Secure Function Evaluation vs. Deniability

May 30, 2012

Secure Function Evaluation vs. Deniability

My friend Bruhns and me were sitting at the Recurity office and discussing crypto stuff. Bruhns raised the question, what a trusted timestamping service could be good for. I told him: timestamps, probably. That wasn’t entirely what he wanted to hear, so he explained: “Uhm, yes. And wouldn’t that affect the deniability of OTR somehow?”. Although we agreed that a trusted timestamping service would probably not suffice to break the deniability of OTR, our general interest in that property remained. After performing some more research, we were able to build a protocol that shows that “deniability” is a property that is not as easy to achieve as one might think. In fact, we tend to believe that deniability is impossible to achieve if one of the parties cooperates with the attacker.

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