Abstract: A method and apparatus for verifying both the content of a transaction and the identity of the parties thereto. The system includes a plurality of terminals connected together over a common communication channel wherein a given pair of users located at different terminals on the system have exchanged a contract comprising a plurality of reference signatures each of which constitutes the final member of a one-way keyed signature sequence and each of which is a one-way function of each user's secret encryption key (K.sub.x) and a number (NUM) known to both parties. Each terminal connected to the system includes means for generating a multidigit ranking vector which is a cryptographic function of the entire message (DATA) tobe transmitted.

Abstract: A method and apparatus whereby the senders and receivers of messages sent over a transmission system including a Host CPU may guarantee the integrity of the data content of the message and also the absolute identity of the sender. Each user of the system as well as the Host CPU contains an identical key-controlled block-cipher cryptographic device with data chaining for encrypting and decrypting messages as required, wherein each user has knowledge of only his own cryptographic key and wherein the Host CPU has access to the unique cryptographic keys of all users of the system stored in a high security storage area available only to said CPU. Stated very generally, the originator of a message A sends a message to a receiver B which includes a transaction or message portion X and a unique digital signature portion Y which is a function both of the message and the senders unique cryptographic key K.sub.A. The receiver then communicates with the CPU for verification of the signature Y.

Abstract: A Cryptographic Architecture for improving the security of Cash-Issuing or similar Terminal Systems when it is necessary to operate Off-Host. Each Terminal is connected to a central Controller which is in turn connected to a central Host. The Master cryptographic key for use in the personal identification mechanism provided in the system is stored in the Controller rather than the terminal. Means are provided whereby said Controller performs customer identification operations when the Host is not available to do so. Only data input at the Terminal is utilized in transmission between the Terminal and the Controller whereby the master system key is never exposed at either the Terminal or the communication link. Additionally, a Terminal status message is utilized with each transaction to prevent a "stale" message from being used to bypass the security procedures by means of eavesdropping or the like.