In cryptography , CAST-128 (alternatively CAST5 ) is a symmetric-key block cipher used in a number of products, notably as the default cipher in some versions of GPG and PGP . It has also been approved for Government of Canada use by the Communications Security Establishment . The algorithm was created in 1996 by Carlisle Adams and Stafford Tavares using the CAST design procedure.
5-542: Another member of the CAST family of ciphers, CAST-256 (a former AES candidate) was derived from CAST-128. According to some sources, the CAST name is based on the initials of its inventors, though Bruce Schneier reports the authors' claim that "the name should conjure up images of randomness". CAST-128 is a 12- or 16-round Feistel network with a 64- bit block size and a key size of between 40 and 128 bits (but only in 8-bit increments). The full 16 rounds are used when
10-613: A patent on the CAST design procedure, CAST-128 is available worldwide on a royalty-free basis for commercial and non-commercial uses. CAST-256 In cryptography , CAST-256 (or CAST6 ) is a symmetric-key block cipher published in June 1998. It was submitted as a candidate for the Advanced Encryption Standard (AES); however, it was not among the five AES finalists . It is an extension of an earlier cipher, CAST-128 ; both were designed according to
15-428: Is composed of 48 rounds, sometimes described as 12 "quad-rounds", arranged in a generalized Feistel network . In RFC 2612, the authors state that, "The CAST-256 cipher described in this document is available worldwide on a royalty-free and licence-free basis for commercial and non-commercial uses." Currently, the best public cryptanalysis of CAST-256 in the standard single secret key setting that works for all keys
20-411: The key size is longer than 80 bits. Components include large 8×32-bit S-boxes based on bent functions , key-dependent rotations, modular addition and subtraction, and XOR operations. There are three alternating types of round function, but they are similar in structure and differ only in the choice of the exact operation (addition, subtraction or XOR) at various points. Although Entrust holds
25-451: The "CAST" design methodology invented by Carlisle Adams and Stafford Tavares . Howard Heys and Michael Wiener also contributed to the design. CAST-256 uses the same elements as CAST-128, including S-boxes , but is adapted for a block size of 128 bits – twice the size of its 64-bit predecessor. (A similar construction occurred in the evolution of RC5 into RC6 ). Acceptable key sizes are 128, 160, 192, 224 or 256 bits. CAST-256
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