Diameter support for EAP - Re-authentication Protocol (ERP)

# Date 1254986986 -32400 # Node ID 409fb7bb22b7eadd59731f1f567fca7a587da1f6 # Parent 1c9b16ee3039d1f72aeecc46942178355b29481f Submitted -02, prepared for new -03 diff -r 1c9b16ee3039 -r 409fb7bb22b7 draft-ietf-dime-erp-02.xml --- a/draft-ietf-dime-erp-02.xml Thu Oct 08 16:23:35 2009 +0900 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000 @@ -1,877 +0,0 @@ - - - - - - - - - - - - - - -]> - - - - - - - - - - - - - - - - - - Diameter support for EAP - Re-authentication Protocol (ERP) - - - Orange Labs - -

- - 38-40 rue du general Leclerc - - Issy-Les-Moulineaux - - 92794 - - France - - - julien.bournelle@orange-ftgroup.com -

- - - - Orange Labs - -

- - 38-40 rue du general Leclerc - - Issy-Les-Moulineaux - - 92794 - - France - - - lionel.morand@orange-ftgroup.com -

- - - - NICT - -

- - 4-2-1 Nukui-Kitamachi - - Tokyo - - 184-8795 - - Koganei, Japan - - - sdecugis@nict.go.jp -

- - - - Huawei Technologies Co., - Ltd - -

- - Site B, Floor 12F, Huihong Mansion, No.91 Baixia - Rd. - - Nanjing - - 210001 - - China - - - sunseawq@huawei.com -

- - - - Network Zen - -

- - 1310 East Thomas Street - - #306 - - Seattle - - Washington - - 98102 - - USA - - - +1 (206) 377-9035 - - gwz@net-zen.net -

- - - - - Operations & Management - - Diameter Maintenance and Extensions (DIME) - - Internet-Draft - - EAP - - Diameter - - Re-authentication - - inter-authenticator roaming - - - EAP Re-authentication Protocol (ERP) defines extensions to the - Extensible Authentication Protocol (EAP) to support efficient - re-authentication between the peer and an EAP Re-authentication (ER) - server through a compatible authenticator. This document specifies - Diameter support for ERP. It defines a new Diameter ERP application to - transport ERP messages between ER authenticator and ER server, and a set - of new AVPs that can be used to transport the cryptographic material - needed by the re-authentication server. - - - - -

- defines the EAP Re-authentication - Protocol (ERP). It consists in the following steps: - Bootstrapping: a root key for re-authentication is derived from - the Extended Master Session Key (EMSK) created during EAP - authentication . This root key is - transported from the EAP server to the ER server. - - Re-authentication: a one-round-trip exchange between the peer and - the ER server, resulting in mutual authentication. To accomplish the - EAP reauthentication functionality, ERP defines two new EAP codes - - EAP-Initiate and EAP-Finish. - - - This document defines how Diameter transports the ERP messages - (Re-authentication step). For this purpose, we define a new Application - Id for ERP, and re-use the Diameter EAP commands (DER/DEA). - - This document also discusses the distribution of the root key - (bootstrapping step), either during the initial EAP authentication - (implicit bootstrapping) or during the first ERP exchange (explicit - bootstrapping). Security considerations for this key distribution are - detailed in . -

- -

- This document uses terminology defined in , , , and . - - "Root key" (RK) or "bootstrapping material" refer to the rRK or rDSRK - derived from an EMSK, depending on the location of the ER server in home - or foreign domain. - - We use the notation "ERP/DER" in this document to refer to a - Diameter-EAP-Request command with its Application Id set to Diameter ERP - application. Similarly, we use the "ERP/DEA", "EAP/DER", and - "EAP/DEA". - -

- The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", - "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this - document are to be interpreted as described in . -

- -

- This document makes the following assumptions. - - The Home EAP server of a peer that wants to use ERP is extended to - support: - Cryptographic operations needed to derive the ERP root key from - the EMSK. By deriving the ERP root key for a specific domain, the - home EAP server implicitly authorizes the use of ERP within this - domain. - - Diameter operations needed to include this root key in a response - message, when a request for this root key was received in a request - message. The two AVP that contain the request for and the root key - material are defined in this document. - - (recommended) Ability to answer a DER message with EAP-Payload - containing an explicit bootstrapping ERP message. - - - The Authenticator (NAS) is extended to support: - Allow the new ERP command codes (EAP-Initiate and EAP-Finish) in - its EAP pass-through mode. - - (optional) Send the EAP-Initiate/Re-Auth-Start message - - (optional) Provide the local domain name via lower layer specific - mechanism or via TLV in the EAP-Initiate/Re-Auth-Start message. - - Encapsulate ERP message and receive corresponding Diameter - answer, as described in this document. - - - If one of the components does not match these assumptions, the ERP - mechanism will fail. In such situation, a full EAP authentication may be - attempted as a fallback mechanism. - - We consider at most one logical ER server entity in a domain. If - several physical servers are deployed for robustness, a replication - mechanism must be deployed to synchronize the ERP states (root keys - FFS: authorization attributes ) between these servers. This - replication mechanism is out of the scope of this document. If several - ER servers are deployed in the domain, we assume that they can be used - interchangeably. -

- -

- The following figure shows the components involved in ERP, and their - interactions. - -

- |Authenticator|<=======>| ER server | <---> | EAP | - +-------------+ +-----------+ | server | - +--------+ - (*) Diameter EAP application, - explicit bootstraping scenario only.]]> - - - The ER server is located either in the home domain (same as EAP - server) or in the visited domain (same as authenticator, when it differs - from the home domain). Can the ER server be located in a third - domain (ex: broker's) according to ERP mechanism? - - When the peer initiates an ERP exchange, the authenticator creates a - Diameter-EAP-Request message, as described in Diameter EAP application - . The Application Id of the message is set - to Diameter ERP application (code: TBD TBD IANA) in the - message. The exact processing to generate the ERP/DER message is - detailed in section . - - If there is an ER server in the same domain as the authenticator - (local domain), Diameter routing MUST SHOULD ? FFS... be - configured so that this ERP/DER message reachs this server, even if the - Destination-Realm is not the local domain. - - If there is no local ER server, the message is routed according to - its Destination-Realm AVP content, extracted from the realm component of - the keyName-NAI attribute. As specified in , this realm is the home domain of the peer in - case of bootstrapping exchange ('B' flag is set in ERP message) or the - domain of the bootstrapped ER server otherwise This actually might - allow the ER server to be in a third party realm. - - If no ER server is available in the home domain either, the ERP/DER - message cannot be delivered, and an error DIAMETER_UNABLE_TO_DELIVER is - generated as specified in and returned to - the authenticator. The authenticator may cache this information (with - limited duration) to avoid further attempts for ERP with this realm. It - may also fallback to full EAP authentication to authenticate the - peer. - - When an ER server receives the ERP/DER message, it searches its local - database for a root key and authorization state ? matching - the keyName part of the User-Name AVP. If such key is found, the ER - server processes the ERP message as described in then creates the ERP/DEA answer as described in - . The rMSK is included in this - answer. - - Finally, the authenticator extracts the rMSK from the ERP/DEA as - described in , and forwards the content of - the EAP-Payload AVP, the EAP-Finish/Re-Auth message, to the peer. - - If the EAP-Initiate/Re-Auth message has its 'B' flag set - (Bootstrapping exchange), the ER server should not possess the root key - in its local database This may not be true in future RFC5296bis - ?. In this case, the ER server acts as a proxy, and forwards the - message to the home EAP server after changing its Application Id to - Diameter EAP and adding an AVP to request the root key. See section - for more detail on this - process. -

- -

- The bootstrapping process involves the home EAP server and the ER - server, but also impacts the peer and the authenticator. In ERP, the - peer must derive the same keying material as the ER server. To achieve - this, it must learn the domain name of the ER server. How this - information is acquired is outside the scope of this specification, but - it may involves that the authenticator is configured to advertize this - domain name, especially in the case of re-authentication after a - handover. - - The bootstrapping of an ER server with a given root key happens - either during the initial EAP authentication of the peer when the EMSK - -- from which the root key is derived -- is created, during the first - re-authentication, or sometime between those events. We only consider - the first two possibilities in this specification, in the following - subsections. - -

- Bootstrapping the ER server during the initial EAP authentication - (also known as implicit bootstrapping) offers the advantage that the - server is immediatly available for re-authentication of the peer, thus - minimizing the re-authentication delay. On the other hand, it is - possible that only a small number of peers will use re-authentication - in the visited domain. Deriving and caching key material for all the - peers (for example, for the peers that do not support ERP) is a waste - of resources and SHOULD be avoided. - - To achieve implicit bootstrapping, the ER server must act as a - Diameter EAP Proxy as defined in Diameter Base Protocol , and routing must be configured so that - Diameter messages of a full EAP authentication are routed through this - proxy. The figure bellow captures this mechanism. - -

- - Diameter EAP/DER - (EAP-Response) - -------------------------> - Diameter EAP/DER - (EAP-Response) - (ERP-RK-Request) - - <==================================================> - Multi-round Diameter EAP exchanges, unmodified - - <------------------------- - Diameter EAP/DEA - (EAP-Success) - (MSK) - (ERP-RK-Answer) - <------------------------- - Diameter EAP/DEA - (EAP-Success) - (MSK) - [ERP-Realm] -]]> - - - The ER server proxies the first DER of the full EAP authentication - and adds the ERP-RK-Request AVP inside, if this AVP is not already in - the message (which might happen if there are ER servers in the visited - and the home domains), then forwards the request. - - If the EAP server does not support ERP extensions, it will simply - ignore this grouped AVP and continue as specified in . If the server supports the ERP extensions, - it caches the ERP-Realm value with the session, and continues the EAP - authentication. When the authentication is complete, if it is - successful and the EAP method generated an EMSK, the server MUST - compute the rRK or rDSRK (depending on the value of ERP-Realm) as - specified in , and add an ERP-RK-Answer - AVP in the Diameter-EAP-Request message, in addition to the MSK and - EAP-Success payloads. - - When the ER server proxies a Diameter-EAP-Answer message with a - Session-Id corresponding to a message to which it added an - ERP-RK-Answer, and the Result-Code is DIAMETER_SUCCESS, it MUST - examine the message, extract and remove any ERP-RK-Answer AVP from the - message, and save its content. If the message does not contain an - ERP-RK-Answer AVP, the ER server MAY save this information to avoid - possible subsequent re-authentication attempts for this session. In - any case, the information stored SHOULD NOT have a lifetime greater - than the EMSK lifetime how does the ER server knows the EMSK - lifetime, if there is no ERP-RK-Answer? What is the lifetime of the - MSK for example? - - If the ER server is successfully bootstrapped, it MAY also add the - ERP-Realm AVP after removing the ERP-RK-Answer AVP in the EAP/DEA - message. This could be used by the authenticator to notify the peer - that ERP is bootstrapped, with the ER domain information. How this - information can be transmitted to the peer is outside the scope of - this document. Is it possible? It would be useful... -

- -

- Bootstrapping the ER server during the first re-authentication - (also known as explicit bootstrapping) offers several advantages: it - saves resources, since we generate and cache only root key that we - actually need, and it can accomodate inter-domain handovers or ER - servers that loose their state (for example after reboot) This - last point might not be true currently, since the peer would not issue - a bootstrapping exchange... But this might change also with RFC5296bis - AFAIU. On the other hand, the first re-authentication with the - ER server requires a one-round-trip exchange with the home EAP server, - which adds some delay to the process (but it is more efficient than a - full EAP authentication in any case). It also requires some - synchronization between the peer and the visited domain: since the ERP - message is differentand the root key used also ? for - explicit bootstrapping exchange and for normal re-authentication, - explicit bootstrapping should not be used if implicit bootstrapping - was already performed. - - What should we do if the ER server receives an explicit - bootstrapping request but already possess the rDSRK? Can it answer - without going to the home server? That would be simpler -- planned in - rfc5296bis ? - - The ER server receives the ERP/DER message containing the - EAP-Initiate/Re-Auth message with the 'B' flag set. It proxies this - message, and do the following processing in addition to standard proxy - operations: - Change the Application Id in the header of the message to - Diameter EAP Application (code 5). - - Change the content of Application-Auth-Id accordingly. Is - it better to leave it unmodified? - - Add the ERP-RK-Request AVP, which contains the name of the - domain where the ER server is located. - - Add the Destination-Host to reach the appropriate EAP - server, the one with the EMSK. How does the ER server know this - information ? - Then the server forwards the EAP/DER request, which is routed - to the home EAP server. - - If the home EAP server does not support ERP extensions, it replies - with an error since the encapsulated EAP-Initiate/Re-auth command is - not understood. Otherwise, it processes the ERP request as described - in . In particular, it includes the - Domain-Name TLV attribute with the content from the ERP-Realm AVP. It - creates the EAP/DEA reply message following standard processing from - (in particular EAP-Master-Session-Key - AVP is used to transport the rMSK), and includes the ERP-RK-Answer - AVP. What about authorization AVPs ? - - The ER server receives this EAP/DEA and proxies it as follow, in - addition to standard proxy operations: - Set the Application Id back to Diameter ERP (code TBDTBD - IANA) - - Extract and cache the content of the ERP-RK-Answer. And - authorization AVPs ? - The DEA is then forwarded to the authenticator, that can use - the rMSK as described in . - - The figure below captures this proxy behavior: - -

- - Diameter ERP/DER - (EAP-Initiate) - ------------------------> - Diameter EAP/DER - (EAP-Initiate) - (ERP-RK-Request) - - <------------------------ - Diameter EAP/DEA - (EAP-Finish) - (ERP-RK-Answer) - (rMSK) - <---------------------- - Diameter ERP/DEA - (EAP-Finish) - (rMSK) -]]> - -

- -

- This section describes in detail a re-authentication exchange with a - (bootstrapped) ER server. The following figure summarizes the - re-authentication exchange. - -

- - EAP-Initiate/Re-auth - ==================================> - Diameter ERP, cmd code DER - User-Name: Keyname-NAI - EAP-Payload: EAP-Initiate/Re-auth - - <================================== - Diameter ERP, cmd code DEA - EAP-Payload: EAP-Finish/Re-auth - EAP-Master-Session-Key: rMSK - <---------------------- - EAP-Finish/Re-auth -]]> - - - In ERP, the peer sends an EAP-Initiate/Re-auth message to the ER - server via the authenticator. Alternatively, the NAS may send an - EAP-Initiate/Re-auth-Start message to the peer to trigger the start of - ERP. In this case, the peer responds with an EAP-Initiate/Re-auth - message to the NAS. - - If the authenticator does not support ERP (pure support), it discards the EAP packets with - unknown ERP-specific code (EAP-Initiate). The peer may fallback to full - EAP authentication in such case. - - When the authenticator receives an EAP-Initiate/Re-auth message from - the peer, it process as described in with - regards to the EAP state machine. It creates a Diameter EAP Request - message following the general process of Diameter - EAP, with the following differences: - The Application Id in the header is set to Diameter ERP (code TBD - TBD IANA). - - The value in Auth-Application-Id AVP is also set to Diameter ERP - Application. - - The keyName-NAI attribute from ERP message is used to create the - content of User-Name AVP and Destination-Realm AVP. - - FFS: What about Session-ID AVP -- in case of re-auth at the - same place, and in case of handover? - - The Auth-Request-Type AVP content is set to [Editor's note: - FFS]Do we really do authorization with Diameter ERP ? -- need - to pass the authorization attrs to the ER server in that case. Idea - FFS: we do authorization only for explicit bootstrapping - exchanges.... - - The EAP-Payload AVP contains the ERP message, - EAP-Initiate/Re-Auth. - Then this ERP/DER message is sent as described in . - - The ER server receives and processes this request as described in - . It then creates a Diameter answer - ERP/DEA, following the general processing described in , with the following differences: - The Application Id in the header is set to Diameter ERP (code - TBDTBD IANA). - - The value in Auth-Application-Id AVP is also set to Diameter ERP - Application. - - The Result-Code AVP is set to version -00 stated a SHOULD - here, not sure why ? an error value in case ERP - authentication fails, or to DIAMETER_SUCCESS if ERP is - successful. - - The EAP-Payload AVP contains the ERP message, - EAP-Finish/Re-auth. - - In case of successful authentication, the EAP-Master-Session-Key - AVP contains the Re-authentication Master Session Key (rMSK) derived - by ERP. - - What about all the authorization attributes? If we want to - include them, they have to be present on the ER server... - - - When the authenticator receives this ERP/DEA answer, it processes it - as described in Diameter EAP and : the content of EAP-Payload AVP content is - forwarded to the peer, and the content of EAP-Master-Session-Key AVP is - used as a shared secret for Secure Association Protocol. -

- -

- We define a new Diameter application in this document, Diameter ERP - Application, with an Application Id value of TBDTBD IANA. - Diameter nodes conforming to this specification in the role of ER server - MUST advertise support by including an Auth-Application-Id AVP with a - value of Diameter ERP Application in the of the - Capabilities-Exchange-Request and Capabilities-Exchange-Answer commands, - as described in . - - The primary use of the Diameter ERP Application Id is to ensure - proper routing of the messages, and that the nodes that advertise the - support for this application do understand the new AVPs defined in - section , although these AVP have the 'M' - flag cleared. -

- -

- This specification defines the following new AVPs. FFS: to - align with draft-wu-dime-local-keytran-02 if it becomes a WG - item - -

- The ERP-RK-Request AVP (AVP Code TBDTBD IANA) is of - type grouped AVP. This AVP is used by the ER server to indicate its - willingness to act as ER server for a particular session. - - This AVP has the M and V bits cleared. - -

- - { ERP-Realm } - * [ AVP ] -]]> - -

- -

- The ERP-Realm AVP (AVP Code TBDTBD IANA) is of type - DiameterIdentity. It contains the name of the realm in which the ER - server is located. - - FFS: We may re-use Origin-Realm here instead? On the other - hand, ERP-Realm may be useful if the ER server is not in a third-party - realm, if this is possible. - - This AVP has the M and V bits cleared. -

- -

- The ERP-RK-Answer AVP (AVP Code TBDTBD IANA) is of - type grouped AVP. It is used by the home EAP server to provide ERP - root key material to the ER server. - - This AVP has the M and V bits cleared. - -

- - { ERP-RK } - { ERP-RK-Name } - { ERP-RK-Lifetime } - * [ AVP ] -]]> - -

- -

- The ERP-RK AVP (AVP Code TBDTBD IANA) is of type - OctetString. It contains the root key (either rRK or rDSRK) sent by - the home EAP server to the ER server, in answer to request containing - an ERP-RK-Request AVP. How this material is derived and used is - specified in . - - Can we re-use EAP-Master-Session-Key here instead? Must check - the exact definition... - - This AVP has the M and V bits cleared. -

- -

- The ERP-RK-Name AVP (AVP Code TBDTBD IANA) is of type - OctetString. This AVP contains the EMSKname which identifies the - keying material. How this name is derived is beyond the scope of this - document and defined in . - - Can we re-use EAP-Key-Name here instead ? - - This AVP has the M and V bits cleared. -

- -

- The ERP-RK-Lifetime AVP (AVP Code TBDTBD IANA) is of - type Unsigned32 do we really need 64 as in -00 ? 2^32 secs is - already more than 100 years, which is too long for a key lifetime - ! and contains the root key material remaining lifetime in - seconds. It MUST not be greater than the remaining lifetime of the - EMSK it is derived from. FFS: is it better to pass an absolute - value here, for example expiration date? How to express it then (TZ, - ...)? Synchronization problems? - - This AVP has the M and V bits cleared. -

- -

- We do not define any new command in this specification. We reuse the - Diameter-EAP-Request and Diameter-EAP-Answer commands defined in . - - Since the original ABNF of these commands allow other optional AVPs - ("* [ AVP ]"), and the new AVPs defined in this specification do not - have the 'M' flag set, the ABNF does not need any change. Anyway, a - Diameter node that advertizes support for the Diameter ERP application - MUST support the new AVPs defined in this specification. - -

- - -

- -

- This document does not address some known issues in Diameter ERP - mechanism. The authors would like to hear ideas about how to address - them. - - The main issue is the use of ERP for authentication after a handover - of the peer to a new authenticator (or different authenticator port). - Diameter ERP is not meant to be a mobility protocol. A number of issues - appear when we try to do handover in Diameter ERP (alone): how to manage - the Session-Id AVP; how does the ER server provide the Authorization - AVPs; how does the peer learn the ERP domain of the new authenticator; - how does the home server reachs the peer to for example terminate the - session; and so on... Therefore, the management of the session for a - mobile peer is not (yet) addressed in this document. It must be studied - how Diameter ERP can be for example used in conjunction with a mobility - application (Diameter MIP4, Diameter MIP6) to support the optimized - re-authentication in such situation. - - Another issue concerns the case where the home realm contains several - EAP servers. In multi rounds full EAP authentication, the - Destination-Host AVP provides the solution to reach the same server - across the exchanges. Only this server possess the EMSK for the session. - In case of explicit bootstrapping, the ER server must therefore be able - to reach the correct server to request the DSRK. A solution might - consist in saving the Origin-Host AVP of all successful EAP/DEA in the - ER server, which is a bit similar to the implicit bootstrapping scenario - described here -- only we save the server name instead of the root key, - and we must then be able to match the DSRK with the user name. - - Finally, this document currently lacks a description of what happens - when a Re-Auth-Request is received for a peer on the authenticator. -

- -

- Hannes Tschofenig wrote the initial draft for this document and - provided useful reviews. - - Vidya Narayanan reviewed a rough draft version of the document and - found some errors. - - Lakshminath Dondeti contributed to the early versions of the - document. - - Many thanks to these people! -

- -

- This document requires IANA registration of the following new - elements in the Authentication, - Authorization, and Accounting (AAA) Parameters registries. - -

- This specification requires IANA to allocate a new value "Diameter - ERP" in the "Application IDs" registry created by in . - -

- - -

- -

- This specification requires IANA to allocate new values from the - "AVP Codes" registry defined in for the - following AVPs: - ERP-RK-Request - - ERP-Realm - - ERP-RK-Answer - - ERP-RK - - ERP-RK-Name - - ERP-RK-Lifetime - These AVPs are defined in section . -

- -

- The security considerations from the following RFC apply here: , , , , and . - - FFS: Do we really respect these security considerations with - the mechanism we describe here? Is it safe to use ERP-RK-Request / - Answer AVPs? What is the worst case? - - EAP channel bindings may be necessary to ensure that the Diameter - client and the server are in sync regarding the key Requesting Entity's - Identity. Specifically, the Requesting Entity advertises its identity - through the EAP lower layer, and the user or the EAP peer communicates - that identity to the EAP server (and the EAP server communicates that - identity to the Diameter server) via the EAP method for user/peer to - server verification of the Requesting Entity's Identity.Editor: I - really don't understand this paragraph ^^'... -

- - - - - &RFC2119; - - &RFC3588; - - &RFC4072; - - &RFC5295; - - &RFC5296; - - &RFC3748; - - - - &RFC4187; - - &RFC5247; - - &I-D.ietf-hokey-key-mgm; - - &I-D.wu-dime-local-keytran; - - &I-D.ietf-dime-app-design-guide; - - - diff -r 1c9b16ee3039 -r 409fb7bb22b7 draft-ietf-dime-erp-03.xml --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/draft-ietf-dime-erp-03.xml Thu Oct 08 16:29:46 2009 +0900 @@ -0,0 +1,877 @@ + + + + + + + + + + + + + + +]> + + + + + + + + + + + + + + + + + + Diameter support for EAP + Re-authentication Protocol (ERP) + + + Orange Labs + +

+ + 38-40 rue du general Leclerc + + Issy-Les-Moulineaux + + 92794 + + France + + + julien.bournelle@orange-ftgroup.com +

+ + + + Orange Labs + +

+ + 38-40 rue du general Leclerc + + Issy-Les-Moulineaux + + 92794 + + France + + + lionel.morand@orange-ftgroup.com +

+ + + + NICT + +

+ + 4-2-1 Nukui-Kitamachi + + Tokyo + + 184-8795 + + Koganei, Japan + + + sdecugis@nict.go.jp +

+ + + + Huawei Technologies Co., + Ltd + +

+ + Site B, Floor 12F, Huihong Mansion, No.91 Baixia + Rd. + + Nanjing + + 210001 + + China + + + sunseawq@huawei.com +

+ + + + Network Zen + +

+ + 1310 East Thomas Street + + #306 + + Seattle + + Washington + + 98102 + + USA + + + +1 (206) 377-9035 + + gwz@net-zen.net +

+ + + + + Operations & Management + + Diameter Maintenance and Extensions (DIME) + + Internet-Draft + + EAP + + Diameter + + Re-authentication + + inter-authenticator roaming + + + EAP Re-authentication Protocol (ERP) defines extensions to the + Extensible Authentication Protocol (EAP) to support efficient + re-authentication between the peer and an EAP Re-authentication (ER) + server through a compatible authenticator. This document specifies + Diameter support for ERP. It defines a new Diameter ERP application to + transport ERP messages between ER authenticator and ER server, and a set + of new AVPs that can be used to transport the cryptographic material + needed by the re-authentication server. + + + + +

+ defines the EAP Re-authentication + Protocol (ERP). It consists in the following steps: + Bootstrapping: a root key for re-authentication is derived from + the Extended Master Session Key (EMSK) created during EAP + authentication . This root key is + transported from the EAP server to the ER server. + + Re-authentication: a one-round-trip exchange between the peer and + the ER server, resulting in mutual authentication. To accomplish the + EAP reauthentication functionality, ERP defines two new EAP codes - + EAP-Initiate and EAP-Finish. + + + This document defines how Diameter transports the ERP messages + (Re-authentication step). For this purpose, we define a new Application + Id for ERP, and re-use the Diameter EAP commands (DER/DEA). + + This document also discusses the distribution of the root key + (bootstrapping step), either during the initial EAP authentication + (implicit bootstrapping) or during the first ERP exchange (explicit + bootstrapping). Security considerations for this key distribution are + detailed in . +

+ +

+ This document uses terminology defined in , , , and . + + "Root key" (RK) or "bootstrapping material" refer to the rRK or rDSRK + derived from an EMSK, depending on the location of the ER server in home + or foreign domain. + + We use the notation "ERP/DER" in this document to refer to a + Diameter-EAP-Request command with its Application Id set to Diameter ERP + application. Similarly, we use the "ERP/DEA", "EAP/DER", and + "EAP/DEA". + +

+ The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in . +

+ +

+ This document makes the following assumptions. + + The Home EAP server of a peer that wants to use ERP is extended to + support: + Cryptographic operations needed to derive the ERP root key from + the EMSK. By deriving the ERP root key for a specific domain, the + home EAP server implicitly authorizes the use of ERP within this + domain. + + Diameter operations needed to include this root key in a response + message, when a request for this root key was received in a request + message. The two AVP that contain the request for and the root key + material are defined in this document. + + (recommended) Ability to answer a DER message with EAP-Payload + containing an explicit bootstrapping ERP message. + + + The Authenticator (NAS) is extended to support: + Allow the new ERP command codes (EAP-Initiate and EAP-Finish) in + its EAP pass-through mode. + + (optional) Send the EAP-Initiate/Re-Auth-Start message + + (optional) Provide the local domain name via lower layer specific + mechanism or via TLV in the EAP-Initiate/Re-Auth-Start message. + + Encapsulate ERP message and receive corresponding Diameter + answer, as described in this document. + + + If one of the components does not match these assumptions, the ERP + mechanism will fail. In such situation, a full EAP authentication may be + attempted as a fallback mechanism. + + We consider at most one logical ER server entity in a domain. If + several physical servers are deployed for robustness, a replication + mechanism must be deployed to synchronize the ERP states (root keys + FFS: authorization attributes ) between these servers. This + replication mechanism is out of the scope of this document. If several + ER servers are deployed in the domain, we assume that they can be used + interchangeably. +

+ +

+ The following figure shows the components involved in ERP, and their + interactions. + +

+ |Authenticator|<=======>| ER server | <---> | EAP | + +-------------+ +-----------+ | server | + +--------+ + (*) Diameter EAP application, + explicit bootstraping scenario only.]]> + + + The ER server is located either in the home domain (same as EAP + server) or in the visited domain (same as authenticator, when it differs + from the home domain). Can the ER server be located in a third + domain (ex: broker's) according to ERP mechanism? + + When the peer initiates an ERP exchange, the authenticator creates a + Diameter-EAP-Request message, as described in Diameter EAP application + . The Application Id of the message is set + to Diameter ERP application (code: TBD TBD IANA) in the + message. The exact processing to generate the ERP/DER message is + detailed in section . + + If there is an ER server in the same domain as the authenticator + (local domain), Diameter routing MUST SHOULD ? FFS... be + configured so that this ERP/DER message reachs this server, even if the + Destination-Realm is not the local domain. + + If there is no local ER server, the message is routed according to + its Destination-Realm AVP content, extracted from the realm component of + the keyName-NAI attribute. As specified in , this realm is the home domain of the peer in + case of bootstrapping exchange ('B' flag is set in ERP message) or the + domain of the bootstrapped ER server otherwise This actually might + allow the ER server to be in a third party realm. + + If no ER server is available in the home domain either, the ERP/DER + message cannot be delivered, and an error DIAMETER_UNABLE_TO_DELIVER is + generated as specified in and returned to + the authenticator. The authenticator may cache this information (with + limited duration) to avoid further attempts for ERP with this realm. It + may also fallback to full EAP authentication to authenticate the + peer. + + When an ER server receives the ERP/DER message, it searches its local + database for a root key and authorization state ? matching + the keyName part of the User-Name AVP. If such key is found, the ER + server processes the ERP message as described in then creates the ERP/DEA answer as described in + . The rMSK is included in this + answer. + + Finally, the authenticator extracts the rMSK from the ERP/DEA as + described in , and forwards the content of + the EAP-Payload AVP, the EAP-Finish/Re-Auth message, to the peer. + + If the EAP-Initiate/Re-Auth message has its 'B' flag set + (Bootstrapping exchange), the ER server should not possess the root key + in its local database This may not be true in future RFC5296bis + ?. In this case, the ER server acts as a proxy, and forwards the + message to the home EAP server after changing its Application Id to + Diameter EAP and adding an AVP to request the root key. See section + for more detail on this + process. +

+ +

+ The bootstrapping process involves the home EAP server and the ER + server, but also impacts the peer and the authenticator. In ERP, the + peer must derive the same keying material as the ER server. To achieve + this, it must learn the domain name of the ER server. How this + information is acquired is outside the scope of this specification, but + it may involves that the authenticator is configured to advertize this + domain name, especially in the case of re-authentication after a + handover. + + The bootstrapping of an ER server with a given root key happens + either during the initial EAP authentication of the peer when the EMSK + -- from which the root key is derived -- is created, during the first + re-authentication, or sometime between those events. We only consider + the first two possibilities in this specification, in the following + subsections. + +

+ Bootstrapping the ER server during the initial EAP authentication + (also known as implicit bootstrapping) offers the advantage that the + server is immediatly available for re-authentication of the peer, thus + minimizing the re-authentication delay. On the other hand, it is + possible that only a small number of peers will use re-authentication + in the visited domain. Deriving and caching key material for all the + peers (for example, for the peers that do not support ERP) is a waste + of resources and SHOULD be avoided. + + To achieve implicit bootstrapping, the ER server must act as a + Diameter EAP Proxy as defined in Diameter Base Protocol , and routing must be configured so that + Diameter messages of a full EAP authentication are routed through this + proxy. The figure bellow captures this mechanism. + +

+ + Diameter EAP/DER + (EAP-Response) + -------------------------> + Diameter EAP/DER + (EAP-Response) + (ERP-RK-Request) + + <==================================================> + Multi-round Diameter EAP exchanges, unmodified + + <------------------------- + Diameter EAP/DEA + (EAP-Success) + (MSK) + (ERP-RK-Answer) + <------------------------- + Diameter EAP/DEA + (EAP-Success) + (MSK) + [ERP-Realm] +]]> + + + The ER server proxies the first DER of the full EAP authentication + and adds the ERP-RK-Request AVP inside, if this AVP is not already in + the message (which might happen if there are ER servers in the visited + and the home domains), then forwards the request. + + If the EAP server does not support ERP extensions, it will simply + ignore this grouped AVP and continue as specified in . If the server supports the ERP extensions, + it caches the ERP-Realm value with the session, and continues the EAP + authentication. When the authentication is complete, if it is + successful and the EAP method generated an EMSK, the server MUST + compute the rRK or rDSRK (depending on the value of ERP-Realm) as + specified in , and add an ERP-RK-Answer + AVP in the Diameter-EAP-Request message, in addition to the MSK and + EAP-Success payloads. + + When the ER server proxies a Diameter-EAP-Answer message with a + Session-Id corresponding to a message to which it added an + ERP-RK-Answer, and the Result-Code is DIAMETER_SUCCESS, it MUST + examine the message, extract and remove any ERP-RK-Answer AVP from the + message, and save its content. If the message does not contain an + ERP-RK-Answer AVP, the ER server MAY save this information to avoid + possible subsequent re-authentication attempts for this session. In + any case, the information stored SHOULD NOT have a lifetime greater + than the EMSK lifetime how does the ER server knows the EMSK + lifetime, if there is no ERP-RK-Answer? What is the lifetime of the + MSK for example? + + If the ER server is successfully bootstrapped, it MAY also add the + ERP-Realm AVP after removing the ERP-RK-Answer AVP in the EAP/DEA + message. This could be used by the authenticator to notify the peer + that ERP is bootstrapped, with the ER domain information. How this + information can be transmitted to the peer is outside the scope of + this document. Is it possible? It would be useful... +

+ +

+ Bootstrapping the ER server during the first re-authentication + (also known as explicit bootstrapping) offers several advantages: it + saves resources, since we generate and cache only root key that we + actually need, and it can accomodate inter-domain handovers or ER + servers that loose their state (for example after reboot) This + last point might not be true currently, since the peer would not issue + a bootstrapping exchange... But this might change also with RFC5296bis + AFAIU. On the other hand, the first re-authentication with the + ER server requires a one-round-trip exchange with the home EAP server, + which adds some delay to the process (but it is more efficient than a + full EAP authentication in any case). It also requires some + synchronization between the peer and the visited domain: since the ERP + message is differentand the root key used also ? for + explicit bootstrapping exchange and for normal re-authentication, + explicit bootstrapping should not be used if implicit bootstrapping + was already performed. + + What should we do if the ER server receives an explicit + bootstrapping request but already possess the rDSRK? Can it answer + without going to the home server? That would be simpler -- planned in + rfc5296bis ? + + The ER server receives the ERP/DER message containing the + EAP-Initiate/Re-Auth message with the 'B' flag set. It proxies this + message, and do the following processing in addition to standard proxy + operations: + Change the Application Id in the header of the message to + Diameter EAP Application (code 5). + + Change the content of Application-Auth-Id accordingly. Is + it better to leave it unmodified? + + Add the ERP-RK-Request AVP, which contains the name of the + domain where the ER server is located. + + Add the Destination-Host to reach the appropriate EAP + server, the one with the EMSK. How does the ER server know this + information ? + Then the server forwards the EAP/DER request, which is routed + to the home EAP server. + + If the home EAP server does not support ERP extensions, it replies + with an error since the encapsulated EAP-Initiate/Re-auth command is + not understood. Otherwise, it processes the ERP request as described + in . In particular, it includes the + Domain-Name TLV attribute with the content from the ERP-Realm AVP. It + creates the EAP/DEA reply message following standard processing from + (in particular EAP-Master-Session-Key + AVP is used to transport the rMSK), and includes the ERP-RK-Answer + AVP. What about authorization AVPs ? + + The ER server receives this EAP/DEA and proxies it as follow, in + addition to standard proxy operations: + Set the Application Id back to Diameter ERP (code TBDTBD + IANA) + + Extract and cache the content of the ERP-RK-Answer. And + authorization AVPs ? + The DEA is then forwarded to the authenticator, that can use + the rMSK as described in . + + The figure below captures this proxy behavior: + +

+ + Diameter ERP/DER + (EAP-Initiate) + ------------------------> + Diameter EAP/DER + (EAP-Initiate) + (ERP-RK-Request) + + <------------------------ + Diameter EAP/DEA + (EAP-Finish) + (ERP-RK-Answer) + (rMSK) + <---------------------- + Diameter ERP/DEA + (EAP-Finish) + (rMSK) +]]> + +

+ +

+ This section describes in detail a re-authentication exchange with a + (bootstrapped) ER server. The following figure summarizes the + re-authentication exchange. + +

+ + EAP-Initiate/Re-auth + ==================================> + Diameter ERP, cmd code DER + User-Name: Keyname-NAI + EAP-Payload: EAP-Initiate/Re-auth + + <================================== + Diameter ERP, cmd code DEA + EAP-Payload: EAP-Finish/Re-auth + EAP-Master-Session-Key: rMSK + <---------------------- + EAP-Finish/Re-auth +]]> + + + In ERP, the peer sends an EAP-Initiate/Re-auth message to the ER + server via the authenticator. Alternatively, the NAS may send an + EAP-Initiate/Re-auth-Start message to the peer to trigger the start of + ERP. In this case, the peer responds with an EAP-Initiate/Re-auth + message to the NAS. + + If the authenticator does not support ERP (pure support), it discards the EAP packets with + unknown ERP-specific code (EAP-Initiate). The peer may fallback to full + EAP authentication in such case. + + When the authenticator receives an EAP-Initiate/Re-auth message from + the peer, it process as described in with + regards to the EAP state machine. It creates a Diameter EAP Request + message following the general process of Diameter + EAP, with the following differences: + The Application Id in the header is set to Diameter ERP (code TBD + TBD IANA). + + The value in Auth-Application-Id AVP is also set to Diameter ERP + Application. + + The keyName-NAI attribute from ERP message is used to create the + content of User-Name AVP and Destination-Realm AVP. + + FFS: What about Session-ID AVP -- in case of re-auth at the + same place, and in case of handover? + + The Auth-Request-Type AVP content is set to [Editor's note: + FFS]Do we really do authorization with Diameter ERP ? -- need + to pass the authorization attrs to the ER server in that case. Idea + FFS: we do authorization only for explicit bootstrapping + exchanges.... + + The EAP-Payload AVP contains the ERP message, + EAP-Initiate/Re-Auth. + Then this ERP/DER message is sent as described in . + + The ER server receives and processes this request as described in + . It then creates a Diameter answer + ERP/DEA, following the general processing described in , with the following differences: + The Application Id in the header is set to Diameter ERP (code + TBDTBD IANA). + + The value in Auth-Application-Id AVP is also set to Diameter ERP + Application. + + The Result-Code AVP is set to version -00 stated a SHOULD + here, not sure why ? an error value in case ERP + authentication fails, or to DIAMETER_SUCCESS if ERP is + successful. + + The EAP-Payload AVP contains the ERP message, + EAP-Finish/Re-auth. + + In case of successful authentication, the EAP-Master-Session-Key + AVP contains the Re-authentication Master Session Key (rMSK) derived + by ERP. + + What about all the authorization attributes? If we want to + include them, they have to be present on the ER server... + + + When the authenticator receives this ERP/DEA answer, it processes it + as described in Diameter EAP and : the content of EAP-Payload AVP content is + forwarded to the peer, and the content of EAP-Master-Session-Key AVP is + used as a shared secret for Secure Association Protocol. +

+ +

+ We define a new Diameter application in this document, Diameter ERP + Application, with an Application Id value of TBDTBD IANA. + Diameter nodes conforming to this specification in the role of ER server + MUST advertise support by including an Auth-Application-Id AVP with a + value of Diameter ERP Application in the of the + Capabilities-Exchange-Request and Capabilities-Exchange-Answer commands, + as described in . + + The primary use of the Diameter ERP Application Id is to ensure + proper routing of the messages, and that the nodes that advertise the + support for this application do understand the new AVPs defined in + section , although these AVP have the 'M' + flag cleared. +

+ +

+ This specification defines the following new AVPs. FFS: to + align with draft-wu-dime-local-keytran-02 if it becomes a WG + item + +

+ The ERP-RK-Request AVP (AVP Code TBDTBD IANA) is of + type grouped AVP. This AVP is used by the ER server to indicate its + willingness to act as ER server for a particular session. + + This AVP has the M and V bits cleared. + +

+ + { ERP-Realm } + * [ AVP ] +]]> + +

+ +

+ The ERP-Realm AVP (AVP Code TBDTBD IANA) is of type + DiameterIdentity. It contains the name of the realm in which the ER + server is located. + + FFS: We may re-use Origin-Realm here instead? On the other + hand, ERP-Realm may be useful if the ER server is not in a third-party + realm, if this is possible. + + This AVP has the M and V bits cleared. +

+ +

+ The ERP-RK-Answer AVP (AVP Code TBDTBD IANA) is of + type grouped AVP. It is used by the home EAP server to provide ERP + root key material to the ER server. + + This AVP has the M and V bits cleared. + +

+ + { ERP-RK } + { ERP-RK-Name } + { ERP-RK-Lifetime } + * [ AVP ] +]]> + +

+ +

+ The ERP-RK AVP (AVP Code TBDTBD IANA) is of type + OctetString. It contains the root key (either rRK or rDSRK) sent by + the home EAP server to the ER server, in answer to request containing + an ERP-RK-Request AVP. How this material is derived and used is + specified in . + + Can we re-use EAP-Master-Session-Key here instead? Must check + the exact definition... + + This AVP has the M and V bits cleared. +

+ +

+ The ERP-RK-Name AVP (AVP Code TBDTBD IANA) is of type + OctetString. This AVP contains the EMSKname which identifies the + keying material. How this name is derived is beyond the scope of this + document and defined in . + + Can we re-use EAP-Key-Name here instead ? + + This AVP has the M and V bits cleared. +

+ +

+ The ERP-RK-Lifetime AVP (AVP Code TBDTBD IANA) is of + type Unsigned32 do we really need 64 as in -00 ? 2^32 secs is + already more than 100 years, which is too long for a key lifetime + ! and contains the root key material remaining lifetime in + seconds. It MUST not be greater than the remaining lifetime of the + EMSK it is derived from. FFS: is it better to pass an absolute + value here, for example expiration date? How to express it then (TZ, + ...)? Synchronization problems? + + This AVP has the M and V bits cleared. +

+ +

+ We do not define any new command in this specification. We reuse the + Diameter-EAP-Request and Diameter-EAP-Answer commands defined in . + + Since the original ABNF of these commands allow other optional AVPs + ("* [ AVP ]"), and the new AVPs defined in this specification do not + have the 'M' flag set, the ABNF does not need any change. Anyway, a + Diameter node that advertizes support for the Diameter ERP application + MUST support the new AVPs defined in this specification. + +

+ + +

+ +

+ This document does not address some known issues in Diameter ERP + mechanism. The authors would like to hear ideas about how to address + them. + + The main issue is the use of ERP for authentication after a handover + of the peer to a new authenticator (or different authenticator port). + Diameter ERP is not meant to be a mobility protocol. A number of issues + appear when we try to do handover in Diameter ERP (alone): how to manage + the Session-Id AVP; how does the ER server provide the Authorization + AVPs; how does the peer learn the ERP domain of the new authenticator; + how does the home server reachs the peer to for example terminate the + session; and so on... Therefore, the management of the session for a + mobile peer is not (yet) addressed in this document. It must be studied + how Diameter ERP can be for example used in conjunction with a mobility + application (Diameter MIP4, Diameter MIP6) to support the optimized + re-authentication in such situation. + + Another issue concerns the case where the home realm contains several + EAP servers. In multi rounds full EAP authentication, the + Destination-Host AVP provides the solution to reach the same server + across the exchanges. Only this server possess the EMSK for the session. + In case of explicit bootstrapping, the ER server must therefore be able + to reach the correct server to request the DSRK. A solution might + consist in saving the Origin-Host AVP of all successful EAP/DEA in the + ER server, which is a bit similar to the implicit bootstrapping scenario + described here -- only we save the server name instead of the root key, + and we must then be able to match the DSRK with the user name. + + Finally, this document currently lacks a description of what happens + when a Re-Auth-Request is received for a peer on the authenticator. +

+ +

+ Hannes Tschofenig wrote the initial draft for this document and + provided useful reviews. + + Vidya Narayanan reviewed a rough draft version of the document and + found some errors. + + Lakshminath Dondeti contributed to the early versions of the + document. + + Many thanks to these people! +

+ +

+ This document requires IANA registration of the following new + elements in the Authentication, + Authorization, and Accounting (AAA) Parameters registries. + +

+ This specification requires IANA to allocate a new value "Diameter + ERP" in the "Application IDs" registry created by in . + +

+ + +

+ +

+ This specification requires IANA to allocate new values from the + "AVP Codes" registry defined in for the + following AVPs: + ERP-RK-Request + + ERP-Realm + + ERP-RK-Answer + + ERP-RK + + ERP-RK-Name + + ERP-RK-Lifetime + These AVPs are defined in section . +

+ +

+ The security considerations from the following RFC apply here: , , , , and . + + FFS: Do we really respect these security considerations with + the mechanism we describe here? Is it safe to use ERP-RK-Request / + Answer AVPs? What is the worst case? + + EAP channel bindings may be necessary to ensure that the Diameter + client and the server are in sync regarding the key Requesting Entity's + Identity. Specifically, the Requesting Entity advertises its identity + through the EAP lower layer, and the user or the EAP peer communicates + that identity to the EAP server (and the EAP server communicates that + identity to the Diameter server) via the EAP method for user/peer to + server verification of the Requesting Entity's Identity.Editor: I + really don't understand this paragraph ^^'... +

+ + + + + &RFC2119; + + &RFC3588; + + &RFC4072; + + &RFC5295; + + &RFC5296; + + &RFC3748; + + + + &RFC4187; + + &RFC5247; + + &I-D.ietf-hokey-key-mgm; + + &I-D.wu-dime-local-keytran; + + &I-D.ietf-dime-app-design-guide; + + +