Hide-as-you-Type: An Approach to Natural Language Steganography through Sentence Modification

In this paper, we describe and evaluate Hide-as-you-Type, a prototype steganographic system, designed to hide secret bits in the digest chains of natural language sentences. Through an interactive embedding process that incorporates keyed hash functions and human reviewed sentences, the system generates two innocuous natural language carriers that ultimately optimise payload secrecy. Conventionally, the first carrier (carrier-text) hosts a payload of secret bits. The second carrier, referred to as an open-stego-key, hosts sentences used as keys to extract a payload from a carrier-text. Notable aspects of our approach include the scope to offset embedding distortion from a carrier-text to an open-stego-key, as well as the scope to resize a carrier-text for optimal transmission via capacity constrained channels (e.g. Twitter, SMS), at the expense of a larger open-stego-key, that is transmitted via an alternative channel (e.g. Social media, blog, forum, email).