Network Security: Private Communications in a Public World, 3rd Edition

3 Secret Key Cryptography

3.1 Introduction

Secret key encryption schemes require that both the party that does the encryption and the party that does the decryption share a secret key. We will discuss two types of secret key encryption schemes:

• block cipher. This takes as input a secret key and a plaintext block of fixed size (older ciphers used 64-bit blocks, modern ciphers use 128-bit blocks). It produces a ciphertext block the same size as the plaintext block. To encrypt messages larger than the blocksize, the block cipher is used iteratively with algorithms called modes of operation that are the subject of the next chapter. A block cipher also has a decryption operation that does the reverse computation.

• stream cipher. This uses the key ...