AN IMAGE AUTHENTICATION SCHEME USING MSB-LSB STEGANOGRAPHY AND HASH BASED MESSAGE AUTHENTICATION CODE

Abstract

Image encryption prevents unauthorized access to images it does not provide verification that the encrypted image has not been altered or modified. This paper presents a mathematical authentication framework for encrypted images based on Most Significant Bit (MSB) extraction, HMAC based tag generation and the Least Significant Bit (LSB) embedding. The authentication process is performed after image encryption. For each encrypted pixel, the leftmost bit is extracted to construct an MSB-derived authentication representation. A shared secret is processed through the Hash based Message Authentication Code (HMAC) based Key Derivation Function (HKDF) to generate authentication-specific key material, which is subsequently used to generate an authentication tag using HMAC. The generated tag is embedded in designated LSB positions of the encrypted image. At the receiving end, the embedded authentication tag is extracted and the MSB-derived representation is reconstructed. A corresponding authentication tag is recomputed using the same derived authentication key, and the extracted and recomputed tags are compared to determine authentication validity. Finally, theoretical properties of the construction are established addressing MSB invariance under LSB embedding, authentication correctness, sensitivity to modifications affecting the authenticated MSB representation, authentication-tag integrity, domain separation, and random tag-forgery probability.

DOI: https://doi.org/10.5281/zenodo.22165095