Research On Secure Text Steganography Based On Semantics

With the rapid development of Multimedia Technology and maturity of computernetwork technology，information hiding has been an important means for secretcommunication and widely accepted by people. As the difference of cover,information hiding is classified into graphic, video, software, audio and textsteganography. As a widely used data format, text takes important role insteganographic technology. As its extraordinary superiority, steganography based onnatural language represents the trend of text steganography.The emergence and development of steganography promotes the emergence ofsteganalysis, which judges the existence of secret message by distinguishing thedifference between the cover text and the stego text. So, how to improve theinvisibility and security has become a hot research area. Taking text as research object,we propose two methods to make the steganographic system much securer. The firstone is a steganographic method against steganalysis based on synonymy pairs and theother is a repetitive embedding method in cover text.The steganography based on synonymy substitution makes the statisticalcharacteristic of synonymy pairs in stego text changed from cover text, breaking thecover characteristic and making the steganographic system easier to be attacked bysteganalysis. A steganographic method against steganalysis based on synonym pairswas proposed to deal with this disadvantage. The proposed method dynamicallydivided the synonyms of a synonym set into coded words and backupwords by the useof which the number of synonym pairs was avoided increasing. Therefore, thestatistical characteristics of synonymy pairs were kept unchanged. Experimentalresults showed haleness of this steganographic method when attacked by steganalysisusing the feature derived from synonym pairs.Decreasing positions that need to be modified when embed1bit secret messageon average can keep original characteristic of cover text at utmost,being an efficientway to ensure invisibility. Combining block coding and matrix coding in binary data,we propose a repetitive embedding steganography method in text. For the first timesecret message is embedded with traditional method of synonymy substitution,for thesecond and third time with matrix coding method.Repetitive embedding for threetimes improves the data that every modified position carries and ensures the security f steganographic system.