FIELD: radio engineering, communication.
SUBSTANCE: invention relates to data encryption and specifically to encryption of image data organised into bit streams. A layered audiovisual packet data stream (CNT'), such as one obtained by a JPEG2000 encoder (810), is received together with information (metadata) about the contribution of each packet to the reduction of image distortion. The distortion-to-rate ratio for each packet is calculated (710) and the packets are ordered (720) in descending ratio. The non-encrypted packet having the highest ratio is encrypted (730) until the target distortion is obtained.
EFFECT: facilitating adaptation to a different type of applications and minimising the amount of data for encryption, while maximising protection of the encrypted content.
6 cl, 8 dwg
