Let us consider the case of the company president who delegates the power to sign certain documents to her secretary. If the president never cheats, then many existing mechanisms are sufficient to implement this. But what if the president suddenly announces that her secretary has been sacked because of a mistake in a very important document? It may well be that the secretary did not made a mistake: but with almost all the existing mechanisms, she has no way of demonstrating that it was the president, and not she, who created or authorised the disputed document.
We will explain why the traditional approaches to delegation are unsatisfactory, particularly in the context of financial or commercial environments. We are interested in problems characterised by the fact that none of the entities involved can be assumed to be trusted a priori. In this seminar we will survey most of the previously proposed delegation mechanisms and analyse their limits when faced with problems like the one above. We will then suggest new semantics of delegation that allow this class of problems to be dealt with. Finally, we will briefly present some examples of protocols that implement our new semantics.