Encryption algorithm is used to ensure the transmission safety of multimedia data. Not only the security of algorithm

but also the compression efficiency and encryption complexity should be taken into consideration when design an encryption scheme. A new encryption scheme for image transmission is proposed in this paper

which is based on duple permutation. Firstly the original image is divided into several macro blocks in the light of certain size

and macro block within each row are permuted. Then

the first random S of AC coefficients in each 8×8 matrix are permuted after DCT （discrete cosine transform)and quantization. Theoretical analysis and experimental results indicate that the scheme proposed in this paper is secure and fast. It has little adverse impact on the compact ratio

6.478％ by average. Moreover

it is format compatible and robust to transmission errors. All the attributes mentioned above make this algorithm suitable to be the encryption approach for image transmission.