Research On VoIP Steganography Algorithm Under Low Modification Rate Constraints

The VoIP steganography is to hide a secret into VoIP traffic by modifying the protocol domain or data domain of an IP packet.It is difficult to achieve the steganography in the VoIP,which due to its characteristics of real-time,high compressibility and low redundancy.However,it is also difficult for the VoIP steganalysis due to these same characteristics.This paper studied the existing steganography methods in the protocol domain or data domain of the VoIP traffic.Based on the principle that “The less modifications there are,the harder it is detected”,two steganographic methods are proposed,which can reduce the modification on carriers to improve the steganography performance.The main work is as follows:(1)The CNV optimal matching path algorithm(OM-CNV)is proposed,which improves the imperceptibility of the steganography without decreasing the capacity.A steganography operation unit is defined in this method,which is composed of N consecutive audio frames.Each frame includes M LPC parameters.An M×N parameters formed a steganography operation unit.Each parameter in the operation unit is converted into a one-bit binary digit based on the Complementary Neighbor Vertex(CNV)method.Thus,every traversal path has a corresponding binary string.By computing the hamming distance between the binary secret and the binary string of every traversal path,the binary string of the traversal path with minimal hamming distance expected value is selected,the secret message is hidden via the CNV embedding method into the traversal path.The experimental results show that the proposed steganography algorithm has a good performance in audio quality,whose PESQ was over than 4.0.The modified bit rate decreases from 50% to 37.4% when only 6 traversal paths are predefined.The processing time can satisfy the real-time requirement of VoIP services.Moreover,it doesn't change the audio size.Both the experiments show that its KL divergence can reach below 0.1,which indicates its undetectability is good.(2)The codeword replacement algorithm is proposed based on shortest Euclidean distance for VoIP(SED-CR).Based on the principle that the less modification to a cover will achieve the high imperceptibility,the SED-CR is proposed to decrease the modification on the cover and improve the steganography efficiency,and its invisibility is enhanced without reducing the audio quality.Firstly,A steganography unit is defined.Secondly,the Euclidean distance between the secret message and the Linear Predictive Coding(LPC)parameters in the unit is calculated.Finally,the LPC parameter,which has the shortest distance,is replaced with the secret message,and the Complementary Neighbor Vertex(CNV)method is employed to indicate which LPC parameters are modified.By comparing with other methods,the experimental results show that the proposed method has higher steganography efficiency.Its modification rate reduces to22.7% and the KL divergence indicates the good security.The PESQ exceeds 4.0,which indicates a good speech quality.In summary,we propose two steganography methods for VoIP with the constraint of the low modification to the LPC parameters.The proposed methods achieve a good performance of speech quality,modified bit rate,security and undetectability.