Steganographic key recovery for adaptive steganography under “known-message attacks”

Since the performance of STC (Syndrome-Trellis Codes) is approaching the theoretical optimum in minimizing embedded distortion, STC-based adaptive steganography has become the focus of forward improvement and the difficulty of reverse analysis of steganography algorithms. At present, the researches on secret message extraction from STC-based adaptive steganography are mainly focused on the scenario where the secret message is plaintext and part of the plaintext format information is known, while it needs to be studied when these characteristics are unknown. Analogous to the “known-plaintext attack” in cryptanalysis, this manuscript proposes a steganographic key recovery algorithm under the condition of “known-message attack”. Firstly, by studying the structure characteristics of STC parity-check matrix, the concept of basic row vector is proposed, and the problem of secret message extraction attack is transformed into the problem of solving the basic row vectors. Then, the existence of bit string with special structure in the differential sequences of stego sequences is proved. Finally, using the distribution characteristics of the special bit strings in the differential sequence, the problem of solving the basic row vectors is transformed into the problem of solving the simple linear equation system through the differential analysis, and good code judgment criteria is used to filter out the correct steganographic key. The research results of this manuscript can realize the secret message extraction attack when the secret message is ciphertext, which is expected to solve the application requirements of actual scenarios. At the same time, the experimental results also show that, based on the algorithm proposed in this manuscript, only a PC can be used to extract secret message from the common STC-based adaptive steganography algorithm.