Method and apparatus for transaction and identity verification

A transaction verification method for use in a computer based communication system comprising a central Host CPU which includes a high security Verify Unit therein said system including a plurality of remotely located terminals selectively connectable to each other and to said Host CPU via said communications system and wherein said Verify Unit and each of said terminals includes substantially identical key-controlled block-cipher cryptographic devices with block chaining, said method comprising User A (originator), at a first terminal sending User B (receiver) at a second terminal a message M having a data (X) portion and a signature portion (Y) said signature portion being a block-cipher function of User A's key K.sub.A and the data portion (X) such that:

• M=(X,Y);
• User B on receipt of said message M reencrypting said entire message M under his own key K.sub.B to form a message U, sending said message U to the Host CPU together with the identities of User A and User B and requesting a verification operation from said Host CPU;
• the Host CPU, upon receipt of said message from User B, requesting a verify operation from its associated Verify Unit and providing the message information U to said Verify Unit;
• said Verify Unit obtaining the keys K.sub.A and K.sub.B from a secure storage means located in said Host CPU and decrypting U under key K.sub.B to obtain message U which comprises a data portion U.sub.1 and a signature portion U.sub.2, the Verify Unit then forming a signature utilizing the data portion U.sub.1 as the data input and the key K.sub.A as the key input to its associated cryptographic device and comparing the signature so generated with the signature value U.sub.2 received from User B, said Verify Unit after determining the validity of the received signature U.sub.2 then generating a new signature V for the message U which signature is a predetermined function of the key K.sub.B and the previously decrypted message U the particular function being dependent upon the result of said signature comparison operation and sending the message V to User B;
• User B upon receipt of the message V computing a signature V' which is a predetermined function of his own key K.sub.B and the message (X,Y) initially received from User A and comparing same with the message V for correspondence;
• and
• wherein all signature generation operations in the previous enumerated signature generating steps comprise selecting as said signatures a predetermined final number of bytes of the block chained encryption of the full data input to said associated key-controlled block-cipher cryptographic devices with chaining wherein each said signature is a direct function of and fully dependent upon the entire data content supplied to said cryptographic device.

A computer based communications system having a high security transaction verification feature incorporated therein, said system comprising a Host CPU which includes a high security Verify Unit therein, said system further including a plurality of remotely located terminals including means for selectively connecting each terminal to said Host CPU or to another terminal via the communications network associated therewith, said Verify Unit and each of said terminals including substantially identical key-controlled block-cipher cryptographic devices equipped with a block chaining feature, each terminal including means actuable when said terminal is used as an originating device (Terminal A) in a transaction to send a message M to another terminal acting as a receiver (Terminal B) said message M having a data portion (X) and a signature portion (Y), means for actuating the cryptographic device located in said terminal to form said signature (Y) as a block-cipher function of Terminal A's key K.sub.A and the data portion (X) such that M=(X,Y);

• means in the receiving terminal (Terminal B) actuable on receipt of the message M from (Terminal A) for reencrypting said message under the terminal's own key K.sub.B to form a message U and means for sending said message U to the Host CPU together with the identities of the originating and receiving terminals (Terminal A and Terminal B) and means for requesting a verification operation from said Host CPU;
• means in said Host CPU actuable upon the receipt of said message for obtaining the keys K.sub.A and K.sub.B from memory and for requesting a verify operation from the Verify Unit associated therewith;
• means in said Verify Unit for decrypting the message U under terminal B's key K.sub.B to obtain a decrypted message U which comprises a message portion U.sub.1 and a signature portion U.sub.2, means in said Verify Unit for forming a signature utilizing U.sub.1 as a data input and the originating terminal's key K.sub.A as the key input to the cryptographic device contained therein and means for comparing the signature so generated with the signature value U.sub.2 received from terminal B;
• means in said Verify Unit for returning an accept/reject signal to receiving terminal B depending upon whether the two signatures are identical.