An improved block based joint reversible data hiding in encrypted images by symmetric cryptosystem.

• Embedding capacity is increased by embedding n (n = 2,3,4...) secret bits per block. • After decryption, secret message is extracted and cover image is recovered using spatial correlation of image. • The proposed method demonstrates higher PSNR values as compared to Zhang [12] and Young et al. [17] for all test images. Earlier joint EIRDH (Encrypted Image Reversible Data Hiding) techniques divided cover image into equal sized blocks and embedded one secret bit per block and after decryption of stego image with same key as encryption key, secret message is extracted through data hiding key and original cover image is recovered using spatial correlation of the image. After carrying out a feasibility analysis, improved block based joint EIRDH algorithm is employed in this paper which embedded n (n = 2 , 3 , 4.....) secret bits per block by dividing blocks of same size (4 × 4, 8 × 8, 16 × 16, 32 × 32.....)into n sub-blocks. Optimal visual quality and enhanced embedding rate are acquired by the proposed scheme. Test results and correlations are exhibited to outline the viability and focal points of the proposed technique with conventional ones. [ABSTRACT FROM AUTHOR]