Identity management Tuomas Aura CSE-C3400 Information security Aalto
Identity management Tuomas Aura CSE-C3400 Information security Aalto University, autumn 2014 Outline 1. 2. 3. 4. 5. 6. Single sign-on SAML and Shibboleth OpenId OAuth (Corporate IAM) Strong identity
2 Single sign-on (SSO) Users have too many user accounts Cannot remember the passwords Service access slow and inconvenient Forgotten, unmanaged accounts are a security risk Need for an SSO solution SSO types: Pseudo-SSO: separate authentication to each service; client software manages the credentials and hides the login from user Proxy-based SSO: pseudo-SSO implemented in a proxy; proxy in the network manages user credentials and hides the login details from the client True SSO: user authenticates to a separate authentication service, which asserts user identity to other services Federated SSO: authentication between administrative domains Main problem with SSO systems: therere so many of them
3 SAML AND SHIBBOLETH 4 SAML 2.0 architecture Principal Service provider SP Identity provider IdP Trust relation Register user Authenticate Security assertion markup language (SAML 2.0) OASIS standard (combines ideas from SAML 1.1, Liberty Alliance identity-federation
framework 1.2, and Shibboleth 1.3) Service provider (SP) and identity provider (IdP) establish a trust relation by exchanging metadata Principal (= user, subject) registers with the IdP Principal authenticates to IdP and then to SP 5 SAML SAML is a complex family of protocols: Assertions are statements by IdP about a principal, written in XML Protocols define message flows for requesting assertions Bindings define how protocol messages are transported over HTTP, SOAP etc. Profiles define useful combinations of assertions, protocols and bindings Metadata defines trust relations SAML is based on contractual relations Metadata must be first exchanged between IdP and SP
Federation may set rules for its member IdPs and SPs User cannot decide which id to use where Typical profile: SAML web browser SSO profile 6 SAML web browser SSO profile IdP-initiated or SP-initiated SSO: User first logs into the IdP, or first connects to SP Bindings to HTTP messages Redirect: message from SP to IdP is sent in GET URL via browser, with help of HTTP redirection POST: message between SP and IdP is sent in HTTP form via browser, submitted by user click or script Artifact: reference to message is sent in GET URL via browser, with the help of HTTP redirection, and the actual message is retrieved directly from the sender SOAP binding is not used in this profile
7 SAML web browser SSO profile Principal Service provider SP Identity provider IdP SP-initiated SSO 1. Access request 2. 3. User login to IdP 4. Resource access Protocol for SP-initiated SSO: AuthnRequest and Response
How to send these messages over HTTP? Need to choose bindings; 6 different combinations 8 SAML web browser SSO profile Principal Service provider SP Identity provider IdP SP-initiated SSO 1. Access request 2. Redirect: 3. User login to IdP SAML RedirectArtifact binding
4. Redirect with artifact 7. Resource access 5. Resolve artifact 6. Artifact response () Example: redirect-artifact binding: SP sends to IdP in GET URL with HTTP redirect IdP sends an artifact to SP in GET URL with HTTP redirect SP retrieves from IdP with artifact resolution protocol 9 SAML security Principal Service provider SP
1. Access request 2. Redirect: Identity provider IdP TLS for all connections 3. User login to IdP 4. Redirect with artifact 7. Resource access 5. Resolve artifact 6. Artifact response Sign with IdP signature key Response must be signed by IdP TSL needed for all connections: Protects password; protects secrecy of user attributes; prevents redirections to wrong site;
protects the created session and resource access Attributes in the Response are signed by the IdP SP gets the IdP public key from the federation metadata Response contains the request id 10 Shibboleth 2 Open-source implementation of SAML 2.0 for web SSO (wiki) Developed by the Internet 2 project Used mainly in research and educational institutions; many other commercial and open-source SAML implementation exist If SP supports multiple IdPs, SP-initiated authentication goes via the where are you from (WAYF) page One more step of redirection for the AuthnRequest Federation is a group of IdPs and SPs that share metadata in one signed file agree on an attribute schema
agree on CA for TLS have a service agreement that sets out rules for the federation e.g. Haka federation 11 SAML attributes In addition to user identity, from IdP to SP contains user attributes Attributes sent to each SP are selected based on attribute filters in metadata Example: CN=Aura Tuomas eduPersonAffiliation = employee;member;faculty Try https://rr.funet.fi/haka/ User attributes are personal data For legal reasons, IdP needs user confirmation before transferring attributes to SP
12 Sessions in Shibboleth Shibboleth implements two kinds of sessions: IdP session between browser and the IdP (IdP cookies) user only needs to type in password once SP session between browser and each SP (SP cookies) Additional application sessions: Web middleware incl. PHP, JSP and ASP.NET implements sessions using cookies, URL or web form) Applications may set their own cookies No single logout Logging out of SP does not usually log the user out of the IdP can log back to SP without password Logging out of IdP does not log the user out of SPs Logging out of one SO does not log the user out of other SPs Application sessions complicate the situation further
Shibboleth logout behavior is hard to understand 13 OPENID 14 OpenId architecture End user / user agent UA Relying party RP Identity provider OP Create OpenId Register OpenId for user account Authenticate Standard for SSO to web sites
http://openid.net/developers/specs/ End user creates an OpenId (=identity) at some OpenId provider (OP) End user registers the OpenId at various relaying parties (RP) i.e. web sites End user authenticates to RP with the help of OP The end user needs a web browser i.e. user agent (UA) 15 OpenId 2.0 protocol End user / user agent UA Relying party RP Identity provider OP
1. Identifier 2. OP discovery [3. Association: DH] 4. Redirect: authentication request 5. User authentication: e.g. password 6. Redirect: authentication approved/failed [7. Direct verification] (only if no step 3) 8. Service access Identifier is an HTTP URL (or XRI): gives the OP address e.g. username.myopenid.com, https://me.yahoo.com/username Direct messages use HTTP POST Indirect messages use HTTP GET and Redirect Data fields sent as URL parameters via the browser Method of user authentication not specified; typically a password
16 OpenId 2.0 security End user / user agent UA Relying party RP Identity provider OP 1. Identifier 2. OP discovery [3. Association: DH] TLS to authenticate the DH key exchange 4. Redirect: authentication request User must check OP name and RP name
TLS to protect the password 6. Redirect: authentication approved/failed MAC with the association key [7. Direct verifivation] 8. Service access (only if no step 3) TLS to authenticate result Approval /failure message from OP to RP is authenticated with a MAC and timestamp RP can either establish a MAC key with Diffie-Hellman (step 3) or ask OP to verify the MAC for it (step 7) TLS is not required by OpenId spec but needed for real security: RP must authenticate OP in the Diffie-Hellman or direct verification step UA must authenticate OP before user types in the password TLS can be used between UA and RP to protect service access (Q: does it matter?)
User must pay attention: Check https and the OP name in the browser address bar before typing in the password Check RP name on OP login page before approving login 17 OpenId notes What does open mean? Anyone can become an identity provider User can choose any identity provider Services accept the identity chosen by the user Works on any web browser without proprietary software In practice, not always so open: RP policy may determine which OPs are accepted OP policy may determine which RPs are accepted For privacy, user-provided id may just point to OP without user id e.g. https://www.google.com/accounts/o8/id
OpenId specification is poorly written Assumes the reader knows previous versions Uses XRI, Yadis and XRDS: very complex and incomplete specifications Security not obvious from the specification: Focus on implementation, not on secure protocol design Vague security claims especially when used without TLS 18 OAUTH 2.0 19 OAuth 2.0 OAuth was designed for authorization (i.e. delegation) Allow an external web site or app to access a service on the users behalf Password sharing not required, and access can be revoked
Examples: Authorize an external web site or app to update your Facebook profile or page Authorize continuous integration tool to monitor a GitHub repository Standardized by IETF (RFC 6749, RFC 6750) Many implementation options cause interoperability issues OAuth 2.0 security is based only on TLS (Oath 1.0 used client signatures) 20 OAuth 2.0 protocol User Client (website or app) Service Provider 1. Use
2. Redirect: Authorization request (scope) TLS for all connections 3. User authentication and approving access to scope 4. Redirect: Authorization (access token, scope) 7. Continued use 5. Delegated access: (access token) User authorizes the client (web site or mobile app) to access the service Client may restrict the scope of delegated access Security based on an opaque access token and TLS Token is typically a random number Service providers remembers the scope of authorized access for each token
21 OAuth for authentication? The message flow in OAuth looks like OpenId or SAML tempting to use the same protocol for authentication User would prove its identity by delegating access to a (dummy) resource associated with the user account In principle, this is a bad idea: OAuth access token enables client to access a resource on the service provider The client in OAuth does not know or care who gives it the token, as long as the token works for accessing SP The protocol does not prevent the client from sharing the token with others Malicious client can impersonate its users to other clients Businesses have made proprietary extensions to make OAuth work for authentication as well 22
STRONG IDENTITY 26 Strong authentication Goal: authentication equivalent to verifying national identity card or passport Why is it needed? Initial id check when registering new users, e.g. students enrolling to university Required by law for access to government services and personal information Increasing trust in commercial online transactions but this has long since been solved in other ways Why not use OpenId or SAML? OpenId allows user to choose identifier no secure link to a real person SAML works internally in organizations and between organizations
that have a contract not for new, open online services 27 Finnish electronic identity card Finnish identity cards (HST-kortti) have a smartcard chip with three key pairs Signature, encryption and authentication keys http://www.fineid.fi/ Keys are certified by the national population register (VRK) Has not gained popularity; few people have an id card; even fewer ever use it for electronic authentication Why? 28 Tupas authentication Tupas uses bank accounts for strong authentication
Defined by Federation of Finnish Financial Services http://www.fkl.fi/teemasivut/sahkoinen_asiointi/tupas/ Developed from online the payment system (commonly used in Finland for online purchases) User authentication with one-time passwords Advantage: everyone has a bank account, and banks are required to know the identity of their customers no cost for identity proofing Example: https://password.aalto.fi/ 29 Tupas authentication User Online service 1. Bank selection 2. POST redirection
Bank TLS for all connections 3. One-time password login to bank 4. POST redirection: name, name,national nationalididnumber, number,MAC MAC 5. Service access Authenticated with a shared key; id number (Hetu) may be encrypted Three-corner authentication model: user, users bank, online service
Each service must set up a shared key with each bank Smaller banks are not supported by all online services 30 Mobile signature Mobile phone operators install a signature key on the SIM ETSI standard, developed from earlier business SIM No direct access from phone to signature key; signatures are requested via the operators mobile signature service provider (MSSP) Advantages: everyone has a SIM card, and operators have 24/7 service for revocation Four-corner authentication model: Mobile operators have contracts with each other Each service and user only needs to have a contract with one operator Deployment and adoption has been slow Requires identity proofing i.e. checking if the subject identity before issuing the certificate (now done with Tupas in Finland) Operators want a fee for every transaction low number of
transactions may not be a viable business 31 Reading material Online: OpenId 2.0, http://openid.net/developers/specs/ SAML 2.0 Technical Overview, http://www.oasis-open.org/committees/downloa d.php/27819/sstc-saml-tech-overview-2.0-cd-02.p df OAuth specification http:// tools.ietf.org/html/rfc6749 32 Exercises How much security does OpenId exactly give if TLS is not used? Learn about XRI name space and XRI discovery. If XRI is used as the user identifier in OpenId, how is the user supposed to authenticate the OP before typing in the password?
How much difference does it make to security and privacy if the user-provided id points to the OP without identifying the user, and the user identity is entered only at the OP site? Look at the Haka federation metadata for Shibboleth 2. How does this create trust between an IdP and SP? What ways are there to limit the trust? Can you capture the AuthnRequest and Response messages when logging into Noppa? Which bindings are used? Why exactly is TLS needed at each stage in SAML/Shibboleth authentication, or is it? Compare the logout (and re-login) behavior of Noppa, Oodi and nelliportaali.fi. Which sessions get deleted, when and how? Despite similarities in the protocols, OpenId, SAML, Oauth, and Tupas have different goals and make different assumptions about the relations between entities. What differences are there? 33
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