Identity management

Tuomas AuraCSE-C3400 Information security

Aalto University, autumn 2014

Outline

1. Single sign-on

2. SAML and Shibboleth

3. OpenId

4. OAuth

5. (Corporate IAM)

6. Strong identity

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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: there’re so many of them

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SAML AND SHIBBOLETH

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SAML 2.0 architecture

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

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Service provider SP

Trust relation

Principal

Register user

Identity provider IdP

Authenticate

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

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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

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SAML web browser SSO profile

Protocol for SP-initiated SSO:– AuthnRequest and Response

How to send these messages over HTTP? Need to choose bindings; 6 different combinations

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Service provider SPPrincipal Identity provider IdP

1. Access request

Resource access

3. User login to IdP

2. <AuthnRequest>

4. <Response>

SP-initiated

SSO

SAML web browser SSO profile

Example: redirect-artifact binding: – SP sends <AuthnRequest> to IdP in GET URL with HTTP redirect– IdP sends an artifact to SP in GET URL with HTTP redirect– SP retrieves <Response> from IdP with artifact resolution protocol

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Service provider SPPrincipal Identity provider IdP

1. Access request

7. Resource access

3. User login to IdP

4. Redirect with artifact

2. Redirect: <AuthnRequest>

6. Artifact response

(<Response>)

SAML Redirect-

Artifact binding

SP-initiated

SSO

5. Resolve artifact

SAML security

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

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Service provider SPPrincipal Identity provider IdP

1. Access request

7. Resource access

3. User login to IdP

4. Redirect with artifact

2. Redirect: <AuthnRequest>

6. Artifact response

5. Resolve artifact

Sign with IdP signature key<Response>

TLS for all

connections

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

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SAML attributes

In addition to user identity, <Response> 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

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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

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OPENID

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OpenId architecture

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)

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Identity provider OPRelying party RP

Register OpenId for

user account

End user / user agent UA

Authenticate

Create OpenId

OpenId 2.0 protocol

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

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Identity provider OPRelying party RP

1. Identifier

[3. Association: DH]

End user / user agent UA

8. Service access

[7. Direct verification]

5. User authentication: e.g. password

6. Redirect: authentication approved/failed

4. Redirect: authentication request

2. OP discovery

(only if no step 3)

OpenId 2.0 security

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

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2. OP discovery

Identity provider OPRelying party RP

1. Identifier

[3. Association: DH]

End user / user agent UA

8. Service access

[7. Direct verifivation]

6. Redirect: authentication approved/failed

4. Redirect: authentication request

TLS to authenticate

the DH key exchange

TLS to protect

the password

MAC with the association key

TLS to

authenticate result

(only if no step 3)

User must check OP

name and RP name

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

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OAUTH 2.0

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OAuth 2.0 OAuth was designed for authorization (i.e. delegation)

– Allow an external web site or app to access a service on the user’s 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)

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OAuth 2.0 protocol

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

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Client (website or app)User Service Provider

1. Use

3. User authentication and approving access to scope

4. Redirect: Authorization (access token, scope)

2. Redirect: Authorization request (scope)

TLS for all

connections

5. Delegated access:

(access token)7. Continued use

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 othersMalicious client can impersonate its users to other clients

Businesses have made proprietary extensions to make OAuth work for authentication as well

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CORPORATE IAM

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Corporate IAM Federated identity and authentication is not sufficient:

– Need to configure access permissions for users in the services– Need to monitor access control state in the system– Need to revoke access rights

Identity and access management (IAM) systems– Define roles and groups for the organization – Enable centralized role assignment, revocation and monitoring

Example:– student enrolls to university, then becomes employee, then

graduates, finally leaves employment

Central IAM server and IAM agent at each supported service more expensive to develop and deploy than federated

authentication

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25[Internet 2 Middleware Initiative]

STRONG IDENTITY

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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

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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?

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Tupas authentication

Tupas uses bank accounts for strong authentication

– Defined by Federation of Finnish Financial Serviceshttp://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/

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Tupas authentication

Three-corner authentication model: user, user’s bank, online service Each service must set up a shared key with each bankSmaller banks are not supported by all online services

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Online serviceUser Bank

1. Bank selection

5. Service access

3. One-time password login to bank

4. POST redirection: name, national id number, MAC

2. POST redirection

Authenticated with

a shared key;

id number (Hetu)

may be encrypted

name, national id number, MAC

TLS for all

connections

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 operator’s 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

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Reading material

Online:

– OpenId 2.0, http://openid.net/developers/specs/

– SAML 2.0 Technical Overview, http://www.oasis-open.org/committees/download.php/27819/sstc-saml-tech-overview-2.0-cd-02.pdf

– OAuth specificationhttp://tools.ietf.org/html/rfc6749

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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?

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