Trust and security in decentralised distributed systemsPaul KearneySecurity Research Centre (Acting Head)

Why the agent and web services communities should work together• I will

– give an overview of the current situation regarding web service security

– argue that MAS should build upon a web-service-based platform rather than duplicating effort

– argue that trust and security for web services would benefit from ideas and techniques from the agent world.

• Platform and message syntax from web services, semantics and ‘intelligence’ from agents

Agents, web services and me• Agents + speech acts

• Involved in early days of FIPA (at Sharp)

• Eurescom P907: MESSAGE– AOSE methodology, AO modelling language

• Eurescom P1106– B2B Framework merging generic eBusiness (e.g. ebXML,

RosettaNet) with TMF eTOM– PJK: security case study + semantics

• Web Services security (message level)

• TrustCoM FP6 project– Trust, Security and Contract management framework for

dynamic Virtual Organisations

Service oriented architecture (SOA)• SO application = collection of coarse grained, loosely coupled

‘services’

• Service = computational entity exposing ‘operations’ via abstract, high level interface – black box, subject to certain ‘behavioural expectations’– WSDL: operation = input message and / or output message

type + 0 or more fault message types• 4 op patterns: Input -> output; output -> input; input only; output only

• wrt a particular operation, a service plays a provider or client role

• Discovery (at run time) => dynamic binding

• Service is an autonomous message processing system ‘agent’

A network of SOAP nodes

Ultimate sender

Ultimate receiver

Intermediate node

Intermediate node

HTTP

MQSMTP

The new (XML-based) protocol stack

Transport / connection: HTTP, FTP, MQ Series, ...

Message level: SOAP + extensions

Basic message pattern level: one-way, synchronous request-response, asynchronous request-response

...

Conversation level

Collaboration level

Transaction level

Basic architectural building blocks

• Web services:– originators and ultimate destinations for messages– primarily process the body of the message

• Intermediate nodes– message processing elements in the message path

• XML Firewalls, XML ‘routers’, Axis Handlers

– can check and block or pass a message (generate a fault)– modify the header and/or redirect

– Mainly interested in signing/checking signatures, inserting / checking / replacing tokens and other header elements

– could call services from intermediate nodes.

State of the art in web service security• Except in simple situations, it is difficult to provide end-end

security via transport layer mechanisms (HTTPS / SSL) alone. Need message level security.

• Growing consensus on conceptual building blocks for message level security.

• ‘Foundation’ specifications firming up (XML Encryption, XML Signature, WS-Security, SAML, ...), but still fluid, vendor implementation patchy and interoperability doubtful. Further layers of specification need to be added.

• You can implement message level security, but need to establish local conventions. Vision of carefree, open interoperability still some way off. (Not just due to security).

Web Services Security building blocks

• public key cryptography and digital certificates

• digital signatures used to bind elements of the message and assure integrity

• encryption of messages for message confidentiality (where required)

• use of security software tokens carried in message header to communicate ‘claims’

• use of trusted identity service to issue authentication tokens

• policy-based access control

The emerging WS security model (IBM/MS)

From MS/IBM WS security roadmap

•XML encryption (msgconfidentiality)•XML DSIG (msg integrity)•Tokens: claims

Language for asserting requirements on msg features• confidentiality• integrity• token• visibility• header• age

To do with requesting, issuing and checking tokens

Introduces security contexts and security context tokens

Deals with issues of crossing ‘trust domains’ -- pretty vague

… and the other lot: Liberty + SAML• Project Liberty / Liberty Alliance

– Federated identity management

• Security Assertion Mark-up Language (SAML)– OASIS standard

– XML-based language for making ‘assertions’ about security

• Assertion– a statement made by an ‘authority’

– can be signed to identify authority reliably

– if you trust the authority, you tend to trust the truth of the statement

– can be time-stamped, etc., to establish bounds to validity

• Defines three types of assertion– Authentication

– Authorisation

– Attribute

and correspond query and response messages• Authentication assertion:

– states what checks have been done to authenticate an identity claim

• So, there seems to be a fair consensus on the basic model

PPP - another TLM

Tomcat + Axis

PlatformTomcat +

AxisHTTPS/SSL

Processes Application

services

Securityservices

+ handlers

Application

services

Securityservices

+ handlers

SOAP Messages

Signatures and tokens

Principals

Commitmentsrequestsservices

Semantic modelSemantic model

Web service• View a WS as providing managed access to a resource

• Simple transaction types:– request that an operation is performed on a resource (and

return result)– request information about service (or resource?)– notification

• WS has an owner (e.g. an enterprise)• WS acts on behalf of a ‘legal entity’ (user, enterprise, etc.)

– can have ‘pure client’ WSs that only represent their agent in interactions with other WS (I.e. no associated resource)

• WS runs on a platform

Declarative semantics • For message body

– speech acts concerning operations on and information about encapsulated resource and other topics of conversation

• For tokens / claims– claims about parties to message / transaction

• Claim– assertion + id of authority– trust in authority tendency to belief assertion– assertion speech act

• statement of belief, commitment, intention, etc.

Security decisions

Web Service

Operations on resources

managed by WS

<Message from WS1 -> WS2 <Request on behalf of User A <Perform operation X on Resource Y/> />/>

Is the message genuine? (Authentication)

Is the request permitted?(Authorisation)

• Check message signature to ensure from trusted source and unaltered• Subject of request? (Operation? Resource?)• Claimed identity of requester (A)?• Verify identity claim (Is request really on behalf of A?)• Is A permitted to perform X on Y?

Token services

Validation and policy dialogues

Issue tokens

Check based on info carried with the message

(tokens) • direct evidence• explicit assertion by authority• implicit assertion by authority (e.g. ticket)

Policy dialogues

Verify tokens

Security architecture

Policy management service

Target service

Handler chains (PEPs)

Client service

Security service

(e.g. PDP)

Policy management

service

Company 1 Company 2

Security service

(e.g. PDP)

Trust and mediation

services

Policy management

service

Implicit speech acts

agent

Invokes message service

Transmits FIPA / KQML message

Transmits SOAP / WS message

Maps to appropriate XML standard

Interprets as speech act

agent

TrustCoM project (http://www.eu-trustcom.com/)

• EU FP6, started February this year• framework for trust, security and contract management in

dynamically-evolving virtual organisations. • enable secure collaborative business process management and

sharing in an on-demand, self-managed, dynamic value-chains of businesses and governments.

• leverage Web Services, Grid technologies and protocols for inter-enterprise interactions

• Partners:– BT, SAP, BAE Systems, Microsoft, IBM, ATOS ORIGIN (S-SEMA)

– CCLRC, SICS, HLRS, NRCCL, SINTEF

– ETH, IC, KCL, U. Milano, U. Salford

Summary• Agents and web services are addressing similar

problems in similar ways

• Web Services provide a layer on which agents can build

• Agents / AI provide semantics + machinery for intelligent processing of messages

• Have indicated how speech acts can give semantics WS messages and security claims

• Web Services standards are being adopted and used: if agent community tries to compete (vs. augment) it will lose

Questions?