Security in Computing, Third Edition

2.8. The Uses of Encryption

Encryption algorithms alone are not the answer to everyone's encryption needs. Although encryption implements protected communications channels, it can also be used for other duties. In fact, combining symmetric and asymmetric encryption often capitalizes on the best features of each.

Public key algorithms are useful only for specialized tasks because they are very slow. A public key encryption can take 10,000 times as long to perform as a symmetric encryption because the underlying modular exponentiation depends on multiplication and division, which are inherently slower than the bit operations (addition, exclusive OR, substitution, and shifting) on which symmetric algorithms are based. For this reason, symmetric ...