Key Independence – the strongest property Sample Clauses

Key Independence – the strongest property. It guarantees that a passive adversary who knows a proper subset of group keys K^ K cannot discover any other group keyK 2 (K K^ ). The relationship among the properties is intuitive. Either of Backward or Forward Secrecy subsumes Group Key Secrecy and Key Independence subsumes the rest. Also, the combination of Backward and Forward Secrecy yields Key Independence. Our definitions of Backward and Forward Secrecy are stronger than those typically found in the literature. The two are often defined (respectively) as [21, 17]: The difference is that the adversary here is assumed to be a current or a former group member. Our definition additionally includes the cases of inadvertently leaked or otherwise compromised group keys. We refer to the above as Weak Forward Secrecy and Weak Backward Secrecy, respectively. In this paper we do not consider implicit key authentication as part of the group key management protocols. All communication channels are public but authentic. The latter means that (as mentioned later in the paper) that all messages are digitally signed by the sender using some sufficiently strong public key signature method such as DSA or RSA. All receivers are required to verify signatures on all received messages. Since no other long-term secrets or keys are used, we are not concerned with Perfect Forward Secrecy (PFS) as it is achieved trivially.