JPEG Encryption with File Size Preservation

Nowadays, many traditional approaches which encrypt multimedia data directly are not suitable for the special nature of multimedia data. So many new encryption approaches have merged to overcome shortcomings and provide confidentiality. But the file size increases after encryption. The objective of our work is to keep the file size for JPEG image after encryption and do not affect the signal processing of JPEG. The DC differential residues are encrypted through XOR with the key that is the same length with the data stream. DCT blocks are scrambled using a key-controlled chaotic map which we proposed. The information of pre-steps is encrypted by cipher and embedded in the second category of AC coefficients. So our scheme is also well supported by cryptographic theory. Experiments show that the scheme is of high security and quality. What´s more, it did not have any impact on signal processing and transmission.