CAST-256

CAST-256, also known as CAST6, is a symmetric-key block cipher published in June 1998. It was submitted as a candidate for the Advanced Encryption Standard but was not among the five finalists. It extends the earlier CAST-128, and both were designed according to the CAST design methodology invented by Carlisle Adams and Stafford Tavares, with Howard Heys and Michael Wiener also contributing to the design. CAST-256 uses the same elements as CAST-128, including S-boxes, but is adapted to a block size of 128 bits, twice the 64 bits of its predecessor. Acceptable key sizes are 128, 160, 192, 224 or 256 bits. The cipher has 48 rounds, sometimes described as 12 quad-rounds, arranged in a generalized Feistel network. RFC 2612 states that it is available worldwide on a royalty-free and licence-free basis.