Patent ID: 7681227

Claim:
A method of generating an encrypted stream of video information that represents video frames, the video frames comprising a plurality of first video frames accessible during a special mode of play and a plurality of second video frames not accessible during a special mode of play, the method comprising: encrypting the video information to produce an encrypted stream for decryption with control words, the stream of encrypted video information being divided into successive crypto-periods, each of the successive crypto-periods requiring a respective control word for decryption of the encrypted stream of video information: identifying a plurality of sections of the source stream of video information that represent the plurality of first video frames; providing items of decryption information each comprising a first control word and a second control word for decryption of the encrypted stream of video information; and inserting items of decryption information into the encrypted stream in each of the plurality of successive crypto-periods, at least some of the items of decryption information being inserted into the encrypted stream of video information at times synchronized to first video frames, wherein: the first control word is configured to decrypt the encrypted stream during a current crypto-period that is the crypto-period in which the decryption information is inserted; the second control word is configured to decrypt the encrypted stream during another one of the plurality of crypto-periods; for the items of decryption information located substantially in a first half of a crypto-period, the second control word is configured to decrypt the encrypted stream during the crypto-period that precedes the crypto-period in which the decryption information is inserted thereby providing the next past control word required for reverse play; and for items of decryption information located substantially in a second half of a crypto-period, the second code word is configured to decrypt the encrypted video stream during the crypto-period that follows the crypto-period in which the decryption information is inserted thereby providing the next future control word required for forward play.