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In mathematics, a Boolean function is a function whose arguments and result assume values from a two-element set (usually {true, false}, {0,1} or {-1,1}). [1] [2] Alternative names are switching function, used especially in older computer science literature, [3] [4] and truth function (or logical function), used in logic.
Mathematically, an S-box is a nonlinear [1] vectorial Boolean function. [2] In general, an S-box takes some number of input bits, m, and transforms them into some number of output bits, n, where n is not necessarily equal to m. [3] An m×n S-box can be implemented as a lookup table with 2 m words of n bits each.
Most block cipher algorithms are classified as iterated block ciphers which means that they transform fixed-size blocks of plaintext into identically sized blocks of ciphertext, via the repeated application of an invertible transformation known as the round function, with each iteration referred to as a round.
SHA-512 – NESSIE selection hash function, FIPS 180-2, 512-bit digest; CRYPTREC recommendation; SHA-3 – originally known as Keccak; was the winner of the NIST hash function competition using sponge function. Streebog – Russian algorithm created to replace an obsolete GOST hash function defined in obsolete standard GOST R 34.11-94.
Comparison of supported cryptographic hash functions. Here hash functions are defined as taking an arbitrary length message and producing a fixed size output that is virtually impossible to use for recreating the original message.
In cryptography, the avalanche effect is the desirable property of cryptographic algorithms, typically block ciphers [1] and cryptographic hash functions, wherein if an input is changed slightly (for example, flipping a single bit), the output changes significantly (e.g., half the output bits flip).
The functions studied are often, but not always, Boolean-valued, making them Boolean functions. The area has found many applications in combinatorics , social choice theory , random graphs , and theoretical computer science, especially in hardness of approximation , property testing , and PAC learning .
Balanced Boolean functions are used in cryptography, where being balanced is one of "the most important criteria for cryptographically strong Boolean functions". [3] If a function is not balanced, it will have a statistical bias, making it subject to cryptanalysis such as the correlation attack.