Extensible Authentication Protocol J. Arkko Working Group Ericsson Internet-Draft P. Eronen Expires: April 27, 2006 Nokia October 24, 2005 Authenticated Service Information for the Extensible Authentication Protocol (EAP) draft-arkko-eap-service-identity-auth-04 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 27, 2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract EAP is typically used in an arrangement where the actual service (such as a wireless LAN access point) is separated from the authentication server. However, EAP itself does not have a concept of a service identity or its parameters, and thus the client usually does not authenticate any information about the service itself, even when a mutually authenticating EAP method is used. This document Arkko & Eronen Expires April 27, 2006 [Page 1] Internet-Draft Service Info Authentication for EAP October 2005 specifies a backward compatible extension to popular EAP methods for authenticating service related information, such as the identity and type of the offered service. A common parameter name space is created in order to ensure that the same kinds of identifiers can be authenticated independent of the choice of the EAP authentication method, retaining the EAP media independence principle. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Authenticated Service Information . . . . . . . . . 3 2. Design Considerations . . . . . . . . . . . . . . . . . . . . 6 2.1. Media Independence . . . . . . . . . . . . . . . . . 6 2.2. Verifying Party . . . . . . . . . . . . . . . . . . 8 2.3. Communication within EAP vs. within AAA . . . . . . 9 3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 10 4. Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.1. Format . . . . . . . . . . . . . . . . . . . . . . . 12 4.2. General Parameters . . . . . . . . . . . . . . . . . 13 4.2.1. Service Type Parameter . . . . . . . . . . 13 4.2.2. Service Provider Parameter . . . . . . . . 14 4.2.3. Country Code Parameter . . . . . . . . . . 14 4.3. Parameters for IEEE 802.11 wireless LANs . . . . . . 14 4.3.1. SSID Parameter . . . . . . . . . . . . . . 14 4.3.2. BSSID Parameter . . . . . . . . . . . . . 14 4.4. Parameters for IEEE 802.16 Networks . . . . . . . . 14 4.5. Parameters for IKEv2 . . . . . . . . . . . . . . . . 14 4.5.1. Responder Address Parameter . . . . . . . 15 4.5.2. IDr Parameter . . . . . . . . . . . . . . 15 5. EAP Method Extensions . . . . . . . . . . . . . . . . . . . . 15 5.1. EAP-TLS . . . . . . . . . . . . . . . . . . . . . . 15 5.2. PEAPv2 . . . . . . . . . . . . . . . . . . . . . . . 17 5.3. EAP-AKA . . . . . . . . . . . . . . . . . . . . . . 17 5.4. EAP-SIM . . . . . . . . . . . . . . . . . . . . . . 20 6. Security Considerations . . . . . . . . . . . . . . . . . . . 21 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 7.1. Allocations Requested in This Document . . . . . . . 21 7.2. Future Allocation Policy . . . . . . . . . . . . . . 22 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23 8.1. Normative References . . . . . . . . . . . . . . . . 23 8.2. Informative References . . . . . . . . . . . . . . . 23 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 24 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25 Intellectual Property and Copyright Statements . . . . . . . . . . 26 Arkko & Eronen Expires April 27, 2006 [Page 2] Internet-Draft Service Info Authentication for EAP October 2005 1. Introduction EAP is typically used in an arrangement where the actual service (such as a wireless LAN access point) is separated from the authentication server. However, EAP itself does not have a concept of a service identity or its parameters, and thus the client usually does not authenticate any information about the service itself, even when a mutually authenticating EAP method is used. However, if a method supports channel bindings as specified in RFC 3748 [4] it becomes possible to ensure that the client, the node providing the service, and the authentication server all have the same information about this information. This does not, by itself, ensure that the information is correct, just that everyone has the same information; a service node might be providing a service that this particular node should not be providing. A method that supports authenticated service information ensures in addition that the authentication server knows this information to be correct. This document specifies a backwards compatible extension to popular EAP methods for supporting both channel bindings and authenticated service information. It does so in a media-independent manner, making it possible to run the same EAP mechanisms across different media, and introducing new information elements without affecting interoperability. This extension is intended for the verification of service information. It is not intended as a means for communicating information about parameters that EAP clients would not otherwise be aware of based on their communication with the node providing the service. This rest of the document is organized as follows. In Section 1.1 we discuss the need for authenticated service information in more detail. Section 2 discusses the design considerations and alternatives for solutions in this space. Section 3 gives an overview of how our protocol operates and Section 4 describes the kind of information that can be verified. We have provided only an initial list of parameters for IEEE 802.11 and IKEv2, but additional parameters can be defined through IANA. Section 5 describes the extensions necessary for certain popular EAP methods. Support for other EAP methods can be added in other specifications. 1.1. Authenticated Service Information EAP is run for the purposes of providing granting access to a service, such as network access. The nodes providing such services (called authenticators in EAP) typically have an identifier or Arkko & Eronen Expires April 27, 2006 [Page 3] Internet-Draft Service Info Authentication for EAP October 2005 identifiers, and offer a specific type of a service with an associated set of parameters. Collectively, this identifier, type and parameter information is called service information. In the Extensible Authentication Protocol (EAP) framework, different authentication methods can provide varying security properties. One such property is called "channel bindings", which is described in RFC 3748 [4] as follows: "The communication within an EAP method of integrity-protected channel properties such as endpoint identifiers which can be compared to values communicated via out of band mechanisms (such as via a AAA or lower layer protocol)." The document continues by describing the security implications of not being able to verify service information: "It is possible for a compromised or poorly implemented EAP authenticator to communicate incorrect information to the EAP peer and/or server. This may enable an authenticator to impersonate another authenticator or communicate incorrect information via out-of-band mechanisms (such as via a AAA or lower layer protocol). Where EAP is used in pass-through mode, the EAP peer typically does not verify the identity of the pass-through authenticator, it only verifies that the pass-through authenticator is trusted by the EAP server. This creates a potential security vulnerability. Section 4.3.7 of [11] describes how an EAP pass-through authenticator acting as a AAA client can be detected if it attempts to impersonate another authenticator (such by sending incorrect NAS-Identifier [9], NAS-IP-Address [9] or NAS-IPv6- Address [10] attributes via the AAA protocol). However, it is possible for a pass-through authenticator acting as a AAA client to provide correct information to the AAA server while communicating misleading information to the EAP peer via a lower layer protocol. For example, it is possible for a compromised authenticator to utilize another authenticator's Called-Station-Id or NAS- Identifier in communicating with the EAP peer via a lower layer protocol, or for a pass-through authenticator acting as a AAA client to provide an incorrect peer Calling-Station-Id [9] [12] to the AAA server via the AAA protocol. In order to address this vulnerability, EAP methods may support a protected exchange of channel properties such as endpoint Arkko & Eronen Expires April 27, 2006 [Page 4] Internet-Draft Service Info Authentication for EAP October 2005 identifiers, including (but not limited to): Called-Station-Id [9] [12], Calling-Station-Id [9] [12], NAS-Identifier [9], NAS-IP- Address [9], and NAS-IPv6-Address [10]. Using such a protected exchange, it is possible to match the channel properties provided by the authenticator via out-of-band mechanisms against those exchanged within the EAP method. Where discrepancies are found, these SHOULD be logged; additional actions MAY also be taken, such as denying access." Unfortunately, such verification is currently not possible in popular network scenarios. For instance, in IEEE 802.11 networks a rogue operator can actually advertise the same identity (BSSID or SSID) as the local operator; the parameters advertised by the access point information are not authenticated end-to-end to the home network. There is no support is in the commonly used EAP methods for authentication of service information, and there are no alternative verification means in the IEEE 802 lower layer. For instance, rogue access points can present a different identity to the client and to the home network. Or a rogue IKEv2 gateway can claim to be a 802.11 access point to its clients, but still appear as an IKEv2 gateway towards the authentication server. There are cases where the lower layer does provide its own means of authenticating the service information. For instance, in IKE2, EAP is used together with certificate-based authentication of the responder. However, this document may be useful with proposed IKEv2 extensions like [15] that remove the need to deploy a PKI. Also, even a lower layer that performs some kind of authentication for its service information may be unable to do so in all cases, such as distinguishing between different services offered by the nodes belonging to a group of nodes certified in the same manner. This situation is further complicated by the fact that services do not necessarily have just a single identifier, but several different identifiers of different types. For instance, an IEEE 802.11 access point could be identified by a BSSID, an IPv4 address (e.g., NAS-IP- Address), or a domain name (e.g., NAS-Identifier). Other identifiers, such as SSID, do not necessarily identify a single access point, but may be more interesting to the client (if you consider the "service" to be wireless LAN network access in some hotspot, rather than a single physical box). Ongoing development in the network access technology is opening up vulnerabilities that go beyond simple identifiers. For instance, protocol mechanisms are being developed to indicate the "cost" of access, such as whether the access is free or for a charge. Without a secure way to agree about the cost among the parties, fraudulent Arkko & Eronen Expires April 27, 2006 [Page 5] Internet-Draft Service Info Authentication for EAP October 2005 local networks can get customers via an attractive offer and subsequently charge them for usage with less attractive conditions. Prevention of such attacks is of high interest, as without technical measures they are expected to occur due to the economic incentives. It is important to make a distinction between channel bindings and authenticating information related to the the pass-through authenticator. Channel bindings only ensure that the same information is available to the EAP peer and the AAA server. This alone does not prevent an authenticator from impersonating another authenticator if the AAA server blindly accepts any information received from the authenticator. To provide authentication, the AAA server has to verify that the information actually corresponds to the entity the AAA-Key is sent to. 2. Design Considerations The following considerations deserve some discussion: o Retaining media independence in EAP o Choosing the party (or parties) to perform the verification o Communication within EAP vs. within AAA protocols These are discussed in following subsections. 2.1. Media Independence An EAP-based channel binding solution can fail to retain EAP's independence from media in three ways. First, an EAP method might support channel bindings only for some media, or make the addition of parameters for new media types hard. This would make it harder for users to switch to new media. Second, if channel bindings are provided only by some EAP methods, the choice of authentication methods and credentials would be limited in an environment that requires channel binding support [13]. Third, the EAP layer or EAP methods might have to interpret or understand the channel binding parameter information in some manner. This would result in a need to update EAP peer and server implementations when new media or new parameters on an existing media are developed. This draft avoids these problems by (1) defining the channel binding support simultaneously to the most popular EAP methods, (2) providing Arkko & Eronen Expires April 27, 2006 [Page 6] Internet-Draft Service Info Authentication for EAP October 2005 a common parameter name space across these methods in order to ensure that the same kind of information can be authenticated independent of the choice of the EAP method, and (3) treating the channel binding information as opaque data at the EAP layer and within EAP methods. Note that while the parameters are represented as opaque data at the EAP layer, it is still necessary to specify the parameters in a publicly avaible, stable specification for interoperability. This is why this document defines both the EAP transport and the actual parameters. Figures 1 and 2 illustrate how information is expected to be conveyed to upper layers where authorization decisions can be made. Peer Pass-through Authenticator Authentication (optional) Server +-----------+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+ | | | | | | | Control | | Control | | Control | |application| | application | |application| | | | | | | +-------+ + +----------+ +----------+ + +-------+ | | | | | | | | | | | EAP | | | EAP | | EAP | | | EAP | | layer | | | layer | | layer | | | layer | | | | | | | | | | | +-------+---+ +----------+--+--+----------+ +---+-------+ | | | | | | | |Lower layer| | Lower layer| AAA/IP | | AAA/IP | | | | | | | | +-----+-----+ +-------+-----+-----+-------+ +-----+-----+ ! ! ! ! ! ! ! ! +-------->--------+ +--------->-------+ Figure 1: Architecture Arkko & Eronen Expires April 27, 2006 [Page 7] Internet-Draft Service Info Authentication for EAP October 2005 +----------------------------------------------------+ | | | Control application | | | | | | | | Lower /|\ /|\ Opaque channel | | layer | | binding data | | information| | to/from EAP | | | | layer | | \|/ \|/ | +-------------------------+--------------------------+ | | | | | | | | | | Lower layer <----+----> EAP layer | | | | | | | | | | | | | | | | | | | +-------------------------+--------------------------+ Figure 2: Flow of information to and from EAP 2.2. Verifying Party The main idea of channel bindings is to be able to verify information from two sources, such as comparing what the EAP authenticator has told the peer and the server. Different designs could implement this check at different nodes: at the peer, the server, or both. Assuming a secure exchange of opaque data through EAP, both the peer and the server can have the same information available to them, including what the authenticator has communicated over AAA to the server and what it has told the peer over the lower layer. (Note that there are vulnerabilities in both AAA and lower layer protocols; what matters, however, is that both ends see the same information. Assuming the EAP method is secure, this can be arranged.) However, the server may be in a better position to have an understanding of what roaming contracts exist, what authenticators are expected to exist and what services they should be offering. Similarly, fraud detection and policy rules are easier to arrange at a central site than in clients. Finally, server-side verification is the model already adopted in PEAPv2 [7], it makes the introduction of a general channel binding model easier for this method. Arkko & Eronen Expires April 27, 2006 [Page 8] Internet-Draft Service Info Authentication for EAP October 2005 As a result, it seems reasonable to assume a model where the server is in charge of the verification process. 2.3. Communication within EAP vs. within AAA As discussed in [16], the communication of the verified parameters can occur in two ways: Within EAP Here the set of verified parameters is communicated end-to-end within EAP as an opaque string. Within AAA and Lower Layer Here the set of verified parameters is communicated from the authenticator (a) to the peer via the lower layer protocol and (b) to the server via the AAA protocol. In order to prevent fraudulent claims about the parameters, the AAA protocol calculates AAA-Key based on the parameters, and communicates only this key (not the current MSK) to the authenticator. As a result, the peer and the authenticator can not complete their network attachment process if there's a mismatch in the set of parameters. The overall result of both approaches is the same, but there are subtle security differences: One difference is that in the EAP approach we need to trust the endpoints to actually perform the check, whereas the key-based check is implicit and "non-skippable" in the latter approach; if the parameters mismatch the keys simply do not work. Another difference is in the timing of the check; in conventional AAA protocols the user is considered authenticated when the RADIUS Access-Accept or equivalent message is sent. This ensures that the AAA server is aware of the result of the access request. But in the AAA-based approach a mismatch in the parameters is learned after this, and may be hard to report in a secure way. For instance, the authenticator could claim that a session was started, even if in reality the secure association protocol failed due to a mismatch. There is also a difference in terms of deployment implications. The EAP-based approach means that EAP implementations and methods have be updated. Existing credentials can continue to be used, however, and it is expected that the opaque data approach makes it possible to add new media and new parameters without additional code changes in EAP. There are no EAP updates in the AAA-based approach, but it is still necessary to add support for the new parameter communication means Arkko & Eronen Expires April 27, 2006 [Page 9] Internet-Draft Service Info Authentication for EAP October 2005 and AAA-Key calculation to peers, authenticators, and servers. The main difference to the EAP-based approach is that authenticators need to be changed. Because of the above considerations, this draft employs the EAP-based approach. 3. Protocol Overview The basic idea in this extension is that the EAP peer sends the EAP server a statement that it going to accept service from an access device associated with particular set of identifiers and other information. In order to protect this statement, an EAP method needs to be able to pass data from the EAP peer to the EAP server, and be able to protect this exchange using keys known only them and not the access device. The Transient EAP Keys (TEKs) can be used for this purpose, as these keys are only known to the EAP endpoints and not communicated to the access device. After receiving this information, the EAP server can compare the information provided from the EAP peer to the information it has received directly from the access device. If the information does not match, the access device has provided different information to the peer and to the AAA protocol. This is disallowed, and the authentication SHOULD be terminated and the discrepancy MUST be logged. In order to provide a generic solution where any EAP method can be used on a given lower layer, the same format is used for the exchanged information. This format consists of Tag-Length-Value triplets with IANA managed tag space. The parameter information is sent along the other messages in an EAP method. The exact message sequences depend on the used EAP method, but Figure 1 shows a typical sequence. Peer Authenticator Server | | | | 802.11 attachment | | |<------------------------>| | | | | +----------------------+ | | | Information received | | | | at this point is | | | | not authenticated | | | Arkko & Eronen Expires April 27, 2006 [Page 10] Internet-Draft Service Info Authentication for EAP October 2005 +----------------------+ | | | | | | EAP Identity Request | | |<-------------------------| | | | | | EAP Identity Response | | |------------------------->| | | | RADIUS Access-Request | | |------------------------->| | | | | | +----------------------+ | | | Server authenticates | | | | the RADIUS request | | | +----------------------+ | | | | | RADIUS Access-Challenge | | EAP TLS Start |<-------------------------| |<-------------------------| | | | | +-----------------------+ | | | Peer sends the | | | | authenticator's info | | | | to the server in EAP | | | +-----------------------+ | | | | | | EAP TLS C-Hello + id. | | |------------------------->| | | | RADIUS Access-Request | | |------------------------->| | | | | | +-------------------------+ | | | Server can now verify | | | | that the information | | | | is what was expected | | | +-------------------------+ | | | | | RADIUS Access-Challenge | | EAP TLS S-Hello . |<-------------------------| |<-------------------------| | | | | +-------------------------+ | | | Peer learns here that | | | | the information was | | | | verified (EAP continues)| | | +-------------------------+ | | | | | | | | | EAP TLS Finished | | Arkko & Eronen Expires April 27, 2006 [Page 11] Internet-Draft Service Info Authentication for EAP October 2005 |------------------------->| RADIUS Access-Request | | |------------------------->| | | | | | RADIUS Access-Challenge | | EAP TLS Finished |<-------------------------| |<-------------------------| | | | | | | | | EAP TLS | | |------------------------->| RADIUS Access-Request | | |------------------------->| | | | | | RADIUS Access-Accept + | | | AAA-Key | | EAP Success |<-------------------------| |<-------------------------| | | | | +-----------------------------+ | Authentication is completed | | when the authenticator | | proves it knows the AAA-Key | +-----------------------------+ Zero or more parameters are sent from the peer to the server. Each parameter is of the format explained in the next section. 4. Parameters 4.1. Format Nodes supporting this extension pass parameters in the following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Res | Parameter Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . . . Value . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The meaning of the fields is described as follows: Arkko & Eronen Expires April 27, 2006 [Page 12] Internet-Draft Service Info Authentication for EAP October 2005 Res A 4-bit field reserved for future use. The value MUST be initialized to zero by the sender, and MUST be ignored by the receiver. Parameter Identifier A 16-bit field that specifies what parameter is being communicated. Length A 12-bit field that indicates the length of the Value field, in bytes. Value The actual parameter value. The interpretation of this value depends on the Parameter Identifier field. Integers are represented as four bytes in all cases, whereas addresses and strings are represented in as many octets as they are long. The EAP or the EAP method layer SHOULD NOT attempt to interpret the information beyond this format. In other words, the Parameter Identifier and Value fields are interpreted as opaque data in order to ensure EAP media independence. EAP implementations SHOULD pass the information to higher layers that are in charge of authorization decisions, such as AAA server authorization logic. The encapsulation of this sequence of parameters is EAP method dependent. 4.2. General Parameters These parameters are for any type of nodes and lower layers. The Service Type parameter MUST be supported by all nodes conforming to this specification, and MUST be the first parameter in all messages containing a sequence of parameters defined here. 4.2.1. Service Type Parameter The Parameter Identifier for this parameter is 0, and the Value is a 32-bit integer, represented in network byte order. The following values have been currently defined: Arkko & Eronen Expires April 27, 2006 [Page 13] Internet-Draft Service Info Authentication for EAP October 2005 0 IEEE 802.11 1 IEEE 802.16 2 IKEv2 The receiver SHOULD fail the authentication if the Value field is either not recognized by it or is not the same one for which it thinks access is being provided. 4.2.2. Service Provider Parameter The Parameter Identifier for this parameter is 1, and the Value is an UTF-8 encoded string describing the human readable name of the service provider. As EAP is used primarily for network access, this is typically the name of the access network provider. 4.2.3. Country Code Parameter The Parameter Identifier for this parameter is 2, and the Value is an ASCII string of at most 3 characters, conforming to the ISO 3166 [8] country code. 4.3. Parameters for IEEE 802.11 wireless LANs All the following parameters MUST be supported when IEEE 802.11 is accepted as a Service Type. 4.3.1. SSID Parameter The Parameter Identifier for this parameter is 3, and the Value is an octet string containing the Service Set Identifier (SSID). 4.3.2. BSSID Parameter The Parameter Identifier for this parameter is 4, and the Value is a 6-octet string containing the BSSID. 4.4. Parameters for IEEE 802.16 Networks No parameters have yet been defined for the IEEE 802.16 networks. 4.5. Parameters for IKEv2 All the following parameters MUST be supported when IKEv2 is accepted as the Service Type. Arkko & Eronen Expires April 27, 2006 [Page 14] Internet-Draft Service Info Authentication for EAP October 2005 4.5.1. Responder Address Parameter The Parameter Identifier for this parameter is 14, and the Value is the IP address of the node who acted as the responder for this IKEv2 EAP exchange. The Value is either 4 or 16 bytes depending on whether IPv4 or IPv6 is used. 4.5.2. IDr Parameter The Parameter Identifier for this parameter is 16, and the Value is an octet string containing the IKEv2 responder identity payload (IDr). 5. EAP Method Extensions This section describes an initial set of extensions to some current EAP methods so that they can be transport the parameter information. The extensions are optional and backwards compatible, so that, where allowed by policy, EAP peers without these extensions can still contact EAP servers with these extensions and vice versa. The default policy SHOULD be that such usage is allowed. 5.1. EAP-TLS A TLS extension [3] is added to the EAP TLS [2] client_hello/ server_hello messages. The extension type of the extension is EAP Service Information and it has the number < To Be Assigned By IANA >. The extension contains a sequence of parameters, followed by each other. The extension sent in the server_hello message SHOULD contain zero parameters, and is only used to confirm that the server supports this specification. As discussed in RFC 3546, when these extensions appear in a client hello message, they are ignored by old server implementations. The lack of this extension in the authenticator's server hello response SHOULD be taken as an indication that the authenticator does not support the mechanisms defined in this document. The authenticator MUST NOT use this extension unless the client provided the same extension in its own hello message, as per RFC 3546 the client is required to terminate the TLS session otherwise. The client_hello/server_hello messages are included in MACs in the TLS Finished messages, which ensures that modifications will be detected. Arkko & Eronen Expires April 27, 2006 [Page 15] Internet-Draft Service Info Authentication for EAP October 2005 The following sequence illustrates the operation of the EAP TLS protocol with this extension: Peer Authenticator | | | PPP EAP-Request/ | | EAP-Type=EAP-TLS | | (TLS Start) | |<---------------------------------------------------------| | | | PPP EAP-Response/ | | EAP-Type=EAP-TLS | | (TLS client_hello + extension) | |--------------------------------------------------------->| | | | PPP EAP-Request/ | | EAP-Type=EAP-TLS | | (TLS server_hello + extension, | | TLS certificate, | | [TLS server_key_exchange,] | | [TLS certificate_request,] | | TLS server_hello_done) | |<---------------------------------------------------------| | | | PPP EAP-Response/ | | EAP-Type=EAP-TLS | | (TLS certificate, | | TLS client_key_exchange, | | [TLS certificate_verify,] | | TLS change_cipher_spec, | | TLS finished) | |--------------------------------------------------------->| | | | PPP EAP-Request/ | | EAP-Type=EAP-TLS | | (TLS change_cipher_spec, | | TLS finished) | |<---------------------------------------------------------| | | | PPP EAP-Response/ | | EAP-Type=EAP-TLS | |--------------------------------------------------------->| | | | PPP EAP-Success | |<---------------------------------------------------------| | | Arkko & Eronen Expires April 27, 2006 [Page 16] Internet-Draft Service Info Authentication for EAP October 2005 This works the same way when resuming session. Note that the parameters can change from the initial authentication. 5.2. PEAPv2 In PEAPv2 [7], the Connection-Binding TLV is used to carry parameter objects. One Connection-Binding TLV for this purpose is exchanged in each direction, containing all the parameters that need to be exchanged. The Connection-Binding TLV carries a set of PEAPv2 TLVs. The transport of parameters for the purposes of this document takes place through the PEAPv2 Service Information Parameter TLV defined in the following: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |M|R| TLV Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Parameter... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The fields of this TLV are as follows: M 0 - Optional TLV. R Reserved, set to zero (0). TLV Type < To Be Assigned By IANA > Length Length of the TLV. Parameter... The parameter in the format described in Section 4.1. 5.3. EAP-AKA For EAP-AKA, a new attribute AT_SERVICEID is added to the EAP- Request/AKA/Challenge message. Arkko & Eronen Expires April 27, 2006 [Page 17] Internet-Draft Service Info Authentication for EAP October 2005 The format of the AT_SERVICEID attribute is shown below: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AT_SERVICEID | Length | Actual data length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . Parameters... . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The fields of this attribute are as follows: AT_SERVICEID < To Be Assigned By IANA > Length Length of the attribute. Actual data length This field specifies the length of the following field in bytes, because the length of the parameter must be a multiple of 4 bytes, the sender pads the data with zero bytes when necessary. Parameters... The parameters in the format described in Section 4.1. The following sequence illustrates the operation of the EAP-AKA protocol with this extension: Arkko & Eronen Expires April 27, 2006 [Page 18] Internet-Draft Service Info Authentication for EAP October 2005 Peer Authenticator | EAP-Request/Identity | |<------------------------------------------------------| | | | EAP-Response/Identity | | (Includes user's NAI) | |------------------------------------------------------>| | | | +------------------------------+ | | Server runs UMTS algorithms, | | | generates RAND and AUTN. | | +------------------------------+ | | | EAP-Request/AKA-Challenge | | (AT_RAND, AT_AUTN, AT_MAC, AT_SERVICEID) | |<------------------------------------------------------| | | +-------------------------------------+ | | Peer runs UMTS algorithms on USIM, | | | verifies AUTN and MAC, derives RES | | | and session key | | +-------------------------------------+ | | | | EAP-Response/AKA-Challenge | | (AT_RES, AT_MAC, AT_SERVICEID) | |------------------------------------------------------>| | | | +--------------------------------+ | | Server checks the given RES, | | | and MAC and finds them correct.| | +--------------------------------+ | | | EAP-Success | |<------------------------------------------------------| The AT_SERVICEID attribute from the server to the peer is empty, and is only used for capability detection. A peer MUST NOT send a AT_SERVICEID attribute if no such attribute was seen from the server previously. In this case, the peer MAY disconnect if its policy requires the channel binding support. Note that the AT_SERVICEID attribute is used also in the EAP-Request/ AKA/AKA-Reauthentication message, and that the set of parameters exchanged in this case may differ from those agreed upon earlier in the initial authentication. The use of the AT_SERVICEID attribute is backward compatible, because existing implementations ignore unknown parameters. Arkko & Eronen Expires April 27, 2006 [Page 19] Internet-Draft Service Info Authentication for EAP October 2005 5.4. EAP-SIM For EAP-SIM, a new attribute AT_SERVICEID is added to the EAP- Request/SIM/Challenge message. The format of the AT_SERVICEID attribute is as shown for EAP-AKA. The following sequence illustrates the operation of the EAP-SIM protocol with this extension: Peer Authenticator | | | EAP-Request/Identity | |<---------------------------------------------------------| | | | EAP-Response/Identity | |--------------------------------------------------------->| | | | EAP-Request/SIM/Start | | (AT_VERSION_LIST) | |<---------------------------------------------------------| | | | EAP-Response/SIM/Start | | (AT_NONCE_MT, AT_SELECTED_VERSION) | |--------------------------------------------------------->| | | | EAP-Request/SIM/Challenge | | (AT_RAND, AT_MAC, AT_SERVICEID) | |<---------------------------------------------------------| | | +-------------------------------------+ | | Peer runs GSM algorithms, | | | verifies AT_MAC and derives | | | session keys | | +-------------------------------------+ | | | | EAP-Response/SIM/Challenge | | (AT_MAC, AT_SERVICEID) | |--------------------------------------------------------->| | | | | | EAP-Success | |<---------------------------------------------------------| | | As with EAP-AKA, the AT_SERVICEID attribute must be passed also in the EAP-Request/SIM/SIM-Reauthentication message. Similarly, the AT_SERVICEID attribute from the server to the client is empty and only used for capability detection. Arkko & Eronen Expires April 27, 2006 [Page 20] Internet-Draft Service Info Authentication for EAP October 2005 6. Security Considerations The implications of being unable to verify service information have been described in Section 7.15 of RFC 3748 [4]. These include vulnerabilities related to compromised access points or fraudulent service providers. When properly used, the mechanism provided in this document removes these vulnerabilities. The mechanism is generic and not tied to any specific EAP method or use of EAP over a specific link layer, and as such can be expected to be more easily deployed as alternative suggestions such as those described in PEAPv2 [7] or EAP FAST [14]. Authenticating the service information may complicate operation in some deployment scenarios, since it requires that the AAA server is able to authenticate the expected kinds of information. For instance, RADIUS is often deployed in situations where the only authenticated information related to the RADIUS client is the IP address; other information may be present in the Access-Request message (such as BSSID/SSID in the Called-Station-Id attribute), but this is simply claimed information not authenticated information. Where such information is not available, some vulnerabilities still remain. In the deployment phase, it is possible that clients and servers do not get support for the mechanism described in this document at the same time. It is a policy decision to accept an EAP exchange from a party that does not support this mechanism. This decision is protected from a bidding down attack by a man-in-the-middle, because EAP methods have integrity protection for the exchanged messages. Therefore, the removal or modification of the parameter block would be detected. 7. IANA Considerations 7.1. Allocations Requested in This Document This document requests an IANA allocation of TLS Extension type [3] for EAP Service Identity (see Section 5.1). This document requests an IANA allocation of a PEAPv2 [7] TLV type number for the Service Identity Parameter TLV (see Section 5.2). This document requests an IANA allocation for the attribute type number AT_SERVICEID in the [6] and [5] protocols (see Section 5.3 and Section 5.4). The same value should be allocated for both protocols. Arkko & Eronen Expires April 27, 2006 [Page 21] Internet-Draft Service Info Authentication for EAP October 2005 7.2. Future Allocation Policy New Parameter Identifier values can be defined through Specification Required [1]. The following values have been currently allocated: 0 Service Type 1 Service Provider 2 Country Code 3 802.11/SSID 4 802.11/BSSID 6 IKEv2/Responder Address 7 IKEv2/IDr Values 65000 through 65530 and for Experimental Use and can be used without allocation. Values 65531 through 65535 are Reserved. New Service Type values can be defined through IETF Consensus [1]. The following values have been currently allocated: 0 IEEE 802.11 1 IEEE 802.16 2 IKEv2 Values 429496700 through 4294967289 are for Experimental Use and can be used without allocation. Values 4294967290 through 4294967295 are Reserved. Values in other enumerated parameters can be defined through First Come, First Served[1]. However, this extension is intended only for the verification of service information. Its use for communicating other information not already known by the EAP client (such as for service discovery) is discouraged. In all enumarated parameters, values 429496700 through 4294967289 are for Experimental Use and can be used without allocation. Values 4294967290 through 4294967295 are Reserved. 8. References Arkko & Eronen Expires April 27, 2006 [Page 22] Internet-Draft Service Info Authentication for EAP October 2005 8.1. Normative References [1] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. [2] Aboba, B. and D. Simon, "PPP EAP TLS Authentication Protocol", RFC 2716, October 1999. [3] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J., and T. Wright, "Transport Layer Security (TLS) Extensions", RFC 3546, June 2003. [4] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. Levkowetz, "Extensible Authentication Protocol (EAP)", RFC 3748, June 2004. [5] Haverinen, H. and J. Salowey, "EAP SIM Authentication", draft-haverinen-pppext-eap-sim-16 (work in progress), December 2004. [6] Arkko, J. and H. Haverinen, "EAP AKA Authentication", draft-arkko-pppext-eap-aka-15 (work in progress), December 2004. [7] Josefsson, S., Palekar, A., Simon, D., and G. Zorn, "Protected EAP Protocol (PEAP)", draft-josefsson-pppext-eap-tls-eap-10 (work in progress), October 2004. [8] International Organization for Standardization, "Codes for the representation of names of countries, 3rd edition", ISO Standard 3166, August 1988. 8.2. Informative References [9] Rigney, C., Willens, S., Rubens, A., and W. Simpson, "Remote Authentication Dial In User Service (RADIUS)", RFC 2865, June 2000. [10] Aboba, B., Zorn, G., and D. Mitton, "RADIUS and IPv6", RFC 3162, August 2001. [11] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication Dial In User Service) Support For Extensible Authentication Protocol (EAP)", RFC 3579, September 2003. [12] 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. Arkko & Eronen Expires April 27, 2006 [Page 23] Internet-Draft Service Info Authentication for EAP October 2005 [13] Stanley, D., Walker, J., and B. Aboba, "Extensible Authentication Protocol (EAP) Method Requirements for Wireless LANs", RFC 4017, March 2005. [14] Cam-Winget, N., McGrew, D., and J. Salowey, "EAP Flexible Authentication via Secure Tunneling (EAP-FAST)", draft-cam-winget-eap-fast-01 (work in progress), October 2004. [15] Eronen, P. and H. Tschofenig, "Extension for EAP Authentication in IKEv2", draft-eronen-ipsec-ikev2-eap-auth-03 (work in progress), April 2005. [16] Yanagiya, M. and Y. Ohba, "AAA-Key Derivation with Lower-Layer Parameter Binding", draft-ohba-eap-aaakey-binding-01 (work in progress), July 2005. Appendix A. Acknowledgments The authors would like to thank Bernard Aboba, Yoshihiro Ohba, Mohan Parthasarathy, Hannes Tschofenig, Joe Salowey, Glen Zorn, and David Mariblanca for interesting discussions in this problem space. Arkko & Eronen Expires April 27, 2006 [Page 24] Internet-Draft Service Info Authentication for EAP October 2005 Authors' Addresses Jari Arkko Ericsson FI-02420 Jorvas Finland Email: jari.arkko@ericsson.com Pasi Eronen Nokia Research Center P.O. Box 407 FI-00045 Nokia Group Finland Email: pasi.eronen@nokia.com Arkko & Eronen Expires April 27, 2006 [Page 25] Internet-Draft Service Info Authentication for EAP October 2005 Intellectual Property Statement 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. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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