenticate itself. 8. Client Key Exchange: The client generates a secret key to be shared between the client and server. If the Rivest-Shamir-Adelman (RSA) encryption algorithm is used, the client encrypts the key using the server's public key and sends it to the server. The server uses its private or secret key to decrypt the message and retrieves the shared secret key. Now, client and server share a secret key that has been distributed securely. 9. Certificate Verify: If the server requested to authenticate the client, this message allows the server to complete the authentication process. 10.Change Cipher Spec: The client asks the server to change to encrypted mode. 11.Finished: The client tells the server it is ready for secure communication. 12.Change Cipher Spec: The server asks the client to change to encrypted mode. 13.Finished: The server tells the client it is ready for secure communication. This marks the end of the SSL handshake. 14.Encrypted Data: The client and server can now start exchanging encrypted messages over a secure communication channel 70

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

3.3 Java Secure Socket Extension 'JSSE' Any information transmitted over computer networks, or the Internet, is subject to interception. Some of that information could be sensitive, such as credit card numbers and other personal data. To make the Internet more useful in an enterprise setting and for e-commerce, applications must protect their users' information, using encryption, authentication, and secure communications protocols. The secure Hypertext Transfer Protocol (HTTPS), which is HTTP over the Secure Sockets Layer (SSL), is already being used successfully for ecommerce applications. The Java Secure Socket Extension (JSSE), which is a set of Java packages that enable secure Internet communications, is a framework and 100% Pure Java implementation of the Secure Socket Layer (SSL). These packages enable you, the Java developer, to develop secure network applications that feature the secure passage of data between a client and a server running any application protocol, such as HTTP, FTP, Telnet, or NTTP, over TCP/IP. The good news is that JSSE has been integrated into the Java 2 SDK, Standard Edition, version 1.4 (J2SE 1.4). This means if you have J2SE 1.4 installed, then you can build secure Internet applications based on SSL without downloading any additional packages. By abstracting the complex underlying security algorithms and "handshaking" mechanisms, JSSE minimizes the risk of creating subtle, but dangerous security vulnerabilities. Furthermore, it simplifies application development by serving as a building block which developers can integrate directly into their applications. JSSE provides both an application programming interface (API) framework and an implementation of that API. The JSSE API supplements the "core" cryptographic services defined in the Java 2 71

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa SDK, v 1.4

java.security

and

java.net

Faculty of computer studies packages by providing extended

networking socket classes, trust managers, key managers, SSLContexts, and a socket factory framework for encapsulating socket creation behavior. The JSSE API is capable of supporting SSL versions 2.0 and 3.0 and Transport Layer Security (TLS) 1.0. These security protocols encapsulate a normal bidirectional stream socket and the JSSE API adds transparent support for authentication, encryption, and integrity protection. The JSSE implementation in the J2SDK, v 1.4 implements SSL 3.0 and TLS 1.0. It does not implement SSL 2.0. The JSSE API contains the following three packages:-

3.3.1 The javax.net Package This package is not specific to SSL and has two classes in it, namely SocketFactory and ServerSocketFactory, which represent the basic socket and server socket factories respectively: •SocketFactory class This class creates sockets. It may be subclassed by other factories, which create particular subclasses of sockets and thus provide a general framework for the addition of public socket-level functionality. •ServerSocketFactory class

This class creates server sockets. It may be subclassed by other factories, which create particular types of server sockets. This provides a general framework for the addition of public socket-level functionality. It is the server-side analog of a socket factory, and similarly provides a way to capture a variety of policies related to the sockets being constructed. Like socket factories, ServerSocketFactory instances 72

Public key Infrastructure

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International University of Africa

Faculty of computer studies

have methods used to create sockets. There is also an environment specific default server socket factory; frameworks will often use their own customized factory.

3.3.2 The javax.net.ssl Package The javax.net.ssl package is an SSL API, but it does not provide full access to specialized features, sometimes needed by applications, such as the control on what private keys get used.There are five basic features in this API: 1. SSL sockets and SSL server sockets 2. SSL socket factories 3. SSL-specific session capabilities 4. A handshake completion event facility 5. SSL-specific exceptions This package has six classes, four interfaces and five exceptions: •SSLSocket class SSLSocket is an abstract class extended by sockets that support SSL or IETF Transport Layer Security (TLS) protocols. Such sockets are normal stream sockets (java.net.Socket), but they add a layer of security over the underlying network transport protocol, such as TCP. Those security features include integrity protection, confidentiality, and authentication. •SSLServerSocket class The server-side implementation of the SSLSocket class is SSLServerSocket. This class is extended by server sockets that return connections protected using the SSL protocol, and that extend the SSLSocket class. 73

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

•SSLSocketFactory class

Instances of this kind of socket factory return SSL sockets. An SSL implementation may be established as the default factory. •SSLServerSocketFactory class

The

server-side

equivalent

of

the

SSLSocketFactory

class

is

SSLServerSocketFactory. This class creates SSL server sockets. •SSLSession interface This interface can be used to describe the current relationship between the server and the client. •SSLSessionContext interface An SSLSessionContext is a grouping of SSL sessions associated with a single entity. For example, they could be associated with a server or client who participates in many sessions concurrently. This interface provides methods for retrieving an SSLSession based on its ID, and allows such IDs to be listed. •SSLSessionBindingListener interface This interface is implemented by objects that want to know when they are being bound to or unbound from an SSLSession. When either event occurs, it is communicated through an SSLSessionBindingEvent identifying the session into which the object is being bound, or from which the object is being unbound.

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Faculty of computer studies

•SSLSessionBindingEvent class

This event is communicated to an SSLSessionBindingListener whenever such a listener is bound to or unbound from an SSLSession value. The events source is the SSLSession to which the listener is being bound, or from which the listener is being unbound. •HandshakeCompletedListener interface This interface is implemented by any class that wants to receive notifications about the completion of an SSL protocol handshake on a given SSL connection. When an SSL handshake completes, new security parameters will have been defined. Those parameters always include the security keys used to protect messages. They may also include parameters associated with a new session such as authenticated peer identity and a new SSL cipher suite. •HandshakeCompletedEvent class This event indicates that an SSL handshake has completed on a given SSL connection. All of the core information about that handshake’s result is captured through an SSLSession object. As a convenience, this event class provides direct access to some important session attributes. The source of this event is the SSLSocket on which handshaking just completed. •SSLException class Indicates some kind of error detected by an SSL subsystem.

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•SSLHandshakeException class Indicates that the client and server could not negotiate the desired level of security. The connection is no longer usable. •SSLKeyException class Reports a bad SSL key. Normally, this indicates misconfiguration of the server or client SSL certificate and private key. •SSLPeerUnverifiedException class Indicates that the peers identity has not been verified. You may request the identity of the peer. When the peer is not able to identify itself (for example, no certificate, or the particular cipher suite being used does not support authentication, or no peer authentication was established during SSL handshaking) this exception may be thrown. •SSLProtocolException class Reports an error in the operation of the SSL protocol. Normally this indicates a flaw in one of the protocol implementations.

3.3.3 The javax.security.cert Package This package contains two classes and five exceptions, but it can be safely replaced by the more powerful java.security.cert package shipped with the Java 2 SDK. •Certificate class 76

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International University of Africa

Faculty of computer studies

This is an abstract class for managing a variety of identity certificates that have different formats but important common uses. For example, different types of certificates, such as X.509, Pretty Good Privacy (PGP) and Simple Distributed Security Infrastructure (SDSI), share general certificate functionality (like encoding and verifying) and some types of information (like a public key).X.509, PGP, and SDSI certificates can all be implemented by subclassing the Certificate class, even though they contain different sets of information, and they store and retrieve the information in different ways. •X509Certificate class This is an abstract class for X.509 V1 certificates. This provides a standard way to access all the Version 1 attributes of an X.509 certificate. Attributes that are specific to X.509 V2 or V3 are not available through this class, but you can make use of the classes provided by the java.security.cert package of the Java 2 SDK. •CertificateEncodingException class A certificate encoding exception is thrown whenever an error occurs while attempting to encode a certificate. •CertificateException class This exception indicates one of a variety of certificate problems. •CertificateExpiredException class This kind of exception is thrown whenever the current date or the specified date is after the notAfter date and time specified in the validity period of the certificate.

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•CertificateNotYetValidException class This kind of exception is thrown whenever the current date or the specified date is before the notBefore date and time in the certificate validity period. •CertificateParsingException class This exception is thrown whenever an invalid DER encoded certificate is parsed or unsupported DER features are found in the certificate.

3.3.4 Installing and Customizing JSSE As we have already stated in the previous sections the java secure socket extension JSSE cryptographic toolkit does not come free with the earlier Java 2 SDKs, but are shipped as part of other products, such as Java Server Toolkit (JST) and the HotJava browser; however, the sun Microsystems started to integrate the JSSE with the later versions starting with

v 1.4.x

and greater. Therefore, to

install the JSSE in thoses earlier versions just download the jssse version you want and save it any where in your local disk. Note that JSSE version you downloaded requires that you have Java(tm) 2 SDK v1.2.x or 1.3.x already installed on your computer. After that Uncompress and extract the downloaded file and as a result a directory named jsse v will be created, with two subdirectories named doc and lib then perform the following two steps:Step 1. Install the JSSE jar files The JSSE lib subdirectory contains the extension files jsse.jar, jcert.jar, and jnet.jar.you can either install these files in the JDK/JRE ("installed extension") or bundle them with your applet or application ("bundled extension"). If you wish to install them as an installed extension, place them in the following directory: <java78

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home>/lib/ext, where <java-home> refers to the directory in which the Java 2 Runtime Environment (JRE) was installed. If you do not know your <java-home>, here is a simple application that allows you to find it: public class FindJavaHome { public static void main(String argv[]) { System.out.println(System.getProperty("java.home")); } }

Step 2. Register the SunJSSE provider. JSSE comes standard with a Cryptographic Service Provider, or "provider" for short, named "SunJSSE". Although the "SunJSSE" provider is supplied with every JSSE installation, it still needs to be configured explicitly, either statically or dynamically, before its services can be accessed. if you are statically registering the SunJSSE provider, add the "SunJSSE" provider to your list of approved providers. This is done statically by editing the security properties file: <java-home>\lib\security\java.security . One of the types of properties contained in the java.security file is of the following form: security.provider.n=providerClassName This declares a provider, and specifies its preference order "n". The preference order is the order in which providers are searched for requested algorithms (when no specific provider is requested). The order is 1-based; 1 is the most preferred, followed by 2, and so on. Add the above line to java.security, replacing providerClassName with com.sun.net.ssl.internal.ssl.Provider, and substituting n with the priority that you would like to assign to the "SunJSSE" provider. For 79

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International University of Africa

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example, to add the Sun internal SSL provider to the standard provider shipped with the JRE, your entries would look like: security.provider.1=sun.security.provider.Sun security.provider.2=com.sun.net.ssl.internal.ssl.Provider. "SunJSSE" would now be the second preferred provider. Instead of registering the provider statically, you can add the provider dynamically at runtime by adding the following line of code at the beginning of your program: Security.addProvider(

3.4

new com.sun.net.ssl.internal.ssl.Provider());

Programming with JSSE

The JSSE APIs supplement the

java.security

and

java.net

packages by

providing extended networking socket classes, trust and key managers, and a socket factory framework for encapsulating socket creation behavior. These classes are included in the packages javax.net and javax.net.ssl  SSLSocket and SSLServerSocket The

javax.net.ssl.SSLSocket

is a subclass of the

java.net.Socket

class.

Therefore, it supports all the standard Socket methods and adds additional methods specific to secure sockets. The

javax.net.ssl.SSLServerSocket

class is

analogous to the SSLSocket class except that it is used to create server sockets. Creating an instance of SSLSocket can be done in two ways: 1. As an instance of createSocket

SSLSocketFactory

by invoking one of the

methods on that class.

2. Through the accept method on the SSLServerSocket. 80

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 SSLSocketFactory and SSLServerSocketFactory The

javax.net.ssl.SSLSocketFactory

secure sockets, and the

class is an object factory for creating

javax.net.ssl.SSLServerSocketFactory

is an object

factory for creating server sockets. An SSLSocketFactory instance can be obtained in two ways: 1. Get the default factory by calling SSLSocketFactory.getDefault. 2. Construct a new factory with specified configured behavior. Note that the default factory is configured to enable server authentication only.

3.4.1 Making Existing Client/Server Applications Secure Incorporating SSL into existing client/server applications to make them secure can be easily done using a few lines of JSSE code. The lines highlighted in bold in the following example show the code necessary to make a server secure: import java.io.*; import javax.net.ssl.*; public class Server { int port = portNumber; SSLServerSocket server; try { SSLServerSocketFactory factory = (SSLServerSocketFactory) SSLServerSocketFactory.getDefault(); server = (SSLServerSocket) factory.createServerSocket(portNumber); 81

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International University of Africa

Faculty of computer studies

SSLSocket client = (SSLSocket) server.accept(); // Create input and output streams as usual // send secure messages to client through the // output stream // receive secure messages from client through // the input stream } catch(Exception e) { }}

The lines highlighted in bold in the following example show the code necessary to make a client secure: import java.io.*; import javax.net.ssl.*; public class Client { ... try { SSLSocketFactory factory = (SSLSocketFactory) SSLSocketFactory.getDefault(); server = (SSLServerSocket) factory.createServerSocket(portNumber); SSLSocket client = (SSLSOcket) factory.createSocket(serverHost, port); // Create input and output streams as usual // send secure messages to server through the // output stream receive secure // messages from server through the input stream } catch(Exception e) { }}

3.4.2

A Complete Example

We found that the most complex issue when working with JSSE is related to system configuration and managing certificates and keys. Throughout this

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example, we demonstrate how to develop, configure, and run a complete HTTP server application that supports the GET request method.  Overview of HTTP The Hypertext Transfer Protocol (HTTP) is a request-reply application protocol. This protocol supports a fixed set of methods such as DELETE,

etc. The

GET

GET, POST, PUT,

method is commonly used to request resources from a Web

server. Here are two sample GET requests: GET / HTTP/1.0 <empty-line> GET /names.html HTTP/1.0 <empty-line>

 Insecure HTTP Server In order to develop an HTTP server, you need to understand how the HTTP protocol works. This server, however, is simple since it only supports the GET request method. A sample implementation is shown in Code Sample 1. This is a multi-threaded HTTP server where the

ProcessConnection

class is used to run

each new request in a different thread. When the server receives a request from the browser, it parses the request to find out which document is being requested. If the requested document is available on the server, the shipDocument method is used to send the requested document to the server. If the document is not found, an error message is sent to the server. Code Sample 1: HttpServer.java import java.io.*; import java.net.*; import java.util.StringTokenizer;

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/** * This class implements a multithreaded simple HTTP * server that supports the GET request method. * It listens on port 8080, waits client requests, and * serves documents. */ public class HttpServer { // The port number which the server // will be listening on public static final int HTTP_PORT = 8080; public ServerSocket getServer() throws Exception { return new ServerSocket(HTTP_PORT); } // multi-threading -- create a new connection // for each request public void run() { ServerSocket listen; try { listen = getServer(); while(true) { Socket client = listen.accept(); ProcessConnection cc = new ProcessConnection(client); } } catch(Exception e) { System.out.println("Exception: "+e.getMessage());

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International University of Africa

Faculty of computer studies

} } // main program public static void main(String argv[]) throws Exception { HttpServer httpserver = new HttpServer(); httpserver.run(); } }

class ProcessConnection extends Thread { Socket client; BufferedReader is; DataOutputStream os; public ProcessConnection(Socket s) { // constructor client = s; try { is = new BufferedReader(new InputStreamReader (client.getInputStream())); os = new DataOutputStream(client.getOutputStream()); } catch (IOException e) { System.out.println("Exception: "+e.getMessage()); } this.start(); // Thread starts here...this start() will call run() }

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Faculty of computer studies

public void run() { try { // get a request and parse it. String request = is.readLine(); System.out.println( "Request: "+request ); StringTokenizer st = new StringTokenizer( request ); if ( (st.countTokens() >= 2) && st.nextToken().equals("GET") ) { if ( (request = st.nextToken()).startsWith("/") ) request = request.substring( 1 ); if ( request.equals("") ) request = request + "index.html"; File f = new File(request); shipDocument(os, f); } else { os.writeBytes( "400 Bad Request" ); } client.close(); } catch (Exception e) { System.out.println("Exception: " + e.getMessage()); } } /** * Read the requested file and ships it * to the browser if found. */ public static void shipDocument(DataOutputStream out,

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File f) throws Exception { try { DataInputStream in = new DataInputStream(new FileInputStream(f)); int len = (int) f.length(); byte[] buf = new byte[len]; in.readFully(buf); in.close(); out.writeBytes("HTTP/1.0 200 OK\r\n"); out.writeBytes("Content-Length: " + f.length() +"\r\n"); out.writeBytes("Content-Type: text/html\r\n\r\n"); out.write(buf); out.flush(); } catch (Exception e) { out.writeBytes(" \r\n\r\n"); out.writeBytes("HTTP/1.0

400

"

+

e.getMessage()

+

"\r\n"); out.writeBytes("Content-Type: text/html\r\n\r\n"); out.writeBytes(""); out.flush(); } finally { out.close(); } } }

To experiment with the HttpServer class: 87

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1. Copy HttpServre and save it in a file called HttpServer.java in a directory of

your choice, mostly in the bin directory of Java 2 SDK version on your

machine. 2. Compile the HttpServer.java using javac.

3. Create some sample HTML file, like the one below, including "index.html", which is the default document served in this example

<style> .tx01{background-color:#000088;font-family:arial;fontsize:22pt; font-weight:bold;color:#ffff00;text-align:left} .tx03{font-size:18pt;color:#00ff00} .butSt{background-color:#aaffaa;font-family:arial;fontweight:bold; font-size:14pt;color:#880000;width:250px;height:35px} Welcome the httpServer




4. Run the HttpServer. The server runs on port 8080.

5. Open a web browser and make a request such as http://localhost:8080 or http://127.0.0.1:8080/index.html to load the default page"index.html"

Fig 3.2 the index.html page

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3.4.3 Extending HttpServer to Handle https:// URLs Now, let's modify the HttpServer class, making it secure. We'd like the HTTP server to be capable of handling https:// URLs. As we mentioned earlier, JSSE allows you to integrate SSL into your applications quite easily.

3.4.3.1 Creating a Server Certificate As we mentioned earlier, SSL uses certificates for authentication. Certificates must be created for clients and servers that need to communicate securely using SSL. JSSE uses certificates created using the Java keytool shipped with J2SE. We used the following command to create an RSA certificate for the HTTP server. prompt> keytool -genkey -keystore serverkeys -keyalg rsa -alias muhedin

This command will generate a certificate referenced by the alias Muhedin, and will be stored in a file named serverkeys. The tool prompted us for information to generate the certificate. The information we entered is shown in the below command window.

Fig 3.3 Certificate Creation 90

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As you can see, the keytool prompted us to enter a password for the keystore meaning that in order for the server to access the keystore it must know that password. Also, the tool asked us to enter a password for the alias. If you like, such password information can be related on the keytool command line using the options -storepass and -keypass. Note that we used the IP address "192.168.100.1" for the first and last name. This IP address is that of the machine we used. You should enter the hostname or the IP address of the server's machine. When you run the keytool command, it may take a few seconds to generate the certificate depending on the speed of your machine. Once a certificate for our server has been generated, we can revise our HttpServer

to make it secure. If you examine the HttpServer class, you'll notice

that the getServer method is used to return a server socket. This means, the only method we need to modify is the getServer method so that it returns a secure server socket. The changes are highlighted in bold in Code Sample 2. Notice that we have changed the port number to 443. This is the default port number for HTTPs.

It is important to note that port numbers between 0 and 1023 are reserved. If

you run HttpsServer on a different port number, the url should be: https://localhost:portnumber

but if you run it on 443 then the URL is:

https://localhost.

Code Sample 2: HttpsServer.java import java.io.*; import java.net.*; import javax.net.*; import javax.net.ssl.*; import java.security.*; 91

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import java.util.StringTokenizer; /** * This class implements a multithreaded simple HTTPS * server that supports the GET request method. * It listens on port 443, waits client requests * and serves documents. */ public class HttpsServer { String keystore = "serverkeys"; char keystorepass[] = "africa".toCharArray(); char keypassword[] = "computer".toCharArray(); // The port number which the server will be listening on public static final int HTTPS_PORT = 443;

public ServerSocket getServer() throws Exception { KeyStore ks = KeyStore.getInstance("JKS"); ks.load(new FileInputStream(keystore), keystorepass); KeyManagerFactory kmf = KeyManagerFactory.getInstance("SunX509"); kmf.init(ks, keypassword); SSLContext sslcontext = SSLContext.getInstance("SSLv3"); sslcontext.init(kmf.getKeyManagers(), null, null); ServerSocketFactory ssf =

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International University of Africa

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sslcontext.getServerSocketFactory(); SSLServerSocket serversocket = (SSLServerSocket) ssf.createServerSocket(HTTPS_PORT); return serversocket; }

// multi-threading -- create a new connection // for each request public void run() { ServerSocket listen; try { listen = getServer(); while(true) { Socket client = listen.accept(); ProcessConnection cc = new ProcessConnection(client); } } catch(Exception e) { System.out.println("Exception: "+e.getMessage()); } } // main program public static void main(String argv[]) throws Exception { HttpsServer https = new HttpsServer(); https.run(); } }

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The lines: String keystore = "serverkeys"; char keystorepass[] = "africa".toCharArray(); char keypassword[] = "computer".toCharArray();

specify the name of the keystore, its password, and the key password. Hardcoding the passwords into the code is not a good idea for production code, however. They can be specified on the command line when running the server. The rest of the JSSE related code is in the getServer method: It accesses the serverkeys keystore. The JKS is the Java KeyStore (a type of keystore created by keytool). The KeyManagerFactory is used to create an X.509 key manager for the keystore. An SSLContext is an environment for implementing JSSE. It is used to create a ServerSocketFactory that in turn used to create a SSLServerSocket. Although we specify SSL 3.0, the implementation that is returned will often support other protocol versions, such as TLS 1.0. Older browsers, however, use SSL 3.0 more widely. Note that by default client authentication is not required. If you wish for your server to require client authentication, use: serversocket.setNeedClientAuth(true). To experiment with the HttpsServer class: 1. Copy the HttpsServer and ProcessConnection classes into a file named HttpsServer.java 94

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International University of Africa

Faculty of computer studies

2. Save this file in the same directory where the serverkeys file was created by the keytool 3. Compile the HttpsServer.java using javac as seen before in the HttpServer. 4. Run the HttpsServer. By default it runs on port 443, but if you cannot start it on this port, choose another port number greater than 1024. 5. Open a web browser and enter the request: https://localhost or https://127.0.0.1. This assumes the server is running on port 443. If not, then use: https://localhost:port

When you enter an https:// URL in the browser, you get a security alert popup window like the one in Figure 3.3 This is because the HTTP server certificate was self-generated. In other words, it was generated by an unknown certification authority, one that was not found among the certification authorities your browser keeps in its store. You have the option to view the certificate (check whether it is a proper certificate and discover who signed it) and then install it, reject the certificate, or accept the certificate.

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Figure 3.4: Server certificate issued by an unknown certification authority

If you just view the certificate by clicking the Examine Certificate button,you will see the certificate we have already generated. The figure below shows this.Note we are using the Mozilla Firefox as our default browser.

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Fig 3.5 A view of the generated certificate

Note: Generating your own certificate is fine for internal private systems. For public systems, however, it is a good idea to get a certificate from a well known Certification Authority in order to avoid the browser security alert. If you accept the certificate you will be able to see the page behind the secure connection, and future access to the same Web site will not cause the browser to issue a security alert. Note that there are many Web sites that use HTTPS whose certificates were either self-generated or generated by unknown 97

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CAs. As an example, try to visit: https://www.jam.ca. If you have never visited this Web site, you will see a security alert like the one in Figure 3. Note: When you accept the certificate, it is only for that session. In other words, once you completely exit the browser it is forgotten. Both Netscape and Microsoft Internet Explorer (MSIE) allow you to install a certificate permanently. To do this in MSIE, select "View Certificate" from Figure 3 and from the new window select "Install Certificate".

3.4 Programming Client Applications with JSSE As stated earlier in the previous section, The JSSE APIs supplement the java.security and java.net packages by providing extended networking socket classes, trust and key managers, and a socket factory framework for encapsulating socket creation behavior. These classes are included in the packages javax.net and javax.net.ssl. The javax.net.ssl.SSLSocketFactory class is an object factory for creating secure sockets. An instance of SSLSocketFactory can be obtained in two ways: 1. Get the default factory by calling SSLSocketFactory.getDefault. The default factory is configured to enable server authentication only (no client authentication). Note that most e-commerce web sites do not require client authentication. 2. Construct a new factory with specified configured behavior (this is beyond the scope of this project). Once an instance of SSLSocketFactory has been created, you can create an instance of SSLSocket by invoking a createSocket method on the SSLSocketFactory instance. Here is an example that creates a socket 98

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International University of Africa

Faculty of computer studies

connection to Sun's WWW server through the SSL port 443, which is the default port number for HTTPS. // Get a Socket factory SocketFactory factory = SSLSocketFactory.getDefault(); // Get Socket from factory Socket socket = factory.createSocket("www.sun.com", 443);

3.5.1

Working with Low-level SSL Sockets Now, let's see a complete example of opening an SSL socket connection to

an HTTPS server using low-level sockets. In this example, an SSL socket connection will be opened to an HTTPS server, and then we read the content of the default document. Code Sample 1 shows this application. The instructions that open the SSL socket are highlighted in bold. As you can see, the rest of the application is regular Java code for input/output streams.

Code Sample 1: ReadHttpsURL1 import java.net.*; import javax.net.*; import javax.net.ssl.*; public class ReadHttpsURL1 { static final int HTTPS_PORT = 443; public static void main(String argv[]) throws Exception { if (argv.length != 1) { 99

Public key Infrastructure

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International University of Africa

Faculty of computer studies

System.out.println("Usage: java ReadHttpsURL1 "); System.exit(0); } // Get a Socket factory SocketFactory factory = SSLSocketFactory.getDefault(); // Get Socket from factory Socket socket = factory.createSocket(argv[0], HTTPS_PORT); BufferedWriter out = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())); BufferedReader in = new BufferedReader( new InputStreamReader(socket.getInputStream())); out.write("GET / HTTP/1.0\n\n"); out.flush(); String line; StringBuffer sb = new StringBuffer(); while((line = in.readLine()) != null) { sb.append(line); } out.close(); in.close(); System.out.println(sb.toString()); } }

To experiment with this application: 100

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1. Copy and paste the code of the ReadHttpsURL1 class into a file named ReadHttpsURL1.java, and save this file in a directory of your choice. 2. Compile the ReadHttpsURL1.java using javac. 3. Run the ReadHttpsURL1 and provide the domain of an HTTPS url. Here is an example: Prompt> java ReadHttpsURL1 www.sun.com

After a few seconds, you will note that tons of HTML code is displayed on your screen. Note that even though we are providing the domain www.sun.com, we are opening a connection to https://www.sun.com. This is because the port number we are using, 443, is the default port number for HTTPS. Try another example, such as: Prompt> java ReadHttpsURL1 www.jam.ca

This will throw the following exception. Can you guess why? Exception in thread "main" javax.net.ssl.SSLHandshakeException: java.security.cert.CertificateException: Couldn't find

trusted certificate at com.sun.net.ssl.internal.ssl.BaseSSLSocketImpl.a(DashoA 6275) It didn't work for a good reason. This was caused by the remote server sending a certificate that is unknown to the client. As we mentioned in the previous sections, when a client connects to a server, the server sends its certificate to the client for authentication. Well, in the first example, where you entered www.sun.com, that server did send its certificate, but Java checks the default 101

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certificate store and realized that the certificate was generated by one of the trusted Certificate Authorities that Java trusts by default. In the second example where you entered www.jam.ca, the certificate for that site was either self-generated or generated by a Certification Authority unknown to Java, and therefore it wasn't trusted.

3.5.2 Exporting and Importing Certificates To explain how to export and import certificates, we will use our own HTTPS server which is discussed in the 3.4.3 section (sample code 2). To get started, do the following: 1. Run the HTTPS server as discussed in section 3.4.3. 2. Run the ReadHttpsURL1: java ReadHttpsURL1 localhost. You will receive the same exception as the one described above. 3. Export the server's certificate using the following keytool command that says:  Export the server's certificate from the file serverkeys, whose alias is Muhedin. 

Save the exported certificate in a file called server.cert, which will be created by the keytool. As you can see, we are asked to enter the password. Upon successful entry of the password, the server's certificate got exported and saved in the file server.cert.

Prompt> keytool -export -keystore serverkeys -alias muhedin file server.cert.

The following command window shows the process;

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4. Copy the server.cert file to the directory where ReadHttpsURL1 is

located. Use the keytool to create a new keystore and import the server's server.cert certificate into it. Here is a sample command: Prompt>

keytool -import -keystore trustedcerts -alias muhedin -

file server.cert

This command produces the following output. We were asked to enter a password. This is a new password for the trustedcerts keystore. This keystore is created by the keytool. At the end of the output, we got asked if we wish to trust this certificate our answer was yes.

5. Now run the ReadHttpsURL1 and inform it where to look for certificates using the following command: Prompt> java -Djavax.net.ssl.trustStore=trustedcerts ReadHttpsURL1 localhost 103

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International University of Africa

Faculty of computer studies

This will contact your HTTPS server, verify its certificate and if it is valid, will download the default page index.html as following window shows.

Note: A trust manager is responsible for determining if the remote authentication credentials should be trusted. The following rules are used: 1. If a truststore is specified by the javax.net.ssl.trustStore system property, then the trust manager will use the file provided to check for credentials. If, however, the system property exists but the file specified doesn't exist, then no truststore is utilized and a CertificateException will be thrown. 2. If the javax.net.ssl.trustStore system property is not defined, then a default trust store is searched for: o

If a trust store named jssecacerts exists in the lib/security subdirectory of your java.home directory, it will be used.

o

If jssecacerts doesn't exist, but cacerts does (which is shipped with the J2SDK with a limited number of trusted root certificates), it will be used.

On our Windows client machine we used, the java.home directory is C:\j2sdk1.4.1\jre. In the above example, if you change the name of trustStore to jssecacerts and move it to the lib/security subdirectory, then you no 104

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International University of Africa

Faculty of computer studies

longer need to specify the javax.net.ssl.trustStore property on the command line as window below shows.

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Chapter four

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International University of Africa

Faculty of computer studies

4.1 Results After a deep study of the public key infrastructure and its security protocols especially the secure socket layer protocol that is implemented in our project, we reached the following main results:1. The SSL protocol together with some other protocols like SET,PGP and TLS form the backbone of the e-commerce and secure communications. 2. The java programming language offers a great network programming tools as well as network security implementations. 3. When using the Http protocol under the SSL (meaning Https), some problems may appear. Those problems are mainly due to authentication; for example,

a client initiates a communication using a secure channel to

defined server; the initiated server sends a certificate which is not trusted by the client e.g. self generated certificate. 4. In any PKI system, there must be a trusted third party on condition that both communicating parties trust it. This third party is called Certification Authority (CA). The main function of the CA is the production of digital certificates. 5. The JSSE API is implementable on either JDK 1.1.x or Java TM 2 Platform, Standard Edition. This implementation is not intended for use in the J2SDK version 1.4, which has a version of JSSE already bundled. 6. Modern encryption and security technologies are mostly dominated and restricted by west especially the united state of America. This relates greatly the political aspect to the scientific development.

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International University of Africa

Faculty of computer studies

4.2 Project’s Problems During the course of our project research, which took approximately four months, we come across a number of problems of which its prominent ones are:1. The Public key infrastructure is a new technology of internet security which is not broadly explored and searched before, this resulted scarcity of the required information. Therefore, we spent much time and hardly collected the needed information 2. Another problem, which the most important, is the unavailability of the implementation of the newly discovered security protocols or even a clue of its implementation idea. To further explain this, we used the java programming language to implement the practical part of our project which we introduced the SSL protocol. The java security packages that are necessary for the implementation of the SSL protocol is called java security socket extension 'JSSE'. The JSSE does not freely come with earlier versions of the java development kits. It therefore needs to be downloaded from Sun's official Website and then integrated to the JDKs.The problem came after we tried to download the JSSE packages and the reason is that the JSSE packages obey the American exportation law. This means that any American product can not be exported to US embargoed country. Knowing that Sudan is an American embargoed country we could not download the packages. To solve that problem, we were assisted by some of our friends in the US. 3. One last problem that we met which may also face any developer, using the internet security or PKI protocols is software integration of the encryption toolkits. 108

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

4.3 Recommendations The purpose of this research is to discover the general idea about the Public Key Infrastructure (PKI). How ever, there were problems that we faced during the preparation of this research, but we eventually recovered and got solutions for them. In this section we recommend the upcoming researchers in PKI to give special attention to the following recommendations: 1. An improved background of cryptography is a necessary step towards the understanding the Public Key Infrastructure (PKI). 2. Researchers, who are performing study on PKI technology, are recommended to continue developing where we stopped. 3. We highly recommend making a lot of studies to this field so as to utilize the technology behind PKI. 4. We also recommend manipulating the SSL built in software tools like OpenSSL instead of using programming language. 5. Any one who is studying the PKI protocols is recommended to concentrate on the Secure Socket Layer protocol (SSL), because the SSL is considered to be the basic protocol among the PKI protocols.

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

4.4 Glossary American National Standards Institute (ANSI) Founded in 1918, ANSI is a voluntary organization composed of over 1,300 members that creates standards for the computer industry. Application Programming Interface (API) A set of routines or functions that are available to developers and applications to provide specific services used by a system. Bytecode The compiled format for Java source programs. Once a Java program has been converted to bytecode, it can be transferred across a network and executed by JVM or JRE. By convention, Java bytecode files end with a .class file extension. Certificate (or digital certificate) An attachment to an electronic message used for security purposes. The common purpose of a digital certificate is to verify the identity of the sender. Certification Authority (CA) A trusted third-party organization or company that issues digital certificates. The CA guarantees that the identity of the party in the certificate is genuine. Client A computer or device on a network that calls another computer for resources. Connection A link between two or more computers, processes, applications, devices, networks, and so on. Connections may be logical, physical, or both. Cryptography

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

A general term for the encryption and decryption methods used for data transmission and protection.

E-commerce Conducting business online. This includes, for example, buying and selling products on the Internet. Email Electronic messages transmitted on a network. It is a general term for electronic mail or Internet mail. Event handler A routine inside an application to be triggered by an event such as a mouse click. Event listener A routine inside an application to listen to any event generated by the user. File Transfer Protocol (FTP) The protocol used on the Internet for sending and receiving files. Hyper Text Transfer Protocol (HTTP) The underlying protocol defining how messages are formatted and transmitted on the Web, and what actions Web servers and browsers should take in respond to various commands. Internet Sometimes called the TCP/IP network, this is the vast collection of interconnected networks that all use the TCP/IP suite. Internet Engineering Task Force (IETF) The main standards organization for the Internet concerned with Internet architecture and operations. It is open to anyone who is interested. Internet Explorer (IE) 111

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

The Web browser developed by Microsoft for Windows platforms. IE is the most popular browser used on the Web.

IP address (or IP number) A unique number consisting of four parts separated by dots, e.g., 165.113.223.2 Each part can have values from 0 to 255. For the TCP/IP network (or Internet), IP addresses can be used to uniquely identify a computer on the network. J2SDK A Java development environment from Sun Microsystems used to develop Java applications. It converts Java source file to bytecode to be executed by the JVM and JRE. Java A high-level programming language developed by Sun Microsystems. Java is an object-oriented language similar to C++, but simplified to eliminate language features that cause common programming errors. By convention, Java program files end with a .java file extension. Java Runtime Environment (JRE) A run time environment developed by Sun Microsystems to convert Java bytecode into machine language and execute it locally. Java Vitural Machine (JVM) An abstract computing machine, or virtual machine, JVM is a platformindependent execution environment that converts Java bytecode into machine language and executes it locally. LINUX

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

An implementation of UNIX that runs on PCs and many other platforms. It was developed mainly by Linus Torvalds. LINUX is freely distributable with open source code. Multipurpose Internet Mail Extension (MIME) A specification for formatting non-ASCII messages so that graphics, audio, and video can be sent over the Internet. Netscape browser (NS) The Web browser developed by Netscape Communications. It runs on all the major platforms such as Windows, MacOS, and UNIX/LINUX. Network News Transfer Protocol (NNTP) The protocol used to post, distribute, and retrieve USENET messages. The official specification is RFC 977. Port A number used to identify TCP/IP applications. Generally a port is an entry or exit point Pretty Good Privacy (PGP) A method developed by Phil Zimmermann to encrypt or disguise computer information so that it can be securely transmitted over a network. Private Key The digital key that is kept secret in a public-key cryptographic structure Protocol Rules governing the behavior or method of operation. Public key The digital key mode available to the public in a public-key cryptographic structure. Public-key cryptography 113

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

A cryptographic technique that uses two digital keys, a public key known to everyone and a private or secret key to keep secret. When, say, John wants to send a secure message to Mary, he uses Mary's public key to encrypt the message. Only Mary or the owner of the corresponding secret key can decrypt the message.

Public-Key Infrastructure (PKI) A system of digital certificates, Certification Authorities, and other registration authorities that verify and authenticate the validity of each party involved in an Internet transaction. Secure Electronic Transfer (SET) A standard used by major credit card companies to set up secure credit card transactions on the Internet. SET allows your credit card number to go direct to the credit card company without being seen by the merchant. Secure Sockets Layer (SSL) A protocol developed by Netscape to set up a public-key cryptography connection on the Web. SSL allows a Web browser to locate and display a Web page in secure mode. The

Web

browser

and

server, in

this

case,

are

performing

encryption/decryption using public-key technologies online. Server A computer or device on a network that manages network resources. Usually, servers are set up on a network to provide services to clients. Socket In the TCP/IP network, an addressable point that consists of an IP address and a TCP or UDP port number that provides applications with access to TCP/IP. TCP/IP network 114

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

The network using the TCP and IP suite. TCP guarantees data transmission; IP deals with packets and address. TCP/IP networks are generally called Internet. Transmission Control Protocol (TCP) One of the main protocols in TCP/IP networks. TCP enables two hosts to establish a connection and exchange data. It guarantees delivery of data and also that packets will be delivered in the same order in which they were sent. Data will be retransmitted if necessary. Transport Layer Security (TLS) Based on Netscape's SSL 3.0, TLS is an extension of SSL. Uniform Resource Locator (URL) The global address of documents and other resources on the Web. For example, http://www.pwt-ex.com/ex01-01.htm and ftp://www.pwt-ex.com/ex01-01.htm are two URLs to identify the same file on the Web. UNIX An operating system written by Ken Thompson of Bell Labs and used for mainframes and minicomputers. It is now available for personal computers (PCs). Web A community of Internet servers that support HTML/XHTML formatted documents. The documents or Web pages support a feature that links to other documents, as well as graphics, audio, and video files. Web browser A software application used to locate and display Web pages on the Internet. Web client A computer or device running a Web browser to request network resources. Web page A document on the Web. Every Web page is identified by a unique address called the uniform resource locator (URL). 115

Public key Infrastructure

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

Web server A machine running server software such as Apache or IIS, assigned an IP address, and connected to the Internet so that it can provide documents on the Web. A Web server is sometimes called a host computer. Web site A Web server with a global unique URL.

Web site address Refers to the IP address (such as 165.181.109.11) of the host computer or the name (such as www.iua.com) that can be translated into an IP address.

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

4.5 Books Referred 1- Cryptography For Dummies By Chey Cobb John Wiley & Sons © 2004 Publisher: Wiley publishing Inc 2- An article from the net Under title of "what is cryptography" Written by Dan Blacharski 3- Information security (an overview) Printed by Mohan Makhajan Publisher: Asoke K.Ghosh New Delhi 2004 4- An introduction to cryptography Printed in USA Author not found 5- A paper from the internet Under title of "An overview of cryptography" By Gary C.Kessler Pub date: May 1998 6- Secure XML: the new syntax for signatures & encryption By Donald E.Eastlake, Kitty Niles Publisher: Adison Wesley Pub date: July 19, 2002 7- Article from (wikipedia – the free encyclopedia on the net) 8- Practical web technologies 117

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

By P.K. yuen, V.Lau Publisher: Adison Wesley Printed in Great Britain Pub date: September 09, 2003 9- Public key infrastructure overview By Joel weise Publisher: Sun Microsystems Pub date: August 2001 10- Cryptography & Network security principle and practices Fourth edition By William stallings Publisher: Prentice Hall November 16, 2005

11- The Internet 12- Data Communication & Networking By Behrouz A.Forouzan Deanza College Publisher: Tofa McGrow.Hill New Delhi 13- Secure programming cookbook for c and c++ By Matt Messier , John viega Published by O'Reily Pub date : July 2003 14- network security with OpenSSL By Pravir Chandra, john Viega Publisher : O'Reily 118

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Muhedin Abdullahi Mohammed

International University of Africa

Faculty of computer studies

Pub date: June 2002 15- An article from the net Written by Qusay H. Mahmoud November 2002

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