Abstract: An approach for handling data representative of invalid transaction cards is disclosed. A memory area 34 in a transaction terminal 16 is divided into a plurality of stacks. Two digits of the invalid account number are used to identify the stack into which the remainder of the account number is added. Stack start pointers are provided for file management. As the newest entries are added to the list, the oldest entries are purged. The subject system allows a large number of accounts to be stored in a minimum of space. Updates of the file can be easily handled during direct communication sessions between a central processor 12 and the terminal 16.

Abstract: An improved system is disclosed for detecting invalid transaction cards at remote transaction terminals. The system includes providing each terminal with a master table having data corresponding to invalid cards. The data in the master table is less than the actual account numbers of the invalid cards. By using a compressed version of the data, the file can be shortened to facilitate storage and transmission. The compressed data file is arranged such that when an invalid card is presented, it will be identified and routed on for further processing. In the preferred embodiment, the probability that a valid card will be identified as potentially invalid is on the order of one of three percent.

Abstract: The subject invention relates to a new and improved key management system particularly suited to facilitate communication between point of sale terminals and a host processor. The system provides for the generation of a table of keys in the terminal. The terminal includes a counter which is related to the table of keys. During a transaction, information, such as a personal identification number (PIN) is encrypted using one of the keys in the table. This information is transmitted, along with other transaction data, and the number stored in the counter. By utilizing the information in the counter, the host processor can generate the key used for encrypting the PIN. By this arrangement, security is enhanced and there is no need for large storage of keys at the central host.

Abstract: An apparatus and method for generating a unique working key variable for controlling the operation of an encryption/decryption device during each user specified time period. The apparatus generates each working key variable by encrypting a user specified value, unique for each specified time period, under control of a fixed key variable stored in the apparatus. After the user specified value has been encrypted, the apparatus utilizes the encrypted (working) key variable to control the encryption/decryption of data during the corresponding user specified time period.

Abstract: An authenticator device designed to preclude undetected compensating text modifications in a message by sequentially processing each character of the message and producing an authenticator code as a result of said processing.As each message is received, it is modulo added to the contents of a first register and the result is used to simultaneously address first and second memories, the values stored in the first memory consisting of a specified permutation of preselected decimal values, the values stored in the second memory consisting of non-linear transformations of a 16 digit authentication key. The data read out of the second memory is used to address a third memory, the values stored in the third memory consisting of another specified permutation of preselected decimal values. The data read out of the third memory replaces the value previously stored in the first register.

Abstract: A device for generating an authenticator code by encrypting the contents of a plain text message in accordance with a unique user supplied authenticator key variable. The device operates in two phases, the first of which processes every character in the plain text message and produces a first sequence of 16 check bits. The second phase processes this first 16 check bit sequence and transforms it into a second sequence of 16 check bits which may be utilized as an authenticator code.

Abstract: An apparatus for insertion in a communications line for providing message secrecy within a significant portion of existing communications networks. At the transmitter end, the apparatus receives messages from the communications line, enciphers them and retransmits them onto the communications line. At the receiver end, the apparatus receives messages from the communications line, deciphers them and retransmits them onto the communications line. The apparatus contains both a transmitter and receiver and is capable of full duplex operation in a bidirectional communications line. According to the invention, data is enciphered by combining the data received with the output of an algorithm, the algorithm output being dependent on the data previously enciphered and a unique key entered by the user. As data is received it is combined with the output of the algorithm, transmitted and using cipher feedback techniques fed back as an input to the algorithm to be used to encipher subsequently received data.

Abstract: An apparatus for insertion in a communications line for providing both message integrity and message secrecy within a significant portion of existing communications networks. At the transmitter end, the apparatus receives messages from the communications line, enciphers them on a bit-by-bit basis and retransmits them onto the communications line. At the receiver end, the apparatus receives messages from the communications line, deciphers them on a bit-by-bit basis and retransmits them onto the communications line. The apparatus contains both a transmitter and receiver and is capable of full duplex operation in a bidirectional communications line. According to the invention, data is enciphered by combining the data received with the output of an algorithm, the algorithm output being responsive to data previously received and a unique key entered by the user.

Abstract: A device for insertion in a communications line for verifying message integrity within a significant portion of existing communications networks. At the transmitter end, the device receives plain text messages from the communications line, generates an authentication field by encrypting the plain text message received and retransmits the plain test message received, with the authentication field appended thereto, onto the communications line.At the receiver end, the device receives messages from the communications line, generates an authentication field by encrypting the plain text portion of the message received and compares the authentication field generated with the authentication field appended to the plain text portion of the message received.