A Selective Bitplane Based Encryption of Grayscale Images with Tamper Detection, Localization and Recovery Based on Watermark

Ciphered data need an additional level of protection in order to safeguard them from being tampered after the decryption phase. Ciphered data, upon being deciphered by the intended receiver, is unprotected and it can be easily doctored by ever-developing, sophisticated image processing softwares. In the proposed scheme, we introduce a selective bitplane based encryption of grayscale images coupled with the facility of tamper detection, localization and restoration based on DWT based digital watermark. The original image is first sub-divided into blocks where Discrete Wavelet Transform (DWT) is applied to generate the watermark. This is embedded in four disjoint portions of the image to increase the probability of restoration of the tampered image from tampers. To add another level of security to the transmission of the watermarked image a selective bitplane based encryption based on chaos is applied. The watermarked image is first partitioned into its constituent bitplanes and then first four bitplanes from Most Significant Bitplane (MSB) is encrypted by a chaos based pseudorandom binary number generator (PRBG). The enciphered bitplanes are concatenated with unencrypted ones to produce the cipher watermarked image. The validity and novelty of the proposed scheme is verified through exhaustive simulations using different images of two well-known image databases.