Enhancing Imperceptibility: Zero-width Character-based Text Steganography for Preserving Message Privacy

Background: Text steganography preserves the privacy of secret messages by hiding them in cover text. However, existing text steganography techniques embed messages by introducing distortions in text, reducing the similarity between the cover and stegotext. Objective: The objective of this study was to design a method that increases the number of embedding choices and locations to hide more secret bits per distortion in the cover text. The goal is to enhance both embedding capacity and imperceptibility.Methods: A text steganography method is proposed that uses eight zero-width characters (ZWCs) to embed secret messages in the cover text. The proposed method also treats every character in the cover text as a potential embedding location. With eight embedding choices and bit encoding based on embedding locations, more bits can be hidden with fewer insertions in cover text.Results: Experimental results confirm that the proposed method embeds a greater number of bits per insertion of ZWC in the cover text. It also requires a smaller number of insertions to embed secret messages of comparable length. Consequently, the proposed method achieves higher embedding capacity and better imperceptibility compared to existing text steganography methods.Conclusion: The proposed method presents a substantial improvement in text steganography by increasing embedding capacity per distortion and preserving high similarity between cover and stegotext, thus enabling more secure covert communication.