Abstract
Problem statement: The strength of the block ciphers depend on the degree of confusion and diffusion induced in the cipher. Most of the transformations used for this purpose are well known to every one and can be broken by a crypt analyzer. Therefore, in order to counter attack the crypt analyzer, there is a need for better transformations in addition to the existing one. Approach: We tried to use key based random interlacing and key based random decomposition for this purpose. So that, a crypt analyzer cannot understand how interlacing and decomposition is done in every round unless the key is known. Results: The strength of the cipher is assessed by avalanche effect which is proved to be satisfactory. Conclusion/Recommendations: Key based random interlacing and decomposition can be used for introducing confusion and diffusion in block ciphers. The cryptanalysis carried out in this regard shows that the cipher cannot be broken by any cryptanalytic attack.
Highlights
MATERIALS AND METHODSIn the survey of literature of cryptography, majority of block ciphers are based on the feistel cipher (Tavares and Heys, 1995; Stallings, 2003)
In our recent investigations (Kumar and Kumar, 2008; Kumar and Sastry, 2009); we have demonstrated how a large block cipher of 256 bits can be generated using key based random permutations and involving interlacing and decomposition in feistel structure; providing good strength to cipher
Cryptanalysis: To asses the strength of our encryptiondecryption algorithms, we first show that brute force attack is not possible on our algorithm, we show that even the well known “known plaintext attack” cannot break our cipher, followed by an analysis for avalanche effect to prove the strength of the cipher
Summary
In the survey of literature of cryptography, majority of block ciphers are based on the feistel cipher (Tavares and Heys, 1995; Stallings, 2003) In this process, bits of plaintext undergo a series of permutations, substitutions and exclusive OR operations. Bits of plaintext undergo a series of permutations, substitutions and exclusive OR operations This creates confusion and diffusion in cipher which is achieved by the classical round function F of feistel structure. Our interest is to develop a block cipher of 256 bits by using a stronger version of interlacing and decomposition. This is accomplished by using key based random interlacing and key based random decomposition. An attacker cannot understand how interlacing and decomposition is done in each round unless the key is known
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