Multiple size cryptographic key system

摘要

A system is employed for providing two different levels of protection for cryptographic devices transmitting digital information. The system is independent of the cryptographic algorithm used and works with any keyed cryptographic algorithm. High grade encryption (18) is used for data transmitted from the transmitter device (10) and employs an encryption key of "Y" bits. This information is decrypted at the receiver (21) by a decryption circuit (22) also having a "Y" key size. At the receiver, return information is encrypted by an encryption key (30) having "X" bits, where X = Y-Z, with Z being a variable. The low grade information encrypted at the receiver (21) is supplied back to the transmitter (10), which incorporates a decryption circuit (32) having an "X" key size for decrypting the lower grade information.