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Unlike many schemes, RC5 has a variable block size (32, 64 or 128 bits), 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.
RC5 makes extensive use of data-dependent rotations, a relatively unusual cryptographic operation — they were used previously only in Madryga — and combines them with modular addition and eXclusive OR (XOR) in a Feistel-like network. The encryption and decryption routines can be specified in remarkably few lines of code, though the key schedule is more complex. 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.
12-round RC5 (with 64-bit blocks) is susceptible to a differential attack using 244 chosen plaintexts (Biryukov and Kushilevitz, 1998). 18–20 rounds are suggested as sufficient protection.
RSA Security, who have a patent on the algorithm, offer a series of US$10,000 prizes for breaking a ciphertext encrypted with RC5. Several groups have attempted these challenges using distributed computingDistributed programming Distributed computing is the process of running a single computational task on more than one distinct computer. Introduction This differs from cluster computing in that computers in a distributed computing environment are typically, the largest and most successful being Distributed.netdistributed. net is a world-wide distributed computing effort that is attempting to solve large scale problems using otherwise idle CPU time. It is similar to the SETI@home project in that sense. It started out as an effort to break RC5-56, a 56- bit encr. Distributed.net has brute-forced messages encrypted with RC5 in 56- and 64-bit keys, and is currently working on cracking a 72-bit key.
| Block ciphers [ }|action=edit}} Edit }] |
| Algorithms: 3-Way | AES | Akelarre | Blowfish | Camellia | CAST-128 | CAST-256 | CMEA | DEAL | DES | DES-X | FEAL | FROG | G-DES | GOST | ICE | IDEA | Iraqi | KASUMI | KHAZAD | Khufu and Khafre | LOKI89/91 | LOKI97 | Lucifer | MacGuffin | Madryga | MAGENTA | MARS | MISTY1 | MMB | NewDES | RC2 | RC5 | RC6 | REDOC | Red Pike | S-1 | SAFER | SEED | Serpent | SHACAL | SHARK | Skipjack | Square | TEA | Triple DES | Twofish | XTEA |
| Design: Feistel network | Key schedule | Product cipher | S-box | SPN Attacks: Brute force | Linear / Differential cryptanalysis | Mod n | XSL Standardisation: AES process | CRYPTREC | NESSIE Misc: Avalanche effect | Block size | IV | Key size | Modes of operation | Piling-up lemma | Weak key |