University of Khartoum

Design & Implementation of An Analog Voice Encryption System Using Dsp

Design & Implementation of An Analog Voice Encryption System Using Dsp

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Title: Design & Implementation of An Analog Voice Encryption System Using Dsp
Author: Ahmed, Israa Abuobied Elsir
Abstract: Speech scramblers are considered for communication applications where secured speech signal transmission is an important requirement. Analog voice encryption is appropriate for the use of securing the mobile communications system where the requirements of no bandwidth expansion and very low delay is achieved rather than digital voice encryption. The primary goal of the project is to design and implement high secure algorithm for analog voice encryption that is suitable for wireless mobile communication and to overcome the limitations of the digital voice encryption. The implementation was carried out using FFT (Fast Fourier transform) algorithm, which is based on the rearrangement of the FFT coefficients, that was processed using MATLAB. The procedures have gone through phases. Firstly, generating a key that conforms to the key generation criteria to produce to transmitter side. Then the procedures for providing an encrypted speech by using the generated key in the transmitter side. Lastly, decrypted speech was recovered from descrambled speech using procedures in the receiver side. The DSP (Digital Signal Processing) processes (A/D and D/A convertor, framing, windowing, compressing and expanding) are used to prepare the signal for encryption/decryption procedures. The FFT and IFFT )Inverse Fast Fourier Transform) function is used to convert the signal from the time domain to the frequency domain and from frequency domain to time domain, respectively in the both transmitter and receiver sides. The results show that the FFT algorithm has very low residual intelligibility when the value of HD (Hamming Distance) is 90% for the scrambled speech, low encoding delay, very large key space and no bandwidth expansion. The descrambled speech is recognizable but suffers from distortion and noise which can be solved by applying a filter and an amplifier in the receiver side.
URI: http://khartoumspace.uofk.edu/123456789/25768
Date: 2017


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