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Introduction to SAML

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					 SAML: An XML Framework for Exchanging
Authentication and Authorization Information
                     +
                SPML, XCBF
               Prateek Mishra
                  August 2002
Agenda
  •   SAML Status and Impact

  •   SAML in a Nutshell

  •   SAML and Web Services

      [thanks to Eve Maler (SUN) and Marc Chanliau
      (Netegrity) for the materials used in this
      presentation]
SAML Status
•   The SAML 1.0 Specification Set is at Commitee
    Specification maturity level
•   Entered a balloting period in pursuit of OASIS
    Standard status on 1 June 2002.
•   Available at http://www.oasis-
    open.org/committees/security/#documents
•   SSTC discussion around next steps ongoing
     •   WS-Security Profile of SAML
SAML Impact
• Implementations available from
  http://www.opensaml.org,
  http://www.phaos.com, …
• JSR-155 Java API standard and Reference
  Implementation ongoing (complete in 2002)
• Liberty Alliance uses and extends SAML 1.0
• Several products available (Baltimore,
  Entegrity) and many more announced
  (Netegrity, Tivoli, Oblix, RSA, SUN,
  Quadrasis, CrossLogic, Sigaba, ePeople, …)
SAML 1.0: Main Features
•   Normative Specification is in two parts:
     •   Assertion and Protocol XML Schema
     •   Bindings and Profiles

•   Assertion: a set of statements in a standard envelope
     •   Statement: a declaration of fact about a subject
     •   Three types: attribute, authentication and authorization
         decision

•   Protocol: SAML web services defined as XML
    request-response pairs
     •   Services consume and/or produce SAML assertions
Bindings and Profiles
•   SAML 1.0 includes a SOAP-over-HTTP
    binding for SAML protocol
     •   Trust model and SOAP-over-HTTP details required
         for interoperability

•   Profile: use of SAML to solve a business
    problem
     •   SAML 1.0 includes a family of Web Browser SSO
         profiles
All assertions have some common information
      •   Issuer and issuance timestamp
      •   Assertion ID
      •   Subject
           •   Name plus the security domain
           •   Optional subject confirmation, e.g. public key
      •   “Conditions” under which assertion is valid
           •   SAML clients must reject assertions containing
               unsupported conditions
           •   Special kind of condition: assertion validity period
      •   Additional “advice”
           •   E.g., to explain how the assertion was made
Authentication Statement
   •   An issuing authority asserts that:
        •   subject S
        •   was authenticated by means M
        •   at time T

   •   Caution: Actually checking or revoking of
       credentials is not in scope for SAML!
        • Password exchange
        • Challenge-response
        • Etc.
Attribute Statement
   •   An issuing authority asserts that:
        •   subject S
        •   is associated with attributes X, Y, Z
        •   with values “a”, “b”, “c”…(XML fragments)
   •   Often this would be gotten from an LDAP
       repository
        •   “john.doe” in “example.com”
        •   is associated with attribute “Department”
        •   with value “Human Resources”
Example
     “John Doe” logged in at 9AM at example.com. He is a
     manager with spending limit of $10K.
     <saml:assertion Issuer=“example.com”…>
         <saml:Conditions NotBefore=… NotAfter=…/>
         <saml:AuthenticationStatement
           AuthenticationMethod=…
           AuthenticationInstant=… >
           <saml:subject …>John Doe</saml:subject>
         </saml:AuthenticationStatement>
         <saml:AttributeStatement>
           <saml:subject …>John Doe</saml:subject>
           <saml:Attribute AttributeName=“Title” …>
           <saml:AttributeValue>Manager</AttributeValue>
           </saml:Attribute>
          <saml:Attribute AttributeName=“SpendLimit” …>
          <saml:AttributeValue>10,000</AttributeValue>
          </saml:Attribute>
         </saml:AttributeStatement>
       </saml:Assertion>
Authorization decision assertion
   •   An issuing authority decides whether to
       grant the request:
        •   by subject S
        •   to perform action A
        •   on resource R
        •   given evidence E (other assertions)
   •   The subject could be a human or a
       program
   •   The resource could be a web page or a
       web service, for example
Example authorization decision assertion
     <saml:Assertion …>
       <saml:Conditions …/>
       <saml:AuthorizationDecisionStatement
         Decision=“Permit”
         Resource=“http://jonesco.com/rpt_12345.htm”>
         <saml:Action>READ</saml:Action>
         <saml:Evidence>…</saml:Evidence>
         <saml:Subject>
           <saml:NameIdentifier
             SecurityDomain=“smithco.com”
             Name=“joeuser” />
         </saml:Subject>
       </saml:AuthorizationDecisionStatement>
     </saml:Assertion>
SAML Protocol Actors
                   Responder




           SAML

            Request for        Response
            Assertion of
                               Assertion
            Certain Type




                   Requester
SAML Protocol
•   Defined via XML request-response pairs
•   A <samlp:Request> includes one of two query forms

     •   Assertion Lookup based on simple query language
          • Assertion Lookup by id or artifact
          • Query for assertions with AuthN statements by matching
            against subject name and authentication method
          • Query for assertions with Attribute statements by
            matching against subject name and attribute name(s)

     •   Authorization Decision Assertion Request
Authorization decision assertion request
•   “Is this subject allowed to access the specified
    resource in the specified manner, given this
    evidence?”

•   This type of request is the most complex

•   Models classical PEP (policy enforcement
    point) and PDP (policy decision point) dialog
SAML and Web Services
• SAML Protocol describes a class of security
  services (expressed as web services)
• SAML responders support:
     • Lookup by assertion id
     • (remote) lookup of attributes or authentication
       information,
     • Interaction between a PEP and a remote PDP


•   SOAP Binding for SAML 1.0 provides
    interoperable implementation
Securing a web service using SAML
 •   WS-Security Profile of SAML
 •   draft-sstc-ws-sec-profile-03 available at
     http://lists.oasis-open.org/archives/security-services/200208/msg00015.html


 •   <wsse:Security> element carries SAML
     assertions or assertion identifier references.

 •   Additional signatures may be added to provide
     proof-of-possession (and data integrity)
WS-Security profile
           SAML
                  SOAP Message
                  SOAP Header
              WS-Security Header

                  SAML Assertion



                   SOAP Body

                       ...
Messaging Use-Case
•   Two parties: a buyer and a seller
•   Asymmetrical relationship is assumed
     •   Seller is already known to buyer, but buyer is not
         known to seller, a common situation
     •   E.g., server-side certificates might be used to
         authenticate seller
•   If it were symmetrical, additional SAML steps
    would happen on the right side too
     •   This would be an extension of this scenario
Web service secured by SAML
                               Authentication Authority            Policy Decision Point +
                                + Attribute Authority             Policy Enforcement Point

                                         Trusted
    Buyer                                                                  Seller
                                          Issuer


            Authenticate (out of band)

        Request authentication and
           attribute assertions
        Receive authentication and
           attribute assertions
        Attach assertions to P.O.
                                         Send P.O.

                                                 Process assertions and P.O.
                          Send P.O. response (out of band)
Service Provisioning Markup Language
•   What is SPML?
      •   Open standard for defining and exchanging identity provisioning
          requests in XML
      •   Loosely-coupled model for integration and operation of identity
          provisioning request flows
•   What does it look like?
      • An XML Schema – data layout for expressing the request (C.R.U.D)
        and attributes required for a given provisioning request
      • A Protocol – a basic request/response dialog for exchanging request
        schema
      • A Binding – the definition of how you pack the schema and protocol in a
        message transport like HTTP or SOAP.
•   When is it available?
      •   Expected December 2002
XCBF – Common Biometric Format
 •   The XCBF TC will define a common set of
     secure XML encodings for the patron formats
     specified in CBEFF, the Common Biometric
     Exchange File Format (NISTIR 6529).

 •   http://www.oasis-open.org/committees/xcbf/

				
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