Video H.264 encryption preserving synchronization and compatibility of syntax
A method for encrypting data exchanged between an encoder and a decoder in a video system is disclosed. A set of bits which, when encoded, do not have any influence upon the decoding stage, are determined during the encoding stage. At least one part or all of the bits selected in stage 1 is/are encoded prior to transmission to the decoding stage. The bit selection stage determines the parts of the flow of bits that only modify the contexts of the decoding process in an insignificant manner in the sense that the modification due to encryption does cause desynchronization or does not lead to non-compatible bit flows with regard to encoding contexts and visual impact. The present invention is used with H.264 encoders/decoders.
1. A method of enciphering a data bit stream exchanged between a coder and a decoder in a video system, comprising:
selecting, during a coding stage for the data bit stream according to a video standard, in the data bit stream a set of code words to be ciphered according to a predetermined encipherment algorithm and a key; and
enciphering at least one code word of the selected set of code words to generate a unique ciphered bit stream, the enciphering comprising:
extracting at least a sub word from the at least one code word of the selected set of code words; and
substituting the extracted sub word with another sub word according to the predetermined encipherment algorithm and the key, the another sub word being arranged so that the data bit stream after the substitution of the extracted sub word is compatible with the decoder according to the video standard without causing desynchronization,
wherein the video standard is H.264 video standard, and the at least one code word of the selected set of code words is an H.264 Intra prediction mode code word.
2. A method of enciphering a data bit stream exchanged between a coder and a decoder in a video system, comprising:
selecting, during a coding stage for the data bit stream according to a video standard, in the data bit stream a set of code words to be ciphered according to a predetermined encipherment algorithm and a key; and
enciphering at least one code word of the selected set of code words to generate a unique ciphered bit stream, the enciphering comprising:
extracting at least a sub word from the at least one code word of the selected set of code words; and
substituting the extracted sub word with another sub word according to the predetermined encipherment algorithm and the key, the another sub word being arranged so that the data bit stream after the substitution of the extracted sub word is compatible with the decoder according to the video standard without causing desynchronization,
wherein the video standard is H.264 video standard, and the at least one code word of the selected set of code words is an H.264 Intra 16*16 macroblock type code word, and the sub word comprising:
a chrominance block coding symbol containing a value of coded sample blocks for chrominance (0=no chrominance residual is coded, 1=only DC (continuous component) chrominance residual is coded, and 2=all the DC chrominance residual and AC (frequency components) residuals of the chrominance are coded);
a luminance block coding symbol containing a value of samples for luminance (0=no AC residual is coded and 15=all the AC residuals are coded); or
a prediction mode symbol which defines a way in which a prediction is made (0=vertical, 1=horizontal, 2=DC, and 3=diagonal).
3. A method of enciphering a data bit stream exchanged between a coder and a decoder in a video system, comprising:
selecting, during a coding stage for the data bit stream according to a video standard, in the data bit stream a set of code words to be ciphered according to a predetermined encipherment algorithm and a key; and
enciphering at least one code word of the selected set of code words to generate a unique ciphered bit stream, the enciphering comprising:
extracting at least a sub word from the at least one code word of the selected set of code words; and
substituting the extracted sub word with another sub word according to the predetermined encipherment algorithm and the key, the another sub word being arranged so that the data bit stream after the substitution of the extracted sub word is compatible with the decoder according to the video standard without causing desynchronization,
wherein the video standard is H.264 video standard, and the at least one code word of the selected set of code words is an H.264 Mb_QP_delta symbol corresponding to a delta value of a quantization parameter QP of a macroblock, and the sub word comprising suffix bits which follow a first ‘1’ in the at least one code word of the selected set of code words.
4. A system for encipherment and/or decipherment of a data bit stream exchanged between a coder and a decoder in a video system, comprising:
the coder configured to
select, in the data bit stream, a set of code words to be ciphered according to a predetermined encipherment algorithm and a key;
extract at least a sub word from at least one code word of the selected set of code words; and
substitute the extracted sub word with another sub word according to the predetermined encipherment algorithm and the key, and thereby generate a unique ciphered bit stream, the another sub word being arranged so that the data bit stream after the substitution of the extracted sub word is compatible with the decoder according to a video standard without causing desynchronization; and
the decoder configured to
receive the unique ciphered bit stream from the coder; and
decipher the unique ciphered bit stream from the coder according to the key,
wherein the video standard is H.264 video standard, and the at least one code word of the selected set of code words is an H.264 Mb_QP_delta symbol corresponding to a delta value of a quantization parameter QP of a macroblock, and the sub word comprising suffix bits which follow a first ‘1’ in the at least one code word of the selected set of code words.