ENCRYPTION BASED DIGITAL WATERMARKING USING TRANSFORM DOMAIN TECHNIQUES

Abstract

The digital media became very popular and data is generally transmitted in digital form over public channel. So there are some chances that digital data can easily be used in an illegal way-being copied, modified and distributed again. Copy right protection, intellectual and material right protection for authors, owners, buyers and distributors and the authenticity of content has become an urgent issue. In such scenario digital watermarking techniques has grown up as a valid solution. Encryption technique is also used here to provide more security. Chaos encryption method is used in our work because it is a kind of pseudorandom, irreversible and dynamical signal generated by the deterministic nonlinear equation, which process good characteristics of pseudorandom sequences. Watermark image is first encrypted using chaos encryption method then the encrypted watermark message is embedded into the cover image. In this report, digital watermarking is performed on the basis of discrete cosine transform and discrete wavelet transform combined with chaos encryption. In DCT method, cover image is divided into 8 X 8 numbers of blocks then transforms each block to DCT domain. Watermark message is encrypted using chaos encryption. For embedding the encrypted watermark, two DCT coefficients that their difference is big enough and they are in low frequencies are chosen. A range of this distance is found for acceptable human perception watermarked image. In DWT method cover image is decomposed using sub bands. Watermark message is also encrypted here using chaos encryption technique. Then the encrypted message is embedded into the selected sub bands for more robustness. Range of scaling factor a is calculated so that the watermarked image and extracted watermark message are acceptable by human perception. These method is analyzed on basis of PSNR (Peak to Signal Noise Ratio), Accuracy Rate and MSE (Mean Square Error). The above mentioned methods are implemented by using MATLAB Software.