Abstract: To obtain samples of encrypted data and plaintext in data link layer,an encrypted data identification scheme was provided based on the run test,meanwhile,and the fast Fourier transform was used to process the encrypted data and plaintext.Based on the principle of maximum difference,the characteristic point of the result of the fast Fourier transform was determined.Then the value of the characteristic point and the feature template were determined using the principle of normal distribution.Finally,the identification rate of the proposed scheme was verified,taking a wireless network data as the identification object.The experimental results demonstrate that the rate of the proposed scheme achieves 95% both for the encrypted data and the plaintext.

Key words: Encrypted bit stream,Runs test,Fast Fourier transform