An optimized data hiding scheme for Deflate codes

Compression file is a common form of carriers in network data transmission; therefore, it is essential to investigate the data hiding schemes for compression files. The existing data hiding schemes embed secret bits by shrinking the length of symbols, while they are not secure enough since the shrinking of symbol length is easily detected. First, we propose a longest match detecting algorithm that can detect the data hiding behavior of shrinking the length of symbols, by checking whether items of the generated dictionary are longest matches or not. Then, we propose a secret data hiding scheme based on Deflate codes, which reversibly embeds secret data by altering the matching process, to choose the proper matching result that the least significant bit of length field in [distance, length] pair is equal to the current embedded secret bit. The proposed data hiding scheme can resist on the longest match detection, and the embedding rate is higher than DH-LZW algorithm. The experiment shows that the proposed scheme achieves 5.12% of embedding rate and 10.18% size increase in the compressed file. Moreover, an optimization is made in providing practical suggestion for DH-Deflate data hiding. One can choose which format and size of files are to be selected based upon the optimization, and thus, data hiding work can be achieved in a convenient and targeted way.