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In cryptography, linear cryptanalysis is a general form of cryptanalysis based on finding affine approximations to the action of a cipher. Attacks have been developed for block ciphers and stream ciphers. Linear cryptanalysis is one of the two most widely used attacks on block ciphers; the other being differential cryptanalysis.
The closer the approximation is to zero or one, the more helpful the approximation is in linear cryptanalysis. However, in practice, the binary variables are not independent, as is assumed in the derivation of the piling-up lemma. This consideration has to be kept in mind when applying the lemma; it is not an automatic cryptanalysis formula.
In cryptography, decorrelation theory is a system developed by Serge Vaudenay in 1998 [1] for designing block ciphers to be provably secure against differential cryptanalysis, linear cryptanalysis, [2] and even undiscovered cryptanalytic attacks meeting certain broad criteria.
Introduced by Martin Hellman and Susan K. Langford in 1994, the differential-linear attack is a mix of both linear cryptanalysis and differential cryptanalysis.. The attack utilises a differential characteristic over part of the cipher with a probability of 1 (for a few rounds—this probability would be much lower for the whole cipher).
The cipher is resistant against differential and linear cryptanalysis after a small number of rounds. However it was broken in 1996 by Thomas Jakobsen and Lars Knudsen, using interpolation attack. Denote by SHARK ( n , m , r ) {\displaystyle (n,m,r)} a version of SHARK with block size n m {\displaystyle nm} bits using n {\displaystyle n ...
The cipher is susceptible to various forms of cryptanalysis, and has acted as a catalyst in the discovery of differential and linear cryptanalysis. There have been several different revisions of FEAL, though all are Feistel ciphers , and make use of the same basic round function and operate on a 64-bit block .
While DES was designed with resistance to differential cryptanalysis in mind, other contemporary ciphers proved to be vulnerable. An early target for the attack was the FEAL block cipher. The original proposed version with four rounds (FEAL-4) can be broken using only eight chosen plaintexts , and even a 31-round version of FEAL is susceptible ...
Another theoretical attack, linear cryptanalysis, was published in 1994, but it was the Electronic Frontier Foundation's DES cracker in 1998 that demonstrated that DES could be attacked very practically, and highlighted the need for a replacement algorithm. These and other methods of cryptanalysis are discussed in more detail later in this article.