Design of secure speech encryption systems
Jie Fang · QUT ePrints (Queensland University of Technology) · 1990
This thesis investigates the design of digital speech encryption systems based on low bit rate vocoders. The speech quality and the cryptographic strength of the system are determined by vocoder and encryptor respectively. Three different low bit rate vocoders, 2400 BPS LPC ( Linear Prediction Coding) vocoder, 9600 BPS MELPC (Mul tipulse Excited Linear Prediction Coding) vocoder and 4800 BPS CELP (Codebook Excited Linear Prediction coding) vocoder, have been simulated. The performances of these vocoders are evaluated by using four objective measures. The thesis considers the follows aspects of digital encryption system: * Security * Speech quality * Robustness * System delay Several choices of the cryptosystem for the encryption of digital speech are investigated, and the performance of the overall system is discussed. The work presented in this thesis enables a secure communication system designer to select a speech coding scheme and a cipher system to meet required level of security and speech quality. encryption systems throughout this thesis refers to mathematics analysis and simulation of such systems rather than the actual construction of electronic circuits.