Secure speech communication has been of great significance in civil,
commercial and particularly in military communication systems. Speech
scramblers play a major role in these systems. Transform-domain,
specially, DCT (Discrete Cosine Transform) based encryption of speech
signals has often been a preferable choice for researchers. In such
systems, besides security, removal of redundant information and
execution speed of the algorithms have also been main focus of research
and exploration. In this book, these three attributes, redundancy, speed
and security are envisaged by exploiting ITU-T G.723.1 speech codec,
Texas Instruments' 32-bit floating-point DSP TMS320C6711 and a newly
developed DCT based algorithm using sub-framing and lookup table
respectively. The vigorous results show that the original signal is
compressed more than 90%, which helps in the removal of redundant
information. To enhance the execution speed, G.723.1 codec is optimized
on advanced level thereby reducing execution time from 299 msec to 140
msec. In respect of security, the newly introduced scheme yielded 0%
residual intelligibility of the encrypted signal thereby rendering
highest level of security.