A Block-Cipher Cryptographic System utilizing a unique user supplied key to control the cryptographic function and including means for modifying an input data block prior to performing a key-controlled transformation operation thereon. Said means includes means for extracting a segment of data utilized...http://www.google.fr/patents/US4078152?utm_source=gb-gplus-shareBrevet US4078152 - Block-cipher cryptographic system with chaining
