Cryptography Reference
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assume
=3 spots with marks are drawn as ones in this matrix and
the unmarked spots are left as zeros:
0001000000000000
0001000000000000
0001000000000000
1111111111111111
0001000000000000
0001000000000000
0001000000000000
0001000000000000
0001000000000000
0001000000000000
0001000000000000
0001000000000000
0001000000000000
0001000000000000
0001000000000000
0001000000000000
Nowassume that there's another user out therewith an Idnumber
of 7 . Thematrix of marksmade in 7 's copy of the content will look like
this:
a
0000000100000000
0000000100000000
0000000100000000
0000000100000000
0000000100000000
0000000100000000
0000000100000000
1111111111111111
0000000100000000
0000000100000000
0000000100000000
0000000100000000
0000000100000000
0000000100000000
0000000100000000
0000000100000000
Let's assume that 3 and 7 decide to collude to strip out their
marks. They don't understand the watermarking algorithm. They
don't know how the data is inserted into the files. They just have two
versions of the content and they can compare them with each other.
If they do this, they'll find a number of places where there are differ-
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