Speech Scrambling Based on Wavelet Transform

The increased interest in analog speech scrambling techniques are due to the increased visibility and publicity given to the vulnerability of communication systems to eavesdropping of unauthorized remote access (Gersho & Steele, 1984). In wireless communications, including High Frequency (H.F) and satellite communications, it is almost impossible to prevent unauthorized people from eavesdropping unless speech scramblers may be used to protect privacy. Among speech scramblers, analog scramblers are attractive and wide applicable. The conventional analog scramblers manipulate speech signal in the frequency or time domain or both. A typical frequency domain scrambler is the band splitting scrambler, which breaks the speech signal into several sub bands and permutes them. A typical time domain scrambler is the time division scrambler, which breaks the speech signal into short time segments and permutes them within a block of several segments(Sakurai et al., 1984). These conventional analog scramblers cannot provide sufficient security against cryptanalysis because the number of permutable elements in these scramblers is not large enough to provide an adequate number of different permutations due to hardware limitation and processing delays.