Methods and apparatus for content scrambling in a communications system
View Patent ↗Methods and apparatus for improved scrambling and/or descrambling of packets in a communications network are described, e.g., improved scrambling/descrambling of MPEG-2 transport stream packets over an Internet Protocol network. Advance Encryption Standard (AES) under cipher block chaining is utilized in scrambling some transport stream packets. Methods and apparatus for computing an initialization vector or vectors used by the AES are also described. The initialization vector can be set to either a constant or a programmable random number. Scrambling methods and apparatus directed to scrambling solitary termination blocks with a reduced size packet payload e.g., less than 128 bits in an MPEG-2 transport stream packet, are also described. Various features are useful for and can be implemented in set-top boxes and IPTV scramblers in the headsets.
1. A method of processing a first packet including a first portion including at least one header field and a payload portion, the method comprising utilizing a hardware module for:
generating an encryption initialization vector by controllable selecting, under control of an initialization vector flag, between at least a first and second initialization value, wherein the first value is generated by performing an encryption operation on a third constant, using a generated encryption control key by performing an encryption operation on said third constant under control of another encryption control key; and
performing an encryption operation on at least a portion of said payload portion as a function of said generated encryption initialization vector.
2. The method of claim 1 , wherein said initialization vector flag is received in an MPEG-2 transport stream.
3. The method of claim 1 , wherein said initialization vector flag is used to process packets included in an MPEG-2 program stream.
4. The method of claim 1 , wherein said initialization vector flag is updated on a per packet basis.
5. A method of processing a first packet including a scrambled packet payload including a first scrambled block of a first predetermined size and one scrambled remainder block of a second size which is less than said first predetermined size, the method comprising operating a communications device to:
subject the first scrambled block to a decryption operation to produce a first decrypted result;
perform a first exclusive ORing operation using the first decrypted result to produce a first descrambled payload portion;
perform a second exclusive ORing operation using the first scrambled block and a constant;
encrypt the output of the second exclusive ORing; and
subject the scrambled remainder block to an exclusive ORing operation with the second size number of least significant bits obtained from the encryption operation to produce the remainder payload.
6. The method of claim 5 , further comprising:
combining the first descrambled payload portion and descrambled remainder payload portion with a copy of a header portion obtained from the first packet to generate a second packet including a descrambled payload.
7. The method of claim 6 , wherein said decryption operation is an AES decryption operation and wherein said encryption operation is an AES encryption operation.
8. The method of claim 7 , wherein said second packet is an MPEG-2 compliant transport packet.
9. The method of 6 , further comprising:
performing said encryption operation, said encryption operation including using a result of an exclusive OR operation of a scrambled payload packet portion located in said first packet immediately preceding the scrambled remainder payload portion with a constant H as an encryption input.