Agreement and Contract Signing Sample Clauses

Agreement and Contract Signing. { } We denote by Agreement a class of problems where a set of n parties P := X0, . . . , Xx start with initial inputs x1, . . . , xn. Some parties might be xxxxxx- est and arbitrary deviate from their programs. All honest parties must eventually, or with some high probability, terminate and agree on a common result, y, which is “valid”. Validity defines a particular agreement problem: – In Interactive Consistency [20], the parties must agree on a vector y, where the ith element must be xi for all honest parties Pi, otherwise it can be any value. – In Consensus [9], if there is a value x such that xi = x for all honest parties Pi, then y = x. Other agreement problems include Byzantine Generals Problem (also called Byzantine Agreement) [17], Weak Byzantine Agreement [16], Atomic Commitment [22], Strong Consensus [10], Validated Byzantine Agreement [15]. In contrast to Secure Multi-Party Computation [12], the inputs of the parties do not need to be secret or independent. Contract signing [7] can be considered as an agreement problem where the parties must agree either on a contract text or on a special value failed, which means that no contract was signed. The signed contract can be an outcome of the contract signing protocol only if all honest parties want to sign the same contract text. The signed contract must be verifiable. Informally, verifiability can be described as follows: – Each honest party can convince a verifier V , which knows nothing about a particular protocol run, that this protocol run yielded the result y. – If some protocol run yielded the result y, no party can convince V that the protocol yielded some result y′ /= y. The result failed is usually left non-verifiable. This reflects the real-world situ- ation where no proof of the fact that a contract was not signed is required.