RC2
| RC2
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The MIX transformation of RC2; four of these comprise a MIXING round.
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| General
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| Designer(s) | Ron Rivest
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| First published | source code leaked 1996 (designed 1987)
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| Derived from | -
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| Cipher(s) based on this design | -
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| Algorithm detail
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| Block size(s) | 64 bits
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| Key size(s) | 8–128 bits, in steps of eight bits; default 64 bits
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| Structure | Source-heavy Feistel network
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| Number of rounds | 16 of type MIXING; 2 of type MASHING
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| Best cryptanalysis
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| A related-key attack is possible requiring 234 chosen plaintexts (Kelsey et al, 1997).
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The development of RC2 was sponsored by Lotus, who were seeking a custom cipher that, after evaluation by the NSA, could be exported as part of their Lotus Notes software. The NSA suggested a couple of changes, which Rivest incorporated. After further negotiations, the cipher was approved for export in 1989. Along with RC4, RC2 with a 40-bit key size was treated favourably under US export regulations for cryptography.
Initially, the details of the algorithm were kept secret — proprietary to RSA Security — but on 29th January, 1996, source code for RC2 was anonymously posted to the Internet on the Usenet forum, sci.crypt. A similar disclosure had occurred earlier with RC4. It is unclear whether the poster had access to the specifications or whether it had been reverse engineered.
RC2 is a 64-bit block cipher with a variable size key. Its 18 rounds are arranged as a source-heavy Feistel network, with 16 rounds of one type (MIXING) punctuated by two rounds of another type (MASHING). A MIXING round consists of four applications of the MIX transformation, as shown in the following diagram:
RC2 is vulnerable to a related-key attack using 234 chosen plaintexts (Kelsey et al, 1997).
Sources
References
- Lars R. Knudsen, Vincent Rijmen, Ronald L. Rivest, Matthew J. B. Robshaw: On the Design and Security of RC2. Fast Software Encryption 1998: 206–221
- John Kelsey, Bruce Schneier, David Wagner: Related-key cryptanalysis of 3-WAY, Biham-DES, CAST, DES-X, NewDES, RC2, and TEA. ICICS 1997: 233–246
