A speech scrambler for use with conventional mobile communications systems is described including signal gating circuitry so that it may be operated by a simple push button transmitter switch and in the scramble or clear modes without modification of the equipment with which it is used.
A digital voice privacy electronic communication system and method provides protection for an information signal. Either a clear voice signal or a scrambled digitized version of the voice signal is selected for transmission. At the receive end of the system a determination that a clear voice signal or a scrambled signal has been sent is made. This information is used to automatically switch the clear audio signal if present to an output circuit or to switch to the output circuit either a regenerated version of the scrambled signal or an unscrambled version of the information signal. The switching is done automatically so that a user does not have to manually select the proper receiver mode in response to reception of a signal, that is, whether the received signal was a clear voice signal or a scrambled signal. At the transmitter the information signal to be scrambled is analog-to-digital converted and the digital signal is then put into a scrambled form. The scrambled signal may be then processed through base stations, repeaters, satellite receivers, etc., while still in the digitally scrambled form, thereby providing a high degree of protection for such a signal. A receiver may regenerate, or reshape, the scrambled digital signals or the signal may be unscrambled in the receiver depending upon whether the receiver is part of, for example, a repeater system or is a terminal destination for the signal. The digital privacy system of this invention may also be utilized in signal voting systems, either analog or digital, while still maintaining, if necessary, the secure format of the scrambled information.
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.
