Patent ID: 7624273

Claim:
A method implemented by a circuit of detecting watermark information embedded in a content, the watermark information being a concatenation of component codes, the method comprising: receiving said content through an input from an external device; detecting said watermark information from the received content; dividing the detected watermark information into the component codes in a code divider circuit; decoding each of the component codes in a decoder circuit, thereby to obtain a plurality of residues pairs each comprising two residues, taking a plurality of predetermined integers which are relatively prime to each other, as moduli; calculating user identification of a colluder who made a collusion attack on the content, from the plurality of residue pairs; and outputting said calculated user identification from an output, wherein the codes are component codes that have a possibility to have a method of decoding at least one of the residues with respect to the user identification of the colluder.