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ENHANCEMENT OF RC6 (RC6_EN) BLOCK CIPHER ALGORITHM AND COMPARISON WITH RC5 & RC6

Vikas Tyagi, Shrinivas Singh

In this paper, we present an enhanced version of RC6 Block Cipher Algorithm (RC6_En – RC6 enhanced version), which is a symmetric encryption algorithm [1] designed for 256-bit plain text block. RC6 uses four (w-bit) registers for storing plain text and for data-dependent rotations [2, 3], but this enhanced version (RC6_En) uses eight (w-bit) register that helps to increase the performance as well as improve security. Its salient feature includes two-variable algebraic expression modulo 2w and 2 Box-Type operations, Box-Type I & Box-Type II. Each Box-Type operation uses two (w-bit) registers. Box-Type I works much like two registers (A & B or C & D) operation in RC6 but in Box-Type II bitwise exclusive-or is swapped by integer addition modulo 2w used in Box-Type I and vice-versa, it improves Diffusion in each round. This enhanced version needs 2r+4 additive round-keys and uses every round-key twice for encrypting the file. This enhanced version performs better with respect to RC5[4, 5] and RC6[2, 3] when file size is larger.