The invention discloses a 
JPEG image bit 
stream encryption method based on 
alternating current statistical characteristic change. The method comprises: in a 
JPEG bit 
stream, a user selects the last non-zero communication coefficient entropy code in a part of image blocks by using a user key to encrypt; hiding the secret information into a part of image block entropy codes through a 
histogram translation method; statistical characteristics are obtained through a user secret key and an 
alternating current coefficient, a 
direct current coefficient 
encryption secret key and an alternating currentcoefficient 
encryption secret key are generated in a self-adaptive mode, inter-group scrambling and 
differential coding iteration scrambling are carried out on the 
direct current coefficient, and intra-block scrambling and inter-block scrambling are carried out on the 
alternating current coefficient; and the 
receiver extracts secret information from the encrypted bit 
stream and decrypts the secretinformation, recovers the 
direct current coefficient and the alternating current coefficient encryption key according to the user key and the alternating current coefficient statistical characteristics in the encrypted bit stream, decrypts the alternating current coefficient and the direct current coefficient, recovers the alternating current coefficient entropy code in each image block entropy code, and obtains the original bit stream. The method is high in security and small in encrypted file expansion.