NCJ Number
62296
Date Published
1979
Length
5 pages
Annotation
ANALOG SPEECH SECURITY SYSTEMS OR SCRAMBLERS ARE DISCUSSED, AND WAYS OF ACHIEVING HIGH SECURITY AND MEASURING THE EFFECTIVENESS OF ANALOG SPEECH COMMUNICATION SECURITY DEVICES (CSD'S) ARE PROPOSED.
Abstract
SPEECH COMMUNICATION SECURITY REQUIREMENTS ARE DIVIDED INTO THREE BROAD CATEGORIES OR LEVELS. THE FIRST IS PROTECTION FROM A LISTENER WITHOUT ELECTRONIC ASSISTANCE. THE SECOND INVOLVES PROTECTION FROM COMMON ELECTRONIC PENETRATION TECHNIQUES, SUCH AS REINVERTERS, BALANCED MODULATORS, TUNABLE OSCILLATORS, NOTCH FILTERS, AND TAPE RECORDINGS, AND MODIFICATION OF CDS'S TO DECODE OTHER SIMILAR UNITS. THE HIGHEST LEVEL OF PROTECTION IS THAT AGAINST SOPHISTICATED PENETRATION USING SUCH TECHNIQUES AS COMPUTER ANALYSIS, SONOGRAMS, AND SPECTRUM ANALYSIS. THERE ARE STATIC AND DYNAMIC CSD SYSTEMS. STATIC SYSTEMS CODE SIGNALS IN A MANNER THAT DOES NOT CHANGE DURING THE COURSE OF TRANSMISSION. DYNAMIC SYSTEMS REARRANGE PERMUTATIONS OR CHANGE A CODE PERIODICALLY FROM TWICE A SECOND IN SOME EQUIPMENT TO 750 TIMES A SECOND IN OTHER UNITS. THE EMPHASIS IS ON DYNAMIC SYSTEMS WHERE BASIC PROCESSING OF VOICE SIGNALS CAN BE ACCOMPLISHED IN THE FOLLOWING WAYS: (1) ANALOG PROCESSING AND TRANSMISSION IN TIME AND/OR FREQUENCY DOMAINS; (2) ANALOG TO DIGITAL CONVERSION, WITH DIGITAL PROCESSING AND ANALOG TRANSMISSION; AND (3) ANALOG TO DIGITAL CONVERSION, WITH DIGITAL PROCESSING AND DIGITAL TRANSMISSION. THE MOST USEFUL ANALOG TECHNIQUES ARE FREQUENCY INVERSION, BANDSPLITTERS, TIME DIVERSION MULTIPLEXING, AND THE EMPLOYMENT OF A DYNAMIC ROLLING CODE. ELEMENTS OR PARAMETERS THAT CAN BE MANIPULATED IN THE CODING PROCESS OF CSD'S ARE TIME, FREQUENCY, AND AN OVERLAY OR MASKING SIGNAL. METHODS FOR PERMUTATING SPEECH SEGMENTS, THE DERIVATION OF EVALUATION FACTORS FOR ASSESSING THE SECURITY OF ANALOG SPEECH CSD'S AND CALCULATIONS FOR REPRESENTATIVE ANALOG SPEECH SECURITY SYSTEMS ARE DISCUSSED. SUPPORTING TABLES AND FIGURES ARE PROVIDED. (DEP)