Proofs of Work and Bread Pudding Protocols(Extended Abstract)

Abstract

W e formalize the notion of a pr of of work ?PO o W?? In man y crypto? graphic protocols? a pro er seeks to con v vince a v eri?er that she possesses kno wledge of a secret or that a certain mathematical relation holds true? By con trast? in a PO W? a pro er demonstrates to a v v eri?er that she has performed a certain amoun t of computational w ork in a speci?ed in ter? v al of time? PO Ws ha e serv v ed as the basis of a n um ber of securit y protocols in the literature? but ha e hitherto lac ed careful c v k haracteri? zation? In this paper? w e o?er de?nitions treating the notion of a PO W and related concepts? W e also in troduce the dependen t idea of a br ad pudding pr e oto ol? c Bread pudding is a dish that originated with the purpose of reusing bread that has gone stale? In the same spirit? w e de?ne a bread pudding protocol to be a PO Wsuc h that the computational e?ort in ested in v the proof ma ybe reused b y the v eri?er to ac hiev e a separate? useful? and v eri?ably correct computation? As an example of a bread pudding protocol? w esho who w the MicroMin tsc heme of Riv est and Shamir can be brok en up in to a collection of PO Ws? These PO Ws can not only serv e in their o wn righ tas mec hanisms for securit y protocols? but can also be harv ested in order to outsource the MicroMin t min ting operation to a large group of un trusted computational devices?