A secure text steganography based on synonym substitution

In text steganography based on synonym substitution, the synonym number in synonym set is not always some powers of 2. In traditional methods, the redundant synonyms are always abandoned. Two different coding schedules, which made full use of the abandoned synonym to improve the security of the steganographic system, are proposed in this paper. The synonyms in a synonym set are dynamically divided into coded words and backup words. One method divides the cover text into blocks to hide the secret information for the first time and then uses a highly efficient coding schedule to embed the secret information for the second and third time. The other method employs the backup words to prevent the increase the number of synonym pairs, keeping the statistical characteristics of synonym pairs unchanged.