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diff --git a/doc/rfc/rfc4072.txt b/doc/rfc/rfc4072.txt new file mode 100644 index 0000000..dd0b3a1 --- /dev/null +++ b/doc/rfc/rfc4072.txt @@ -0,0 +1,1851 @@ + + + + + + +Network Working Group P. Eronen, Ed. +Request for Comments: 4072 Nokia +Category: Standards Track T. Hiller + Lucent Technologies + G. Zorn + Cisco Systems + August 2005 + + + Diameter Extensible Authentication Protocol (EAP) Application + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2005). + +Abstract + + The Extensible Authentication Protocol (EAP) provides a standard + mechanism for support of various authentication methods. This + document defines the Command-Codes and AVPs necessary to carry EAP + packets between a Network Access Server (NAS) and a back-end + authentication server. + +Table of Contents + + 1. Introduction ...................................................2 + 1.1. Conventions Used in This Document ........................3 + 2. Extensible Authentication Protocol Support in Diameter .........3 + 2.1. Advertising Application Support ..........................3 + 2.2. Protocol Overview ........................................4 + 2.3. Sessions and NASREQ Interaction ..........................6 + 2.3.1. Scenario 1: Direct Connection .....................7 + 2.3.2. Scenario 2: Direct Connection with Redirects ......8 + 2.3.3. Scenario 3: Direct EAP, Authorization via Agents ..9 + 2.3.4. Scenario 4: Proxy Agents .........................10 + 2.4. Invalid Packets .........................................10 + 2.5. Retransmission ..........................................11 + 2.6. Fragmentation ...........................................12 + 2.7. Accounting ..............................................12 + 2.8. Usage Guidelines ........................................13 + + + +Eronen, et al. Standards Track [Page 1] + +RFC 4072 Diameter EAP Application August 2005 + + + 2.8.1. User-Name AVP ....................................13 + 2.8.2. Conflicting AVPs .................................13 + 2.8.3. Displayable Messages .............................14 + 2.8.4. Role Reversal ....................................14 + 2.8.5. Identifier Space .................................14 + 3. Command-Codes .................................................14 + 3.1. Diameter-EAP-Request (DER) Command ......................15 + 3.2. Diameter-EAP-Answer (DEA) Command .......................16 + 4. Attribute-Value Pairs .........................................18 + 4.1. New AVPs ................................................18 + 4.1.1. EAP-Payload AVP ..................................18 + 4.1.2. EAP-Reissued-Payload AVP .........................18 + 4.1.3. EAP-Master-Session-Key AVP .......................19 + 4.1.4. EAP-Key-Name AVP .................................19 + 4.1.5. Accounting-EAP-Auth-Method AVP ...................19 + 5. AVP Occurrence Tables .........................................19 + 5.1. EAP Command AVP Table ...................................20 + 5.2. Accounting AVP Table ....................................21 + 6. RADIUS/Diameter Interactions ..................................22 + 6.1. RADIUS Request Forwarded as Diameter Request ............22 + 6.2. Diameter Request Forwarded as RADIUS Request ............23 + 6.3. Accounting Requests .....................................24 + 7. IANA Considerations ...........................................24 + 8. Security Considerations .......................................24 + 8.1. Overview ................................................24 + 8.2. AVP Editing .............................................26 + 8.3. Negotiation Attacks .....................................27 + 8.4. Session Key Distribution ................................28 + 8.5. Privacy Issues ..........................................28 + 8.6. Note about EAP and Impersonation ........................29 + 9. Acknowledgements ..............................................29 + 10. References ....................................................30 + 10.1. Normative References ....................................30 + 10.2. Informative References ..................................30 + +1. Introduction + + The Extensible Authentication Protocol (EAP), defined in [EAP], is an + authentication framework which supports multiple authentication + mechanisms. EAP may be used on dedicated links, switched circuits, + and wired as well as wireless links. + + To date, EAP has been implemented with hosts and routers that connect + via switched circuits or dial-up lines using PPP [RFC1661], IEEE 802 + wired switches [IEEE-802.1X], and IEEE 802.11 wireless access points + [IEEE-802.11i]. EAP has also been adopted for IPsec remote access in + IKEv2 [IKEv2]. + + + + +Eronen, et al. Standards Track [Page 2] + +RFC 4072 Diameter EAP Application August 2005 + + + This document specifies the Diameter EAP application that carries EAP + packets between a Network Access Server (NAS) working as an EAP + Authenticator and a back-end authentication server. The Diameter EAP + application is based on the Diameter Network Access Server + Application [NASREQ] and is intended for environments similar to + NASREQ. + + In the Diameter EAP application, authentication occurs between the + EAP client and its home Diameter server. This end-to-end + authentication reduces the possibility for fraudulent authentication, + such as replay and man-in-the-middle attacks. End-to-end + authentication also provides a possibility for mutual authentication, + which is not possible with PAP and CHAP in a roaming PPP environment. + + The Diameter EAP application relies heavily on [NASREQ], and in + earlier versions was part of the Diameter NASREQ application. It can + also be used in conjunction with NASREQ, selecting the application + based on the user authentication mechanism (EAP or PAP/CHAP). The + Diameter EAP application defines new Command-Codes and Attribute- + Value Pairs (AVPs), and can work together with RADIUS EAP support + [RFC3579]. + +1.1. Conventions Used in This Document + + 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 [RFC2119]. + +2. Extensible Authentication Protocol Support in Diameter + +2.1. Advertising Application Support + + Diameter nodes conforming to this specification MUST advertise + support by including the Diameter EAP Application ID value of 5 in + the Auth-Application-Id AVP of the Capabilities-Exchange-Request and + Capabilities-Exchange-Answer command [BASE]. + + If the NAS receives a response with the Result-Code set to + DIAMETER_APPLICATION_UNSUPPORTED [BASE], it indicates that the + Diameter server in the home realm does not support EAP. If possible, + the access device MAY attempt to negotiate another authentication + protocol, such as PAP or CHAP. An access device SHOULD be cautious + when determining whether a less secure authentication protocol will + be used, since this could result from a downgrade attack (see + Section 8.3). + + + + + + +Eronen, et al. Standards Track [Page 3] + +RFC 4072 Diameter EAP Application August 2005 + + +2.2. Protocol Overview + + The EAP conversation between the authenticating peer and the access + device begins with the initiation of EAP within a link layer, such as + PPP [RFC1661] or IEEE 802.11i [IEEE-802.11i]. Once EAP has been + initiated, the access device will typically send a Diameter-EAP- + Request message with an empty EAP-Payload AVP to the Diameter server, + signifying an EAP-Start. + + If the Diameter home server is willing to do EAP authentication, it + responds with a Diameter-EAP-Answer message containing an EAP-Payload + AVP that includes an encapsulated EAP packet. The Result-Code AVP in + the message will be set to DIAMETER_MULTI_ROUND_AUTH, signifying that + a subsequent request is expected. The EAP payload is forwarded by + the access device to the EAP client. This is illustrated in the + diagram below. + + User NAS Server + | | | + | (initiate EAP) | | + |<------------------------------>| | + | | Diameter-EAP-Request | + | | EAP-Payload(EAP Start) | + | |------------------------------->| + | | | + | | Diameter-EAP-Answer | + | Result-Code=DIAMETER_MULTI_ROUND_AUTH | + | | EAP-Payload(EAP Request #1) | + | |<-------------------------------| + | EAP Request #1 | | + |<-------------------------------| | + : : : + : ...continues... : + + The initial Diameter-EAP-Answer in a multi-round exchange normally + includes an EAP-Request/Identity, requesting the EAP client to + identify itself. Upon receipt of the EAP client's EAP-Response, the + access device will then issue a second Diameter-EAP-Request message, + with the client's EAP payload encapsulated within the EAP-Payload + AVP. + + A preferred approach is for the access device to issue the + EAP-Request/Identity message to the EAP client, and forward the + EAP-Response/Identity packet, encapsulated within the EAP-Payload + AVP, as a Diameter-EAP-Request to the Diameter server (see the + diagram below). This alternative reduces the number of Diameter + message round trips. When the EAP-Request/Identity message is issued + by the access device, it SHOULD interpret the EAP-Response/Identity + + + +Eronen, et al. Standards Track [Page 4] + +RFC 4072 Diameter EAP Application August 2005 + + + packet returned by the authenticating peer, and copy its value to a + User-Name AVP in Diameter-EAP-Request. This is useful in roaming + environments, since the Destination-Realm is needed for routing + purposes. Note that this alternative cannot be universally employed, + as there are circumstances in which a user's identity is not needed + (such as when authorization occurs based on a calling or called phone + number). + + User NAS Server + | | | + | (initiate EAP) | | + |<------------------------------>| | + | | | + | EAP Request(Identity) | | + |<-------------------------------| | + | | | + | EAP Response(Identity) | | + |------------------------------->| | + | | Diameter-EAP-Request | + | | EAP-Payload(EAP Response) | + | |------------------------------->| + : : : + : ...continues... : + + The conversation continues until the Diameter server sends a + Diameter-EAP-Answer with a Result-Code AVP indicating success or + failure, and an optional EAP-Payload. The Result-Code AVP is used by + the access device to determine whether service is to be provided to + the EAP client. The access device MUST NOT rely on the contents of + the optional EAP-Payload to determine whether service is to be + provided. + + + + + + + + + + + + + + + + + + + + +Eronen, et al. Standards Track [Page 5] + +RFC 4072 Diameter EAP Application August 2005 + + + : ...continued... : + : : : + | EAP Response #N | | + |------------------------------->| | + | | Diameter-EAP-Request | + | | EAP-Payload(EAP Response #N) | + | |------------------------------->| + | | | + | | Diameter-EAP-Answer | + | | Result-Code=DIAMETER_SUCCESS | + | | EAP-Payload(EAP Success) | + | | [EAP-Master-Session-Key] | + | | (authorization AVPs) | + | |<-------------------------------| + | | | + | EAP Success | | + |<-------------------------------| | + + If authorization was requested, a Diameter-EAP-Answer with + Result-Code set to DIAMETER_SUCCESS SHOULD also include the + appropriate authorization AVPs required for the service requested + (see Section 5 and [NASREQ]). In some cases, the home server may not + be able to provide all necessary authorization AVPs; in this case, a + separate authorization step MAY be used as described in + Section 2.3.3. Diameter-EAP-Answer messages whose Result-Code AVP is + set to DIAMETER_MULTI_ROUND_AUTH MAY include authorization AVPs. + + A Diameter-EAP-Answer with successful Result-Code MAY also include an + EAP-Master-Session-Key AVP that contains keying material for + protecting the communication between the user and the NAS. Exactly + how this keying material is used depends on the link layer in + question, and is beyond the scope of this document. + + A home Diameter server MAY request EAP re-authentication by issuing + the Re-Auth-Request [BASE] message to the Diameter client. + + Should an EAP authentication session be interrupted due to a home + server failure, the session MAY be directed to an alternate server, + but the authentication session will have to be restarted from the + beginning. + +2.3. Sessions and NASREQ Interaction + + The previous section introduced the basic protocol between the NAS + and the home server. Since the Diameter-EAP-Answer message may + include a Master Session Key (MSK) for protecting the communication + between the user and the NAS, one must ensure that this key does not + fall into wrong hands. + + + +Eronen, et al. Standards Track [Page 6] + +RFC 4072 Diameter EAP Application August 2005 + + + Basic Diameter security mechanisms (IPsec and TLS) protect Diameter + messages hop-by-hop. Since there are currently no end-to-end + (NAS-to-home server) security mechanisms defined for Diameter, this + section describes possible scenarios on how the messages could be + transport protected using these hop-by-hop mechanisms. + + This list of scenarios is not intended to be exhaustive, and it is + possible to combine them. For instance, the first proxy agent after + the NAS could use redirects as in Scenario 2 to bypass any additional + proxy agents. + +2.3.1. Scenario 1: Direct Connection + + The simplest case is when the NAS contacts the home server directly. + All authorization AVPs and EAP keying material are delivered by the + home server. + + NAS home server + | | + | Diameter-EAP-Request | + | Auth-Request-Type=AUTHORIZE_AUTHENTICATE | + | EAP-Payload(EAP Start) | + |---------------------------------------------------------------->| + | | + | Diameter-EAP-Answer | + | Result-Code=DIAMETER_MULTI_ROUND_AUTH | + | EAP-Payload(EAP Request) | + |<----------------------------------------------------------------| + | | + : ...more EAP Request/Response pairs... : + | | + | Diameter-EAP-Request | + | EAP-Payload(EAP Response) | + |---------------------------------------------------------------->| + | | + | Diameter-EAP-Answer | + | Result-Code=DIAMETER_SUCCESS | + | EAP-Payload(EAP Success) | + | EAP-Master-Session-Key | + | (authorization AVPs) | + |<----------------------------------------------------------------| + + This scenario is the most likely to be used in small networks, or in + cases where Diameter agents are not needed to provide routing or + additional authorization AVPs. + + + + + + +Eronen, et al. Standards Track [Page 7] + +RFC 4072 Diameter EAP Application August 2005 + + +2.3.2. Scenario 2: Direct Connection with Redirects + + In this scenario the NAS uses a redirect agent to locate the home + server. The rest of the session proceeds as before. + + NAS Local redirect agent Home server + | | | + | Diameter-EAP-Request | | + | Auth-Request-Type=AUTHORIZE_AUTHENTICATE | + | EAP-Payload(EAP Start) | | + |------------------------------->| | + | | | + | Diameter-EAP-Answer | + | Redirect-Host=homeserver.example.com | + | Redirect-Host-Usage=REALM_AND_APPLICATION | + |<-------------------------------| | + | : | + | Diameter-EAP-Request : | + | Auth-Request-Type=AUTHORIZE_AUTHENTICATE | + | EAP-Payload(EAP Start) : | + |---------------------------------------------------------------->| + | : | + : ...rest of the session continues as in first case... : + : : : + + The advantage of this scenario is that knowledge of realms and home + servers is centralized to a redirect agent, and it is not necessary + to modify the NAS configuration when, for example, a new roaming + agreement is made. + + + + + + + + + + + + + + + + + + + + + + +Eronen, et al. Standards Track [Page 8] + +RFC 4072 Diameter EAP Application August 2005 + + +2.3.3. Scenario 3: Direct EAP, Authorization via Agents + + In this scenario the EAP authentication is done directly with the + home server (with Auth-Request-Type set to AUTHENTICATE_ONLY), and + authorization AVPs are retrieved from local proxy agents. This + scenario is intended for environments in which the home server cannot + provide all the necessary authorization AVPs to the NAS. + + NAS Local proxy agent Home server + | : | + | Diameter-EAP-Request : | + | Auth-Request-Type=AUTHENTICATE_ONLY | + | EAP-Payload(EAP Start) : | + |---------------------------------------------------------------->| + | : | + | : Diameter-EAP-Answer | + | Result-Code=DIAMETER_MULTI_ROUND_AUTH | + | : EAP-Payload(EAP Request) | + |<----------------------------------------------------------------| + | : | + : ...more EAP Request/Response pairs... : + | : | + | Diameter-EAP-Request : | + | EAP-Payload(EAP Response) : | + |---------------------------------------------------------------->| + | : | + | : Diameter-EAP-Answer | + | : Result-Code=DIAMETER_SUCCESS | + | : EAP-Payload(EAP Success) | + | : EAP-Master-Session-Key | + | : (authorization AVPs) | + |<----------------------------------------------------------------| + | | | + | AA-Request | | + | Auth-Request-Type=AUTHORIZE_ONLY | + | (some AVPs from first session) | | + |------------------------------->| | + | | | + | AA-Answer | | + | Result-Code=DIAMETER_SUCCESS | | + | (authorization AVPs) | | + |<-------------------------------| | + + The NASREQ application is used here for authorization because the + realm-specific routing table supports routing based on application, + not on Diameter commands. + + + + + +Eronen, et al. Standards Track [Page 9] + +RFC 4072 Diameter EAP Application August 2005 + + +2.3.4. Scenario 4: Proxy Agents + + This scenario is the same as Scenario 1, but the NAS contacts the + home server through proxies. Note that the proxies can see the EAP + session keys, thus it is not suitable for environments where proxies + cannot be trusted. + + NAS Local proxy/relay agent Home server + | | | + | Diameter-EAP-Request | | + | Auth-Request-Type=AUTHORIZE_AUTHENTICATE | + | EAP-Payload(EAP Start) | | + |------------------------------->|------------------------------->| + | | | + | | Diameter-EAP-Answer | + | Result-Code=DIAMETER_MULTI_ROUND_AUTH | + | | EAP-Payload(EAP Request) | + |<-------------------------------|<-------------------------------| + | : | + : ...more EAP Request/Response pairs... : + | : | + | Diameter-EAP-Request | | + | EAP-Payload(EAP Response) | | + |------------------------------->|------------------------------->| + | | | + | | Diameter-EAP-Answer | + | | Result-Code=DIAMETER_SUCCESS | + | | EAP-Payload(EAP Success) | + | | EAP-Master-Session-Key | + | | (authorization AVPs) | + |<-------------------------------|<-------------------------------| + +2.4. Invalid Packets + + While acting as a pass-through, the NAS MUST validate the EAP header + fields (Code, Identifier, Length) prior to forwarding an EAP packet + to or from the Diameter server. On receiving an EAP packet from the + peer, the NAS checks the Code (Code 2=Response) and Length fields, + and matches the Identifier value against the current Identifier, + supplied by the Diameter server in the most recently validated EAP + Request. On receiving an EAP packet from the Diameter server + (encapsulated within a Diameter-EAP-Answer), the NAS checks the Code + (Code 1=Request) and Length fields, then updates the current + Identifier value. Pending EAP Responses that do not match the + current Identifier value are silently discarded by the NAS. + + + + + + +Eronen, et al. Standards Track [Page 10] + +RFC 4072 Diameter EAP Application August 2005 + + + Since EAP method fields (Type, Type-Data) are typically not validated + by a NAS operating as a pass-through, despite these checks it is + possible for a NAS to forward an invalid EAP packet to or from the + Diameter server. + + A Diameter server receiving an EAP-Payload AVP that it does not + understand SHOULD determine whether the error is fatal or non-fatal + based on the EAP Type. A Diameter server determining that a fatal + error has occurred MUST send a Diameter-EAP-Answer with a failure + Result-Code and an EAP-Payload AVP encapsulating an EAP Failure + packet. A Diameter server determining that a non-fatal error has + occurred MUST send a Diameter-EAP-Answer with + DIAMETER_MULTI_ROUND_AUTH Result-Code, but no EAP-Payload AVP. To + simplify RADIUS translation, this message MUST also include an + EAP-Reissued-Payload AVP encapsulating the previous EAP Request sent + by the server. + + When receiving a Diameter-EAP-Answer without an EAP-Payload AVP (and + DIAMETER_MULTI_ROUND_AUTH Result-Code), the NAS SHOULD discard the + EAP-Response packet most recently transmitted to the Diameter server + and check whether additional EAP Response packets that match the + current Identifier value have been received. If so, a new EAP + Response packet, if available, MUST be sent to the Diameter server + within an Diameter-EAP-Request. If no EAP Response packet is + available, then the previous EAP Request is resent to the peer, and + the retransmission timer is reset. + + In order to provide protection against Denial of Service (DoS) + attacks, it is advisable for the NAS to allocate a finite buffer for + EAP packets received from the peer, and to discard packets according + to an appropriate policy once that buffer has been exceeded. Also, + the Diameter server is advised to permit only a modest number of + invalid EAP packets within a single session, prior to terminating the + session with DIAMETER_AUTHENTICATION_REJECTED Result-Code. By + default, a value of 5 invalid EAP packets is recommended. + +2.5. Retransmission + + As noted in [EAP], if an EAP packet is lost in transit between the + authenticating peer and the NAS (or vice versa), the NAS will + retransmit. + + It may be necessary to adjust retransmission strategies and + authentication time-outs in certain cases. For example, when a token + card is used, additional time may be required to allow the user to + find the card and enter the token. Since the NAS will typically not + have knowledge of the required parameters, these need to be provided + by the Diameter server. + + + +Eronen, et al. Standards Track [Page 11] + +RFC 4072 Diameter EAP Application August 2005 + + + If a Multi-Round-Time-Out AVP [BASE] is present in a Diameter-EAP- + Answer message that also contains an EAP-Payload AVP, that value is + used to set the EAP retransmission timer for that EAP Request and + that Request alone. + +2.6. Fragmentation + + Using the EAP-Payload AVP, it is possible for the Diameter server to + encapsulate an EAP packet that is larger than the MTU on the link + between the NAS and the peer. Since it is not possible for the + Diameter server to use MTU discovery to ascertain the link MTU, a + Framed-MTU AVP may be included in a Diameter-EAP-Request message in + order to provide the Diameter server with this information. + + A Diameter server having received a Framed-MTU AVP in a + Diameter-EAP-Request message MUST NOT send any subsequent packet in + this EAP conversation containing EAP-Payload AVP whose length exceeds + that specified by the Framed-MTU value, taking the link type + (specified by the NAS-Port-Type AVP) into account. For example, as + noted in [RFC3580] Section 3.10, for a NAS-Port-Type value of IEEE + 802.11, the RADIUS server may send an EAP packet as large as + Framed-MTU minus four (4) octets, taking into account the additional + overhead for the IEEE 802.1X Version (1 octet), Type (1 octet) and + Body Length (2 octets) fields. + +2.7. Accounting + + When a user is authenticated using EAP, the NAS MAY include an + Accounting-Auth-Method AVP [NASREQ] with value 5 (EAP) in + Accounting-Request messages. This document specifies one additional + AVP for accounting messages. One or more Accounting-EAP-Auth-Method + AVPs (see Section 4.1.5) MAY be included in Accounting-Request + messages to indicate the EAP method(s) used to authenticate the user. + + If the NAS has authenticated the user with a locally implemented EAP + method, it knows the method used and SHOULD include it in an + Accounting-EAP-Auth-Method AVP. + + If the authentication was done using Diameter-EAP-Request/Answer + messages, the Diameter server SHOULD include one or more + Accounting-EAP-Auth-Method AVPs in Diameter-EAP-Answer packets with a + successful result code. In this case, the NAS SHOULD include these + AVPs in Accounting-Request messages. + + + + + + + + +Eronen, et al. Standards Track [Page 12] + +RFC 4072 Diameter EAP Application August 2005 + + +2.8. Usage Guidelines + +2.8.1. User-Name AVP + + Unless the access device interprets the EAP-Response/Identity packet + returned by the authenticating peer, it will not have access to the + user's identity. Furthermore, some EAP methods support identity + protection where the user's real identity is not included in + EAP-Response/Identity. Therefore, the Diameter Server SHOULD return + the user's identity by inserting a User-Name AVP to + Diameter-EAP-Answer messages that have a Result-Code of + DIAMETER_SUCCESS. A separate billing identifier or pseudonym MAY be + used for privacy reasons (see Section 8.5). If the user's identity + is not available to the NAS, the Session-Id AVP MAY be used for + accounting and billing; however operationally this could be very + difficult to manage. + +2.8.2. Conflicting AVPs + + A Diameter-EAP-Answer message containing an EAP-Payload of type + EAP-Success or EAP-Failure MUST NOT have the Result-Code AVP set to + DIAMETER_MULTI_ROUND_AUTH. + + Some lower layers assume that the authorization decision is made by + the EAP server, and thus the peer considers EAP Success as an + indication that access was granted. In this case, the Result-Code + SHOULD match the contained EAP packet: a successful Result-Code for + EAP-Success, and a failure Result-Code for EAP-Failure. If the + encapsulated EAP packet does not match the result implied by the + Result-Code AVP, the combination is likely to cause confusion, + because the NAS and peer will conclude the outcome of the + authentication differently. For example, if the NAS receives a + failure Result-Code with an encapsulated EAP Success, it will not + grant access to the peer. However, on receiving the EAP Success, the + peer will be led to believe that access was granted. + + This situation can be difficult to avoid when Diameter proxy agents + make authorization decisions (that is, proxies can change the + Result-Code AVP sent by the home server). Because it is the + responsibility of the Diameter server to avoid conflicts, the NAS + MUST NOT "manufacture" EAP result packets in order to correct the + contradictory messages that it receives. This behavior, originally + mandated within [IEEE-802.1X], is now deprecated. + + + + + + + + +Eronen, et al. Standards Track [Page 13] + +RFC 4072 Diameter EAP Application August 2005 + + +2.8.3. Displayable Messages + + The Reply-Message AVP [NASREQ] MUST NOT be included in any Diameter + message containing an EAP-Payload AVP. + +2.8.4. Role Reversal + + Some environments in which EAP is used, such as PPP, support + peer-to-peer operation. Both parties act as authenticators and + authenticatees at the same time, in two simultaneous and independent + EAP conversations. + + This specification is intended for communication between EAP + (passthrough) authenticator and backend authentication server. A + Diameter client MUST NOT send a Diameter-EAP-Request encapsulating an + EAP Request packet, and a Diameter server receiving such a packet + MUST respond with a failure Result-Code. + +2.8.5. Identifier Space + + In EAP, each session has its own unique Identifier space. Diameter + server implementations MUST be able to distinguish between EAP + packets with the same Identifier existing within distinct EAP + sessions and originating on the same NAS. This is done by using the + Session-Id AVP. + + If a Diameter NAS is in the middle of a multi-round authentication + exchange, and it detects that the EAP session between the client and + the NAS has been terminated, it MUST select a new Diameter Session-Id + for any subsequent EAP sessions. This is necessary in order to + distinguish a restarted EAP authentication process from the + continuation of an ongoing process (by the same user on the same NAS + and port). + + In RADIUS, the same functionality can be achieved through the + inclusion or omission of the State attribute. Translation rules in + [NASREQ] ensure that an Access-Request without the State attribute + maps to a new Diameter Session-Id AVP value. Furthermore, a + translation agent will always include a State attribute in + Access-Challenge messages, making sure that the State attribute is + available for a RADIUS NAS. + +3. Command-Codes + + This section defines new Command-Code values that MUST be supported + by all Diameter implementations conforming to this specification. + The following commands are defined in this section: + + + + +Eronen, et al. Standards Track [Page 14] + +RFC 4072 Diameter EAP Application August 2005 + + + Command-Name Abbrev. Code Reference + -------------------------------------------------------- + Diameter-EAP-Request DER 268 3.1 + Diameter-EAP-Answer DEA 268 3.2 + + When the NASREQ AA-Request (AAR) or AA-Answer (AAA) commands are used + for AUTHORIZE_ONLY messages in conjunction with EAP (see + Section 2.3.3), an Application Identifier value of 1 (NASREQ) is + used, and the commands follow the rules and ABNF defined in [NASREQ]. + + When the Re-Auth-Request (RAR), Re-Auth-Answer (RAA), + Session-Termination-Request (STR), Session-Termination-Answer (STA), + Abort-Session-Request (ASR), Abort-Session-Answer (ASA), + Accounting-Request (ACR), and Accounting-Answer (ACA) commands are + used together with the Diameter EAP application, they follow the + rules in [NASREQ] and [BASE]. The accounting commands use + Application Identifier value of 3 (Diameter Base Accounting); the + others use 0 (Diameter Common Messages). + +3.1. Diameter-EAP-Request (DER) Command + + The Diameter-EAP-Request (DER) command, indicated by the Command-Code + field set to 268 and the 'R' bit set in the Command Flags field, is + sent by a Diameter client to a Diameter server, and conveys an + EAP-Response from the EAP client. The Diameter-EAP-Request MUST + contain one EAP-Payload AVP containing the actual EAP payload. An + EAP-Payload AVP with no data MAY be sent to the Diameter server to + initiate an EAP authentication session. + + The DER message MAY be the result of a multi-round authentication + exchange that occurs when the DEA is received with the Result-Code + AVP set to DIAMETER_MULTI_ROUND_AUTH [BASE]. A subsequent DER + message MUST include any State AVPs [NASREQ] that were present in the + DEA. For re-authentication, it is recommended that the Identity + request be skipped in order to reduce the number of authentication + round trips. This is only possible when the user's identity is + already known by the home Diameter server. + + Message format + + <Diameter-EAP-Request> ::= < Diameter Header: 268, REQ, PXY > + < Session-Id > + { Auth-Application-Id } + { Origin-Host } + { Origin-Realm } + { Destination-Realm } + { Auth-Request-Type } + [ Destination-Host ] + + + +Eronen, et al. Standards Track [Page 15] + +RFC 4072 Diameter EAP Application August 2005 + + + [ NAS-Identifier ] + [ NAS-IP-Address ] + [ NAS-IPv6-Address ] + [ NAS-Port ] + [ NAS-Port-Id ] + [ NAS-Port-Type ] + [ Origin-State-Id ] + [ Port-Limit ] + [ User-Name ] + { EAP-Payload } + [ EAP-Key-Name ] + [ Service-Type ] + [ State ] + [ Authorization-Lifetime ] + [ Auth-Grace-Period ] + [ Auth-Session-State ] + [ Callback-Number ] + [ Called-Station-Id ] + [ Calling-Station-Id ] + [ Originating-Line-Info ] + [ Connect-Info ] + * [ Framed-Compression ] + [ Framed-Interface-Id ] + [ Framed-IP-Address ] + * [ Framed-IPv6-Prefix ] + [ Framed-IP-Netmask ] + [ Framed-MTU ] + [ Framed-Protocol ] + * [ Tunneling ] + * [ Proxy-Info ] + * [ Route-Record ] + * [ AVP ] + +3.2. Diameter-EAP-Answer (DEA) Command + + The Diameter-EAP-Answer (DEA) message, indicated by the Command-Code + field set to 268 and the 'R' bit cleared in the Command Flags field, + is sent by the Diameter server to the client for one of the following + reasons: + + 1. The message is part of a multi-round authentication exchange, and + the server is expecting a subsequent Diameter-EAP-Request. This + is indicated by setting the Result-Code to + DIAMETER_MULTI_ROUND_AUTH, and MAY include zero or more State + AVPs. + + + + + + +Eronen, et al. Standards Track [Page 16] + +RFC 4072 Diameter EAP Application August 2005 + + + 2. The EAP client has been successfully authenticated and + authorized, in which case the message MUST include the + Result-Code AVP indicating success, and SHOULD include an + EAP-Payload of type EAP-Success. This event MUST cause the + access device to provide service to the EAP client. + + 3. The EAP client has not been successfully authenticated and/or + authorized, and the Result-Code AVP is set to indicate failure. + This message SHOULD include an EAP-Payload, but this AVP is not + used to determine whether service is to be provided. + + If the message from the Diameter client included a request for + authorization, a successful response MUST include the authorization + AVPs that are relevant to the service being provided. + + Message format + + <Diameter-EAP-Answer> ::= < Diameter Header: 268, PXY > + < Session-Id > + { Auth-Application-Id } + { Auth-Request-Type } + { Result-Code } + { Origin-Host } + { Origin-Realm } + [ User-Name ] + [ EAP-Payload ] + [ EAP-Reissued-Payload ] + [ EAP-Master-Session-Key ] + [ EAP-Key-Name ] + [ Multi-Round-Time-Out ] + [ Accounting-EAP-Auth-Method ] + [ Service-Type ] + * [ Class ] + * [ Configuration-Token ] + [ Acct-Interim-Interval ] + [ Error-Message ] + [ Error-Reporting-Host ] + * [ Failed-AVP ] + [ Idle-Timeout ] + [ Authorization-Lifetime ] + [ Auth-Grace-Period ] + [ Auth-Session-State ] + [ Re-Auth-Request-Type ] + [ Session-Timeout ] + [ State ] + * [ Reply-Message ] + [ Origin-State-Id ] + * [ Filter-Id ] + + + +Eronen, et al. Standards Track [Page 17] + +RFC 4072 Diameter EAP Application August 2005 + + + [ Port-Limit ] + [ Callback-Id ] + [ Callback-Number ] + [ Framed-Appletalk-Link ] + * [ Framed-Appletalk-Network ] + [ Framed-Appletalk-Zone ] + * [ Framed-Compression ] + [ Framed-Interface-Id ] + [ Framed-IP-Address ] + * [ Framed-IPv6-Prefix ] + [ Framed-IPv6-Pool ] + * [ Framed-IPv6-Route ] + [ Framed-IP-Netmask ] + * [ Framed-Route ] + [ Framed-Pool ] + [ Framed-IPX-Network ] + [ Framed-MTU ] + [ Framed-Protocol ] + [ Framed-Routing ] + * [ NAS-Filter-Rule ] + * [ QoS-Filter-Rule ] + * [ Tunneling ] + * [ Redirect-Host ] + [ Redirect-Host-Usage ] + [ Redirect-Max-Cache-Time ] + * [ Proxy-Info ] + * [ AVP ] + +4. Attribute-Value Pairs + + This section both defines new AVPs, unique to the EAP Diameter + application and describes the usage of AVPs defined elsewhere (if + that usage in the EAP application is noteworthy). + +4.1. New AVPs + +4.1.1. EAP-Payload AVP + + The EAP-Payload AVP (AVP Code 462) is of type OctetString and is used + to encapsulate the actual EAP packet that is being exchanged between + the EAP client and the home Diameter server. + +4.1.2. EAP-Reissued-Payload AVP + + The EAP-Reissued-Payload AVP (AVP Code 463) is of type OctetString. + The use of this AVP is described in Section 2.4. + + + + + +Eronen, et al. Standards Track [Page 18] + +RFC 4072 Diameter EAP Application August 2005 + + +4.1.3. EAP-Master-Session-Key AVP + + The EAP-Master-Session-Key AVP (AVP Code 464) is of type OctetString. + It contains keying material for protecting the communications between + the user and the NAS. Exactly how this keying material is used + depends on the link layer in question, and is beyond the scope of + this document. + +4.1.4. EAP-Key-Name AVP + + The EAP-Key-Name AVP (Radius Attribute Type 102) is of type + OctetString. It contains an opaque key identifier (name) generated + by the EAP method. Exactly how this name is used depends on the link + layer in question, and is beyond the scope of this document (see + [EAPKey] for more discussion). + + Note that not all link layers use this name, and currently most EAP + methods do not generate it. Since the NAS operates in pass-through + mode, it cannot know the Key-Name before receiving it from the AAA + server. As a result, a Key-Name AVP sent in a Diameter-EAP-Request + MUST NOT contain any data. A home Diameter server receiving a + Diameter-EAP-Request with a Key-Name AVP with non-empty data MUST + silently discard the AVP. In addition, the home Diameter server + SHOULD include this AVP in Diameter-EAP-Response only if an empty + EAP-Key-Name AVP was present in Diameter-EAP-Request. + +4.1.5. Accounting-EAP-Auth-Method AVP + + The Accounting-EAP-Auth-Method AVP (AVP Code 465) is of type + Unsigned64. In case of expanded types [EAP, Section 5.7], this AVP + contains the value ((Vendor-Id * 2^32) + Vendor-Type). + + The use of this AVP is described in Section 2.7. + +5. AVP Occurrence Tables + + The following tables use these symbols: + + 0 The AVP MUST NOT be present in the message + 0+ Zero or more instances of the AVP MAY be present in the message + 0-1 Zero or one instance of the AVP MAY be present in the message + 1 One instance of the AVP MUST be present in the message + + Note that AVPs that can only be present within a Grouped AVP are not + represented in these tables. + + + + + + +Eronen, et al. Standards Track [Page 19] + +RFC 4072 Diameter EAP Application August 2005 + + +5.1. EAP Command AVP Table + + The following table lists the AVPs that may be present in the DER and + DEA Commands, as defined in this document; the AVPs listed are + defined both here and in [NASREQ]. + + +---------------+ + | Command-Code | + |-------+-------+ + Attribute Name | DER | DEA | + ------------------------------------|-------+-------| + Accounting-EAP-Auth-Method | 0 | 0+ | + Acct-Interim-Interval [BASE] | 0 | 0-1 | + Auth-Application-Id [BASE] | 1 | 1 | + Auth-Grace-Period [BASE] | 0-1 | 0-1 | + Auth-Request-Type [BASE] | 1 | 1 | + Auth-Session-State [BASE] | 0-1 | 0-1 | + Authorization-Lifetime [BASE] | 0-1 | 0-1 | + Callback-Id [NASREQ] | 0 | 0-1 | + Callback-Number [NASREQ] | 0-1 | 0-1 | + Called-Station-Id [NASREQ] | 0-1 | 0 | + Calling-Station-Id [NASREQ] | 0-1 | 0 | + Class [BASE] | 0 | 0+ | + Configuration-Token [NASREQ] | 0 | 0+ | + Connect-Info [NASREQ] | 0-1 | 0 | + Destination-Host [BASE] | 0-1 | 0 | + Destination-Realm [BASE] | 1 | 0 | + EAP-Master-Session-Key | 0 | 0-1 | + EAP-Key-Name | 0-1 | 0-1 | + EAP-Payload | 1 | 0-1 | + EAP-Reissued-Payload | 0 | 0-1 | + Error-Message [BASE] | 0 | 0-1 | + Error-Reporting-Host [BASE] | 0 | 0-1 | + Failed-AVP [BASE] | 0 | 0+ | + Filter-Id [NASREQ] | 0 | 0+ | + Framed-Appletalk-Link [NASREQ] | 0 | 0-1 | + Framed-Appletalk-Network [NASREQ] | 0 | 0+ | + Framed-Appletalk-Zone [NASREQ] | 0 | 0-1 | + Framed-Compression [NASREQ] | 0+ | 0+ | + Framed-Interface-Id [NASREQ] | 0-1 | 0-1 | + Framed-IP-Address [NASREQ] | 0-1 | 0-1 | + Framed-IP-Netmask [NASREQ] | 0-1 | 0-1 | + Framed-IPv6-Prefix [NASREQ] | 0+ | 0+ | + Framed-IPv6-Pool [NASREQ] | 0 | 0-1 | + Framed-IPv6-Route [NASREQ] | 0 | 0+ | + Framed-IPX-Network [NASREQ] | 0 | 0-1 | + Framed-MTU [NASREQ] | 0-1 | 0-1 | + Framed-Pool [NASREQ] | 0 | 0-1 | + + + +Eronen, et al. Standards Track [Page 20] + +RFC 4072 Diameter EAP Application August 2005 + + + Framed-Protocol [NASREQ] | 0-1 | 0-1 | + Framed-Route [NASREQ] | 0 | 0+ | + Framed-Routing [NASREQ] | 0 | 0-1 | + Idle-Timeout [NASREQ] | 0 | 0-1 | + Multi-Round-Time-Out [BASE] | 0 | 0-1 | + NAS-Filter-Rule [NASREQ] | 0 | 0+ | + NAS-Identifier [NASREQ] | 0-1 | 0 | + NAS-IP-Address [NASREQ] | 0-1 | 0 | + NAS-IPv6-Address [NASREQ] | 0-1 | 0 | + NAS-Port [NASREQ] | 0-1 | 0 | + NAS-Port-Id [NASREQ] | 0-1 | 0 | + NAS-Port-Type [NASREQ] | 0-1 | 0 | + Originating-Line-Info [NASREQ] | 0-1 | 0 | + Origin-Host [BASE] | 1 | 1 | + Origin-Realm [BASE] | 1 | 1 | + Origin-State-Id [BASE] | 0-1 | 0-1 | + Port-Limit [NASREQ] | 0-1 | 0-1 | + Proxy-Info [BASE] | 0+ | 0+ | + QoS-Filter-Rule [NASREQ] | 0 | 0+ | + Re-Auth-Request-Type [BASE] | 0 | 0-1 | + Redirect-Host [BASE] | 0 | 0+ | + Redirect-Host-Usage [BASE] | 0 | 0-1 | + Redirect-Max-Cache-Time [BASE] | 0 | 0-1 | + Reply-Message [NASREQ] | 0 | 0+ | + Result-Code [BASE] | 0 | 1 | + Route-Record [BASE] | 0+ | 0+ | + Service-Type [NASREQ] | 0-1 | 0-1 | + Session-Id [BASE] | 1 | 1 | + Session-Timeout [BASE] | 0 | 0-1 | + State [NASREQ] | 0-1 | 0-1 | + Tunneling [NASREQ] | 0+ | 0+ | + User-Name [BASE] | 0-1 | 0-1 | + +5.2. Accounting AVP Table + + The table in this section is used to represent which AVPs defined in + this document are to be present in the Accounting messages, as + defined in [BASE]. + + +-----------+ + | Command | + | Code | + |-----+-----+ + Attribute Name | ACR | ACA | + ---------------------------------------|-----+-----+ + Accounting-EAP-Auth-Method | 0+ | 0 | + + + + + +Eronen, et al. Standards Track [Page 21] + +RFC 4072 Diameter EAP Application August 2005 + + +6. RADIUS/Diameter Interactions + + Section 9 of [NASREQ] describes basic guidelines for translation + agents that translate between RADIUS and Diameter protocols. These + guidelines SHOULD be followed for Diameter EAP application as well, + with some additional guidelines given in this section. Note that + this document does not restrict implementations from creating + additional methods, as long as the translation function does not + violate the RADIUS or the Diameter protocols. + +6.1. RADIUS Request Forwarded as Diameter Request + + RADIUS Access-Request to Diameter-EAP-Request: + + o RADIUS EAP-Message attribute(s) are translated to a Diameter + EAP-Payload AVP. If multiple RADIUS EAP-Message attributes are + present, they are concatenated and translated to a single Diameter + EAP-Payload AVP. + + o An empty RADIUS EAP-Message attribute (with length 2) signifies + EAP-Start, and it is translated to an empty EAP-Payload AVP. + + Diameter-EAP-Answer to RADIUS Access-Accept/Reject/Challenge: + + o Diameter EAP-Payload AVP is translated to RADIUS EAP-Message + attribute(s). If necessary, the value is split into multiple + RADIUS EAP-Message attributes. + + o Diameter EAP-Reissued-Payload AVP is translated to a message that + contains RADIUS EAP-Message attribute(s), and a RADIUS Error-Cause + attribute [RFC3576] with value 202 (decimal), "Invalid EAP Packet + (Ignored)" [RFC3579]. + + o As described in [NASREQ], if the Result-Code AVP set to + DIAMETER_MULTI_ROUND_AUTH and the Multi-Round-Time-Out AVP is + present, it is translated to the RADIUS Session-Timeout attribute. + + o Diameter EAP-Master-Session-Key AVP can be translated to the + vendor-specific RADIUS MS-MPPE-Recv-Key and MS-MPPE-Send-Key + attributes [RFC2548]. The first up to 32 octets of the key is + stored into MS-MPPE-Recv-Key, and the next up to 32 octets (if + present) are stored into MS-MPPE-Send-Key. The encryption of this + attribute is described in [RFC2548]. + + o Diameter Accounting-EAP-Auth-Method AVPs, if present, are + discarded. + + + + + +Eronen, et al. Standards Track [Page 22] + +RFC 4072 Diameter EAP Application August 2005 + + +6.2. Diameter Request Forwarded as RADIUS Request + + Diameter-EAP-Request to RADIUS Access-Request: + + o The Diameter EAP-Payload AVP is translated to RADIUS EAP-Message + attribute(s). + + o An empty Diameter EAP-Payload AVP signifies EAP-Start, and is + translated to an empty RADIUS EAP-Message attribute. + + o The type (or expanded type) field from the EAP-Payload AVP can be + saved either in a local state table, or encoded in a RADIUS + Proxy-State attribute. This information is needed to construct an + Accounting-EAP-Auth-Method AVP for the answer message (see below). + + RADIUS Access-Accept/Reject/Challenge to Diameter-EAP-Answer: + + o If the RADIUS Access-Challenge message does not contain an + Error-Cause attribute [RFC3576] with value 202 (decimal), "Invalid + EAP Packet (Ignored)" [RFC3579], any RADIUS EAP-Message attributes + are translated to a Diameter EAP-Payload AVP, concatenating them + if multiple attributes are present. + + o If the Error-Cause attribute with value 202 is present, any RADIUS + EAP-Message attributes are translated to a Diameter + EAP-Reissued-Payload AVP, concatenating them if multiple + attributes are present. + + o As described in [NASREQ], if the Session-Timeout attribute is + present in a RADIUS Access-Challenge message, it is translated to + the Diameter Multi-Round-Time-Out AVP. + + o If the vendor-specific RADIUS MS-MPPE-Recv-Key and/or + MS-MPPE-Send-Key attributes [RFC2548] are present, they can be + translated to a Diameter EAP-Master-Session-Key AVP. The + attributes have to be decrypted before conversion, and the Salt, + Key-Length and Padding sub-fields are discarded. The Key + sub-fields are concatenated (MS-MPPE-Recv-Key first, + MS-MPPE-Send-Key next), and the concatenated value is stored into + a Diameter EAP-Master-Session-Key AVP. + + o If the Diameter-EAP-Answer will have a successful result code, the + saved state (see above) can be used to construct an + Accounting-EAP-Auth-Method AVP. + + + + + + + +Eronen, et al. Standards Track [Page 23] + +RFC 4072 Diameter EAP Application August 2005 + + +6.3. Accounting Requests + + In Accounting-Requests, the vendor-specific RADIUS MS-Acct-EAP-Type + attribute [RFC2548] can be translated to a Diameter + Accounting-EAP-Auth-Method AVP, and vice versa. + + When translating from Diameter to RADIUS, note that the + MS-Acct-EAP-Type attribute does not support expanded EAP types. Type + values greater than 255 should be translated to type 254. + +7. IANA Considerations + + This document does not create any new namespaces to be maintained by + IANA, but it requires new values in namespaces that have been defined + in the Diameter Base protocol and RADIUS specifications. + + o This document defines one new Diameter command (in Section 3) + whose Command Code is allocated from the Command Code namespace + defined in [BASE]. The Command Code for DER / DEA is 268. + + o This document defines four new AVPs whose AVP Codes are allocated + from the AVP Code namespace defined in [BASE] as follows: + + 462 for EAP-Payload (defined in Section 4.1.1), + 463 for EAP-Reissued-Payload (defined in Section 4.1.2), + 464 for EAP-Master-Session-Key (defined in Section 4.1.3), and + 465 for Accounting-EAP-Auth-Method (defined in Section 4.1.5). + + o This document defines one new AVP (attribute) whose AVP Code + (Attribute Type) is to be allocated from the Attribute Type + namespace defined in [RFC2865] and [RFC3575]. The Radius + Attribute Type for EAP-Key-Name (defined in Section 4.1.4) is 102. + + o This document defines one new Diameter application (in + Section 2.1) whose Application ID is to be allocated from the + Application Identifier namespace defined in [BASE]. The + Application ID for Diameter EAP is 5. + +8. Security Considerations + +8.1. Overview + + Diameter peer-to-peer connections can be protected with IPsec or TLS. + These mechanisms are believed to provide sufficient protection under + the normal Internet threat model, that is, assuming the authorized + nodes engaging in the protocol have not been compromised, but the + attacker has complete control over the communication channels between + them. This includes eavesdropping, message modification, insertion, + + + +Eronen, et al. Standards Track [Page 24] + +RFC 4072 Diameter EAP Application August 2005 + + + man-in-the-middle and replay attacks. The details and related + security considerations are discussed in [BASE]. + + In addition to authentication provided by IPsec or TLS, authorization + is also required. Here, authorization means determining if a + Diameter message received from an authenticated Diameter peer should + be accepted (and not authorization of users requesting network access + from a NAS). In other words, when a Diameter server receives a + Diameter-EAP-Request, it has to decide if the client is authorized to + act as a NAS for the specific user, service type, and so on. + Correspondingly, when a NAS contacts a server to send a + Diameter-EAP-Request, it has to determine whether the server is + authorized to act as home server for the realm in question. + + Authorization can involve local Access Control Lists (ACLs), + information contained in certificates, or some other means. See + [BASE] for more discussion and related security considerations. Note + that authorization issues are particularly relevant when Diameter + redirects are used. While redirection reduces the number of nodes + which have access to the contents of Diameter messages, a compromised + Diameter agent may not supply the right home server's address. If + the Diameter client is unable to tell whether this particular server + is authorized to act as the home server for this particular user, the + security of the communications rests on the redirect agent. + + The hop-by-hop security mechanisms (IPsec and TLS) combined with + proper authorization provide good protection against "outside" + attackers, except for denial-of-service attacks. The remaining part + of this section deals with attacks by nodes that have been properly + authorized (to function as a NAS, Diameter agent, or Diameter + server), but abuse their authorization or have been compromised. In + general, it is not possible to completely protect against attacks by + compromised nodes, but this section offers advice on limiting the + extent of the damage. + + Attacks involving eavesdropping or modification of EAP messages are + beyond the scope of these document. See [EAP] for discussion of + these security considerations (including method negotiation, + dictionary attacks, and privacy issues). While these attacks can be + carried out by an attacker between the client and the NAS, + compromised NASes and Diameter agents are naturally also in a good + position to modify and eavesdrop on the EAP messages. + + Similarly, attacks involving the link layer protocol used between the + client and the NAS, such as PPP or IEEE 802.11, are beyond the scope + of this document. + + + + + +Eronen, et al. Standards Track [Page 25] + +RFC 4072 Diameter EAP Application August 2005 + + +8.2. AVP Editing + + Diameter agents can modify, insert, and delete AVPs. Diameter agents + are usually meant to modify AVPs, and the protocol cannot distinguish + well-intentioned and malicious modifications (see [RFC2607] for more + discussion). Similarly, a compromised NAS or server can naturally + include a different set of AVPs than expected. + + Therefore, the question is what an attacker who compromises an + authorized NAS, agent, or server can do using Diameter EAP messages. + Some of the consequences are rather obvious. For instance, a + Diameter agent can give access to unauthorized users by changing the + Result-Code to DIAMETER_SUCCESS. Other consequences are less obvious + and are discussed below and authentication method negotiation attacks + are discussed in the next section. + + By including suitable AVPs in an AA-Answer/Diameter-EAP-Answer + messages, an attacker may be able (depending on implementation and + configuration details) to: + + o Give unauthorized users access, or deny access to authorized users + (Result-Code). + + o Give an attacker a login session to a host otherwise protected by + firewalls, or redirect an authorized user's login session to a + host controlled by the attacker (Login-Host). + + o Route an authorized user's traffic through a host controlled by + the attacker (various tunneling AVPs). + + o Redirect an authorized user's DNS requests to a malicious DNS + server (various vendor-specific AVPs). + + o Modify routing tables at the NAS and thus redirect packets + destined for someone else (Framed-Route, Framed-Routing). + + o Remove packet filters and other restrictions for user (Filter, + Callback, various vendor-specific AVPs). + + o Cause the NAS to call some number, possibly an expensive toll + number controlled by the attacker (callback AVPs). + + o Execute Command Line Interface (CLI) commands on the NAS (various + vendor-specific attributes). + + + + + + + +Eronen, et al. Standards Track [Page 26] + +RFC 4072 Diameter EAP Application August 2005 + + + By modifying an AA-Request/Diameter-EAP-Request, an attacker may be + able to: + + o Change NAS-Identifier/NAS-Port/Origin-Host (or another attribute) + so that a valid user appears to be accessing the network from a + different NAS than in reality. + + o Modify Calling-Station-ID (either to hide the true value, gain + access, or frame someone else). + + o Modify password change messages (some vendor-specific attributes). + + o Modify usage information in accounting messages. + + o Modify contents of Class and State AVPs. + + Some of these attacks can be prevented if the NAS or server is + configured to not accept some particular AVPs, or accepts them only + from some nodes. + +8.3. Negotiation Attacks + + This section deals with attacks where the NAS, any Diameter agents, + or Diameter server attempt to cause the authenticating user to choose + some authentication method other than EAP, such as PAP or CHAP + (negotiation attacks within EAP are discussed in [EAP], Section 7.8). + + The vulnerability can be mitigated via implementation of a per- + connection policy by the authenticating peer, and a per-user policy + by the Diameter server. For the authenticating peer, the + authentication policy should be set on a per-connection basis. + + With a per-connection policy, an authenticating peer will only + attempt to negotiate EAP for a session in which EAP support is + expected. As a result, it is presumed that an authenticating peer + selecting EAP requires that level of security. If it cannot be + provided, there is likely a misconfiguration, or the authenticating + peer may be contacting the wrong server. In this case, the + authenticating peer simply disconnects. + + Similarly, with a per-user policy, the home server will not accept + authentication methods other than EAP for users for which EAP support + is expected. + + For a NAS, it may not be possible to determine whether a peer is + required to authenticate with EAP until the peer's identity is known. + For example, for shared-uses NASes one reseller may implement EAP + while another does not. Alternatively, some peer might be + + + +Eronen, et al. Standards Track [Page 27] + +RFC 4072 Diameter EAP Application August 2005 + + + authenticated locally by the NAS while other peers are authenticated + via Diameter. In such cases, if any peers of the NAS MUST do EAP, + then the NAS MUST attempt to negotiate EAP for every session. This + avoids forcing a peer to support more than one authentication type, + which could weaken security. + +8.4. Session Key Distribution + + Since there are currently no end-to-end (NAS-to-home server) security + mechanisms specified for Diameter, any agents that process + Diameter-EAP-Answer messages can see the contents of the + EAP-Master-Session-Key AVP. For this reason, this specification + strongly recommends avoiding Diameter agents when they cannot be + trusted to keep the keys secret. + + In environments where agents are present, several factors should be + considered when deciding whether the agents that are authorized (and + considered "trustworthy enough") to grant access to users and specify + various authorization and tunneling AVPs are also "trustworthy + enough" to handle the session keys. These factors include (but are + not limited to) the type of access provided (e.g., public Internet or + corporate internet), security level of the agents, and the + possibilities for attacking user's traffic after it has been + decrypted by the NAS. + + Note that the keys communicated in Diameter messages are usually + short-term session keys (or short-term master keys that are used to + derive session keys). To actually cause any damage, those session + keys must end up with some malicious party that must be able to + eavesdrop, modify, or insert traffic between the user and the NAS + during the lifetime of those keys (for example, in 802.11i the + attacker must also eavesdrop the "four-way handshake"). + +8.5. Privacy Issues + + Diameter messages can contain AVPs that can be used to identify the + user (e.g., User-Name) and approximate location of the user (e.g., + Origin-Host for WLAN access points, Calling-Station-Id for fixed + phone lines). Thus, any Diameter nodes that process the messages may + be able to determine the geographic location of users. + + Note that in many cases, the user identity is also sent in clear + inside EAP-Payload AVPs, and it may be possible to eavesdrop this + between the user and the NAS. + + This can be mitigated somewhat by using EAP methods that provide + identity protection (see [EAP], Section 7.3), and using Session-Id or + pseudonyms for accounting. + + + +Eronen, et al. Standards Track [Page 28] + +RFC 4072 Diameter EAP Application August 2005 + + +8.6. Note about EAP and Impersonation + + If the EAP method used does not provide mutual authentication, + obviously anyone can impersonate the network to the user. Even when + EAP mutual authentication is used, it occurs between the user and the + Diameter home server. See [EAPKey] for an extensive discussion about + the details and their implications. + + One issue is worth pointing out here. As described in [EAPKey], the + current EAP architecture does not allow the home server to restrict + what service parameters or identities (such as SSID or BSSID in + 802.11 wireless LANs) are advertised by the NAS to the client. That + is, a compromised NAS can change its BSSID or SSID, and thus appear + to offer a different service than intended. Even if these parameters + are included in Diameter-EAP-Answer messages, the NAS can tell + different values to the client. + + Therefore, the NAS's possession of the session keys proves that the + user is talking to an authorized NAS, but a compromised NAS can lie + about its exact identity. See [EAPKey] for discussion on how + individual EAP methods can provide authentication of NAS service + parameters and identities. + + Note that the usefulness of this authentication may be rather limited + in many environments. For instance, in wireless LANs the user does + not usually securely know the identity (such as BSSID) of the "right" + access point; it is simply picked from a beacon message that has the + correct SSID and good signal strength (something that is easy to + spoof). Thus, simply authenticating the identity may not allow the + user to distinguish the "right" access point from all others. + +9. Acknowledgements + + This Diameter application relies heavily on earlier work on Diameter + NASREQ application [NASREQ] and RADIUS EAP support [RFC3579]. Much + of the material in this specification has been copied from these + documents. + + The authors would also like to acknowledge the following people for + their contributions to this document: Bernard Aboba, Jari Arkko, + Julien Bournelle, Pat Calhoun, Henry Haverinen, John Loughney, + Yoshihiro Ohba, and Joseph Salowey. + + + + + + + + + +Eronen, et al. Standards Track [Page 29] + +RFC 4072 Diameter EAP Application August 2005 + + +10. References + +10.1. Normative References + + [BASE] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and + J. Arkko, "Diameter Base Protocol", RFC 3588, + September 2003. + + [EAP] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and + H. Levkowetz, "Extensible Authentication Protocol + (EAP)", RFC 3748, June 2004. + + [NASREQ] Calhoun, P., Zorn, G., Spence, D., and D. Mitton, + "Diameter Network Access Server Application", RFC + 4005, August 2005. + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + +10.2. Informative References + + [EAPKey] Aboba, B., Simon, D., Arkko, J., Eronen, P., and H. + Levkowetz, "Extensible Authentication Protocol (EAP) + Key Management Framework", Work in Progress, July + 2004. + + [IEEE-802.1X] Institute of Electrical and Electronics Engineers, + "Local and Metropolitan Area Networks: Port-Based + Network Access Control", IEEE Standard 802.1X, + September 2001. + + [IEEE-802.11i] Institute of Electrical and Electronics Engineers, + "IEEE Standard for Information technology - + Telecommunications and information exchange between + systems - Local and metropolitan area networks - + Specific requirements - Part 11: Wireless Medium + Access Control (MAC) and Physical Layer (PHY) + Specifications: Amendment 6: Medium Access Control + (MAC) Security Enhancements", IEEE Standard + 802.11i-2004, July 2004. + + [IKEv2] Kaufman, C., Ed., "Internet Key Exchange (IKEv2) + Protocol", Work in Progress, June 2004. + + [RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", + STD 51, RFC 1661, July 1994. + + + + + +Eronen, et al. Standards Track [Page 30] + +RFC 4072 Diameter EAP Application August 2005 + + + [RFC2548] Zorn, G., "Microsoft Vendor-specific RADIUS + Attributes", RFC 2548, March 1999. + + [RFC2607] Aboba, B. and J. Vollbrecht, "Proxy Chaining and + Policy Implementation in Roaming", RFC 2607, + June 1999. + + [RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, + "Remote Authentication Dial In User Service (RADIUS)", + RFC 2865, June 2000. + + [RFC3575] Aboba, B., "IANA Considerations for RADIUS (Remote + Authentication Dial In User Service)", RFC 3575, + July 2003. + + [RFC3576] Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B. + Aboba, "Dynamic Authorization Extensions to Remote + Authentication Dial In User Service (RADIUS)", + RFC 3576, July 2003. + + [RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote + Authentication Dial In User Service) Support For + Extensible Authentication Protocol (EAP)", RFC 3579, + September 2003. + + [RFC3580] Congdon, P., Aboba, B., Smith, A., Zorn, G., and J. + Roese, "IEEE 802.1X Remote Authentication Dial In User + Service (RADIUS) Usage Guidelines", RFC 3580, + September 2003. + + + + + + + + + + + + + + + + + + + + + + +Eronen, et al. Standards Track [Page 31] + +RFC 4072 Diameter EAP Application August 2005 + + +Authors' Addresses + + Pasi Eronen (editor) + Nokia Research Center + P.O. Box 407 + FIN-00045 Nokia Group + Finland + + EMail: pasi.eronen@nokia.com + + + Tom Hiller + Lucent Technologies + 1960 Lucent Lane + Naperville, IL 60566 + USA + + Phone: +1 630 979 7673 + EMail: tomhiller@lucent.com + + + Glen Zorn + Cisco Systems + 500 108th Avenue N.E., Suite 500 + Bellevue, WA 98004 + USA + + Phone: +1 425 344 8113 + EMail: gwz@cisco.com + + + + + + + + + + + + + + + + + + + + + + +Eronen, et al. Standards Track [Page 32] + +RFC 4072 Diameter EAP Application August 2005 + + +Full Copyright Statement + + Copyright (C) The Internet Society (2005). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, + INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE + INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. 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