| 摘要 |
<p>Methods and systems for fingerprinting digital data are described. In the described embodiment, Direct Sequence Spread Spectrum (DSSS) technology is utilized. Unique fingerprinting words are defined where each includes at least one spread sequence. In the described embodiment, a fingerprinting word comprises a plurality symbols, called 'Η symbols'. Each Η symbol is composed of 2c-1 blocks, where c represents the number of colluders that are desired to be protected against. Each block contains d spread sequence chips. The fingerprinting words are assigned to a plurality of entities to which protected objects embedded with the fingerprinting words are to be distributed. To ascertain the identity of an entity that has altered its unique fingerprinting word, the relative weight of each block is computed in accordance with a defined function and blocks whose weights satisfy a predetermined relationship are 'clipped' to a so-called working range. Each Η-symbol of the altered fingerprinting word is then processed to produce a set of one or more colors that might be the subject of a collusion. Each Η-symbol in the fingerprinting word for each entity is then evaluated against a corresponding produced set and the entity having the most overall Η-symbol coincidences is incriminated.</p> |
