Some modern computer systems are subject to \“infection\” of their programs by reproducing computer viruses.  While it has been shown that detecting such a virus in general is an undecidable problem, there may be large classes of viruses against which effective defenses can be made.  Before an examination of the defenses is possible, a more complete catalog of the capabilities of viruses is necessary in order to determine if such classes exist.

We introduce the RC6 block cipher. RC6 is an evolutionary improvement of RC5, designed to meet the requirements of the Advanced Encryption Standard (AES). Like RC5, RC6 makes essential use of data-dependent rotations. New features of RC6 include the use of four working registers instead of two, and the inclusion of integer multiplication as an additional primitive operation. The use of multiplication greatly increases the diffusion achieved per round, allowing for greater security, fewer rounds, and increased throughput.