Research On Crack And Improvement Methods Of Masked-OFDM Physical Layer Security Algorithm

In recent years, the physical layer security is widely attention for its many advantages, such as effectively protection of the wireless data link security and low implementation complexity. A large number of excellent research achievements appear, the Masked-OFDM physical layer encryption algorithm which was presented by Arsenia Chorti in 2010 is typical. The noise has the same carrier number, bandwidth and different carrier frequency compared with original OFDM signal,which is added to the original OFDM signal to destroy the orthogonality of the original signal carrier so that can realize information encryption. The advantage of algorithm is novel, simple, good effect of data encryption. But we also found that the security of M-OFDM algorithm is not strong and there exist serious security vulnerabilities by deeply analyze for it.A decoding algorithm, using the strong regularity of noise signal in M-OFDM, is proposed in this paper. The algorithm can reconstruct the noise signal by following steps: firstly, a limited comparison signal set is set at the receiving end. Secondly, Each element of the set is modulated by a fixed frequency carrier. Thirdly, each element in set is subtracted from the received signal to get the difference signal. The key of noise signal is obtained by analyze the different signal spectrum and threshold determine, reconstruct the noise signal. This method is regarded to as C-S (Compare-Signal) algorithm. The simulation results show that when the illegal receiver hacking a large number of illegal cases in the ciphertext eavesdropping, even if there are some ciphertext interferences, is able to access the key of noise by the C-S algorithm, break the M-OFDM algorithm and obtain useful information.Aiming at the security vulnerabilities in the M-OFDM algorithm, an improved FH-MOFDM algorithm based on frequency hopping interference (Frequency Hopping-MOFDM) is proposed. Selection of frequency hopping sequence control artificial noise sub carrier frequency, the modulation information on the carriers is control through the scrambling matrix. In this way, the subcarrier frequency of artificial noise in different periods and noise information symbols carried by carrier will jump continuously according to the set frequency hopping rules and scrambling matrix with the change of time. The concealment and security of artificial noise are improved effectively. Simulation experiments results show that the improved algorithm not only keep the merits of the original algorithm, effectively make up for the security flaws of the original algorithm, but also reduce the detrimental effects of PAPRs and transmission power of system.