Python Programming in Context, 3rd Edition

3.4 Transposition Cipher

3.4.1 Encrypting Using Transposition

One way to scramble the letters of a message is to separate the message into two groups of characters, where the first group is composed of the even-numbered characters and the second group is composed of the odd-numbered characters. If we create one string out of the even-numbered characters and another out of the odd-numbered characters, we can concatenate the two new strings together to form the ciphertext string. Because this results in a string with the characters shuffled to new positions, we call this a transposition cipher, also sometimes called the rail fence cipher. FIGURE 3.3 illustrates the idea behind this encryption algorithm.

“In the figure, the original text ...