Introduction to Network Security, 2nd Edition

Chapter 2Data Encryption Algorithms

The history of using secret writing to protect valuable information is probably as long as the history of written language itself. Computer cryptography was created to protect confidential data in digital forms, and it thrives in the Internet era. Data encryption is a critical component of computer cryptography. It uses encryption algorithms and secret keys to transform data from that which is readable to that which is unintelligible. Encryption algorithms must be reversible, so that data can be transformed, using the same secret key, from the unintelligible form back to its original form. Encryption algorithms of this kind are referred to as conventional encryption algorithms or symmetric-key encryption algorithms.

For example, let be a fixed permutation of the 26 English letters, which maps letter to , to , and to . Replacing each letter in a given ...