The eap.arpa domain and EAP provisioning

Introduction In most uses, EAP requires that the EAP peer have pre-provisioned credentials. Without credentials, the device cannot obtain network access in order to be provisioned with credentials. This limitation creates a bootstrapping problem. This specification addresses that problem. It creates a framework by which clients can submit predefined provisioning credentials to a server in order to obtain limited network access. At the same time, servers can know in advance that these credentials are to be used only for provisioning, and that unrestricted network access should not be granted. The device can either use the EAP channel itself for provisioning, as with TEAP , or the EAP server can give the device access to a limited captive portal such as with . Once the device is provisioned, it can use those provisioned credentials to obtain full network access. The pre-defined credentials use a generic identity format. Identifiers in this space are generically referred to as "EAP Provisioning Identifiers" (EPI). The choice of "Provisioning Identifiers for EAP" (PIE) was considered and rejected. Since the identity is predefined, there is little benefit to defining pre-defined passwords. Where supported by the underlying EAP method, this specification provides for password-less access. Where passwords are required, the password is defined to be the same as the identity.

Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Concepts A device which has no device-specific credentials can use a predefined identifier in Network Access Identifier (NAI) format . The NAI is composed of two portions, the utf8-username, and the utf8-realm domain. For simplicity here, we refer to these as the "username" and "realm" fields. The realm is chosen to be independent of, and unused by, any existing organization, and thus to be usable by all organizations. The realm is one which should not be automatically proxied by any any Authentication, Authorization, and Accounting (AAA) proxy framework as defined in . The realm is also one which will not return results for dynamic discovery. This specification does not, however, forbid routing of packets for realms in the "eap.arpa" domain. Instead, it leaves such routing up to individual organizations. We note that this specification is fully compatible with all existing EAP implementations, so it is fail-safe. When presented with a peer wishing to use this specification, existing implementations will return EAP Failure, and will not otherwise misbehave. We now discuss the NAI format in more detail. We first discuss the eap.arpa realm, and second the use and purpose of the username field.

The eap.arpa realm This document defines the "eap.arpa" domain as being used for provisioning within EAP. A similar domain has previously been used for EAP-NOOB , as "eap-noob.arpa". This document extends that concept, and standardizes the practices surrounding it, NOTE: the "arpa" domain is controlled by the IAB. Allocation of "eap.arpa" requires agreement from the IAB.

The realm field The subdomain in realm is assigned via the EAP Provisioning Identifier Registry which is defined in . The subdomain MUST follow the domain name conventions specified in . It is RECOMMENDED that the first subdomain of "eap.arpa" use the EAP method name, as defined in the IANA Extensible Authentication Protocol (EAP) Registry, sub-registry "Method Types". However, that registry does not follow the domain name conventions specified in , so it is not possible to make a "one-to-one" mapping between the Method Type name and the subdomain. Where it is not possible to make a direct mapping between the EAP Method Type name (e.g. "TEAP"), and a subdomain (e.g. "teap.eap.arpa"), the name used in the realm registry SHOULD be similar enough to allow the average reader to understand which EAP Method Type is being used. Additional subdomains are permitted in the realm, which permit vendors and Standards Development organizations (SDOs) the ability to self-assign a delegated range of identifiers which cannot conflict with other identifiers. Any realm defined in this registry (e.g. "teap.eap.arpa") also implicitly defines a subdomain "v." (e.g. "v.teap.eap.arpa"). Vendors or SDOs can self-allocate within the "v." subdomain, using domains which they own. For example, An "example.com" company could self-allocate and use the realm "example.com.v.teap.eap.arpa".

The username field The username field is dependent on the EAP method being used for provisioning. For example, uses the username "noob". Other EAP methods MAY omit the username as RECOMMENDED in . The username of "anonymous" is NOT RECOMMENDED for specifications using this format, even though it is permitted by . The username field is assigned via the EAP Provisioning Identifier Registry which is defined in . The username field MAY be empty, or else hold a fixed value. While recommends omitting the username portion for user privacy, the names here are defined in public specifications. User privacy is therefore not needed for provisioning identifiers, and the username field can be publicly visible.

Operation Having defined the format and contents of NAIs in the eap.arpa realm, we now need to define how those NAIs are used by EAP supplicants and EAP peers.

EAP Peer An EAP peer signals that it wishes a certain kind of provisioning by using a predefined NAI, along with an associated EAP method. The meaning of the NAI, and behavior of the supplicant are defined by a separate specification. That specification will typically define both the NAI, and the EAP method which is used for provisioning. The NAI used by the peer MUST be taken from an entry in the "EAP Provisioning Identifiers" registry, and the EAP method used with that NAI MUST match the corresponding EAP method from that same entry. EAP peers MUST NOT allow these NAIs to be configured directly by end users. Instead the user (or some other process) chooses a provisioning method, and the peer then chooses a predefined NAI which matches that provisioning method. When all goes well, running EAP with the provisioning NAI results in new authentication credentials being provisioned. The peer then drops its network connection, and re-authenticates using the newly provisioned credentials. There are a number of ways in which provisioning can fail. One way is when the server does not implement the provisioning method. EAP peers therefore MUST track which provisioning methods have been tried, and not repeat the same method to the same EAP server when receiving a an EAP Nak. EAP peers MUST rate limit attempts at provisioning, in order to avoid overloading the server. Another way for provisioning to fail is when the new credentials do not result in network access. It is RECOMMENDED that peers immediately try to gain network access using the new credentials, as soon as they have been provisioned. That process allows errors to be quickly discovered and addressed. An EAP peer may be have been provisioned with temporary credentials. It SHOULD therefore attempt to provision new credentials before the current set expires. Unfortunately, any re-provisioning process with EAP will involve the device dropping off of the "full" network, in order to connect to the provisioning network. It is therefore RECOMMENDED that re-provisioning methods be provided which can be used when the device has full network access. See for additional discussion of this topic.

EAP Servers An EAP session begins with the server receiving an initial EAP-Request/Identity message. An EAP server supporting this specification MUST examining the identity to see if it uses the eap.arpa realm. If not, the EAP server MUST process the request through pre-existing methods. If the server receives a malformed NAI in the eap.arpa domain, it MUST reply with an EAP Failure, as per . Similarly, if the server does not support the current provisioning method, and is unable to negotiate a different one, it MUST reply with a NAK of type zero (0) as per . This reply indicates that the requested provisioning method is not available, and that the peer should choose a different method of authentication. That different method may be another provisioning method, or it may be a full authentication. Once the server accepts the provisioning method, it then replies with an EAP method which MUST match the one proposed by the supplicant in the NAI. The EAP process then proceeds as per the EAP state machine outlined in . Implementations MUST treat peers using a provisioning NAI as untrusted, and untrustworthy. Once a peer is authenticated, it MUST be placed into a limited network, such as a captive portal. Systems implementing this specification SHOULD give peers access which is limited in duration. The provisioning process should be fairly quick, and of the order of seconds to tens of seconds in duration. Provisioning times longer than that likely indicate an issue. Implementations SHOULD give peers access which is limited in scope. The provisioning process likely does not need to download large amounts of data, and likely does not need access to a large number of services. The provisioning networks SHOULD allow only traffic which is necessary for the operation of the named provisioning method. Implementations SHOULD use functionality such as the RADIUS Filter-Id attribute () to set packet filters for the peer being provisioned. For ease of administration, the Filter-Id name could simply be the provisioning NAI, or a similar name. Such consistency aids with operational considerations when managing complex networks. Implementations SHOULD rate-limit provisioning attempts. A misbehaving peer should be blocked temporarily, or even permanently. Implementations SHOULD limit the total number of peers being provisioned at the same time. There is no requirement to allow all peers to connect without limit.

Other Considerations Implementations MUST NOT permit EAP method negotiation with provisioning credentials. That is, when a provisioning NAI is used, any EAP NAK sent by a server MUST contain only EAP type zero (0). Similarly, when an EAP peer uses a provisioning NAI and receives an EAP NAK, the contents MUST be ignored. While a server may support multiple provisioning methods, there is no way in EAP to negotiate which provisioning method can be used. It is also expected that the provisioning methods will be specific to a particular type of device. That is, a device is likely to support only one provisioning method. As a result, there is no need to require a method for negotiating provisioning methods.

Considerations for Provisioning Specifications The operational considerations discussed above have a number of impacts on specifications which define provisioning methods.

Negotiation Specifications which define provisioning for an EAP method SHOULD provide a method-specific process by which implementations can negotiate a mutually acceptable provisioning method. For the reasons noted above, however, we cannot make this suggestion mandatory. If it is not possible for a provisioning method to define any negotiation, then that limitation should not be a barrier to publishing the specification.

Renewal of Credentials Where a provisioning method is expected to create credentials which do not expire, the specification SHOULD state this explicitly. Where credentials expire, it is RECOMMENDED that specifications provide guidance on how the credentials are to be updated. For example, an EAP method could permit re-provisioning to be done as part of a normal EAP authentication, using the currently provisioned credentials. It is RECOMMENDED that the provisioning methods provide for a method which can be used without affecting network access. A specification could define provisioning endpoints such as Enrollment over Secure Transport (EST) , or Automatic Certificate Management Environment (ACME) . The provisioning endpoints could be available both on the provisioning network, and on the provisioned (i.e. normal) network. Such an architecture means that devices can be re-provisioned without losing network access.

Notes on AAA Routability When we say that the eap.arpa domain is not routable in an AAA proxy framework, we mean that the domain does not exist, and will never resolve to anything for dynamic discovery as defined in . In addition, administrators will not have statically configured AAA proxy routes for this domain. In order to avoid spurious DNS lookups, RADIUS servers supporting SHOULD perform filtering in the domains which are sent to DNS. Specifically, names in the "eap.arpa" domain SHOULD NOT be looked up in DNS.

Overview In this section, we provide background on the existing functionality, and describe why it was necessary to define provisioning methods for EAP.

Review of Existing Functionality For EAP-TLS, both Section 2.1.1 and provide for "peer unauthenticated access". However, those documents define no way for a peer to signal that it is requesting such access. The presumption is that the peer connects with some value for the EAP Identity, but without using a client certificate. The EAP server is then supposed to determine that the peer is requesting unauthenticated access, and take the appropriate steps to limit authorization. There appears to be no EAP peer or server implementations which support such access, since there is no defined way to perform any of the steps required. i.e. to signal that this access is desired, and then limit access. Wi-Fi Alliance has defined an unauthenticated EAP-TLS method, using a vendor-specific EAP type as part of HotSpot 2.0r2 . However, there appears to be few deployments of this specification. EAP-NOOB takes this process a step further. It defines both a way to signal that provisioning is desired, and also a way to exchange provisioning information within EAP-NOOB. That is, there is no need for the device to obtain limited network access, as all of the provisioning is done inside of the EAP-NOOB protocol. Tunnel Extensible Authentication Protocol (TEAP) provides for provisioning via an unauthenticated TLS tunnel. That document provides for a server unauthenticated provisioning mode, but the inner TLS exchange requires that both end authenticate each other. There are ways to provision a certificate, but the peer must still authenticate itself to the server with pre-existing credentials.

Taxonomy of Provisioning Types There are two scenarios where provisioning can be done. The first is where provisioning is done within the EAP type, as with EAP-NOOB . The second is where EAP is used to obtain limited network access (e.g. as with a captive portal). That limited network access is then used to run IP based provisioning over more complex protocols.

Rationale for Provisioning over EAP It is often useful to do all provisioning inside of EAP, because the EAP / AAA admin does not have control over the network. It is not always possible to define a captive portal where provisioning can be done. As a result, we need to be able to perform provisioning via EAP, and not via some IP protocol.

Interaction with existing EAP types As the provisioning identifier is used within EAP, it necessarily has interactions with, and effects on, the various EAP types. This section discusses those effects in more detail. Some EAP methods require shared credentials such as passwords in order to succeed. For example, both EAP-MSCHAPv2 (PEAP) and EAP-PWD perform cryptographic exchanges where both parties knowing a shared password. Where password-based methods are used, the password MUST be the same as the provisioning identifier. This requirement also applies to TLS-based EAP methods such as EAP Tunneled Transport Layer Security (EAP-TTLS) and Protected Extensible Authentication Protocol (PEAP). Where the TLS-based EAP method provides for an inner identity and inner authentication method, the credentials used there MUST be the provisioning identifier for both the inner identity, and any inner password. It is RECOMMENDED that provisioning be done via a TLS-based EAP methods. TLS provides for authentication of the EAP server, along with security and confidentiality of any provisioning data exchanged in the tunnel. Similarly, if provisioning is done in a captive portal outside of EAP, EAP-TLS permits the EAP peer to run a full EAP authentication session while having nothing more than a few certification authorities (CAs) locally configured.

EAP-TLS This document defines an identifier "portal@tls.eap.arpa", which is the first step towards enabling unauthenticated client provisioning in EAP-TLS. The purpose of the identifier is to allow EAP peers to signal EAP servers that they wish to obtain a "captive portal" style network access. This identifier signals the EAP server that the peer wishes to obtain "peer unauthenticated access" as per Section 2.1.1 and . An EAP server which agrees to authenticate this request MUST ensure that the device is placed into a captive portal with limited network access. Implementations SHOULD limit both the total amount of data transferred by devices in the captive portal, and SHOULD also limit the total amount of time a device spends within the captive portal. Further details of the captive portal architecture can be found in . The remaining question is how the EAP peer verifies the identity of the EAP server. The device SHOULD ignore the EAP server certificate entirely, as the server's identity does not matter. Any verification of servers can be done at the HTTPS layer when the device access the captive portal. Where possible the device SHOULD warn the end user that the provided certificate is unchecked, and untrusted. However, since the device likely is configured with web CAs (otherwise, the captive portal would also be unauthenticated), EAP peers MAY use the CAs available for the web in order to validate the EAP server certificate. If the presented certificate passes validation, the device does not need to warn the end user that the provided certificate is untrusted. It is possible to also use TLS-PSK with EAP-TLS for this provisioning. In which case, the Pre-Shared Key (PSK) identity MUST the same as the EAP Identifier, and the PSK MUST be the provisioning identifier.

TLS-based EAP methods Other TLS-based EAP methods such as TTLS and PEAP can use the same method as defined for EAP-TLS above. The only difference is that the inner identity and password is also the provisioning identifier. It is RECOMMENDED that provisioning methods use EAP-TLS in preference to any other TLS-based EAP methods. As the credentials for other methods are predefined and known in advance, those methods offer little benefit over EAP-TLS.

EAP-NOOB It is RECOMMENDED that server implementations of Nimble out-of-band authentication for EAP (EAP-NOOB) accept both identities "noob@eap-noob.arpa" and "@noob.eap.arpa" as synonyms. It is RECOMMENDED that EAP-NOOB peers use "@noob.eap.arpa" first, and if that does not succeed, use "noob@eap-noob.arpa"

IANA Considerations Three IANA actions are required. The first two are registry updates for "eap.arpa". The second is the creation of a new registry.

.arpa updates IANA is instructed to update the ".ARPA Zone Management" registry with the following entry: DOMAIN

eap.arpa

USAGE

For provisioning within the Extensible Authentication Protocol framework.

REFERENCE

THIS-DOCUMENT

IANA is instructed to update the "Special-Use Domain Names" registry as follows: NAME

eap.arpa

REFERENCE

THIS-DOCUMENT

Domain Name Reservation Considerations This section answers the questions which are required by Section 5 of . At a high level, these new domain names are used in certain situations in EAP. The domain names are never seen by users, and they do not appear in any networking protocol other than EAP.

Users:
User are not expected to recognize these names as special or use them differently from other domain names. The use of these names in EAP is invisible to end users.
Application Software:
EAP servers and clients are expected to make their software recognize these names as special and treat them differently. This document discusses that behavior.
EAP supplicants should recognize these names as special, and should refuse to allow users to enter them in any interface.
EAP servers and RADIUS servers should recognize the ".arpa" domain as special, and refuse to do dynamic discovery () for it.
Name Resolution APIs and Libraries:
Writers of these APIs and libraries are not expected to recognize these names or treat them differently.
Caching DNS Servers:
Writers of caching DNS servers are not expected to recognize these names or treat them differently.
Authoritative DNS Servers:
Writers of authoritative DNS servers are not expected to recognize these names or treat them differently.
DNS Server Operators:
These domain names have minimal impact on DNS server operators. They should never be used in DNS, or in any networking protocol outside of EAP.
Some DNS servers may receive lookups for this domain, if EAP or RADIUS servers are configured to do dynamic discovery for realms as defined in , and where those servers are not updated to ignore the ".arpa" domain. When queried for the "eap.arpa" domain, DNS servers SHOULD return an NXDOMAIN error.
If they try to configure their authoritative DNS as authoritative for this reserved name, compliant name servers do not need to do anything special. They can accept the domain or reject it. Either behavior will have no impact on this specification.
DNS Registries/Registrars:
DNS Registries/Registrars should deny requests to register this reserved domain name.

EAP Provisioning Identifiers Registry IANA is instructed to add the following new registry to the "Extensible Authentication Protocol (EAP) Registry" group. Assignments in this registry are done via "Expert Review" as described in Section 4.5. Guidelines for experts is provided in . The contents of the registry are as follows. Title

EAP Provisioning Identifiers

Registration Procedure(s)

Expert review

Reference

THIS-DOCUMENT

Registry

NAI
- The Network Access Identifier in format. Names are lowercase, and are listed in sorted order.
Method Type
- The EAP method name, taken from the "Description" field of the EAP "Method Types" registry.
Reference
- Reference where this identifier was defined.

Initial Values The following table gives the initial values for this table. NAI,Method-Type,Description,Reference @noob.eap.arpa,EAP-NOOB, and THIS-DOCUMENT portal@tls.eap.arpa,EAP-TLS, and THIS-DOCUMENT

Guidelines for Designated Experts The following text gives guidelines for Designated Experts who review allocation requests for this registry.

NAIs The intent is for the NAI to contain both a reference to the EAP Method Type, and a description of the purpose of the NAI. For example, with an EAP Method Type "name", and a purpose "action", the NAI SHOULD be of the form "action@foo.eap.arpa". The NAI MUST satisfy the requirements of the format. The utf8-username portion MAY be empty. The utf8-username portion MUST NOT be "anonymous". The NAI MUST end with "eap.arpa". NAIs in the registry SHOULD NOT contain more than one subdomain. NAIs with a leading "v." subdomain MUST NOT be registered. That subdomain is reserved for vendor and SDO extensions. The subdomain of the NAI field should correspond to the EAP Method Type name. Care should be taken so that the domain name conventions specified in are followed. The NAIs in this registry are case-insensitive. While notes that similar identifiers of different case can be considered to be different, for simplicity this registry requires that all entries MUST be lowercase. Identifiers MUST be unique when compared in a case-insensitive fashion. While notes that similar identifiers of different case can be considered to be different, this registry is made simpler by requiring case-insensitivity. Entries in the registry should be short. NAIs defined here will generally be sent in a RADIUS packet in the User-Name attribute ( Section 5.1). That specification recommends that implementations should support User-Names of at least 63 octets. NAI length considerations are further discussed in Section 2.3, and any allocations in this registry needs to take those limitations into consideration. Implementations are likely to support a total NAI length of 63 octets. Lengths between 63 and 253 octets may work. Lengths of 254 octets or more will not work with RADIUS .

Method Type Values in "Method Type" field of this registry MUST be taken from the IANA EAP Method Types registry or else it MUST be an Expanded Type which usually indicates a vendor specific EAP method. The EAP Method Type MUST provide an MSK and EMSK as defined in . Failure to provide these keys means that the method will not be usable within an authentication framework which requires those methods, such as with IEEE 802.1X.

Designated Experts For registration requests where a Designated Expert should be consulted, the responsible IESG area director should appoint the Designated Expert. But in order to allow for the allocation of values prior to the RFC being approved for publication, the Designated Expert can approve allocations once it seems clear that an RFC will be published. The Designated Expert will post a request to the EMU WG mailing list (or a successor designated by the Area Director) for comment and review, including an Internet-Draft or reference to external specification. Before a period of 30 days has passed, the Designated Expert will either approve or deny the registration request and publish a notice of the decision to the EAP WG mailing list or its successor, as well as informing IANA. A denial notice must be justified by an explanation, and in the cases where it is possible, concrete suggestions on how the request can be modified so as to become acceptable should be provided.

Organization Self Assignment This registry allows organizations to request allocations from this registry, but explicit allocations are not always required. Any NAI defined in this registry also implicitly defines a subdomain "v.". Organizations can self-allocate in this space, under the "v." subdomain, e.g. "local@example.com.v.tls.eap.arpa". Any domain name which is registered as a Fully Qualified Domain Name (FQDN) within the DNS can use that name within the "v." subdomain. Note that the right to use a self-allocated name is tied the ownership of the corresponding domain. If an organization loses the right to use a domain name, then it is no longer appropriate for it to use that domain name within the "v." self-allocation space.

Privacy Considerations The EAP Identity field is generally publicly visible to parties who can observe the EAP traffic. As the names given here are in a public specification, there is no privacy implication to exposing those names within EAP. The entire goal of this specification is in fact to make those names public, so that unknown (and private) parties can publicly (and anonymously) declare what kind of network access they desire. However, there are many additional privacy concerns around this specification. Most EAP traffic is sent over RADIUS . The RADIUS Access-Request packets typically contain large amounts of information such as MAC addresses, device location, etc. This specification does not change RADIUS or EAP, and as such does not change which information is publicly available, or is kept private. Those issues are dealt with in other specifications, such as . However, this specification can increase privacy by allowing devices to anonymously obtain network access, and then securely obtain credentials.

Security Considerations This specification defines a framework which permits unknown, anonymous, and unauthenticated devices to request and to obtain network access. As such, it is critical that network operators provide limited access to those devices. Future specifications which define an NAI within this registry, should give detailed descriptions of what kind of network access is to be provided.

On-Path Attackers and Impersonation In most EAP use-cases, the server identity is validated (usually through a certificate), or the EAP method allows the TLS tunnel to be cryptographically bound to the inner application data. For the methods outlined here, the use of public credentials, and/or skipping server validation allows "on-path" attacks to succeed where they would normally fail EAP peers and servers MUST assume that all data sent over an EAP session is visible to attackers, and can be modified by them. The methods defined here SHOULD only be used to bootstrap initial network access. All subsequent application-layer traffic SHOULD be full authenticated and secured with systems such as IPsec or TLS.

Provisioning is Unauthenticated We note that this specification allows for unauthenticated supplicants to obtain network access, however limited. As with any unauthenticated process, it can be abused. Implementations should take care to limit the use of the provisioning network.

Privacy Considerations The NAIs used here are contained in a public registry, and therefore do not have to follow the username privacy recommendations of . However, there may be other personally identifying information contained in EAP or AAA packets. This situation is no different from normal EAP authentication, and thus has no additional positive or negative implications for privacy.

Acknowledgements Mohit Sethi provided valuable insight that using subdomains was better and more informative than the original method, which used only the utf8-username portion of the NAI.

Changelog

00 - initial version