Research On Secret Key Generation Utilizing The Wireless Channel Characteristics

To enhance the security of wireless communication, an alternative method that extracted the physical layer characteristics of channels for generating secret keys was proposed. In TDD system, communication terminals extract the identical channel characteristics based on channel reciprocity theory between uplink and downlink, and generate secret key independently in real time, this scheme can avoid transmission of and achieve the aim of secure communication. But there are at least three main problems need to be solved. Firstly, the radio channel usually changes rapidly, it is too difficult to guarantee the agreement of the channel estimation between the users. Secondly, in most of available key generation schemes, they take received signal strength as the channel character resulting in that they can't be adapted to different wireless systems, different modulated signals and different radio environment. Finally, there is no method to ensure both high rate and high consistency of the key generation simultaneously. Therefore, the research on secret key generation based on the wireless channel characteristics is studied in the paper.This research is supported by the National Natural Science Fund─Research on Key Technologies of Wireless Physical Layer Security. After analyzing the advantages and disadvantages of existing schemes, the dissertation proposes a general Physical Layer key generation model and investigates several key processes of this model thoroughly. The main contents are as follows:1. Designs an Physical Layer key generation model based on the channel detection factor. According to the fact that channel detection factor reflects the degree of the users'channel estimation, terminals adjust the channel detection interval dynamically to guarantee the high degree of the channel estimation consistency, and reduce the complexity of two key processes of this model─key generation algorithm and the key agreement scheme.2. Proposes a multipath relative delay-based key generation algorithm. For wideband system, the receiver extracts the multipath relative-delay and generate key by using the difference between the relative-delay and the average -delay. Simulation results demonstrate that this scheme against the noise. Without pre-setting the judging threshold, this algorithm decreases the uncertainty of key generation comparing with the existing schemes, increases the consistency of key agreement.3. Proposes a key agreement scheme based on double hash functions. This scheme employs the single-orientation property of hash's function to guarante the consistency of key generation; using the property of hash's dispersity, this scheme eliminates the co-interference of channel measurement. After analyzing the secure threatens of this scheme, an improved pipeline advanced key agreement scheme is presented, the advanced scheme can ensure that the third party can't uncover the true message even if he receives the checking information.4. Proposes a joint channel characteristics vector quantization (JCQ) scheme. This scheme can insure the high rate and high consistency of the key generation simultaneously. To increasing the key generation rate, extraction secret key from channel characteristics is equal to the minimum error problem of vector quantization; and a single-orientated cells adjustment mechanism is used to reduce negative effect produced by non-simultaneous measurement and the error of channel estimation. Simulation results show that the JCQ scheme can achieve higher secret key generating rate and agreement consistency than available schemes, and the more number of sub-cells, the better.