Fast Fourier transform speech scrambler

The FFT speech encryption algorithm is tested on speech samples which are recorded using a data acquisition system connected to a PC. The speech samples are read from an input file by the simulation program and the scrambling operation performed on them frame-by-frame. The scrambled speech signal is output through the filter card and the DAC card. The scrambled speech samples are also recorded onto an output file on which the descrambling operations are subsequently performed. The algorithms and results of these simulation tests are provided below. An analog I/O card was used with simulation program. A 12-bit ADC and DAC card was used to capture about 4 seconds of speech at the rate of 8 Ksps. The scrambler and descrambler programs written in C processed the speech file. The main parts of the system are (i) scrambler with permutation and (ii) descrambling with depermutation. Some additional parts such as the ADC, the DAC, the IBC (integer to binary convertor) and the BIC are necessary. The basic functions can, thus be identified as follows: 1) Scrambler includes FFT, permutation and IFFT 2) Descrambler includes FFT, depermutation and IFFT 3) Generation of permutation matrices.