A chaos-based joint image compression and encryption scheme using DCT and SHA-1

A chaos-based joint image compression and encryption algorithm using discrete cosine transformation (DCT) and Secure Hash Algorithm-1 (SHA-1) is proposed. As SHA-1 is fast and input-sensitive, it is employed to enhance the diffusion effect on image pixels. The DCT coefficients of the whole image are separated into two sequences for mutual interaction. The sequence of low-frequency coefficients, together with the secret keys, generates a message digest to perturb another sequence composed of high-frequency coefficients. The last cipher block of the high-frequency sequence is used as a feedback to control the diffusion and permutation in the low-frequency sequence. Huffman code is chosen as the entropy coding to compress the encrypted chains. Experimental results confirm that our algorithm is efficient and highly sensitive to both the key and the plain-image.