Research On Key Generation And OFDM Modulation Encryption Algorithm Based On Wireless Channel Characteristics

Currently,security mechanisms of wireless network basically rely upon traditional encryption schemes,which are assessed in terms of computational security.They are difficult to be applied on the terminal with constrained resource,and the secure distribution and management of cryptographic keys in mobile scenarios will become a huge challenge for this scheme.The features of the wireless channel itself,such as reciprocity,spatial uniqueness and time variability,provide the possibility for the key sharing scheme based on the characteristics of the wireless channel.Based on the present situation of wireless communication security and the necessity of physical layer security,this article points out that the physical layer air interface should be encrypted and protected in wireless link.The research work of this paper is as follows:(1)In this part,we studied the security mechanism that the two sides of the legitimate communication use the wireless channel as the Shared random source to generate the uniform communication key.The Shared key generation process and performance evaluation criteria were studied.Taking the ASBG algorithm as an example,the feasibility of the Shared key generation scheme based on the characteristics of wireless channel was proved by theoretical and simulation analysis.(2)Wavelet transform was used to improve the HRUBE algorithm.Different from ASBG scheme,HRUBE scheme can theoretically have a high key generation rate due to the use of all channel eigenvalues and the multi-bit quantization method,but only when the SNR is relatively high can it play its advantages.For this reason,on the basis of the HRUBE scheme,the channel characteristics were firstly decomposed by sym8 wavelet in three layers,and then the channel characteristics would be reconstructed after soft threshold processing of the obtained high frequency coefficients.This method successfully reduced the noise interference and reduced the difference of channel characteristics between the two sides of legitimate communication by about 19%.In addition,in order to enhance the local randomness of the obtained key,the generated key sequences were grouped and interlaced.Simulation results show that the improved HRUBE scheme not only improves the key consistency,but also has higher key generation rate and good randomness.(3)The traditional OFDM modulation method was improved and a secure transmission strategy was proposed to encrypt the OFDM modulation process with the Shared key.TheShared key does not need to carry on the key transmission,does not have the leakage risk,the security and the randomness is better than the previous chaotic key.The core idea of the algorithm was as follows.Under the control of the secret key,data symbols were interpolated randomly after Inverse Fast Fourier Transform(IFFT).And the original OFDM symbol would be reconstructed.It was difficult for illegal users to correctly demodulate the signal.The benefits of the physical layer security mechanism is the convenience to protect air interface and wireless link.And the process of parallel encryption can reduce the complexity of communication system implementation.The results of theoretical analysis and simulation show that,the algorithm has little influence on the original performance of the system and can effectively withstand all kinds of illegal attacks.Furthermore,the algorithm can be well adapted to multipath channel,and shows a good ability to withstand multipath fading.