Protecting Cryptographic Keys: The Trace and Revoke Approach

 Dalit Naor      Moni Naor   


The problem of protecting ownership of digital content has become a target for many cryptographic studies in the past decade. These studies provide myriad technology solutions to attack the problem, both from the aspect of rights management and for piracy prevention. In this article we survey a number of relevant techniques, focusing on methods for  protecting cryptographic keys and in particular for sending encrypted information to a group of users. We present two such methods: the LKH method that is best tailored to scenarios where attentiveness is guaranteed and the Subset-difference scheme that is suited for the stateless case, where users are not necessarily always on-line. The latter is a trace and revoke scheme that allows the detection of keys which are used in a pirate box and, furthermore, can be used to prevent these illegally used keys from decrypting  future content. We comment on the applications of these technological solutions to the ``real" world.

Postscript , gzipped Postscript.

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