Abstract: An apparatus and method for concealing data bursts in an analog scrambler using parts of the audio of a signal in substitution for the data bursts. What otherwise would be periodic data bursts appearing at the audio output are replaced with selected portions from audio portions of the multiplexed signal. Preferably the replaced audio samples come from immediately past and immediately future portions of the audio of the signal. The data bursts are therefore effectively concealed from the audio output which improves on the degradation of audio otherwise caused by the data bursts that are mixed in periodically with the audio portions of the signal.

Abstract: An apparatus and method for maintaining a constant speech envelope using automatic gain control, wherein the level of the audio signal is monitored. If increasing, a first level of gain increase is applied to the gain signal. If decreasing, a second level of gain decrease is applied to the gain signal, the second level being less than the first level. By applying a lower level of change to the gain signal when it is seen as decreasing, a more constant speech envelope is obtained during gaps and interstices in the analog signal that are common in speech.

Abstract: 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.

Abstract: An apparatus and method for improved security in wire or wireless communication systems includes scrambling the audio signal, combining a masking signal with the scrambled audio signal, and then transmitting the scrambled masked signal. To recover the original audio, a receiver must by synchronized and know the characteristics of the masking signal and the scrambling technique. Such a receiver removes the masking signal, descrambles the audio and thus recovers the original audio. Any attempted interception of the communication would hear white noise, and even if the white noise mask where removed, the communication would still have the security level of the scrambling. The mask removes any remnants of the original audio that might be used to try to locate and intercept the communication.

Abstract: 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.

Abstract: An apparatus and method for concealing data bursts in an analog scrambler using audio repetition. What otherwise would be periodic data bursts appearing at the audio output are replaced with samples from audio portions of the multiplexed signal. Preferably the replaced audio samples come from immediately past portions of the audio of the signal. The data bursts are therefore effectively concealed from the audio output which improves on the degradation of audio otherwise caused by the data bursts that are mixed in periodically with the audio portions of the signal.

Abstract: An apparatus and method for creating voice privacy in electronic voice transmission systems includes the steps of digitizing an analog signal and inverting and rotating the frequency spectrum of the digitized audio signal. From the inverted and rotated spectrum, a complex signal is created from which the real component is extracted to produce a real signal suitable for transmitting. The processing method may optionally include the steps of translating the frequency of the signal spectrum, reducing the sampling rate, shifting the spectrum of the signal again, increasing the sample rate, and extracting the real part of the signal to produce a real signal. The digital signal processing is performed entirely with software. The scrambling and descrambling processes are identical, therefore, the same hardware and software may be used to scramble and descramble the signal.

Abstract: 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.

Abstract: An apparatus and method for providing proper bias current and load resistance for a telephone microphone regardless of the type of microphone used. Microphone bias voltage, if any exists at the microphone, is compared to a reference voltage selected to define a distinction between various types of microphones. If the bias voltage exceeds the reference voltage, an impedance matching the correlated type of microphone is interdicted on both sides of the microphone. If reference voltage exceeds bias voltage, a different impedance path is presented to match it with the type of correlated microphone. Therefore, the invention automatically provides proper bias current and load resistance for the microphone.

Abstract: An apparatus and method for determining the presence and polarity of DC bias voltage at a telephone microphone. A circuit can be added in parallel between any hand or headset and a telephone base unit. The circuit converts the DC bias voltage, if any, across the microphone into a pulsed signal. Each pulse charges a capacitor. The output of the capacitor is passed through a resistor transformer network, and sampled. In between each pulse, the capacitor is discharged and the resulting signal is passed through the transistor/resistor network and sampled. By determining the averages of the charging and discharging signals, and sampling them to convert it into digital information, a digital signal processor can derive whether any bias voltage is present across the microphone, and, if so, its polarity. The circuit can be electrically isolated from the microphone and telephone.

Abstract: An apparatus and method for creating voice privacy by performing frequency spectrum inversion in electronic voice transmission systems includes the steps of digitizing an analog signal and inverting the frequency spectrum of the digitized audio signal. From the inverted spectrum, a complex signal is created from which the real component is extracted to produce a real signal suitable for transmitting. The digital signal processing is performed entirely with software. The scrambling and descrambling processes are nearly identical, therefore, the same hardware and software may be used to scramble and descramble the signal. The apparatus may uses a "rolling code" to increase the effectiveness of the scrambling.

Abstract: An apparatus and method for voice privacy for cellular phones includes generic connection points to make it universal for most cellular phones. The connection points include the speaker and microphone and the microphone input and speaker output of the cellular phone. A scrambling or encryption circuit or process is used to secure the audio before it is transmitted over the network, and the unsecured audio once received. Side-tone added by the cellular phone and network echo of the scrambled audio to be transmitted is removed by, for example, adaptive echo cancellation, and unscrambled side-tone is presented to the speaker. The apparatus can be implemented in a digital signal processor.

Abstract: An apparatus and method for accurate synchronization with inbound audio data which packets at relatively low sampling rates. By using previously known information such as the time of arrival of the beginning of the data packet, a reference timer in a digital signal processor can be used to calculate a number of samples and/or portions thereof between a beginning reference time and the beginning of a data packet, and then calculate the timing error between the first sample point after the arrival of the data packet and the beginning of the data packet. Using this information, the actual arrival of the data packet can be derived and utilized to very accurately, within very small margins of error, synchronize the beginning of the data packet with the scrambling algorithm used in the receiver.

Abstract: 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.

Abstract: 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.

Abstract: 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.