| 摘要 |
Watermarks WM1 . . . WMk . . . WMN are applied to sections 1 . . . k . . . N of digital media content on a recording medium having an identification number (CDID) by combining numerical values representing CDID, N and i in accordance with a concatenated hashing function, to derive a numerical value for WM[1]i. The numerical value for WMl is applied to section i, where i is selectively each of 1 . . . N. The watermark of section j is checked by determining the numerical values of CDID, j and N from the read digital media content and determining the watermark WMja actually read from section j. The determined numerical values of CDID, j and N are combined by using the same hashing function that is used to derive WMl to derive a digital signal for the watermark WMjr read from section j. The digital signal for watermark WMjr that should be read from section j is compared with an indication of the numerical value for the watermark WMja actually read from section j. If CDID is read directly from the medium, the WMjr that should be read from section j is derived from H(CDID⋄N⋄j) where H is the hashing number and ⋄ is the concatenation of numbers. If CDID can be read directly, H(CDID) is determined by modular subtraction of H(N⋄k) from the value of WMja actually read from section j.
|
