Robust watermark
View Patent ↗A method and system for embedding a watermark in block encrypted content, including encoding a bit string, the bit string including n bits, denoted b 0 -b n-1 , the encoding including translating each bit, b 0 -b n-1 , into a block of data, according to the following rule if b i =1, then translate b i into a block of data of a first type, and if b i =0, then translate b i into a block of data of a second type, thereby translating the n bits into n blocks of data corresponding to each bit b 0 -b n-1 , arranging a composite block of data including the n blocks of data, and at least one additional block indicating the presence of the n blocks of data, and inserting the composite block of data into a content item as a watermark, wherein the watermarked content item is encrypted using an ECB mode of encryption. Related methods and apparatus are also described.
1. A method for embedding a watermark in block encrypted content, the method comprising:
providing an MPEG packet, the MPEG packet comprising a payload;
dividing the payload into N blocks of equal size, each block denoted as one of b 0 -b n-2 and b x ;
determining b 0 ⊕ . . . ⊕b n-2 =B
providing a byte, denoted A, in an MPEG header, A being an adaptation field comprising proprietary parameters;
encrypting, according to an encryption function f, f(b x , B, A), where an encryption key for the encryption function f comprises g(A,B);
selecting a value k, where 0<=k<32; and
calculating Y=f(bx, B, A), Y being a 16 byte long vector;
calculate P k (Y);
determine if P k (Y)=the k th bit of the watermark;
if P k (Y)=the k th bit of the watermark then continuing to a next MPEG packet;
if P k (Y) does not equal the k th bit of the watermark, then increment A and repeat the above procedure until one of:
P k (Y)=the k th bit of the watermark; and
a predetermined upper bound is reached, in which case, the provided MPEG packet does not participate in the watermarking process.
2. The method according to claim 1 and wherein Y is calculated as follows:
setting A=1, and incrementally performing:
performing the following steps in a loop:
determining Y=f(b x , B, A);
determining if P k (Y)=the k th bit of the watermark;
if P k (Y)=the k th bit of the watermark then setting Y=an encrypted value of b x ;
if P k (Y) !=the k th bit of the watermark then:
if a loop index has exceeded a predetermined upper bound, setting A=0; and stopping the loop and processing another MPEG packet; and
if the loop index has not exceeded a predetermined upper bound, incrementing A and repeating the determining of Y in the loop.
3. The method according to claim 1 wherein the predicate P comprises a secret value.
4. The method according to claim 1 wherein the predicate P comprises a content dependent predicate.
5. The method according to claim 1 and wherein when A=0, utilizing regular encryption.
6. A system for embedding a watermark in block encrypted content, the system comprising:
an MPEG packet comprising a payload;
the payload being divided into N blocks of equal size, each block denoted as one of b 0 -b n-2 , and b x ;
a processor which determines b 0 ⊕ . . . ⊕b n-2 =B
a byte, denoted A, in an MPEG header, A being an adaptation field comprising proprietary parameters;
an encryption function f, operative to encrypt according to f(b x , B, A), where an encryption key for the encryption function f comprises g(A,B);
wherein at least one of the following is performed during encryption:
a value k, where 0<=k<32 is selected;
Y=f(bx, B, A) is calculated, Y being a 16 byte long vector;
P k (Y) is calculated;
determine if P k (Y)=the k th bit of the watermark,
if P k (Y)=the k th bit of the watermark then continue to a next MPEG packet;
if P k (Y) does not equal the k th bit of the watermark then increment A and repeat the above procedure until one of:
P k (Y)=the k th bit of the watermark; and
a predetermined upper bound is reached, in which case, the provided MPEG packet does not participate in the watermarking process.
7. The method according to claim 1 wherein the function g(A,B) comprising the encryption key is g(A,B)=A⊕B.
8. The method according to claim 1 wherein the function g(A,B) comprising the encryption key is g(A,B)=A⊕b x .