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IETF OAuth Proof-of-Possession

IETF OAuth Proof-of-Possession. Hannes Tschofenig. Status. Finished various specifications, including OAuth Core: RFC 6749 Bearer Tokens: RFC 6750 Security Threats: RFC 6819

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IETF OAuth Proof-of-Possession

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  1. IETF OAuth Proof-of-Possession Hannes Tschofenig

  2. Status Finished various specifications, including OAuth Core: RFC 6749 Bearer Tokens: RFC 6750 Security Threats: RFC 6819 Discussion about an enhancement to Bearer Token security (now called “Proof-of-Possession”) since the early days of the working group. Design Team work late 2012/early 2013, which lead to requirements, use cases, and solution strawman proposals. Work on solution documents lead to new work items.

  3. I Architecture Client Authorization Server III II Resource Server Relevant document: http://datatracker.ietf.org/doc/draft-ietf-oauth-pop-architecture/

  4. I AS <-> Client Interaction Client • Variants: • Key Distribution at Access Token Issuance • Key Distribution at Client Registration Authorization Server III II Resource Server Relevant specifications:http://datatracker.ietf.org/doc/draft-ietf-oauth-pop-key-distribution/ http://datatracker.ietf.org/doc/draft-ietf-oauth-proof-of-possession/

  5. AS <-> Client Interaction Example: Symmetric Key Client Authorization Server Request access token.I support PoP tokens Resource Server

  6. AS <-> Client Interaction Example: Symmetric Key Client AS creates PoP-enabled access token Authorization Server Resource Server

  7. PoP Token: Symmetric Key Example { "alg":"RSA1_5", "enc":"A128CBC-HS256", "cty":"jwk+json" } { "iss": "https://server.example.com", "sub": "24400320", "aud": "s6BhdRkqt3", "nonce": "n-0S6_WzA2Mj", "exp": 1311281970, "iat": 1311280970, "cnf":{ "jwk": "eyJhbGciOiJSU0ExXzUiLCJlbmMiOiJB MTI4Q0JDLUhTMjU2IiwiY3R5IjoiandrK ... (remainder of JWE omitted for brevity)" } } Binds a symmetric key to the access token { "kty":"oct", "alg":"HS256", "k":"ZoRSOrFzN_FzUA5XKM YoVHyzff5oRJxl-IXRtztJ6uE" }

  8. AS <-> Client Interaction Example: Symmetric Key Client Authorization Server AS sends access token to Client & symmetric key Resource Server

  9. AS <-> Client Interaction • AS needs to bind a key to the access token. • Key can be an fresh and unique symmetric key, or • (ephemeral) public key • This requires two extensions: • New elements within the JWT to include the (encrypted symmetric key) or the public key. JWT is also integrity protected. • Mechanism for conveying ephemeral key from AS to client and for client to provide directives to AS. • Details in draft-ietf-oauth-pop-key-distribution • Transport symmetric key from AS to client. • Transport (ephemeral) asymmetric key from AS to client. • Transport public key from client to AS. • Algorithm indication

  10. Dynamic Client Registration Attempt to simplify developer interaction with AS when they deploy client applications. Today, developers need to register various parameters (manually), such as Authentication mechanism & client authentication credentials Redirect URIs Grant types Meta data (client name, client logo, scopes, contact information, etc.) Also allows meta-data, including public keys, to be uploaded to AS. Two documents: draft-ietf-oauth-dyn-reg draft-ietf-oauth-dyn-reg-metadata WGLC in progress.

  11. I Client <-> RS Interaction Client • Building Blocks: • Proof of possession of PoP key • Message integrity (+ Channel Binding) • RS-to-client authentication Authorization Server III II Resource Server Relevant specification: http://datatracker.ietf.org/doc/draft-ietf-oauth-signed-http-request/

  12. AS <-> Client Interaction Example: Symmetric Key Client Authenticator = Keyed Message Digest Computed Over Request. Authorization Server Resource Server AS sends access token to Client & Authenticator

  13. AS <-> Client Interaction Example: Symmetric Key Client Authorization Server RS “unwraps” access tokenand obtains symmetric key. RS verifies authenticator. SharedLong Term Key Resource Server

  14. Channel Binding • Channel bindings bind the application layer security to the underlying channel security mechanism. • Various approaches for providing channel bindings: • PoP public key use in TLS (as described in HOTK draft) • tls-unique: TLS Finish message • tls-server-end-point: hash of the TLS server's certificate: • Currently, no channel bindings described in <draft-ietf-oauth-signed-http-request> • Be aware: New attacks have been identified with TLS-based channel bindings, see http://www.ietf.org/proceedings/89/slides/slides-89-tls-3.pdf

  15. I RS <-> AS Interaction [optional] Client • Variants: • a) Token introspection • b) Out-of-band Authorization Server III ` II Resource Server Relevant specification: http://datatracker.ietf.org/doc/draft-richer-oauth-introspection/

  16. Next Steps • Reviews for the document bundle needed. • Open Issues will be added to the WG tracker. • Main issues with the client<->resource server communication. Challenges: • Dealing with intermediaries modifying headers • Offering flexibility to developer • Reducing payload replicating • Minimizing canonicalization • Authentication of the server to the client • Channel binding functionality

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