Information AboutRc5 |
| CATEGORIES ABOUT RC5 | |
| block ciphers | |
RC5 is a Block Cipher notable for its simplicity. Designed by Ronald Rivest in 1994 1, ''RC'' stands for "Rivest Cipher", or alternatively, "Ron's Code" (compare RC2 and RC4 ). The Advanced Encryption Standard (AES) candidate RC6 was based on RC5. DESCRIPTION Unlike many schemes, RC5 has a variable Block Size (32, 64 or 128 Bit s), Key Size (0 to 2040 bits) and number of rounds (0 to 255). The original suggested choice of parameters were a block size of 64 bits, a 128-bit key and 12 rounds. A key feature of RC5 is the use of data-dependent rotations; one of the goals of RC5 was to prompt the study and evaluation of such operations as a cryptographic primitive. RC5 also consists of a number of Modular additions and EXclusive OR (XOR) s. The general structure of the algorithm is a Feistel -like network. The encryption and decryption routines can be specified in a few lines of code. The key schedule, however, is more complex, expanding the key using an essentially One-way Function with the binary expansions of both E and the Golden Ratio as sources of " Nothing Up My Sleeve Number s". The tantalising simplicity of the algorithm together with the novelty of the data-dependent rotations has made RC5 an attractive object of study for cryptanalysts. CRYPTANALYSIS 12-round RC5 (with 64-bit blocks) is susceptible to a Differential Attack using 244 chosen plaintexts.Biryukov A. and Kushilevitz E. (1998). Improved Cryptanalysis of RC5. EUROCRYPT 1998. 18–20 rounds are suggested as sufficient protection. RSA Security , who have a patent on the algorithmRivest, R. L, "Block Encryption Algorithm With Data Dependent Rotation", , issued on 3 March 1998 ., offer a series of US$10,000 prizes for breaking Ciphertext s encrypted with RC5. A number of these challenge problems have been tackled using Distributed Computing , organised by Distributed.net . Distributed.net has brute-forced RC5 messages encrypted with 56- and 64-bit keys, and is, as of December 3rd, 2002, working on cracking a 72-bit key. At the current rate, it will take approximately 1,000 years to test every possible key, and thus guarantee completion of the project. {Link without Title} SEE ALSO REFERENCES EXTERNAL LINKS
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