Question 69. What are the Alternatives to DES?

Over the years, various new block cipher algorithms have been designed as alternatives to DES. One is FEAL (see Question 79), a cipher for which numerous attacks have been discovered. IDEA is a cipher designed by Lai and Massey that seems much more promising (see Question 77) and two more recent designs are RC5 (see Question 76) and SAFER (see Question 78). In addition, the U.S. government announced in 1993 an algorithm called Skipjack (see Question 80) as part of its Capstone project (see Question 150). Skipjack operates on 64-bit blocks of data, as does DES, but uses 80-bit keys, as opposed to the 56-bit keys in DES. However, the details of Skipjack are classified, so Skipjack is only available in hardware from government-authorized manufacturers.

In addition to RC5, Rivest perviously developed the block cipher RC2 (see Question 75) and the stream cipher RC4 (see Question 87). All three algorithms have a variable key size (so that the security they offer can be adjusted) and all three algorithms are faster than DES, at least in software. RC2 and RC4 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.