An XML based Security Assertion Markup Language SAML An XML based Security Assertion Markup Language

Introduction XML standard for exchanging authentication and authorization data between security domains, i.e. identity provider and service provider. Solve the single sign-on (SSO) problem at intranet level using cookies. SAML assumes principal (user) is enrolled at least with one identity provider.

Why is SAML required ? Limitations of Browser cookies Cross-Domain SSO (CDSSO) problem SSO Interoperability SSO and CDSSO are completely proprietary Web Services Authentication/integrity services on an end-to-end basis Federation identity management across organizational boundaries to a single (or at least a reduced set) Federated Identity

SAML Use Cases There are 3 use cases in SAML: - Single sign-on (SSO) - Authorization service - Back office transaction Each use case have one or more scenarios that provide a more detailed roadmap of interaction

SSO Use Case Adaptation

Authorization Service Use Case Adaptation

Back Office Transaction Use Case Adaptation

SAML Overview Specification for exchanging authentication and authorization information using XML-based security - XML schema and definition for security assertions - XML schema and definition for a request/response protocol - Rules on using assertions with standard transport and messaging frameworks. Bindings and Profiles Emerging OASIS standard involving Vendors and Users Codifies current system outputs rather than inventing new technology

SAML Assertions Declaration of facts (statements) about a subject Contains multiple assertion statements Can be digitally signed 3 kinds of assertion statements related to security: 1. Authentication 2. Attribute 3. Authorization Decision

Common Information in all Assertions Issuer and issuance timestamp Assertion ID Subject Name and security domain Optional subject confirmation like public key Conditions under which assertion is valid Special conditions like – assertion validity period, audience restriction and target restriction SAML clients must reject assertions containing unsupported conditions.

Authentication Assertion The Issuing authority asserts that subject S, was authenticated by means M, at time T.

Attribute Assertion The Issuing authority asserts that subject S, is associated with attributes A, B,…, with values a, b, c.

Authorization Decision Assertion The Issuing authority decides whether to grant the request by subject S, for access type A, to resource R

Assertions - continued Assertions without the rest of the structure may be provided for existing tightly coupled environments who may need their own protocol. SAML is fully beneficial when parties with no direct knowledge of each other can interact via a third-party introduction

SAML Protocol simple request-response protocol <samlp:Request xmlns:samlp="urn:oasis:names:tc:SAML:1.0:protocol" MajorVersion="1" MinorVersion="1“ RequestID="..." IssueInstant="..."> <!-- insert other SAML elements here --> </samlp:Request> <samlp:Response xmlns:samlp="urn:oasis:names:tc:SAML:1.0:protocol" MajorVersion="1" MinorVersion="1“ ResponseID="...“ InResponseTo="..." IssueInstant="..."> <!-- insert other SAML elements here, including assertions --> </samlp:Response>

Authentication Assertion Request What are the authentication assertions which are available for this subject Successful responses are in the form of assertions containing an authentication statement It is assumed that the requester and responder have a trust relationship and are talking about the same subject

Authentication Assertion Request - example

Attribute Assertion Request The requested attribute is returned for this subject Response is in the form of an assertion containing attribute statement Requester can be denied access to some of the attributes and allowed access to a partial list of attributes

Attribute Assertion Request example

Authorization Decision Assertion Request Given the evidence is this subject allowed access to the specified resource in the specified manner with the given evidence? Response is in the form of an assertion containing an authorization decision statement

Authorization Decision Assertion Request example

Example Response

Protocol Binding and Profile Binding – mapping of SAML request/response message exchanges into standard communication protocols. SOAP-over-HTTP binding is the baseline Profile – describes how SAML assertions are embedded into and extracted from a framework or protocol. Web browser profile for SSO SOAP profile for securing SOAP payloads

SOAP-over-HTTP Binding SOAP is used as SAML request/response protocol transport mechanism

SOAP Profile SAML is used to provide assertions about a resource in the SOAP Body of the same document

Web Brower Profiles Assumptions Standard commercial browser and HTTP(S) User authenticated to local source site Assertion’s subject refers to the user What happens when user tries to access target site Tiny authentication assertion reference travels with request so real assertion can be de-referenced POST of real assertion can occur

SSO Pull Scenario Using Web Browser

SSO Pull Scenario Using Web Browser - explained Step 1 : Access inter-site transfer URL: User authenticated with http://Company.com Clicks on a link that looks like it will take the user to http://Travel.com/reserve_hotel.cgi It really takes the user to inter-site transfer URL: https://Company.com/intersite?Target=Travel.com/reserve_hotel.cgi Step 2 : Redirect with artifact: Reference to user’s authentication assertion generated as SAML “artifact” (8-byte base64 string) User redirected to assertion consumer URL, with artifact and target attached: https://Travel.com?Target=Travel.com/reserve_hotel.cgi&SAMLart=<artifact>

Back Office Transaction Scenario

References http://www.computerworld.com/developmenttopics/development/webdev/story/0,10801,73712,00.html http://www.simc-inc.org/archive0002/February02/devwed1015_rouault.pdf http://en.wikipedia.org/wiki/SAML http://xml.coverpages.org/saml.html http://xml.coverpages.org/SAML-TechOverviewV20-Draft7874.pdf