What is Substitution Classes

This chapter develops a linguistically robust encryption system, LunabeL, which converts a message into syntactically and semantically innocuous text. Drawing upon linguistic criteria, LunabeL uses word replacement, with substitution classes based on traditional linguistic features (syntactic categories and subcategories), as well as features under-exploited in earlier works: semantic criteria, graphotactic structure, and inflectional class. The original message is further hidden through the use of cover texts—within these, LunabeL retains all function words and targets specific classes of content words for replacement, creating text which preserves the syntactic structure and semantic context of the original cover text. LunabeL takes advantage of cover text styles which are not expected to be necessarily comprehensible to the general public, making any semantic anomalies more opaque. This line of work has the promise of creating encrypted texts which are less detectable to human readers than earlier steganographic efforts.