Abstract: Aiming at the increasing demand for transcoding capacity caused by the aggravating isomerization degree in communication networks,a digital image hierarchical encryption algorithm supporting ciphertext domain transcoding named CT-HEA(Ciphertext Transcoding-Hierarchical Encryption Algorithm) was proposed．Compared with the traditional JPEG2000image encryption algorithms,aiming at the feature of rate-distortion optimized truncation model,CT-HEA truncates and combines the compressed codestream according to image quality layer and resolution,applies hierarchical encryption to the codestream after reorganization by using cryptographic algorithms．It supports transparent transcoding operations directly on the encrypted and compressed bitstream．Simulation results demonstrate that CT-HEA is characterized by low complexity,high performance of secure,high secure transcoding flexibility and low transcoding overhead.

Key words: Image encryption,JPEG2000compression,Secure transcoding