Transcrypt International, Inc.

James E Gilley

Kenneth L Snyder

Paul A Schwartzkopf

An apparatus and method for reducing the overhead of a block cipher includes shortening the length of the initialization vector so that its length is less than the length of each block of information processed by the block cipher. The block cipher is utilized in cipher block chaining mode. The shortened vector is loaded into the block cipher with other pseudo-random bits. Cipher block chaining prevents the overall cycle length of the block cipher from decreasing. Thus, channel burden of repeatedly transmitting the initialization vector is reduced because it is shorter, but security is not unduly diminished because cycle length is not diminished. Late entry can be achieved. Also, combination of this method with coasting can increase accurate synchronization even in severely corrupted channels. Security level versus amount of vector shortening can be selected.

Apparatus for and method of overhead reduction in a block cipher

An apparatus and method for detecting erroneous initialization vectors transmitted over a communications channel and maintaining cryptographic synchronization by comparing a received vector with a predicted correct vector. The vectors are random-like in nature by utilizing a pseudo-random number generator having a long overall cycle length. If the level of bit errors of the comparison is relatively small, considering the predicted vector is considered correct and used for synchronization, but if the number of bit errors of the comparison is relatively large, the predicated vector is considered in correct.

Apparatus for and method of detecting initialization vector errors and maintaining cryptographic synchronization without substantial increase in overhead

A method and apparatus for generating truly random numbers which may be used in a cryptographic key generator is adapted to extract entropy from the output signal of an RC oscillating circuit comprised of a resistor, a capacitor, and two nand gates. The entropy data is extracted by comparing the period of a first cycle with the period of a second cycle where the first and second periods are separated by two cycles. If the compared periods are equal, the data is discarded. If the previous period is greater than the later period, a '1' is assigned to a shift register. Otherwise, a '.O slashed.' is assigned to the shift register. In this way, a plurality of bits are assigned to the shift register. A routine is then called which processes the bit data to reduce any cycle to cycle data correlation.

Method and apparatus for generating truly random numbers

An apparatus and method for controlling the feature set of a programmable device by assigning each programmable device a unique serial number, correlating a secret key with each serial number, and keeping that information in a secure location, such as at the manufacturer. Each optional feature set for the programmable devices is assigned a unique code, and software associated with the programmable device operates according to the feature set identified in the feature set code, if an authentication procedure is passed. The authentication procedure utilizes a secure cryptographic algorithm to calculate an authentication code based on the secret key and the authorized feature set for a programmable device. The authentication code is stored in the programmable device. Periodically, the programmable device automatically self checks itself by recalculating the authentication code. If it matches with the authorized authentication code, the authentication procedure is passed. If it does not match, the authentication procedure is not passed as it tends to indicate that there has been an attempt to tamper with the feature set code or to use an authorization code that is from another programmable device. If the authentication procedure is not passed, the programmable device may be disabled or some other limitation may be imposed on the device.

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Lincoln, NE, United States of America

James E Gilley