The Research Of Chaotic Theory-based Covert Communications Over VoIP Streaming Media Networks

With the development of the Internet and information technology,and the acceleration of global informationization,the national political,economic and other confidential information are digitized gradually.Each country relies on information networks in terms of energy,transportation,finance,commerce and military,which means all these information is vulnerable to attacks.Covert communication is of great importance in military protection and national security.Voice over Internet Protocol(VoIP)is one of the most popular real-time services on the Internet.Since the Internet allows VoIP to provide high-reliability,global and low-cost or even free services,more and more users communicate with each other daily by using VoIP products.VoIP streams also play an increasingly important part in the Internet traffic.VoIP has attracted more and more attention from the researchers in the field of information security,and it is considered to be a better cover object for covert communication.However,these studies did not take into account some unstable factors in the real network,such as packet loss which would lead to the loss of secret information in the voice packet.And the real-time requirement makes it more difficult for ones to introduce more security operations to embed and protect the secret data.Taking into account the above problems,this thesis makes contributions to the covert communication of VoIP network streaming media as follows:(1)At the VoIP signaling phase,a key distribution was designed for initializing the interactive communication session between the communicating parties.The key distribution was achieved using an effective authenticated key agreement scheme for SIP based on the concept of identity-based encryption,which could solve the exchange of session key without affecting the speech quality.(2)Most of the steganographic algorithms are designed in an ideal experimental environment,without considering the impact of the network packet loss and other factors on covert communications,and the secret message to be embedded was often encrypted in whole at the preprocessing phase.A VoIP steganographic algorithm with variable embedding intervals incorporating Advanced Encryption Standard(AES)was proposed.To meet the real-time requirements of VoIP communications,the secret message was encrypted and then embedded into audio packets with different embedding algorithms before sending them.The encryption and embedding processes were almostsynchronized.As the experimental results shown,the stego-speech had little distortion to the cover-speech.And the covert VoIP communication using the proposed steganographic algorithm was undetectable in terms of statistical analysis by using the Mann-Whitney-Wilcoxon method.(3)A self-adaptive audio steganography approach was suggested to realise VoIP covert communications over the Internet.An Active Voice Period Detection function was specially designed for PCM codec to detect whether the voice in an VoIP packet is active or not,solving the problem of automatic recognition of active and inactive voice in the PCM codec.The appropriate voice was selected as the cover speech according to the characteristics of the voice activity,which made the carrier distortion caused by embedding the secret data uneasy to be noticed and reduced the influence of the embedding operation on the speech quality;And the data embedding locations in VoIP streams were chosen randomly according to chaotic sequences generated from a chaotic map,which could improve the security of confidential data.Performance evaluation and security analysis indicated that the self-adaptive VoIP steganographic scheme could withstand statistical detection,and achieve secure real-time communications with high speech quality and negligible signal distortion.(4)To decrease the influence of packet loss on VoIP covert communication,a fractal-based VoIP steganographic approach was proposed to realize covert VoIP communications in the presence of packet loss.The prediction model based on fractal interpolation was built to decide whether a VoIP packet was suitable for data hiding.The Gilbert model with two-state Markov modes was used to create a network environment with packet loss in our laboratory.The scheme for covert VoIP communication with packet loss was implemented on our StegPhone VoIP communication platform.The experimental results revealed that the success rate of the fractal prediction has a significant effect on the performance of VoIP communications with steganography,the higher the data retrieving rate,the greater robustness the covert communication.Besides,the Mann-Whitney-Wilcoxon test showed the undetectability of the approach,and this covert VoIP communication scheme with fractal packet loss prediction has a feature of generalizability,so it can be applied to other speech codecs,such as G.729,G.723.1.