Research On Speech Covert Communication Method Based On G.729 Speech Coding

With the continuous development of digital mobile communication and network communication,when fulfilling human to communicate with each other,speech,as the most direct and the most commonly used form of expression to convey information,brings a lot of speech communication information security problems,such as tampering,replace,cut,and so on,which is easily produced by attacker.Along with the appearance and application of the information hiding technology and the speech compression coding technology,speech covert communication technology has become the main way to solve the problem of speech information secure communication.In combination with G.729 speech coding scheme,aiming at the research of transparency and robustness in the process of speech covert communication,the secure transmission problems of secret information in real-time speech mobile communication environment are solved in the thesis,which makes use of the idea of partial similarity and the means of reliable transmission and adopts speech information hiding method.Specific contents of this thesis are as follows:1.In accordance with the problem which cannot achieve good transparency for secret information that is hidden in original carrier in open network environment,combining with G.729 encoded speech streams,a novel speech covert communication algorithm,which adopts digital logic transform coding strategies and similarity calculation methods,is proposed in the thesis.First,digital logic operations and cyclic shift operations to transform the secret information are adopted in this algorithm.Then,similarity calculation to link the original carrier is conducted,and finally we get its biggest value to complete to embed the secret information.At the receiver,we use corresponding reversible digital logic operations and cyclic shift operations to extract the secret information.Experimental results show that,the proposed algorithm has very good transparency,high efficiency and bigger embedding rate.Meanwhile,it can satisfy the requirement of real-time speech covert communication.2.In accordance with the problem that how to effectively recover the secret carriers,which comes from the original carriers which have been embedded the secret information,when they have suffered from malicious attacks in the process of real-time transmission.Integrated with G.729 speech encoding,an improved speechcovert communication algorithm,adopting the error correction coding means and interweaving technology,is proposed in this thesis.This proposed algorithm has good robustness aiming at tampering attack and substitution attack from the transmission bitstream.But this algorithm introduces the coding redundancy,which reduces the transparency and the embedding capacity of the speech covert communication algorithm.Therefore,a further improvement to the above algorithm is introduced in the thesis.the mute detection(which is also called the voice activity detection,VAD)algorithm is adopted to fetch the speech fragment which contains more than two inactive frames,and then we use it in speech covert communication.At the same time,when actualizing to embed secret information based the above algorithm,we adopt chaotic scrambling method and pseudo random sequences to conduct encrypting processing to the secret information when it transformed,and then conducts to hide the secret information.Experimental results show that,the proposed algorithm can not only improve transparency and efficiency,but also can achieve good robustness,Meanwhile,It can still satisfy the requirement of real-time speech covert communication.3.Combining with speech perceptual hashing authentication,the above improved speech covert communication algorithm is employed in the thesis to design a speech covert communication system.