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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.
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).
Cryptanalysis (from the Greek kryptós, "hidden", and analýein, "to analyze") refers to the process of analyzing information systems in order to understand hidden aspects of the systems. [1] Cryptanalysis is used to breach cryptographic security systems and gain access to the contents of encrypted messages, even if the cryptographic key is ...
Differential cryptanalysis is usually a chosen plaintext attack, meaning that the attacker must be able to obtain ciphertexts for some set of plaintexts of their choosing. There are, however, extensions that would allow a known plaintext or even a ciphertext-only attack. The basic method uses pairs of plaintexts related by a constant difference.
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 .
Differential and linear cryptanalysis are the two major general techniques known for the cryptanalysis of block ciphers. The following year, Matsui was the first to publicly report an experimental cryptanalysis of DES, using the computing power of twelve workstations over a period of fifty days.
For example, encryption using an oversimplified three-round cipher can be written as = ((())), where C is the ciphertext and P is the plaintext. Typically, rounds R 1 , R 2 , . . . {\displaystyle R_{1},R_{2},...} are implemented using the same function, parameterized by the round constant and, for block ciphers , the round key from the key ...