Joint Image Compression And Encryption Synchronous Algorithm Based On SPIHT And SHA-1Algorithm

In recent years, with the popularity of digital images transmitting in public network, the effectiveness and safety of images get more and more attentions. Meanwhile, with the expanding of multimedia information and the growing insecurity in the transmission process, the requirements of the network bandwidth and the security are gradually enhanced. On the one hand, in order to ensure the digital images are transmitted quickly and efficiently, image compression is widely studied. On the other hand, for the purpose of data security in the transmission process, the image encryption technology has become more mature, which disrupts the correlation among data in digital images.Due to the commonalities between compression and encryption isn’t considered, image compression mainly occurs before or after image encryption in current research of image processing, the compressed stream could be analysis and decoded effectively, which reduce the security in transmission process. Simultaneously, the current studies increase the costs of algorithm development and maintenance, therefore, the combination of image compression and encryption is necessary.An image compression and encryption combination algorithm based on SPIHT and SHA-1algorithm is proposed in this paper, which combines Logistic chaotic system and SHA-1algorithm into image compression in order to achieve joint image compression and encryption. Based on depth analysis of EZW and SPIHT coding algorithm, the orientation tree structure in the SPIHT coding algorithm is changed. Three bitmap is used in the improved algorithm instead of list to store coefficients produced in encoding process.The encryption process is divided into diffusion process and confusion process. The pixel location of wavelet coefficients is scrambled using random key generated by Logistic in the diffusion process, it occurs in every sub-band in each level, partly disrupting father and son relationship of the minimum zero-tree generated by wavelet transform in compression algorithm, instead of change the value of the wavelet coefficients. The output stream of the improved SPIHT algorithm is changed and associated with the initial value in order to resist plaintext attack in the confusion process.The algorithm simulation results show that the proposed algorithm achieves the combination of encryption and compression. On the one hand, the reconstructed image quality is higher than SPIHT algorithm, on the other hand, the proposed algorithm has more superior resistance capability to differential attack and linear attack, also, the key space is large and it has excellent encryption effect.