Autokey Cipher - Autokey in Modern Ciphers

Autokey in Modern Ciphers

Modern autokey ciphers use very different encryption methods, but they follow the same approach of using either key bytes or plaintext bytes to generate more key bytes. Most modern stream ciphers are based on pseudorandom number generators: the key is used to initialize the generator, and either key bytes or plaintext bytes are fed back into the generator to produce more bytes.

Some stream ciphers are said to be "self-synchronizing", because the next key byte usually depends only on the previous N bytes of the message. If a byte in the message is lost or corrupted, therefore, the key-stream will also be corrupted—but only until N bytes have been processed. At that point the keystream goes back to normal, and the rest of the message will decrypt correctly.