Apparatus and method for cipher stealing when encrypting MPEG transport packets

摘要

A method of encrypting clear payload data to form encrypted payload data uses a block cipher, the block cipher being characterized by a predetermined block length. The method includes a step of parsing and first and second steps of encrypting. The step of parsing parses the clear payload data into at least one full clear block and a residual block, the at least one full clear block including a last full clear block. Each full clear block is characterized by the predetermined block length. The residual block is characterized by a residual block length, the residual block length being less than the predetermined block length. The step of parsing further parses the last full clear block into a first part and a second part, the second part being characterized by a length equaling a difference between the predetermined block length and the residual block length. The first step of encrypting encrypts a combination of the second part and the residual block to form a first encrypted block, the first encrypted block having a third part and a fourth part. The third part is characterized by a length equaling the second part length. The second step of encrypting encrypts a combination of the first part and the third part to form a second encrypted block, and it is the combination of the second encrypted block and the fourth part that forms the encrypted payload data.