High Quality Content by WIKIPEDIA articles! In cryptography, COCONUT98 (Cipher Organized with Cute Operations and N-Universal Transformation) is a block cipher designed by Serge Vaudenay in 1998. It was one of the first concrete applications of Vaudenay's decorrelation theory, designed to be provably secure against differential cryptanalysis, linear cryptanalysis, and even certain types of undiscovered cryptanalytic attacks. The cipher uses a block size of 64 bits and a key size of 256 bits. Its basic structure is an 8-round Feistel network, but with an additional operation after the first 4 rounds, called a decorrelation module. This consists of a key-dependent affine transformation in the finite field GF(264). The round function makes use of modular multiplication and addition, bit rotation, XORs, and a single 8x24-bit S-box. The entries of the S-box are derived using the binary expansion of e as a source of "nothing up my sleeve numbers".

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