| 摘要 |
<p>The invention relates to a method for securing at least one system protected by a predetermined hierarchy of cryptographic keys, more particularly a Pay-TV system, against unauthorized users. Current key hierarchy systems do not enable detection of unreliable clients who make copies of a group key transmitted by a system provider and pass them on to other persons. According to the invention, this is solved by detecting at least one individual cryptographic key assigned to an unreliable user by forming the intersection of at least two predetermined subsets formed at different times and belonging to the same hierarchy.</p> |
