Linguistic Steganography for Messaging Applications

Steganography is a set of techniques to hide secret information in another medium called the cover. In the case of linguistic steganography, the cover is text itself. Different methods of linguistic steganography have been developed. They are grouped into two main categories: text generation systems and cover text modification methods. Text generation systems do not produce messages that fit naturally into a conversation within a messaging application. Text modification methods revolve around lexical substitution or syntactic modification. In this paper, we present a new method of linguistic steganography for messaging applications. Our method is based on cover text extension and synonym substitution. We analyse the performance of our system as well as its security and show that it outperforms other substitution methods in terms of bandwidth, i.e., average number of encoded secret bits per sentence.