Types of Ciphers

Ciphers come in two basic forms:

  • Transposition ciphers—A transposition cipher rearranges characters or bits of data.

  • Substitution ciphers—A substitution cipher replaces bits, characters, or blocks of information with other bits, characters, or blocks.

Transposition Ciphers

A simple transposition cipher writes characters into rows in a matrix and then reads the columns as output. For example, write the message “ATTACK AT DAWN” into a four-column matrix, as shown in FIGURE 7-2.

A transposition cipher. A table is shown which has 4 rows and 4 columns. The first row has the following column headings. 1. 2. 3. 4. Under these column headings, the next 3 rows have the following letters. Row 2: A. T. T. A. Row 3: C. K. A. T. Row 4: D. A. W. N.

FIGURE 7-2 A transposition cipher.

Then, read the information in columns: ACDTKATAWATN, which would be the ciphertext. The key would be {1,2,3,4}, ...

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