xml web services security march 27, 2003 iids group, vrije universiteit yuri demchenko, nlnet labs

XML Web Services Security

March 27, 2003

IIDS Group, Vrije Universiteit

Yuri Demchenko, NLnet Labs

<[email protected]>

March 27, 2003. Vrije Universiteit, Amsterdam

XML Web Services Security Slide2_2

Outlines

Historical XML Security Web Services Security OGSA Security

XML Web Services technology for IIDS - Discussion



Historical: How all this started (quoting Tim Berners-Lee)

Initial idea to create resource description language Existing technologies: SGML + WAIS, Gopher + Library Catalogues Problems: hyperlinks reference and semantic meaning binding

Past steps: WWW and HTML RDF and Metadata XML and XML Signature

Next step: Semantic Web Ongoing development:

Computer Grids -> Information Grids -> Semantic Grids



XML Basics: DTD, Schema, XML Protocol, etc.

DTD is document-oriented Like HTML

Schema is data-oriented XML Signature SAML

Basic XML Protocol(s) XML-RPC SOAP

XForms, XLink, XML Query, XPath, XPointer, XSL and XSLT, Legal XML



XML Security vs Traditional (Network) security

Traditional Security: Host-to-host or point-to-point security Client/server oriented Connection or connectionless oriented Generically single/common trust domain/association

XML Security Document oriented approach

Security tokens/assertions and policies can be associated with the document or its parts

Intended to be cross-domain Potentially for virtual and dynamic trust domains (security associations)



XML Security - Components

XML Signature XML Encryption Security Assertion

SAML (Security Assertion Mark-up Language) XrML (XML Right Mark-up Language) XACML (XML Access Control Mark-up Language)

XKMS (XML Key Management Specification)



XML Signature: Features

Fundamental feature: the ability to sign only specific portions of the XML tree rather than the whole document. XML document may have a long history when different component are authored

by different parties at different times Different parties may want to sign only those elements relevant to them Important when keeping integrity of certain parts of an XML document is

essential while leaving the possibility for other parts to be changed Allows carrying security tokens/assertions on document/data rather than on

user/client Provides security features for XML based protocols

Provides basic functionality for state assertions



XML Signature structure

<Signature ID?> <SignedInfo>

<CanonicalizationMethod/> <SignatureMethod/>

(<Reference URI? > (<Transforms>)? <DigestMethod> <DigestValue>

</Reference>)+ </SignedInfo><SignatureValue> (<KeyInfo>)? (<Object ID?>)*

</Signature>



XML Web Services

A Web Service is a software system identified by URI, whose public interfaces and bindings are defied and described by XML. Other software systems may discover and interact with the Web Service in a manner prescribed by its definition, using XML based messages conveyed by Internet protocols.

Service oriented architecture for application-to-application interaction Describing Web services – WSDL Exchanging messages – SOAP extensions Publishing and Discovering WS descriptions - UDDI

Programming language-, programming model-, and system software-neutral Standard based: XML/SOAP foundation Industry initiatives (and development platforms)

Sun SunONE/J2EE (SunONE Studio) Microsoft .NET (Visual Studio .NET) IBM Dynamic e-Business (AlphaWorks) XML Spy by Altova



XML WS - Service Oriented Architecture

• WSDL based Service Description

• SOAP based messaging over HTTP, SMTP, TCP, etc.

• UDDI based Publishing/Discovery



Web services features – three stacks



Web Service Description Language (WSDL)

• WSDL is an XML document format for describing Web service as a set of endpoints operating on messages containing either document-oriented or procedure-oriented (RPC) messages.

• The operations and messages are described abstractly and then bound to a concrete network protocol and message format to define an endpoint



WSDL Example – TimeService.wsdl

http://www.Nanonull.com/TimeService/

http://www.Nanonull.com/TimeService/#message(getUTCTimeSoapIn)



Web Services Security Model

WS-Security model provides end-to-end security (as contrary to point-to-point) allowing intermediaries A Web service can require that an incoming message prove a set of claims (e.g.,

name, key, permission, capability, etc.). Set of required claims and related information is referred as a Policy.

A requester can send messages with proof of the required claims by associating security tokens with the messages.

Messages both demand a specific action and prove that their sender has the claim to demand the action.

When a requester does not have the required claims, the requester or someone on its behalf can try to obtain the necessary claims by contacting other Web services.

Security token services broker trust between different trust domains by issuing security tokens.



Web Services Security Model

Security token types

•Username/password

•X.509 PKC

•SAML

•XrML

•XCBF



WS Security Scenarios

All are built on SOAP based security tokens exchange Direct Trust using username/password (using SSL/TLS) Direct Trust using security token Security token acquisition Issued security token Enforcing business policy Web clients Mobile clients (gateway services) Enabling Federations

Using trust chaining, security token exchange, credentials exchange Supporting delegation

Access control Auditing



Web Services Security Architecture

WS-Security: describes how to attach signature and encryption headers to SOAP messages. In addition, it describes how to attach security tokens, including binary security tokens such as X.509 certificates, SAML, Kerberos tickets and others, to messages.

Core Specification - Web Services Security: SOAP Message Securityhttp://www.oasis-open.org/committees/download.php/1043/WSS-SOAPMessageSecurity-11-0303.pdf

WS-Policy

SOAP Foundation

WS Security

WS-SecureConversation

WS-Trust WS-Privacy

WS-AuthorisationWS-Federation



Web Service Security – others specifications

WS-Policy: will describe the capabilities and constraints of the security (and other business) policies on intermediaries and endpoints (e.g. required security tokens, supported encryption algorithms, privacy rules)

WS-Trust: will describe a framework for trust models that enables Web services to securely interoperate

WS-Privacy: will describe a model for how Web services and requesters state privacy preferences and organizational privacy practice statements

WS-SecureConversation: will describe how to manage and authenticate message exchanges between parties including security context exchange and establishing and deriving session keys

WS-Federation: will describe how to manage and broker the trust relationships in a heterogeneous federated environment including support for federated identities

WS-Authorization: will describe how to manage authorization data and authorization policies



WS Security: SOAP Message Security

SOAP Message Security must support a wide variety of security models.

Key driving requirements for the specification: Multiple security tokens for authentication or authorization Multiple trust domains Multiple encryption technologies End-to-end message-level security and not just transport-level security

Primary security concerns Protection against interception – confidentiality

XML Encryption Protection against illegal modification – integrity

XML Signature Security consideration – Auditing

Timestamping and message expiration Sequence number and Messages correlation



SOAP Message Security Model

Describe abstract message security model in terms of security tokens combined with digital signatures as proof of possession of the security token (key).

Security token asserts claims and signatures provide mechanism for proving the sender’s knowledge of key

A claim can be either endorsed or unendorsed by a trusted authority An X.509 Cert, claiming the binding between one’s identity and public key, is an

example of a endorsed/signed security token

An unendorsed claim can be trusted if there is trust relations between the sender and the receiver (usually based on historical relations/communications context)

Proof-of-Possession (e.g. username/password) – special type of unendorsed claim



WS-Security SOAP message structure

SOAP Header

SOAP Routing

Security token

Digital signature

DigSignature description:NormalisationTransformation Signed elements

DigSignature value

Ref to DSign Sec token

SOAP Message payload

URI: http://schemas.xmlsoap.org/ws/2002/04/secext

Namespaces used in WSSL:

SOAP S http://www.w3.org/2001/12/soap-envelope

XML Digital Sign ds http://www.w3.org/2000/09/xmldsig#

XML Encryption xenc http://www.w3.org/2001/04/xmlenc#

XML/SOAP Routing m http://schemas.xmlsoap.org/rp

WSSL wsse

http://schemas.xmlsoap.org/ws/2002/04/secext

Security element Header block targets specific receiver SOAP Actor Multiple header blocks are allowed targeted at different

Actors New header block are added/appended to existing ones



SecurityTokenReference Model

Usage and processing models for the <wsse:SecurityTokenReference> element. Local Reference – A security token, that is included in the message in the

<wsse:Security> header, is associated with an XML Signature. Remote Reference – A security token, that is not included in the message but

may be available at a specific URI, is associated with an XML Signature. Key Identifier – A security token, which is associated with an XML Signature

and identified using a known value that is the result of a well-known function of the security token (defined by the token format or profile).

Key Name – A security token is associated with an XML Signature and identified using a known value that represents a "name" assertion within the security token (defined by the token format or profile).

Format- Specific References – A security token is associated with an XML Signature and identified using a mechanism specific to the token

Non-Signature References – A message may contain XML that does not represent an XML signature, but may reference a security token (which may or may not be included in the message).



Computer Grids

• Originated from Distributing Supercomputing To become “pluggable” computing resource Computer Grids -> Information Grids -> Semantic Grids

• Current de-facto standard – Globus Toolkits

• Open Grid Services Architecture was boosted by developing XML Web Services – 2002 Commercial Grids are starting



Open Grid Services Architecture (OGSA)

WSDL extensions to describe specifics of Grid Services Defines new portType - GridService Provides mechanism to create Virtual Organisation Provides mechanism to create transient services - Factories Provides soft-state registration of GSH - Registry

Grid services can maintain internal state for the lifetime of the service. The existence of state distinguishes one instance of a service from another that provides the same interface.

OGSA services can be created and destroyed dynamically Grid Service is assigned globally (persistent) unique name, the Grid service

handle (GSH) Grid services may be upgraded during their lifetime and referenced by Grid

(dynamic) service reference (GSR)



Security Issues in Grid computing - Specifics

General issues: Traditional systems are user/client/host centric Grid computing is data centric

Traditional systems: Protect system from its users Protect data of one user from compromise

In Grid systems: Protect applications and data from system where computation execute Stronger/mutual authentication needed (for users and code)

Ensure that resources and data not provided by a attacker

Protect local execution from remote systems Different admin domains/Security policies



Security Issues in Grid computing - Components

Authentication Password based Kerberos based (authentication and key distribution protocol) SSL authentication PKI/Cert based

Authorisation Integrity and confidentiality

Cryptography

Assurance Accounting Audit



Authentication

Traditional systems: Authenticate user/client to protect system

Grid systems: Mutual authentication required

Ensure that resources and data not provided by a attacker

Delegation of Identity Process that grants one principal the authority to act as another individual Assume another’s identity to perform certain functions E.g., in Globus: use gridmap file on a particular resource to map authenticated user

user onto another’s account, with corresponding privileges

Data origin authentication



Authorisation

Traditional systems: Determine whether a particular operation is allowed based on authenticated

identity of requester and local information

Grid systems: Determine whether access to resource/operation is allowed

Access control list associated with resources, principal or authorised programs

Distributed Authorisation Distributed maintenance of authorisation information One approach: Embed attributes in certificates

– Restricted proxy: authorisation certificate that grants authority to perform operation on behalf of grantor

Alternative: separate authorisation server



Assurance, Accounting, Audit

Assurance When service is requested, to assure that candidate service provider meets

requirements

Accounting Means of tracking, limiting or changing for consumption of resources

Audit Record operations performed by systems and associate actions with

principals Find out what went wrong: typical role of Intrusion Detection Systems



OGSA Security

Built upon WS Security



OGSA Security Roadmap - Specifications (1)

Naming OGSA Identity Specification OGSA Target/Action Naming Specification OGSA Attribute and Group Naming Specification Transient Service Identity Acquisition Specification

Translating between Security Realms Identity Mapping Service Specification Generic Name Mapping Specification Policy Mapping Service Specification Credential Mapping Service Specification

Authentication Mechanism Agnostic Certificate Validation Service Specification OGSA-Kerberos Services Specifications

Pluggable Session Security GSSAPI-SecureConversation Specification




Pluggable Authorization Service OGSA-Authorization Service Specification

Authorization Policy Management Coarse-grained Authorization Policy Management Specification Fine-grained Authorization Policy Management Specifications

Trust Policy Management OGSA Trust Service Specification

Privacy Policy Management Privacy Policy Framework Specification

VO Policy Management VO Policy Service Specification

Delegation Identity Assertion Profile Specification Capability Assertion Profile Specification




Firewall "Friendly" OGSA Firewall Interoperability Specification

Security Policy Expression and Exchange Grid Service Reference and Service Data Security Policy Decoration

Specification

Secure Service Operation Secure Service’s Policy and Processing Specification Service Data Access Control Specification

Audit and Secure Logging OGSA Audit Service Specification OGSA Audit Policy Management Specification



Trust establishment process (1)

1. Binding an entity identity to a Distinguished Name (“DN” - the subject name in an X.509 identity certificate) Trust in this step is accomplished through the (published and audited) policy based identity

verification procedures of the Certification Authority that issues the identity certificates

2. Binding a public key to the DN (generating an X.509 certificate) Trust in this step is accomplished through the (published and audited) policy based operational

procedures of the issuing Certification Authority (“CA”).

3. Assurance that the public key that is presented actually represents the user Trust in this step comes from the cryptography and protocols of Public Key Infrastructure.

4. Assurance that a message tied to the entity DN could only have originated with that entity: Trust that a message signed by a private key could only have been signed by the private key

corresponding to the public key (and therefore the named entity via X.509 certs) comes from public key cryptography

Trust in this step is also through user key management (the mechanism by which the user limits the use of its identity), which is assured by user education, care in dealing with one’s cyber environment, and shared understanding as to the significance of the private key.



Trust establishment process (2)

5. Mutual authentication, whereby two ends of a communication channel agree on each other’s identity Trust in this step is through the cryptographic techniques and protocols of the Transport

Level Security (“TLS”) standard.

6. Delegation of identity to remote Grid systems Trust in this step is through the cryptographic techniques and protocols for generating,

managing, and using proxy certificates that are directly derived from the CA issued identity certificates.



Remote Authentication, Delegation, and Secure Communication in GRID

Remote authentication is accomplished by techniques that verify a cryptographic identity in a way that establishes trust in an unbroken chain from the relying party back to a named human, system, or service identity. This is accomplished in a sequence of trusted steps, each one of which is essential in order to get from accepting a remote user on a Grid resource back to a named entity.

Delegation involves generating and sending a proxy certificate and its private key to a remote Grid system so that remote system may act on behalf of the user. This is the essence of the single sing-on provided by the Grid: A user / entity proves its identity once, and then delegates its authority to remote systems for subsequent processing steps.

A secure communication channel is derived from the Public Key Infrastructure process and the IETF Transport Level Security protocol.



Globus Grid Security Infrastructure (GSI)

Operational solution providing security infrastructure for Globus Toolkits Targeted problems:

Thousands of users – thousands of Certs – many of CAs (with different policies) Grid-wide user group and roles are needed

– No grid-wide logging or auditing Need for anonymous users

Intended to evolve into OGSA Security

GSI Components Proxy Certificate Profile

Provides proxy credentials to allow for single sign-on and to provide delegated credentials for use by agent and servers

Online Credential Retrieval to create and manage proxy certificates Impersonation certificate and restricted delegation certificate



Proxy Certificate Profile

Impersonation – used for Single-Sign-On and Delegation Unrestricted Impersonation Restricted Impersonation defined by policy

Proxy with Unique Name Allows using in conjunction with Attribute Cert Used when proxy identity is referenced to 3rd party, or interact with VO policy

Proxy Certificate (PC) properties: It is signed by either an X.509 End Entity Certificate (EEC), or by another PC.

This EEC or PC is referred to as the Proxy Issuer (PI). It can sign only another PC. It cannot sign an EEC. It has its own public and private key pair, distinct from any other EEC or PC. It has an identity derived from the identity of the EEC that signed the PC. Although its identity is derived from the EEC's identity, it is also unique. It contains a new X.509 extension to identify it as a PC and to place policies on

the use of the PC. This new extension, along with other X.509 fields and extensions, are used to enable proper path validation and use of the PC.



Reference: PKC vs AC: Purposes

X.509 PKC binds an identity and a public key AC is a component of X.509 Role-based PMI

AC contains no public key AC may contain attributes that specify group membership, role, security clearance,

or other authorisation information associated with the AC holder Analogy: PKC is like passport, and AC is like entry visa

PKC is used for Authentication and AC is used for Authorisation– AC may be included into Authentication message

PKC relies on Certification Authority and AC requires Attribute Authority (AA)



PKC vs AC: Certificates structure

X.509 PKC Version Serial number Signature Issuer Validity Subject Subject Public key info Issuer unique identifier Extensions

AC Version Holder Issuer Signature Serial number Validity Attributes Issuer unique ID Extensions



X.509 PKC Fields and Extensions – RFC 3280

X.509 PKC Fields Serial Number Subject Subject Public Key Issuer Unique ID Subject Unique ID

X.509 PKC Extensions Standard Extensions

Authority Key Identifier Subject Key Identifier Key Usage Extended Key Usage CRL Distribution List Private Key Usage Period Certificate Policies Policy Mappings Subject Alternative Name Issuer Alternative Name Subject Directory Attributes Basic Constraints Name Constraints

X.509 PKC Fields Private Extensions

Authority Information Access Subject Information Access

Custom Extensions



AC Attribute Types and AC Extensions

AC Attribute Types Service Authentication

Information Access Identity Charging Identity Group Role Clearance Profile of AC

AC Extensions Audit Identity

To protect privacy and provide anonymity

May be traceable via AC issuer

AC Targeting Authority Key Identifier Authority Information Access CRL Distribution Points



Other Technologies to look for IIDS

• SIP (Session Initiation Protocol) based technologies

• Instant Messaging and Presence Protocol – SIP based



XML Web Services technologies for IIDS

Discussion

xml web services security march 27, 2003 iids group, vrije universiteit yuri demchenko, nlnet labs

Documents

xml document

xml query

xml basics

xml tree

metadata u xml

legal xml slide

xml signature structure

security features