Security in Computing, Third Edition

10.1. Mathematics for Cryptography

Encryption is a two-edged sword: We want to encrypt important information relatively easily, but we would like an attacker to have to work very hard to break an encryption—so hard that the attacker will stop trying to break the encryption and focus instead on a different method of attack (or, even better, a different potential victim).

To accomplish these goals, we try to force an interceptor to solve a hard problem, such as figuring out the algorithm that selected one of n! permutations of the original message or data. However, the interceptor may simply generate all possible permutations and scan them visually (or with some computer assistance), looking for probable text. Thus, the interceptor need not solve ...