Patent ID: 8526614

Claim:
A method to manage a population of decoders having access to broadcasted data, each decoder being temporarily assigned to a position in a group of decoders sharing a common broadcast encryption scheme, the method comprising the steps of: a. making a decoder a member of the group by performing the steps of: selecting an available position in the group and allocating this position to the decoder, marking the position as not available; sending, in a message to the decoder, the keys pertaining to said position into the group according to the broadcast encryption scheme, as well as a current group access data comprising at least a current group access key common to said group, said message being encrypted with a key that is unique to the decoder; b. accessing broadcast data in the decoder using the current group access data; c. revoking at least one decoder and selectively renewing the current group access key for the group by performing the steps of: sending a global group addressed message comprising at least a next group access data comprising at least a next group access key encrypted using the broadcast encryption scheme so that only the decoders corresponding to non-revoked positions can decrypt it, said group message being further encrypted by the current group access key and declaring the position of the revoked decoder as vacated; in the non-revoked decoders, decrypting the global group addressed message using the current group access key, further decrypting the result using broadcast encryption keys pertaining to the position in the group and storing the next group access data, in particular updating the next group access key; in the revoked decoder, decrypting the global group addressed message using the current group access key, then failing to decrypt the result with the broadcast encryption keys pertaining to the position in the group and thus failing to update the next group access data and in particular the next group access key; d. reusing a position vacated by a previously revoked decoder by performing the steps of: making said next group access key the current group access key; marking the previously vacated position in the group as available; and starting the process from step a.