Pro PHP Security: From Application Security Principles to the Implementation of XSS Defenses, Second Edition

Blocks, Modes, and Initialization Vectors

For better or worse, the available encryption libraries present the developer with a dazzling array of choices beyond just which algorithm to use for the encryption itself. There are three additional concepts you need to be aware of in order to make informed decisions when working with cryptographic ciphers.

Streams and Blocks

Stream ciphers are those that act by XORing a plaintext message against a key. RC4 is an example of a stream cipher, and its recognized failure to provide high-quality encryption is a result of that technique.

The other encryption algorithms we've been discussing are known as block ciphers, because they break the plaintext message into same-sized blocks of data (padding the last ...