Abstract

Abstract. This document describes the RC5 encryption algorithm. RC5 is a fast symmetric block cipher suitable for hardware or software implementations. A novel feature of RC5 is the heavy use of data-dependent rotations. RC5 has a variable word size, a variable number of rounds, and a variable-length secret key. 1 AParameterized Family of Encryption Algorithms RC5 is word-oriented: all of the primitive operations work on w-bit words as their basic unit of information. Here we assume w = 32, although the formal speci cation of RC5 admits variants for other word lengths, such asw = 64 bits. RC5 has two-word (64-bit) input (plaintext) and output (ciphertext) block sizes. RC5 uses an \expanded key table, " S, derived from the user's supplied secret key. The size t of table S depends on the number r of rounds: S has t =2(r +1) words. There are thus several distinct \RC5 " algorithms, depending on the choice of parameters w and r. We summarize these parameters below: w This is the word size, in bits � each word contains u =(w=8) 8-bit bytes. The standard value of w is 32 bits � allowable values of w are 16, 32, and 64. RC5 encrypts two-word blocks: plaintext and ciphertext blocks are each 2w bits long. r This is the number of rounds. Also, the expanded key table S contains t =2(r +1)words. Allowable values of r are 0, 1,..., 255. In addition to w and r, RC5 has a variable-length secret cryptographic key, speci ed parameters b and K: b The number of bytes in the secret key K. Allowable values of b are 0, 1,

Citations

293	Differential Cryptanalysis of the Data Encryption Standard. NewYork - Biham, Shamir - 1993
112	The First Experimental Cryptanalysis of the Data Encryption Standard - Matsui - 1994