Public-key Cryptography: Theory and Practice

A.2. Block Ciphers

Block ciphers encrypt plaintext messages in blocks of fixed lengths and are more ubiquitously used than public-key encryption routines. In a sense, public-key encryption is also block encryption. Since public-key routines are much slower than (secret-key) block ciphers, it is a custom to use public-key algorithms only in specific situations, for example, for encrypting single blocks of data, like keys of symmetric ciphers.

In the rest of this chapter, we use the word bit in the conventional sense, that is, to denote a quantity that can take only two possible values, 0 and 1. It is convenient to use the symbol to refer to the ...