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Opera Group Presentation: Policies in Accountable Contracts

Opera Group Presentation: Policies in Accountable Contracts. Brian Shand 16 April 2002. Contract Negotiation Signing Performance. Overview. PhD Research: Self-Enforcing Automatic Rational Contracts between Computers Contract Framework, Resource Accounting, Trust Model

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Opera Group Presentation: Policies in Accountable Contracts

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  1. Opera Group Presentation:Policies in Accountable Contracts Brian Shand 16 April 2002

  2. Contract Negotiation • Signing • Performance Overview • PhD Research: Self-Enforcing Automatic Rational Contracts between Computers • Contract Framework, Resource Accounting, Trust Model • Application Scenarios • Public compute servers (GRID computation) • Flexible prioritisation in large distributed systems • Web services

  3. Key Terms { { { { {

  4. Contract Framework • Contracts specify promises between participants • Multi-level contracts allow introspection 1. Participant identities 2. Estimated resource consumption 3. Accounting function (payment policy) 4. Actions to perform • Allows risk estimates, with limited resource outlay • All accounting messages signed and timestamped • Message passing substrate assumed

  5. Resource Accounting • Homogeneous model • of scarce resources: bandwidth, CPU cycles, trust, currency • Constrained language for accounting functions • A subset of the Python language • Predictable execution times • Example code: 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+0.002 self.totalCPU += atom.quantity return [ResourceAtom(resources.money, '£', result*atom.quantity) ]

  6. Uncertainty (0,0,1) Trust Distrust (1,0,0) (0,1,0) Trust Model • Subjective Trust Model (Jøsang, A Logic for Uncertain Probabilities, 2001) • Local assessments of trustworthiness • Second-order model incorporates uncertainty • Moderates contractual promises • Constantly updated • Transfer of Trust: Trust delegation certificates • Web of trust, c.f. PGP recommendations • Subsume reputation agencies • Distributed trust management

  7. Accountable Contracts • Separation of task acceptance and performance • introspectible contracts • explicit risk assessments • Multi-scale representation • Accounting of all resources • economic services • Distributed trust model deters cheats • Overhead in a PBIL application: • about 20% of bandwidth, 2% of CPU

  8. Further Work • Explicit integration of reputation into contracts • Prototype applications • Compute Servers • Complex negotiation, pricing by servers • Clients that plan • Active City • Event prioritisation in publish-subscribe • Theoretical basis for trust model • SECURE collaboration • Model risks of stolen signatures • Distrust in own actions

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