Security Level Enhancement in Noisy Environment

Speech scrambling techniques are used to scramble clear speech into unintelligible signal in order to avoid eavesdropping. . Analog scramblers are intended in applications where the degree of security is not too critical and hardware modifications are prohibitive due to its high cost .The residual intelligibility of the speech signal can be reduced by reducing correlation among the speech samples. Security level enhancement in speech encryption system using large set of kasami sequence is described. The speech signal is divided into segments, the polynomial is generated by using chaotic map. Using this polynomial we are generating large set of kasami sequence. Using this sequence as a key the speech signal is encrypted with AES-128 bit algorithm .The evaluation is carried out with respect to noise attack. The security offered by the system depends on the number of PN sequences present in the code set .Also the residual intelligibility is very less if each sample of the speech signal is encrypted with different sequence instead of using same sequence for each sample therefore the signal is better encrypted if the code set contains more number of sequences .