Mcs-42 Des Algorithm

Question 5: Describe the DES algorithm in your own words .What are its variants?

(10 marks)

Encryption is a way of hiding secrets by applying mathematical functions to plain text to produce text that is difficult to decrypt. If we have an equation of the form c = a⊕b then it is quite hard to discern c if we only know a. If we know both inputs we of course know the output but that is true for any function. DES(Data Encryption Standard) is a good cryptography. The Data Encryption Standard (DES) was developed in the 1970s by the National Bureau of Standards with the help of the National Security Agency. Its purpose is to provide a standard method for protecting sensitive commercial and unclassified data. IBM created the first draft of the algorithm, calling it LUCIFER. DES officially became a federal standard in November of 1976. DES is a block cipher with a 64-bit block size. It uses 56-bit keys which is divided into eight 7-bit blocks and an 8th odd parity bit is added to each block (i.e., a "0" or "1" is added to the block so that there are an odd number of 1 bit in each 8-bit block). This makes it susceptible to exhaustive key search with modern computing powers and special-purpose hardware. By using the 8 parity bits for rudimentary error detection, a DES key is actually 64 bits in length for computational purposes (although it only has 56 bits worth of randomness, or entropy). It selects a 64 bit block and modifies it depending on the key, i.e. {0, 1}64 → {0, 1}64.

Fundamentally DES performs only two operations on its input, bit shifting, and bit substitution. The key controls exactly how this process works. By doing these operations repeatedly and in a non-linear manner you end up with a result which can not be used to retrieve the original without the key. Those familiar with chaos theory should see a great deal of similarity to what DES does. By applying relatively simple operations repeatedly a system can achieve a state of near total randomness. DES works on 64 bits of data at a time. Each 64 bits of data is iterated on from 1 to 16 times (16 is the DES standard). For each iteration a 48 bit subset of the 56 bit key is fed into the encryption block represented by the dashed rectangle above. Decryption is the

inverse of the encryption process. The "F" module shown in the diagram is the heart of DES. It actually consists of several different transforms and non-linear substitutions. Consult one of the references in the bibliography for details. DES is the most widely used symmetric algorithm in the world, despite claims that the key length is too short. DES is still strong enough to keep most random hackers, adversaries and individuals out. DES is easily breakable with special hardware by, government, criminal organizations etc. A variant of DES, Triple-DES (also 3DES) is based on using DES three times (normally in an encrypt-decrypt-encrypt sequence with three different, unrelated keys). The Triple-DES is arguably much stronger than (single) DES; however, It is three times slower than regular DES. Please add little more about variant and post it in IMSF. Mohamed Sameer bin Mohamed bin Hasan bin Ali Analyst Programmer

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