Security in Computing, Third Edition

2.3. Transpositions (Permutations)

The goal of substitution is confusion; the encryption method is an attempt to make it difficult for a cryptanalyst or intruder to determine how a message and key were transformed into ciphertext. In this section, we look at a different kind of scrambling with the similar goal. A transposition is an encryption in which the letters of the message are rearranged. With transposition, the cryptography aims for diffusion, widely spreading the information from the message or the key across the ciphertext. Transpositions try to break established patterns. Because a transposition is a rearrangement of the symbols of a message, it is also known as a permutation.

Columnar Transpositions

As with substitutions, we begin ...