Latest Paper On Cryptography

Sundar Rajan. R Total No of Pages: 13 Referred: www.google.com www.wikipedia.org

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9790680719 [17.09.2008]

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An Efficient Operator based Unicode cryptography Algorithm for Text, Audio and Video Files R.Sumathi *, R.Sundarrajan **

ABSTRACT There are many aspects to security and

The same plaintext will encrypt to different

many applications, ranging from secure

cipher text in a stream cipher .This

commerce

private

algorithm increases the complexity of

communications and protecting passwords.

solving the cipher text when handled by

One

intruders. Thereby it provides extremely

and

essential

payments

aspect

to

for

secure

communications is that of secret key cryptography, which the focus of this paper.

better security for all type of files. INTRODUCTION

With secret key cryptography, a Cryptography is the practice and

single key is used for both encryption and decryption. The key selection mechanism and the encoding methodology express the efficiency of the cipher text generated. In this paper, a new method of encoding technique using the mathematical operators

study of hiding information. In modern times, cryptography is considered a branch of both mathematics and computer science, and is affiliated closely with information theory, computer security, and engineering.

over Unicode character set facilitates better encoding algorithm.

Cryptography is used in applications present

in

technologically

advanced

societies; examples include the security of ATM cards, computer passwords, and * Assistant Professor,Dept of CSE, J.J.College of Engg.& Tech.,Trichy-09. Email ID: [email protected]

electronic commerce, which all depend on cryptography.

** Pre Final Year Student, Dept of CSE, J.J College of Engg & Tech., Trichy-09

Cryptography refers to encryption, the

process

of

converting

ordinary

information (plaintext) into unintelligible

Integrity: Assuring the receiver that the

cipher text Decryption is the reverse,

received message has not been altered in any

moving from unintelligible cipher text to

way from the original.

plaintext. A cipher is a pair of algorithms which creates the encryption and the reversing decryption. The detailed operation of a cipher is controlled both by the

This is a secret parameter for a specific message exchange context. Keys are important, as ciphers without variable keys are trivially breakable and therefore less than useful for most purposes. Historically, were

often

used

directly

for

encryption or decryption, without additional procedures

such

as

authentication

that the sender really sent this message. Any new design of Cryptographic technique must

algorithm and, in each instance, by a key.

ciphers

Non-repudiation: A mechanism to prove

accomplish

the above

requisites. Cryptography not only protects data from theft or alteration, but can also be used for user authentication. CRYPTOGRAPHIC SCHEMES In

general,

three

types

of

cryptographic schemes typically used to accomplish these goals:

or

integrity checks. PRE REQUISITES

1. Secret Key Cryptography (SKC): Uses a single key for both encryption and decryption

There are various security requirements for a Cryptographic technique including: Authentication: The process of proving one's identity. (The primary forms of hostto-host authentication on the Internet today

2. Public Key Cryptography (PKC): Uses one key for encryption and another for decryption

are name-based or address-based, both of which are notoriously weak.)

3. Hash Functions:

Privacy/confidentiality: Ensuring that no

Uses a mathematical transformation to

one can read the message except the

irreversibly "encrypt" information

intended receiver.

are the various cryptographic schemes

whereas the same plaintext will encrypt to

available

different cipher text in a stream cipher.

depending

upon

their

application and ease of use. SECRET KEY CRYPTOGRAPHY: With secret key cryptography, a

Block ciphers can operate in one of several modes; the following four are the most important:

single key is used for both encryption and

Electronic Codebook (ECB) mode is the

decryption. As shown in Figure 1A, the

simplest, most obvious application: the

sender uses the key (or some set of rules) to

secret key is used to encrypt the plaintext

encrypt the plaintext and sends the cipher

block to form a cipher text block. Two

text to the receiver. The receiver applies the

identical plaintext blocks, then, will always

same key (or rule set) to decrypt the

generate the same cipher text block.

message and recover the plaintext. Because

Although this is the most common mode of

a single key is used for both functions,

block ciphers, it is susceptible to a variety of

secret key cryptography is also called

brute-force attacks.

symmetric encryption. Secret key cryptography schemes are

Cipher Block Chaining (CBC) mode adds a feedback mechanism to the encryption

generally categorized as being either stream

scheme.

In

CBC,

ciphers or block ciphers. Stream ciphers

exclusively-O

operate on a single bit (byte or computer

previous

word) at a time and implement some form of

encryption. In this mode, two identical

feedback mechanism so that the key is

blocks of plaintext never encrypt to the same

constantly changing. A block cipher is so-

cipher text.

Red

cipher

the

plaintext

(XORed)

text

block

is

with

the

prior

to

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 cipher text when using the same key in a block cipher

Cipher Feedback (CFB) mode is a block cipher

implementation

as

a

self-

synchronizing 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

block; 3DES is also described in FIPS 46-3

1-byte CFB mode, for example, each

and is the recommended replacement to

incoming character is placed into a shift

DES.

register the same size as the block, encrypted, and the block transmitted. At the receiving side, the cipher text is decrypted and the extra bits in the block (i.e., everything above and beyond the one byte)

DESX: A variant devised by Ron Rivets. By combining 64 additional key bits to the plaintext prior to encryption, effectively increases the key length to 120 bits.

are discarded.

Advanced Encryption Standard (AES):-

Output Feedback (OFB) mode is a block

This algorithm use a variable block length

cipher implementation conceptually similar

and key length; the latest specification

to a synchronous stream cipher. OFB

allowed any combination of keys lengths of

prevents the same plaintext block from

128, 192, or 256 bits and blocks of length

generating the same cipher text block by

128, 192, or 256 bits.

using an internal feedback mechanism that is independent of both the plaintext and cipher text bit streams.

Similarly, there are Several Algorithms like Blowfish, International Data Encryption Algorithm (IDEA),Two fish,

Secret key cryptography algorithms that are

Camellia, Secure and Fast Encryption

in use today include

Routine (SAFER),SEED, Skipjack. These are algorithms are designed

Data Encryption Standard (DES): DES is a block-cipher employing a 56-bit

extending the ideas already available.

key that operates on 64-bit blocks. DES has a complex set of rules and transformations

PUBLIC-KEY CRYPTOGRAPHY

that were designed specifically to yield fast hardware

implementations

and

Public-key cryptography has been

slow

software implementations

said to be the most significant new development in secure communication over

Triple-DES (3DES): A variant of DES that employs up to three 56-bit keys and makes three encryption/decryption passes over the

a

non-secure

communications

without having to share a secret key.

channel

Public Key Cryptography or Asymmetric

PKC depends upon the existence of so-

cryptography provides the same message

called one-way functions, or mathematical

security

symmetric

functions that are easy to computer whereas

cryptography, but additionally provides the

their inverse function is relatively difficult to

non-repudiation guarantee. ‘Asymmetric’

compute. Let me give you two simple

refers to the fact that different keys are used

examples: In public-key cryptosystems, the

for encryption and decryption.

public key may be freely distributed, while

guarantees

as

One key is kept secret (‘secret key’) and the other is made public (‘public key’), and are both unique. The recipient’s public key should be used during the encryption process to ensure message confidentiality as only the recipient has the necessary secret key to decrypt the message. If, however, the

its paired private key must remain secret. The public key is typically used for encryption, while the private or secret key is used for decryption. Diffie and Hellman showed that public-key cryptography was possible by presenting the Diffie-Hellman key exchange protocol

message is encrypted using the sender’s

In addition to encryption, public-key

private key the sender cannot deny sending

cryptography can be used to implement

the message as his private key is unique and

digital

is only known to him.

signature is reminiscent of an ordinary

Typical include

asymmetric

RSA,

Asymmetric

ElGamal

cryptography

algorithms and

is

DSA.

extremely

powerful, but this comes at a cost. Especially for longer messages and keys, it is

much

slower

than

its

symmetric

cryptography counterparts. This is due in part to the fact that, in order to achieve

signature

schemes.

A

digital

signature; they both have the characteristic that they are easy for a user to produce, but difficult for anyone else to forge. Digital signatures can also be permanently tied to the content of the message being signed; they cannot then be 'moved' from one document to another, for any attempt will be detectable.

comparable security, asymmetric keys are

In digital signature schemes, there

generally around an order of magnitude

are two algorithms: one for signing, in

longer than symmetric keys.

which a secret key is used to process the message (or a hash of the message, or both),

and one for verification, in which the

message, but encrypted using a public-key

matching public key is used with the

algorithm.

message to check the validity of the

schemes are often used, in which a

signature. RSA and DSA are two of the

cryptographic hash function is computed,

most popular digital signature schemes.

and only the resulting hash is digitally

Digital

signed.

signatures

are

central

to

the

operation of public key infrastructures and many network security schemes (e.g.,

Public-key algorithms are most often based on the computational complexity of "hard" problems, often from number theory. For example, the hardness of RSA is related to the integer factorization problem. recently,

cryptography has

elliptic

developed

curve

in

which

problems involving elliptic curves. Because of the difficulty of the underlying problems, public-key

algorithms

involve

operations such as modular multiplication and exponentiation, which are much more computationally

signature

HASH FUNCTIONS

expensive

and one-way encryption, and are algorithms that, in some sense, use no key. Instead, a fixed-length hash value is computed based upon the plaintext that makes it impossible for either the contents or length of the plaintext to be recovered.

security is based on number theoretic

most

hybrid

Hash functions, also called message digests

SSL/TLS, many VPNs, etc).

More

Similarly,

than

the

techniques used in most block ciphers,

Hash algorithms are typically used to provide a digital fingerprint of a file's contents often used to ensure that the file has not been altered by an intruder or virus. Hash

functions

are

also

commonly

employed by many operating systems to encrypt passwords. Hash functions, then, provide a measure of the integrity of a file. Hash

functions

are

sometimes

especially with typical key sizes. As a result,

misunderstood and some sources claim that

public-key cryptosystems are commonly

no two files can have the same hash value.

hybrid cryptosystems, in which a fast high-

This is, in fact, not correct. Consider a hash

quality symmetric-key encryption algorithm

function that provides a 128-bit hash value.

is used for the message itself, while the

There are, obviously, 2128 possible hash

relevant symmetric key is sent with the

values. But there are a lot more than 2128

possible files. Therefore, there have to be

considered. This similarity can be depicted

multiple files in fact; there have to be an

pictorial as follows.

infinite number of files. By the above

basics about the

Cryptography and the study is about the

VALUE 1

*

Cryptographic Schemes available and their methodology of handling keys and way of Encoding

generated

each

class

VALUE X

VALUE 2

of

Techniques.

The value x is definitely different from the value of value 1 and value 2

PROPOSED ALGORITHM:

depending upon the * operation and the After discussed elaborately about the

values.

various cryptographic schemes available and the structure about the algorithms for the

Similarly in the Cryptography the

schemes, the paper is concerned towards the

plain Text must be encoded into Cipher text

new design of “Operator based Encoding

which must different from the original text

Technique with Unicode Character Set

to ensure the security of the data transacted.

Support”. PLAIN TEXT

OPERATORS IN ENCODING:

ENCODING

This

algorithm

is

designed

considering the fact that “Every input plain

CIPHER TEXT

text can be converted into numeric value whatever may be its magnitude”. When Numeric values are resulted

In the above for the encoding

they can be used for mathematical operators

operation performed, the plain text must be

resulting in a different solution than that of

converted into cipher text which cannot be

the origin.

recognized or more precisely the text which is different from the original text.

This concept seems too analogous to the

Cryptography

operation

that

we

Therefore from this we can define

It is 16 bit based character set which

the cipher text in cryptography as the text

encompasses every character available in all

that is different from the original text where

the formats of files available.

the difference needs elongated complex procedures to be followed.

Therefore we came across two basic steps in this design which includes,

Hence we have proved that an operator based algorithm can be used as Encoding technique to generate the required cipher text.

1. Converting any given plain text into numeric values based on Unicode mapping. 2. After numeric mapping the Text

UNICODE SUPPORT: Now

we

established

input is in operable form which is that

the

operated

through

different

mathematical operators can be used for

operators and the required result

encoding. Such encoding is possible if and

once

only if the given plain text (any text) must

Unicode character set.

be converted into operable manner. Operable manner means that the plain text must be converted into numbers

again

mapped

using

Hence the algorithm basic design is completed using Unicode support over operators.

for operation over them. PLAIN TEXT

CIPHER TEXT

Such a mapping for every character into a numeric value is possible only in Unicode character set. In order to convert

UNICODE FORM

OPERATOR F(x)

any text into number Unicode character set support is needed. In Unicode character set, there are 65536 characters available and is a common standard worldwide independent of the languages used.

SECURITY BY FEED-BACK: One of the major properties of the cryptography is the key providing concept

which

provides

security

as

well

of

as

Feedback based Security the

algorithm is designed as,

authorization. Unicode

1. The First character alone is

mapping and operator based encoding favors

added directly with the security

the generation of cipher text but the security

key.

From

the

above,

the

is not discussed.

2. The

following

operated

In order to provide security we shall

by

character

above

is

designed

bind a numeric key as security with the

method over the first and then the

cipher text generated in the above method.

result is made operated towards the next and soon.

Here we have multiple ways for key

3. This kind of Feedback based

binding with the cipher text to be generated.

security illustrates that the same

1. Entire Text Binding:

character is mapped into different

Due to usage of numeric

cipher text depending on the

values to generate the cipher text the

presence of the character at

usage of key in numbers is possible.

various positions in Plain Text.

It is possible to add each character

4. It is called Feed Back based

with key. But it yields a worst

security because the key for the

method of security since the key will

current character under process

be spread over the text uniformly

of encoding depends on the

which cannot be efficient which is

previous input character.

similar to X-shifting the numeric value bonded with the cipher text. Hence this method of key binding can be mostly avoided. 2. Feed Back based Security: Analyzing the failure of the Entire Text Binding, in the method

Indirectly in this kind of Security, we have built the security for whole cipher text This algorithm since provides a key it comes under the mechanism of Secret Key Cryptography discussed in the basics of this paper.

FIRST INPUT FROM FILE TO BE ENCODED

SECRET

OPERATOR BASED ALGORITH M FOR GENERATI NG CIPHER TEXT

CURRENT INPUT FROM FILE

NEXT INPUT FROM FILE TO BE ENCODED

UNICODE CHARACTER SET

FILE TO BE Mapped to respective Cipher Text

OUTPUT FILE – CIPHER

ALGORITHM FOR ENCODING: No Repetition: In

Operatebasedencode () this

algorithm,

no

{

repetition of cipher text for the same character throughout the plain text occurs,

Read currentin from input file

which is considered to be a demerit of the secret key cryptography which we have cleared in this algorithm. The algorithm is designed as follows

Add secretkey with currentin // any other operator can be employed Start loop until endof inputfile

based on the statements concluded above.

Pastcharin=currentin

Hence it is working

Read currentin from input file

fine for all the set of files since it uses

Precipherchar=pastcharin * currentin

Unicode support for character mapping.

Place Mapoverunicode( precipherchar) in Outputfile

Now the secret key applied by applied in this algorithm is feedback based which undergo following criteria

End loop 1. The key applied will be a numeric

}

value

which

must

be

unique

considered upon user.

Mapoverunicode(precipherchar)

2. Since it uses Unicode character set

{

support the no of unique values will be from 0-65536.

Search given precipherchar in Unicode Character Set

3. The number of keys used in the algorithm range is small and is

Return the appropriate character

possible to exceed over 65536 but it recycles within the range.(without

}

using modulus operator) This algorithm uses feedback based secret key in which the key is bonded with

SERIAL DIGIT SECRET KEY:

the cipher text indirectly and so no repetition

Now in order to clear these criteria the key

is allowed.

can be applied to cipher text in blocks by

VALIDITY OF SECRET KEY: The above algorithm is tested so many times and it is working fine for the input files of various types like text files, documents, and even mp3 files (Audio Files) and video files.

blocks. The operation needs a range of numbers where every figure in the key provided will be added in blocks to the entire cipher text. Suppose

that

for

a

text

“COMPUTER” for certain encoding it may

result in “2we45r6/” and the key provided

in the scheme is the key can be

while encoding is “1532”.then the operation

any range larger.

of encoding can simply depicted as,

3. Since simple users of encoding in this method have to memorize a

2

w

e

4

5

r

6 /

series of digits without fail to obtain the document clearly.

1

5

3

2

1

5

3

2

STRING STRUCTURE KEY BIND: In order to increase the

CIPHER TEXT

difference of key bonded with the cipher text which is only 0-9 arrived a solution as Depending on the * operator used, the key is added with the cipher text in blocks and hence the range of Unicode is

follows in this method namely “STRING STRUCTURE KEY BIND”. 1. The key here handled may be a

different which is better than feedback

series

system.

of

characters

instead

of

numbers.

Here we can note that the key size

2. The string binded can have Unicode

can range from 0 – size of the file. Hence by

equivalent values that are larger than

this method the user can add key to the

the range 0-9.

cipher text up to a larger range when 3. The characters each in the key string

compared to feed back based system.

can range from 0-65536 each. Limitations in this method: 4. The length of the key can be large 1. Even though the key is a series of

enough equivalent to the size of the

digits, the numeric value added

input file which is the maximum

with each character range from

value.

0-9. 5. 2. This

mild

difference

again

checks the security and needs further study and the advantage

Even though the key can be severely large, the optimal performance can

be maintained by the user’s decision over the peak value to be handled. 6. Since it is a series of characters i.e. string,

a

meaningful

string

for

average users can help them to remember enough to recover their documents. Hence upon the various schemes of key binding discussed the string structure secret key again using Unicode support is better and even best of the key binding techniques discussed. Here using various schemes for secret key does not mean the congestion of ideas in illustrating the secret key but it is a real time derivation for deciding the best secret key technique. Once again we can notice that the string structure secret key holding the property “no repetition”.