e-Science Meeting March 2004

1

Trusted Coordination in Dynamic Virtual Organisations

Santosh ShrivastavaSchool of Computing Science

Newcastle University, UKsantosh.shrivastava@ncl.ac.uk

e-Science Meeting March 2004

2Virtual Organisations

• Organisations want to create composite services using services of other organisations

– This leads to resource sharing across organisational boundaries

– Such sharing needs to be encoded as business relationships (“virtual organisations (VOs)” )

– You need to be able to set up, manage and terminate VOs

– A VO however, blurs the distinction between 'outsiders' and 'insiders'

– A central problem in VO management is therefore how organisations can regulate access to their resources by other organisations

– So you need Middleware for regulated interactions

» this is a core requirement

e-Science Meeting March 2004

3Regulated interactions

• Approach:– Follow the practices of the paper based world where contracts are

used

– relationships between organisations for information access and sharing will need to be regulated by electronic contracts

– Interactions need to be traceable (auditable), monitored, and only those that are OK wrt the contract are permitted

• So, Middleware for regulated interactions requires:– Non-repudiable service invocation and data sharing mechanisms

» We call these “trusted coordination” mechanisms

» Trust is achieved through regulation

– Contract management services

» Ways of representing contracts as executable objects, trusted (possibly third party) services for monitoring contract compliance,…

e-Science Meeting March 2004

4Regulated interactions

Non-repudiable interactions require creation of a trust domain through intermediaries

e-Science Meeting March 2004

5Regulated interactions

TTP: Trusted Third Party

Many ways of creating a trust domain:

e-Science Meeting March 2004

6Regulated interactions

Let us consider 2-party, client-server interaction• Server needs evidence that:

– The request originated at the client:non-repudiation of origin (NRO) of the request

– The response was received by the client:non-repudiation of receipt (NRR) of the response

• Client needs evidence that:– The request was received by the server (NRR req.)– The response originated at the server (NRO resp.)

e-Science Meeting March 2004

7Regulated interactions

client interceptor -> server interceptor : req, NROreqserver interceptor -> client interceptor : resp, NRRreq, NROrespclient interceptor -> server interceptor : NRRresp

EXAMPLE: service invocation

e-Science Meeting March 2004

8Regulated interactions

• Information Sharing

• Multi-party, peer-peer interaction

• For an update proposed by A:– B and C need evidence that update originated at

A (NRO update)

– A needs evidence that B and C received the update (NRR update)

– A, B and C need evidence that, after update, the information will be in a consistent, agreed state (NRO agreement, NRR agreement)

Aupdate ii

update

update

B

C

e-Science Meeting March 2004

9

• Use of Interceptors..

upd (5)

Evidence required:• State transition proposed by A

(propose: step 2)• Decisions on validity of

transition from B and C (respond: step 3)

• Collective decision (resolve: step 4)

Shared information is onlyupdated if the collective decision is that A’s proposal is valid

Incentives to good behaviour stronger than for one-off service invocation

upd (1)

C

B

prop

(2)

resp

(3)

reslv

(4)

prop (2)

resp (3)

A ii

reslv (4)

e-Science Meeting March 2004

10Regulated interactions

• Infrastructure Requirements:• Cryptographic primitives

– Digital signatures, secure message digest (hash), secure random number generation

• Credential (certificate) management

• Access control services– Intra-organisation: map user to role

– Inter-organisation: map credential to role

• Non-repudiation log– protocol-specific

– include signed hash of state in evidence

• State store– map hash of state to persistent representation of state

e-Science Meeting March 2004

11Regulated interactions

• Infrastructure Requirements (contd.):• Coordination service to execute NR protocols

(configurable to specific protocol)

• Membership service (for information sharing only)– Maintain group membership information (mapping members to

credentials)

– Membership is coordinated using NR protocols executed by coordination service

• Communication subsystem

• Trusted time-stamping service– To verify a signing key was not compromised at time of use (evidence

generation)

e-Science Meeting March 2004

12Virtual Organisations

• Contract Management– Contracts as executable objects (“active contracts”)

» Declarative ways of specifying rights and obligations» Converting declarative specifications into imperative programs

(cross-organisation ‘business processes’) that control and coordinate multiparty interactions using trusted coordination mechanisms

– Workflow enactment facilities for business process execution – Contract monitoring and violation detection services

• See the poster for additional details– Parts of workflow, contract representation, non-repudiation

subsystems have been designed and implemented (with the help of other EPSRC, EU projects)

• Technologies will be demonstrated through the GOLD project

– See the poster on GOLD project

e-Science Meeting March 2004

13Recent Papers

• C. Molina-Jimenez, S.K. Shrivastava, E. Solaiman and J. Warne, “Contract Representation for Run-time Monitoring and Enforcement”, IEEE Conference on Electronic Commerce (CEC’03), Newport Beach, CA, June 2003, pp. 103-110.

• Paul D Ezhilchelvan and Santosh K Shrivastava, “Systematic Development of a Family of Fair Exchange Protocols”, Seventeenth Annual IFIP WG 11.3 Working Conference on Data and Applications Security, Estes Park, Colorado, August 2003.

• Ellis Solaiman, Carlos Molina-Jimenez, and Santosh Shrivastava, “Model Checking Correctness Properties of Electronic Contracts”, International Conference on Service Oriented Computing 2003, LNCS 2910, pp. 303-318, 2003.

• Nick Cook, Paul Robinson and Santosh Shrivastava, “Component Middleware to Support Non-repudiable Service Interactions”, IEEE/IFIP International Conference on Dependable Systems and Networks, DSN 04, Florence, June 2004.

• Carlos Molina-Jimenez, Santosh Shrivastava, Jon Crowcroft and Panos Gevros, “On the Monitoring of Contractual Service Level Agreements”, IEEE International Workshop on Electronic Contracting (WEC), July 2004, San Diego.

• S.J.Woodman, D.J.Palmer, S.K.Shrivastava, S.M.Wheater, “A System for Distributed Enactment of Composite Web Services”, Forum Session at International Conference on Service Oriented Computing 2003, Tech Report DIT 03 056, University of Trento, Department of Information and Communication Technology