First Year Talk: Self-Enforcing Automatic Rational Contracts between Computers Brian Shand Supervisor: Dr Jean Bacon

2 Overview Motivation –Importance of distributed services –Risk of untrustworthy participants –Self-funding services and quality guarantees Outline of Proposal 1.Contracting architecture, combined with 2.Automatic trustworthiness measurements, in a 3.Resource-based virtual economy

3 Introduction Application Scenarios –Compute servers (‘the Grid’) –Web services –Peer-to-peer services –Publish-subscribe middleware – e.g. Active City Contract definitions –A contract prescribes actions to be taken by each participant –By signing the contract, each participant promises to be bound by it –A contract is agreed upon when all participants have signed it –A contract is cancelled when everyone signs a special cancellation message

4 Contract Description Contract representation –Server and client identities –Expected resource requirements –Accounting function –Contract action Contract Language –Limited language: predictable execution time –High-level description of resource exchange –Allows introspectible contracts Example Accounting Function def processResourceAtom(self, atom, imports): if atom.type != resources.cpuTime: return [] # Charge for CPU only rate = imports[0] if self.totalCPU < 10: result = rate+0.01 else: result = rate self.totalCPU += atom.quantity return [ResourceAtom( resources.money, '£', result*atom.quantity, atom.startTime, atom.endTime) ]

5 Trust Framework Second order trust model –Trust, distrust, uncertainty –Based on subjective opinions –Constantly updated with new data Trust delegation certificates –Web of trust, c.f. PGP recommendations –Distributed trust management –Also local credit bureaux

6 Resource Economy Homogeneous model –of money, trust, CPU, network, storage etc. Multi-scale representation Accounting of all resources Benefits Rational resource allocation Continuous trust update Economic services

7 Proxy prototype Structure Demonstrates charging for web services Charges based on location and bandwidth used Contracts prioritised by profitability –Identifies fraud –Prevents simple Denial of Service attacks Complex pricing schemes possible Client Client proxy Server proxy Server HTTP + contracts

8 Conclusion Contract architecture supports distributed computing services Separation of task acceptance and performance –introspectible contracts –explicit risk assessments Distributed trust model deters cheats Further work Model risks of stolen signatures –Distrust in own actions Compare costs of ad hoc vs trust-based policies Application to publish-subscribe systems –Trusted distribution network –Untrusted distribution network