A structured symmetric-key block cipher

This paper presents a simple and structured symmetric-key block cipher called CHAIN which provides for variation in the block size, the key size, and the number of rounds of ciphering. This cipher performs encryption in three stages: mixing permutation, and key-dependent substitution using the simple operations of XOR, table lookup, and substitution. The structure of CHAIN is byte-oriented, however the algorithm is designed in such a way that it can be expressed in a simple 'compact form' for efficient software or hardware implementation on platforms that support word sizes greater than 8 bits (such as on Intel's Pentium processor). Our C implementation of CHAIN with a 128-bit block size runs at 26 Mbits/Sec on a Pentium Pro 200 Mhz machine which is about 86% faster than RC5. Cryptanalysis of the algorithm indicates that it is very strong against the known attacks. It reaches the avalanche effect quite rapidly and provides very good resistance against linear and differential attacks.