Check Point Software Technologies Ltd.

5 Hasolelim st. Tel Aviv 67897 Israel ynir@checkpoint.com

Huawei Technologies Co., Ltd.

101 Software Avenue, Yuhua District Nanjing, JiangSu 210012 China sunseawq@huawei.com

Security Area This document updates the Internet Key Exchange Protocol version 2 (IKEv2) described in RFC 5996. This extension allows an IKE Security Association (SA) to be created and authenticated using the Extensible Authentication Protocol (EAP) Re-authentication Protocol extension, as described in RFC 6696.

IKEv2, as specified in , allows (Section 2.16) authentication of the initiator using an EAP method. Using EAP significantly increases the count of round trips required to establish the IPsec SA and also may require user interaction. This makes it inconvenient to allow a single remote access client to create multiple IPsec tunnels with multiple IPsec gateways that belong to the same domain. The EAP Re-authentication Protocol (ERP), as described in , allows an EAP peer to authenticate to multiple authenticators while performing the full EAP method only once. Subsequent authentications require fewer round trips and no user interaction. Bringing these two technologies together allows a remote access IPsec client to create multiple tunnels with different gateways that belong to a single domain as well as using the keys from other contexts of using EAP, such as network access within the same domain, to transparently connect to VPN gateways within this domain. Additionally, it allows for faster set up of new tunnels when previous tunnels have been torn down due to things like network outage, device suspension, or a temporary move out of range. This is similar to the session resumption mechanism described in . One exception being that instead of a ticket stored by the client, the re-authentication Master Session Key (rMSK) (see Section 4.6 of ) is used as the session key stored on both the client and the Authentication, Authorization, and Accounting (AAA) server.

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

This work is motivated by the following scenarios: Multiple tunnels for a single remote access VPN client. Suppose a company has offices in New York City, Paris, and Shanghai. For historical reasons, the email server is located in the Paris office, most of the servers hosting the company's intranet are located in Shanghai, and the finance department servers are in New York City. An employee using a remote access VPN may need to connect to servers from all three locations. While it is possible to connect to a single gateway, and have that gateway route the requests to the other gateways (perhaps through site to site VPN), this is not efficient; it is more desirable to have the client initiate three different tunnels. It is, however, not desirable to have the user type in a password three times. Roaming. In these days of mobile phones and tablets, users often move from the wireless LAN in their office, where access may be granted through 802.1x, to a cellular network, where a VPN is necessary, and back again. Both the VPN server and the 802.1x access point are authenticators that connect to the same AAA servers. So it makes sense to make the transition smooth, without requiring user interaction. The device still needs to detect whether it is within the protected network, in which case it should not use VPN. However, this process is beyond the scope of this document. is a now-abandoned attempt at this. Resumption. If a device gets disconnected from an IKE peer, ERP can be used to reconnect to the same gateway without user intervention.

Supporting EAP Re-authentication Extension (ERX) requires an EAP payload in the first IKE_AUTH request. This is a deviation from the rules in , so support needs to be indicated through a Notify payload in the IKE_SA_INIT response. This Notify serves the same purpose as the EAP-Initiate/Re-auth-Start message of ERX, as specified in Section 5.3.1 of . The "Domain Name" field contains the content of the Domain-Name TLV as specified in Section 5.3.1.1 of the same document. A supporting initiator that has unexpired keys for this domain will send the EAP-Initiate/Re-auth message in an EAP payload in the first IKE_AUTH request. The responder sends the EAP payload content to a backend AAA server. If that server has a valid rMSK for that session, it sends those along with an EAP-Finish/Re-auth message. The responder then forwards the EAP-Finish/Re-auth message to the initiator in an EAP payload within the first IKE_AUTH response. The initiator then sends an additional IKE_AUTH request that includes the AUTH payload, which has been calculated using the rMSK in the role of the MSK as described in Sections 2.15 and 2.16 of . The responder replies similarly, and the IKE_AUTH exchange is finished. If the backend AAA server does not have valid keys for the Re-auth-Start message, it sends back a normal EAP request, and no rMSK key. EAP flow continues as in . The following figure is adapted from Appendixes C.1 and C.3 of , with most of the optional payloads removed. Note that the EAP-Initiate/Re-auth message is added.

SA, KE, Ni, | | init response <-- SA, KE, Nr, | N[ERX_SUPPORTED] IKE_AUTH Exchanges: | first request --> EAP(EAP-Initiate/Re-auth), | IDi, | SA, TSi, TSr | | first response <-- IDr, [CERT+], AUTH, | EAP(EAP-Finish/Re-auth) | | last request --> AUTH | | last response <-- AUTH, | SA, TSi, TSr ]]>

The IDi payload MUST have ID Type ID_RFC822_ADDR, and the data field MUST contain the same value as the KeyName-NAI TLV in the EAP-Initiate/Re-auth message. See for details.

Section 3.16 of enumerates the EAP codes in EAP messages that are carried in EAP payloads. The enumeration goes only to 4. It is not clear whether or not that list is supposed to be exhaustive. To clarify, an implementation conforming to this specification MUST accept and transmit EAP messages with at least the codes for Initiate and Finish (5 and 6) from Section 5.3 of , in addition to the four codes enumerated in . This document is intentionally silent about other EAP codes that are not enumerated in those documents.

The authors, as well as participants of the HOKEY and IPsecME working groups, believe that all use cases for this extension to IKE have a single backend AAA server doing both the authentication and the re-authentication. The reasoning behind this is that IKE runs over the Internet and would naturally connect to the user's home network. This section addresses instances where this is not the case. Section 5.3.2 of describes the EAP-Initiate/Re-auth packet, which, in the case of IKEv2, is carried in the first IKE_AUTH request. This packet contains the KeyName-NAI TLV. This TLV contains the username used in authentication. It is relayed to the AAA server in the AccessRequest message and is returned from the AAA server in the AccessAccept message. The username part of the Network Access Identifier (NAI) within the TLV is the EMSKName encoded in hexadecimal digits. The domain part is the domain name of the home domain of the user. The username part is ephemeral in the sense that a new one is generated for each full authentication. This ephemeral value is not a good basis for making policy decisions, and it is also a poor source of user identification for the purposes of logging. Instead, it is up to the implementation in the IPsec gateway to make policy decisions based on other factors. The following list is by no means exhaustive: In some cases, the home domain name may be enough to make policy decisions. If all users with a particular home domain get the same authorization, then policy does not depend on the real username. Meaningful logs can still be issued by correlating VPN gateway IKE events with AAA servers access records. Sometimes users receive different authorizations based on groups to which they belong. The AAA server can communicate such information to the VPN gateway, for example, using the CLASS attribute in RADIUS and Diameter . Logging again depends on correlation with AAA servers. AAA servers may support extensions that allow them to communicate with their clients (in our case -- the VPN gateway) to push user information. For example, a certain product integrates a RADIUS server with the Lightweight Directory Access Protocol (LDAP) , so a client could query the server using LDAP and receive the real record for this user. Others may provide this data through vendor-specific extensions to RADIUS or Diameter. In any case, authorization is a major issue in deployments, if the backend AAA server supporting the re-authentication is different from the AAA server that had supported the original authentication. It is up to the re-authenticating AAA server to provide the necessary information for authorization. A conforming implementation of this protocol MAY reject initiators for which it is unable to make policy decisions because of these reasons.

The Notify payload is as described in :

Protocol ID (1 octet) - MUST be zero, as this message is related to an IKE SA. Security Parameter Index (SPI) Size (1 octet) - MUST be zero, in conformance with Section 3.10 of . ERX Notify Message Type (2 octets) - MUST be 16427, the value assigned for ERX. Domain Name (variable) - contains the domain name or realm, as these terms are used in and encoded as ASCII, as specified in .

This specification changes the behavior of IKE peers, both initiators and responders. The behavior of backend AAA servers is not changed by this specification, but they are required to support . The same goes for the EAP client, if it's not integrated into the IKE initiator (for example, if the EAP client is an operating system component). This specification is silent about key storage and key lifetimes on either the EAP client or the EAP server. These issues are covered in Sections 3, 4, and 5 of . The key lifetime may be communicated from the AAA server to the EAP client via the Lifetime attribute in the EAP-Finish/Re-auth message. If the server does not have a valid key, while the client does have one, regular EAP is used (see ). This should not happen if lifetimes are communicated. In such a case, the IKEv2 initiator / EAP client MAY alert the user and MAY log the event. Note that this does not necessarily indicate an attack. It could simply be a loss of state on the AAA server.

The protocol extension described in this document extends the authentication from one EAP context, which may or may not be part of IKEv2, to an IKEv2 context. Successful completion of the protocol proves to the authenticator, which in our case is a VPN gateway, that the supplicant or VPN client has authenticated in some other EAP context. The protocol supplies the authenticator with the domain name with which the supplicant has authenticated, but does not supply it with a specific identity. Instead, the gateway receives an EMSKName, which is an ephemeral ID. With this variant of the IKEv2 protocol, the initiator never sends its real identity on the wire while the server does. This is different from the usual IKEv2 practice of the initiator revealing its identity first. If the domain name is sufficient to make access control decisions, this is enough. If not, then the gateway needs to find out either the real name or authorization information for that particular user. This may be done using the AAA protocol or by some other federation protocol, which is out of scope for this specification.

IANA has assigned a notify message type of 16427 from the "IKEv2 Notify Message Types - Status Types" registry with the name "ERX_SUPPORTED".

The authors would like to thank Yaron Sheffer for comments and suggested text that have contributed to this document. Thanks also to Juergen Schoenwaelder for his OPS-DIR review comments.

Harvard University

1350 Mass. Ave. Cambridge MA 02138 - +1 617 495 3864 sob@harvard.edu

General keyword In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. Authors who follow these guidelines should incorporate this phrase near the beginning of their 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 RFC 2119. Note that the force of these words is modified by the requirement level of the document in which they are used. In order to provide roaming services, it is necessary to have a standardized method for identifying users. This document defines the syntax for the Network Access Identifier (NAI), the user identity submitted by the client during network authentication. "Roaming" may be loosely defined as the ability to use any one of multiple Internet Service Providers (ISPs), while maintaining a formal, \%customer-vendor relationship with only one. Examples of where roaming capabilities might be required include ISP "confederations" and \%ISP-provided corporate network access support. This document is a revised version of RFC 2486, which originally defined NAIs. Enhancements include international character set and privacy support, as well as a number of corrections to the original RFC. [STANDARDS-TRACK] The Extensible Authentication Protocol (EAP) defined the Extended Master Session Key (EMSK) generation, but reserved it for unspecified future uses. This memo reserves the EMSK for the sole purpose of deriving root keys. Root keys are master keys that can be used for multiple purposes, identified by usage definitions. This document also specifies a mechanism for avoiding conflicts between root keys by deriving them in a manner that guarantees cryptographic separation. Finally, this document also defines one such root key usage: Domain-Specific Root Keys are root keys made available to and used within specific key management domains. [STANDARDS-TRACK] This document describes version 2 of the Internet Key Exchange (IKE) protocol. IKE is a component of IPsec used for performing mutual authentication and establishing and maintaining Security Associations (SAs). This document replaces and updates RFC 4306, and includes all of the clarifications from RFC 4718. [STANDARDS-TRACK] The Extensible Authentication Protocol (EAP) is a generic framework supporting multiple types of authentication methods. In systems where EAP is used for authentication, it is desirable to avoid repeating the entire EAP exchange with another authenticator. This document specifies extensions to EAP and the EAP keying hierarchy to support an EAP method-independent protocol for efficient re- authentication between the peer and an EAP re-authentication server through any authenticator. The re-authentication server may be in the home network or in the local network to which the peer is connecting. [STANDARDS-TRACK] Remote access clients, in particular IPsec-based ones, are heavily deployed in enterprise environments. In many enterprises the security policy allows remote-access clients to switch to unprotected operation when entering the trusted network. This document specifies a method that lets a client detect this situation in a secure manner, with the help of a security gateway. We propose a minor extension to IKEv2 to achieve this goal. This document describes a protocol for carrying authentication, authorization, and configuration information between a Network Access Server which desires to authenticate its links and a shared Authentication Server. [STANDARDS-TRACK] The Diameter base protocol is intended to provide an Authentication, Authorization, and Accounting (AAA) framework for applications such as network access or IP mobility in both local and roaming situations. This document specifies the message format, transport, error reporting, accounting, and security services used by all Diameter applications. The Diameter base protocol as defined in this document obsoletes RFC 3588 and RFC 5719, and it must be supported by all new Diameter implementations. [STANDARDS-TRACK] This document describes the protocol elements, along with their semantics and encodings, of the Lightweight Directory Access Protocol (LDAP). LDAP provides access to distributed directory services that act in accordance with X.500 data and service models. These protocol elements are based on those described in the X.500 Directory Access Protocol (DAP). [STANDARDS-TRACK] The Internet Key Exchange version 2 (IKEv2) protocol has a certain computational and communication overhead with respect to the number of round trips required and the cryptographic operations involved. In remote access situations, the Extensible Authentication Protocol (EAP) is used for authentication, which adds several more round trips and consequently latency.</t><t> To re-establish security associations (SAs) upon a failure recovery condition is time consuming especially when an IPsec peer (such as a VPN gateway) needs to re-establish a large number of SAs with various endpoints. A high number of concurrent sessions might cause additional problems for an IPsec peer during SA re-establishment.</t><t> In order to avoid the need to re-run the key exchange protocol from scratch, it would be useful to provide an efficient way to resume an IKE/IPsec session. This document proposes an extension to IKEv2 that allows a client to re-establish an IKE SA with a gateway in a highly efficient manner, utilizing a previously established IKE SA.</t><t> A client can reconnect to a gateway from which it was disconnected. The proposed approach encodes partial IKE state into an opaque ticket, which can be stored on the client or in a centralized store, and is later made available to the IKEv2 responder for re-authentication. We use the term ticket to refer to the opaque data that is created by the IKEv2 responder. This document does not specify the format of the ticket but examples are provided. [STANDARDS-TRACK]