3.5.5 What are the alternatives to DES?

  Over the years, various bulk encryption algorithms have been designed as alternatives to DES. One is FEAL (Fast Encryption ALgorithm), a cipher for which attacks have been discovered, although new versions have been proposed. Another recently proposed cipher designed by Lai and Massey and known as IDEA seems promising, although it has not yet received sufficient scrutiny to instill full confidence in its security. The U.S. government recently announced a new algorithm called Skipjack (see Question 3.6.5) as part of its Capstone project. Skipjack operates on 64-bit blocks of data, as does DES, but uses 80-bit keys, as opposed to 56-bit keys in DES. However, the details of Skipjack are classified, so Skipjack is only available in hardware from government-authorized manufacturers.

Rivest has developed the ciphers RC2 and RC4 (see Question 3.8.6), which can be made as secure as necessary because they use variable key sizes. Faster than DES, at least in software, they have the further advantage of special U.S. government status whereby the export approval is simplified and expedited if the key size is limited to 40 bits.