| In today’s Network time, Internet phone has been widely applied to various fields of society, for its features of cheap and convenient real-time. So to some extent it replaced the traditional fixed telephone and mobile phone. But its voice and data exchanging based on network. So data security must be considered, such as:network eavesdropping, voice Changer disguise, and so on.In this thesis, a research was made on the security problem of voice communications on the internet, and a practical point to point call was simulated in the local area network. The data encryption and decryption process was put into the voice communication process, so as to achieve the purpose of confidentiality. The main work and innovations are as follows:1. Learning on the audio controls of DirectX and DirectX.DirectSound. In the way of reducing the voice buffer area by half, the imitated voice signal was recorded into the digital signal with the PCM format from analog signal, which completed the A/D transform and get ready for data encryption and decryption.2. At the same time encryption and decryption algorithm was tested screening. It was concluded that only the sequence code can finish the encryption and decryption in time for voice.3. The following are three stream ciphers used for encryption and decryption of voice data in the thesis:1). When studying and designing the A5algorithm of the sequence code which is used in GSM system, some improvement was made on the A5algorithm—increasing the number of the progression of each sub-register and the number of the tapping sequence so as to resist the exhaustive attack to the original A5effectively, on the principle of no changing the encryption efficiency.2). A kind of simple self synchronization sequence code was designed—if the data is lost, it will step out some numerical decryption, and automatically resume to the decryption correctly. This algorithm has high nonlinearity, and resists the exhaustive attack successfully.3). In order to get the expanding secret key algorithm with stable cycle and linear complexity, again a new expanding secret key algorithm which adopts the idea of course interlacing control was designed. After testing this algorithm pseudo randomly, the calculated data proved that this algorithm has great periodicity, stable linear complexity which increases exponentially, and sufficient randomicity. Compared to the traditional clock drive control, this algorithm can not only resist the exhaustive attack, but also can resist similar attacks to the Geffe generator, and can resist the attacks based on the attackers’periodicity analysis according to the statistic characteristics more effectively.4.The encryption key is exchanged by the key exchange protocol before the voice-talk beginning. After studying on the Diffie-Hellman key exchange protocol in-depth, and adding the digital signature, the secret key exchange procedure becomes complex, so the secret key procedure is simplified and improved furthermore, then it can resistance to a variety of key attack.5.Based on the above works, C#was used to establish voice communications under the VS2008compilation environment.And based on this application, the corresponding C/S mode software was designed, which simulated the process of real and safe voice-talk based on IP further. |
