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Unformatted text preview: a common plaintext block (all zeros, the ASCII characters for a space, etc.), this method should work. The storage requirement for a 64-bit plaintext block encrypted with all 1012 possible keys is 8 terabytes—certainly possible. For information on licensing RC2, contact RSADSI (see Section 25.4). 13.9 IDEA
The first incarnation of the IDEA cipher, by Xuejia Lai and James Massey, surfaced in 1990 . It was called PES (Proposed Encryption Standard). The next year, after Biham and Shamir’s demonstrated differential cryptanalysis, the authors strengthened their cipher against the attack and called the new algorithm IPES (Improved Proposed Encryption Standard) [931,924]. IPES changed its name to IDEA (International Data Encryption Algorithm) in 1992 . IDEA is based on some impressive theoretical foundations and, although cryptanalysis has made some progress against reduced-round variants, the algorithm still seems strong. In my opinion, it is the best and most secure block algorithm available to the public at this time. The future of IDEA is not yet clear. There has been no rush to adopt it as a replacement to DES, partly because it is patented and must be licensed for commercial applications, and partly because people are still waiting to see how well the algorithm fares during the coming years of cryptanalysis. Its current claim to fame is that it is part of PGP (see Section 24.12). Overview of IDEA
IDEA is a block cipher; it operates on 64-bit plaintext blocks. The key is 128 bits long. The same algorithm is used for both encryption and decryption. As with all the other block ciphers we’ve seen, IDEA uses both confusion and diffusion. The design philosophy behind the algorithm is one of “mixing operations from different algebraic groups.” Three algebraic groups are being mixed, and they are all easily implemented in both hardware and software: — XOR — Addition modulo 216 — Multiplication modulo 216 + 1. (This operation can be viewed as IDEA’s S-box....
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- Fall '10