Patent ID: 9520993
Filing Date: 2016-12-13
CPC Classification: H04L

Claim Text:
1. A method of preventing re-use of compromised sequence keys in a broadcast encryption system, the method comprising: receiving a distributed protected file and a sequence key block at a receiver, the sequence key block being formulated to cryptographically revoke traitorous receivers; selecting a first Sequence Key from a plurality of Sequence Keys, the plurality of Sequence Keys being associated with the receiver, and the plurality of Sequence Keys being related by the sequence key block; determining by cryptographic testing that the first Sequence Key is compromised, cryptographic testing comprising applying the first Sequence Key to the sequence key block; determining that at least one additional Sequence Key is available; traversing the sequence key block to select a second Sequence Key from the plurality of sequence keys; determining by cryptographic testing that the second sequence key is compromised, cryptographic testing comprising applying the first Sequence Key to the sequence key block; traversing the remainder of the sequence key block and thereby determining that no uncompromised sequence keys can be determined from the sequence key block; identifying the receiver as traitorous based on the lack of uncompromised sequence keys.