CAST (Carlisle Adams and Stafford Tavares) is a symmetric block cipher with a block length of 64 bits and a variable key length from 40 bits to 128 bits (CAST-128), which can be selected in 8-bit increments.
With CAST, a data block is encrypted in 16 rounds. For each round, a key pair is generated that is used for addition, subtraction, and XORing. During decryption, the keys are processed in reverse order. The CAST algorithm is considered very secure and is described in RFC 2144.
The encryption method was developed in Canada in 1996 by Carlisle Adams and Stafford Tavares and is named after them. In the enhanced version CAST-256, the block length is 128 bits and the key length is 256 bits. The CAST-256 block cipher was one of the encryption methods tested by the Advanced Encryption Standard( AES).
CAST works very fast and is not subject to patent protection. It is described in RFC 2144.