Method and device for distributing a multicast encryption key

A method for a primary station to distribute a cryptographic key to a plurality of secondary stations, comprising the steps of:

• determining whether a group key needs to be updated, said group key being used for protected multicast communication from the primary station to the plurality of secondary stations, and
• upon determining that an update is required, transmitting in respective multicast messages to respective sets of secondary station an updated group key, said multicast messages being protected by means of respective set keys associated with each corresponding set,
• wherein the updated cryptographic key is a first set key shared to a first set of secondary stations that allows encrypting multicast messages addressed to the first set of secondary stations, and
• wherein the updated cryptographic key is sent in unicast.

A method for a primary station to distribute a cryptographic key to a plurality of secondary stations, comprising the steps of:

• determining whether a group key needs to be updated, said group key being used for protected multicast communication from the primary station to the plurality of secondary stations,
• upon determining that an update is required, transmit to at least one first subset of the secondary stations through a protected unicast message a first set key by unicast,
• wherein the updated cryptographic key is a first set key shared to the first set of secondary stations that allows encrypting multicast messages addressed to the first set of secondary stations,
• transmitting in a multicast message to the first set of the secondary stations an updated group key, said multicast message being protected by means of the first set key, or alternatively including said updated group key in the protected unicast message, and
• transmitting in respective multicast messages to further respective sets of secondary station the updated group key, said multicast messages being protected by means of respective set keys associated with each corresponding set, and
• wherein the updated cryptographic key is sent in unicast.

A method for a secondary station receiving a cryptographic key in a network, comprising the steps of:

• receiving from the primary station through protected unicast message a first set key by unicast, said first key being associated with a first set of secondary stations, and
• receiving and decrypting a multicast message to the first set of the secondary stations an updated group key, said decrypting using the first set key,
• wherein the updated cryptographic key is a first set key shared to a first set of secondary stations that allows encrypting multicast messages addressed to the first set of secondary stations, and
• wherein the updated cryptographic key is sent in unicast.

A primary station operating in a cellular network and communicating with a plurality of secondary stations, comprising:

• a controller adapted to determine whether a group key needs to be updated, said group key being used for protected multicast communication from the primary station to the plurality of secondary stations, and
• a transmitter coupled to the controller adapted to, upon determining that an update is required, transmit in respective multicast messages to respective sets of secondary station an updated cryptographic key, said multicast messages being protected by means of respective set keys associated with each corresponding set,
• wherein the updated cryptographic key is a first set key shared to a first set of secondary stations that allows encrypting multicast messages addressed to the first set of secondary stations, and
• wherein the updated cryptographic key is sent in unicast.