Stream cipher
Self-synchronizing stream ciphers is another technique that uses part of the previous N ciphertext digits to compute the keystream. Such schemes are known also as asynchronous stream ciphers or ciphertext autokey (CTAK). The idea of self-synchronization was patented in 1946, and has the advantage that the receiver will automatically synchronise with the keystream generator after receiving N ciphertext digits, making it easier to recover if digits are dropped or added to the message stream. Single-digit errors are limited in their effect, affecting only up to N plaintext digits. It is somewhat more difficult to perform active attacks on self-synchronising stream ciphers rather than synchronous counterparts.