Multilayer Partially Homomorphic Encryption Text Steganography (MLPHE-TS): A Zero Steganography Approach

This paper presents a Multilayer Partially Homomorphic Encryption Text Steganography, an invisible approach for covert communication. Existing text-based schemes are either successive in obtaining high concealing capacity, imperceptibility or robusrnes, but failed to achieve the balance between these conflicting parameters. To fill the gaps, we propose a new steganography scheme that successfully addresses the limitations of existing schemes. To achieve high hidden capacity, instead of using conventional secret stream embedding process, we substitute character of secret message with the cover message. Conversion of the multi-variate secret message into alphabets through the alphabetic transformation process is another additive characteristic of our proposed method which resolves the problem of cover message selection. Our proposed scheme is a blind embedding scheme that replaces a character of secret message with a character of cover message and hence-forth makes it zero-perceptible. Furthermore, robustness is achieved through implanting multilayer encoding concept where block encoding, use of partially homomorphic encryption, and alphabetic transformation provide multilayer security to secret message before its actual embedding. This multilayer encryption process also assists in the reduction of secret message size thus creating more space for concealment. Additionally, key generation process is also improved by employing identical range for the selection of both prime numbers in partially homomorphic algorithm to generate public and private keys for encryption process. We compared our scheme with the existing schemes to evaluate capacity, imperceptibility and robustness of the proposed method. Experimental results demonstrate that all identified issues of text steganography are successfully addressed and our proposed scheme outperforms the existing similar steganographic mechanisms.