4/10/2011 Mukesh Chinta, Asst Prof, CSE, VNRVJIET 1 CAST-128 Developed by Carlisle Adams and Stafford Tavares 64-bit block size and key size varies from 40- to 128-bits in 8-bit increments Classical Feistel network structure Sixteen rounds Two subkeys per round, one 32-bit (Km i ), one 5-bit (Kr i ) Three different round functions Four operations: addition(+) and subtraction(-) modulo 2 32 , XOR, and (variable) circular left rotate (<<<) 5-bit subkey (Kr i ) determines rotate amount Encryption L 0 ||R 0 = Plaintext for i = 1 to 16 do L i = R i-1 R i = L i-1 F i [R i-1 , Km i , Kr i ]; Ciphertext = L 16 ||R 16 Mukesh Chinta, Asst Prof, CSE I I a I b I c I d CAST Round Function F The Function F is designed to have good confusion, diffusion and avalanche properties. It uses S-box substitutions, mod 2 addition and subtraction, exclusive OR operations and key dependent rotation. The strength of F depends primarily on strength of S-Boxes and further use of Boolean, arithmetic and rotate operations provide extra strength. Mukesh Chinta, Asst Prof, CSE
CAST-128 Developed by Carlisle Adams and Stafford Tavares 64-bit
block size and key size varies from 40- to 128-bits in
8-bit increments
Classical Feistel network structure
Sixteen rounds Two subkeys per round, one 32-bit (Kmi), one
5-bit (Kri) Three different round functions Four operations:
addition(+) and subtraction(-) modulo 232, XOR, and (variable)
circular left rotate (
