The Decryption Method And SOPC Implementation For BSS-based Speech Encryption

The speech security is an important branch of information security. In order to protect the speech security, many speech encryption methods have been proposed. BSS-based speech encryption is a newly proposed method, which is based on source inseparability for underdetermined mixtures and thus has a high level of security. Because the BSS method has order and magnitude uncertainty, BSS-based decryption needs speech waveform information, which affects the encryption speed to a certain extent. This thesis aims to provide a more rapid and efficient method for decryption, and then design the encryption system based on SOPC (System On Programmable Chip).Correlation calculation decryption is a kind of algebraic method and was originally proposed for fast decryption in BSS-based image encryption. Considering that the structure of speech encryption matrix is similar to that of image encryption matrix, this thesis analyzes the correlation between speech signals and the key signals, and the feasibility of utilizing correlation calculation to decrypt BSS-encrypted speeches, and then provides the speech decryption based on correlation calculation. Compared to traditional BSS decryption methods, correlation calculation needs no waveform information about the original speeches. So it can reduce the computational complexity, improve the decryption speed, and avoid the uncertainty problems. The simulation results show that it is 20 times faster than traditional BSS decryption, and its average SNR improves 3dB.To push this method toward practical application, this thesis further designs a speech encryption SOPC system based on FPGA with EDK (Embed System Design Kit) as a design platform which. The PowerPC hard core is used as the processor, and the open-source IP cores provided by the FPGA manufacture or the third party are used to construct the peripheral devices such as DDR,RS232,GPIO and AC97. Then software programs are developed using C language including speech acquisition, speech storage, speech encryption, speech decryption and speech play. The actual speech encryption experiments show that this system can not only perform speech encryption and decryption, but also has high stability and flexible system extension ability, thus has a high practical value.