Serious Cryptography

1ENCRYPTION

Encryption is the principal application of cryptography; it makes data incomprehensible in order to ensure its confidentiality. Encryption uses an algorithm called a cipher and a secret value called the key; if you don’t know the secret key, you can’t decrypt, nor can you learn any bit of information on the encrypted message—and neither can any attacker.

This chapter will focus on symmetric encryption, which is the simplest kind of encryption. In symmetric encryption, the key used to decrypt is the same as the key used to encrypt (unlike asymmetric encryption, or public-key encryption, in which the key used to decrypt is different ...