Collision Attacks With Budget Constraints on Key Management Schemes for Secure Multimedia Multicast

We address the problem of distributing a confidentially shared session key to a multimedia multicast group for content protection. In two such schemes proposed by Trappe , the session key is distributed by employing a homogenized rekey message format. We show that their rekey algorithm in itself is vulnerable to specialized collision attacks, in which even a completely passive outer adversary, who never joins the system and thus never knows any secret user keys, can still reveal the session key of the multimedia multicast with an observable probability but only involving a time complexity far lower than an exhaustive search.