Transcrypt International, Inc.

Kenneth L Snyder

Douglas E Ehlers

James E Gilley

Mark R Hupp

Paul A Schwartzkopf

Ronald B Kabler

A method for providing improved carrier based data operated squelch (CDOS) includes routines for recovering the carrier signal and for analyzing the received signal. The received signal is sampled at each transition point of the carrier signal as well as the halfway points between the transition points. In addition, extra samples are taken between these samples. Using the samples, a carrier locked loop routine recovers the carrier signal. A CDOS routine analyzes the extra samples to determine the presence of data. If two successive samples are different, this means that a transition has occurred. The CDOS routine analyzes these transitions to determine whether the input signal is encoded with data. If the CDOS routine determines that the input signal is encoded with data, a CDOS counter is incremented. As the input continues to look like data, the value by which the CDOS counter is incremented is increased. When the CDOS counter reaches a certain threshold, the CDOS mutes the output circuit.

Carrier based data operated squelch

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.

Apparatus and method for secured control of feature set of a

A device and method for scrambling and de-scrambling audio and voice communications including radio, cellular telephone, and conventional telephone communication. The audio communication can be scrambled using, for example, time varying pseudo-random spectral modification. Continuous data containing synchronization information is transmitted with the scrambled signal to eliminate time lags that occur with synchronization bursts and without detrimentally affecting audio quality.

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Elmwood, NE, United States of America

Kenneth L Snyder