S. Tenreiro de Magalhães, H. Jahankhani, and A.G. Hessami (Eds.): ICGS3 2010, CCIS 92, pp. 48–54, 2010. © Springer-Verlag Berlin Heidelberg 2010 An Approach to Textual Steganography Michael Morran and George R.S. Weir * Department of Computer and Information Sciences, University of Strathclyde, Glasgow G1 1XH, UK {michael.morran,george.weir}@cis.strath.ac.uk Abstract. Textual steganography is a means of concealing an encoded message within text. The appeal in such a system is its potential for hiding the fact that encoding is taking place. The failure to hide the presence of encoding is a form of information leakage and an inherent risk since it suggests that there is impor- tant or valuable information in transit. This is considered a major limitation of existing cryptographic techniques as applied to secure information transfer. In this paper, we describe an experimental system that we have developed as a test bed for textual steganography. This system allows us to explore the application of part of speech tagging, word sense disambiguation and synonym replacement as component strategies for textual steganography. Keywords: textual steganography, information security, textual analysis, natural language processing. 1 Introduction Information security is vital in today’s society [1]. Conventionally, this issue has been addressed through a range of encryption techniques that serve to protect the content of valuable data. Encryption technology has developed to the point that breaking modern encryption schemes is practically infeasible*. The use of encryption however, imme- diately suggests that certain information must be important. To an adversary, or even the authorities, the presence of encrypted traffic between two individuals may be enough to arouse suspicion. Although the information may be securely encrypted, a third party may be able to intercept the information and either tamper with the mes- sage or prevent it ever reaching its destination. This problem will remain as long as encryption is adopted as the sole solution to information security needs. To illustrate the limitation of an encryption system, and to suggest a more appro- priate solution, Simmons presents the “Prisoners’ Problem” [2]. The scenario tells of Alice and Bob, two prisoners, who attempt to formulate an escape plan. Any commu- nication between the captives must pass through a warder (Wendy). If any suspicious communication is detected between the prisoners Wendy will not pass on the infor- mation. Modern encryption techniques, although secure, result in text which is readily recognisable as cipher text. In this scenario, such techniques would be useless in the presence of Wendy and this indicates the need for information hiding, rather than mere encryption. * Corresponding author.