Text Information Hiding Algorithm Based on Part of Speech Tag Grammar

A method for text information hiding based on word tag language is proposed.The Content Free Grammar (CFG)is constructed according to natural language rules,and CFG language is pattern of natural language sen- tence.Both secretary messages and cover text are transformed into language of CFG,the position of a secretary message sentence appearing in the cover text is found by string matching,the position is a key.With the help of the key,receivers can find out the sentences that carry secretary messages easily,and read the secretary messages through syntactic analysis.Further more,a formula for computing the capacity of hidden information is given.This method does not require to modify cover text,meanwhile,it is a sound solution for cover text which produced by Wayner's scheme which is syntactic but not semantic.