Lossless and Reversible Data Hiding in Asymmetric Cryptography

This technology proposes a lossless, a reversible, and a combined data hiding schemes for cipher text images encrypted by public key cryptosystems with probabilistic and holomorphic properties. In the lossless scheme, the cipher text pixels are replaced with new values to embed the additional data into several LSB-planes of cipher text pixels by multiple layer wet paper coding. Then, the embedded data can be directly extracted from the encrypted domain and the data embedding operation does not affect the decryption of original plaintext image. In the reversible scheme, a pre-processing is employed to shrink the image histogram before image encryption, so that the modification on encrypted images for data embedding will not cause any pixel oversaturation in plaintext domain. Although a slight distortion is introduced, the embedded data can be extracted and the original image can be recovered from the directly decrypted image. Due to the compatibility between the lossless and reversible schemes, the data embedding operations in the two manners can be simultaneously performed in an encrypted image. With the combined technique, a receiver may extract a part of embedded data before decryption, and extract another part of embedded data and recover the original plaintext image after decryption.