Group Key Management (cont.)

• What is a good group key protocol ?
  • Key Independence: an attacker knowing any proper subset of group keys cannot discover any other group keys.
  • Perfect Forward Secrecy: compromise of one member’s long term key, cannot compromise any short-term group keys.
  • Backward/Forward Secrecy: any subset of group keys can not be used to discover previous/subsequent keys.

• When to refresh the group key?
  • ‘Secure’ : every time the group changes.
  • It is an application policy.

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