CAST-128 (or CAST5 ) is a Encryption algorithm per block used by several software of which certain versions of PGP and GnuPG. It was approved with the Canada by the Communications Security Establishment for a governmental use.

The algorithm was designed in 1996 by Carlisle Adams and Stafford Tavares. A version with a larger key, CAST-256 (former candidate for AES, was derived starting from CAST-128. The term of “CAST” would be based on initial inventors.

CAST-128 is based on a Réseau of Feistel of 12 or 16 turns with a block of 64 bits. The size of the key varies between 40 and 128 bits (by increment of 8 bits). The full version with its 16 turns is used when the key is higher than 80 bits. The internal architecture of coding includes/understands S-Box are of 8x32 elements whose contents come from functions known as curve , of rotations which vary according to the key, of the additions and the subtractions. There are three types of turns but they vary only on the exact choice of the operator (addition, subtraction or XOR).

In spite of a patent deposited by Entrust on design CAST, CAST-128 is available everywhere without loads for commercial or not-commercial applications.

References

• C.M. Adams. (1997). " Constructing Symmetric Ciphers Using the CAST Procedure" Design; , Designs, Codes, and Cryptography , 12 (3), pp. 283-316.
• C.M. Adams, " CAST Design Addendum" Procedure;.
• Bruce Schneier, 1996, Applied Cryptography, 2nd edition. John Wiley & Sounds. pp334-335. ISBN 0-471-11709-9

External bonds

• RFC 2144 - algorithm CAST-128 (RFC)
• List of the algorithms approved by the Canadian government