Improved Extensible Authentication Protocol Method for 3rd Generation Authentication and Key Agreement (EAP-AKA')
The information below is for an old version of the document.
This is an older version of an Internet-Draft that was ultimately published as RFC 9048.
|Authors||Jari Arkko , Vesa Lehtovirta , Vesa Torvinen , Pasi Eronen|
|Last updated||2018-11-07 (Latest revision 2018-10-19)|
|RFC stream||Internet Engineering Task Force (IETF)|
IOTDIR Telechat review (of -07) Ready with Issues
SECDIR Last Call review (of -06) Has Nits
GENART Last Call review (of -06) Ready with Issues
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Network Working Group J. Arkko Internet-Draft V. Lehtovirta Obsoletes: 5448 (if approved) V. Torvinen Updates: 4187 (if approved) Ericsson Intended status: Informational P. Eronen Expires: April 22, 2019 Nokia October 19, 2018 Improved Extensible Authentication Protocol Method for 3rd Generation Authentication and Key Agreement (EAP-AKA') draft-ietf-emu-rfc5448bis-03 Abstract This specification defines an EAP method, EAP-AKA', a small revision of the EAP-AKA method. EAP-AKA' provides a key derivation function that binds the keys derived within the method to the name of the access network. The key derivation mechanism has been defined in the 3rd Generation Partnership Project (3GPP). This specification allows its use in EAP in an interoperable manner. In addition, EAP-AKA' employs SHA-256 instead of SHA-1. This specification also updates RFC 4187 EAP-AKA to prevent bidding down attacks from EAP-AKA'. This version of the EAP-AKA' specification provides updates to specify the protocol behaviour for 5G deployments as well. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on April 22, 2019. Arkko, et al. Expires April 22, 2019 [Page 1] Internet-Draft EAP-AKA' October 2018 Copyright Notice Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 5 3. EAP-AKA' . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. AT_KDF_INPUT . . . . . . . . . . . . . . . . . . . . . . 8 3.2. AT_KDF . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.3. Key Generation . . . . . . . . . . . . . . . . . . . . . 13 3.4. Hash Functions . . . . . . . . . . . . . . . . . . . . . 15 3.4.1. PRF' . . . . . . . . . . . . . . . . . . . . . . . . 15 3.4.2. AT_MAC . . . . . . . . . . . . . . . . . . . . . . . 15 3.4.3. AT_CHECKCODE . . . . . . . . . . . . . . . . . . . . 15 4. Bidding Down Prevention for EAP-AKA . . . . . . . . . . . . . 16 5. Peer Identities . . . . . . . . . . . . . . . . . . . . . . . 17 5.1. Username Types in EAP-AKA' Identities . . . . . . . . . . 18 5.2. Generating Pseudonyms and Fast Re-Authentication Identities . . . . . . . . . . . . . . . . . . . . . . . 18 5.3. Identifier Usage in 5G . . . . . . . . . . . . . . . . . 19 5.3.1. Key Derivation . . . . . . . . . . . . . . . . . . . 20 5.3.2. EAP Identity Response and EAP-AKA' AT_IDENTITY Attribute . . . . . . . . . . . . . . . . . . . . . . 21 6. Exported Parameters . . . . . . . . . . . . . . . . . . . . . 23 7. Security Considerations . . . . . . . . . . . . . . . . . . . 23 7.1. Privacy . . . . . . . . . . . . . . . . . . . . . . . . . 26 7.2. Discovered Vulnerabilities . . . . . . . . . . . . . . . 28 7.3. Pervasive Monitoring . . . . . . . . . . . . . . . . . . 29 7.4. Security Properties of Binding Network Names . . . . . . 30 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31 8.1. Type Value . . . . . . . . . . . . . . . . . . . . . . . 31 8.2. Attribute Type Values . . . . . . . . . . . . . . . . . . 31 8.3. Key Derivation Function Namespace . . . . . . . . . . . . 32 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 32 9.1. Normative References . . . . . . . . . . . . . . . . . . 32 Arkko, et al. Expires April 22, 2019 [Page 2] Internet-Draft EAP-AKA' October 2018 9.2. Informative References . . . . . . . . . . . . . . . . . 34 Appendix A. Changes from RFC 5448 . . . . . . . . . . . . . . . 36 Appendix B. Changes from RFC 4187 to RFC 5448 . . . . . . . . . 37 Appendix C. Changes from Previous Version of This Draft . . . . 37 Appendix D. Importance of Explicit Negotiation . . . . . . . . . 38 Appendix E. Test Vectors . . . . . . . . . . . . . . . . . . . . 39 Appendix F. Contributors . . . . . . . . . . . . . . . . . . . . 43 Appendix G. Acknowledgments . . . . . . . . . . . . . . . . . . 44 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 44 1. Introduction This specification defines an Extensible Authentication Protocol (EAP)[RFC3748] method, EAP-AKA', a small revision of the EAP-AKA method originally defined in [RFC4187]. EAP-AKA' provides a new key derivation function, specified in [TS-3GPP.33.402]. This function binds the keys derived within the method to the name of the access network. This limits the effects of compromised access network nodes and keys. This specification defines the EAP encapsulation for AKA when the new key derivation mechanism is in use. 3GPP has defined a number of applications for the revised AKA mechanism, some based on native encapsulation of AKA over 3GPP radio access networks and others based on the use of EAP. For making the new key derivation mechanisms usable in EAP-AKA, additional protocol mechanisms are necessary. Given that RFC 4187 calls for the use of CK (the encryption key) and IK (the integrity key) from AKA, existing implementations continue to use these. Any change of the key derivation must be unambiguous to both sides in the protocol. That is, it must not be possible to accidentally connect old equipment to new equipment and get the key derivation wrong or attempt to use wrong keys without getting a proper error message. The change must also be secure against bidding down attacks that attempt to force the participants to use the least secure mechanism. This specification therefore introduces a variant of the EAP-AKA method, called EAP-AKA'. This method can employ the derived keys CK' and IK' from the 3GPP specification and updates the used hash function to SHA-256 [FIPS.180-4]. But it is otherwise equivalent to RFC 4187. Given that a different EAP method type value is used for EAP-AKA and EAP-AKA', a mutually supported method may be negotiated using the standard mechanisms in EAP [RFC3748]. Note: Appendix D explains why it is important to be explicit about the change of semantics for the keys, and why other approaches would lead to severe interoperability problems. Arkko, et al. Expires April 22, 2019 [Page 3] Internet-Draft EAP-AKA' October 2018 This version of the EAP-AKA' specification obsoletes RFC 5448. The changes are as follows: o Update the reference on how the Network Name field is constructed in the protocol. The update ensures that EAP-AKA' is compatible with 5G deployments. RFC 5448 referred to the Release 8 version of [TS-3GPP.24.302] and this update points to the first 5G version, Release 15. o Specify how EAP and EAP-AKA' use identifiers in 5G. Additional identifiers are introduced in 5G, and for interoperability, it is necessary that the right identifiers are used as inputs in the key generation. In addition, for identity privacy it is important that when privacy-friendly identifiers in 5G are used, no trackable, permanent identifiers are passed in EAP-AKA' either. o Specify session identifiers and other exported parameters, as those were not specified in [RFC5448] despite requirements set forward in [RFC5247] to do so. Also, while [RFC5247] specified session identifiers for EAP-AKA, it only did so for the full authentication case, not for the case of fast re-authentication. o Update the requirements on generating pseudonym usernames and fast re-authentication identities to ensure identity privacy. o Describe what has been learned about any vulnerabilities in AKA or EAP-AKA'. o Describe the privacy and pervasive monitoring considerations related to EAP-AKA'. Some of the updates are small. For instance, for the first update, the reference update does not change the 3GPP specification number, only the version. But this reference is crucial in correct calculation of the keys resulting from running the EAP-AKA' method, so an update of the RFC with the newest version pointer may be warranted. Note: This specification refers only to the 5G specifications. Any further update that affects, for instance, key generation is something that EAP-AKA' implementations should take into account. Upon such updates there will be a need to both update the specification and the implementations. It is an explicit non-goal of this draft to include any other technical modifications, addition of new features or other changes. The EAP-AKA' base protocol is stable and needs to stay that way. If Arkko, et al. Expires April 22, 2019 [Page 4] Internet-Draft EAP-AKA' October 2018 there are any extensions or variants, those need to be proposed as standalone extensions or even as different authentication methods. The rest of this specification is structured as follows. Section 3 defines the EAP-AKA' method. Section 4 adds support to EAP-AKA to prevent bidding down attacks from EAP-AKA'. Section 5 specifies requirements regarding the use of peer identities, including how how EAP-AKA' identifiers are used in 5G context. Section 6 specifies what parameters EAP-AKA' exports out of the method. Section 7 explains the security differences between EAP-AKA and EAP-AKA'. Section 8 describes the IANA considerations and Appendix A and Appendix B explains what updates to RFC 5448 EAP-AKA' and RFC 4187 EAP-AKA have been made in this specification. Appendix D explains some of the design rationale for creating EAP-AKA' Finally, Appendix E provides test vectors. Editor's Note: The publication of this RFC depends on its normative references [TS-3GPP.24.302] and [TS-3GPP.33.501] reaching a stable status for Release 15, as indicated by 3GPP. This is expected to happen shortly. The RFC Editor should check with the 3GPP liaisons that this has happened. RFC Editor: Please delete this note upon publication of this specification as an RFC. 2. Requirements Language 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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 3. EAP-AKA' EAP-AKA' is a new EAP method that follows the EAP-AKA specification [RFC4187] in all respects except the following: o It uses the Type code 50, not 23 (which is used by EAP-AKA). o It carries the AT_KDF_INPUT attribute, as defined in Section 3.1, to ensure that both the peer and server know the name of the access network. o It supports key derivation function negotiation via the AT_KDF attribute (Section 3.2) to allow for future extensions. o It calculates keys as defined in Section 3.3, not as defined in EAP-AKA. Arkko, et al. Expires April 22, 2019 [Page 5] Internet-Draft EAP-AKA' October 2018 o It employs SHA-256, not SHA-1 [FIPS.180-4] (Section 3.4). Figure 1 shows an example of the authentication process. Each message AKA'-Challenge and so on represents the corresponding message from EAP-AKA, but with EAP-AKA' Type code. The definition of these messages, along with the definition of attributes AT_RAND, AT_AUTN, AT_MAC, and AT_RES can be found in [RFC4187]. Arkko, et al. Expires April 22, 2019 [Page 6] Internet-Draft EAP-AKA' October 2018 Peer Server | EAP-Request/Identity | |<-------------------------------------------------------| | | | EAP-Response/Identity | | (Includes user's Network Access Identifier, NAI) | |------------------------------------------------------->| | +--------------------------------------------------+ | | Server determines the network name and ensures | | | that the given access network is authorized to | | | use the claimed name. The server then runs the | | | AKA' algorithms generating RAND and AUTN, and | | | derives session keys from CK' and IK'. RAND and | | | AUTN are sent as AT_RAND and AT_AUTN attributes, | | | whereas the network name is transported in the | | | AT_KDF_INPUT attribute. AT_KDF signals the used | | | key derivation function. The session keys are | | | used in creating the AT_MAC attribute. | | +--------------------------------------------------+ | EAP-Request/AKA'-Challenge | | (AT_RAND, AT_AUTN, AT_KDF, AT_KDF_INPUT, AT_MAC)| |<-------------------------------------------------------| +------------------------------------------------------+ | | The peer determines what the network name should be, | | | based on, e.g., what access technology it is using. | | | The peer also retrieves the network name sent by | | | the network from the AT_KDF_INPUT attribute. The | | | two names are compared for discrepancies, and if | | | necessary, the authentication is aborted. Otherwise,| | | the network name from AT_KDF_INPUT attribute is | | | used in running the AKA' algorithms, verifying AUTN | | | from AT_AUTN and MAC from AT_MAC attributes. The | | | peer then generates RES. The peer also derives | | | session keys from CK'/IK'. The AT_RES and AT_MAC | | | attributes are constructed. | | +------------------------------------------------------+ | | EAP-Response/AKA'-Challenge | | (AT_RES, AT_MAC) | |------------------------------------------------------->| | +--------------------------------------------------+ | | Server checks the RES and MAC values received | | | in AT_RES and AT_MAC, respectively. Success | | | requires both to be found correct. | | +--------------------------------------------------+ | EAP-Success | |<-------------------------------------------------------| Figure 1: EAP-AKA' Authentication Process Arkko, et al. Expires April 22, 2019 [Page 7] Internet-Draft EAP-AKA' October 2018 EAP-AKA' can operate on the same credentials as EAP-AKA and employ the same identities. However, EAP-AKA' employs different leading characters than EAP-AKA for the conventions given in Section 4.1.1 of [RFC4187] for International Mobile Subscriber Identifier (IMSI) based usernames. EAP-AKA' MUST use the leading character "6" (ASCII 36 hexadecimal) instead of "0" for IMSI-based permanent usernames. All other usage and processing of the leading characters, usernames, and identities is as defined by EAP-AKA [RFC4187]. For instance, the pseudonym and fast re-authentication usernames need to be constructed so that the server can recognize them. As an example, a pseudonym could begin with a leading "7" character (ASCII 37 hexadecimal) and a fast re-authentication username could begin with "8" (ASCII 38 hexadecimal). Note that a server that implements only EAP-AKA may not recognize these leading characters. According to Section 4.1.4 of [RFC4187], such a server will re-request the identity via the EAP- Request/AKA-Identity message, making obvious to the peer that EAP-AKA and associated identity are expected. 3.1. AT_KDF_INPUT The format of the AT_KDF_INPUT 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_KDF_INPUT | Length | Actual Network Name Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . Network Name . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The fields are as follows: AT_KDF_INPUT This is set to 23. Length The length of the attribute, calculated as defined in [RFC4187], Section 8.1. Actual Network Name Length Arkko, et al. Expires April 22, 2019 [Page 8] Internet-Draft EAP-AKA' October 2018 This is a 2 byte actual length field, needed due to the requirement that the previous field is expressed in multiples of 4 bytes per the usual EAP-AKA rules. The Actual Network Name Length field provides the length of the network name in bytes. Network Name This field contains the network name of the access network for which the authentication is being performed. The name does not include any terminating null characters. Because the length of the entire attribute must be a multiple of 4 bytes, the sender pads the name with 1, 2, or 3 bytes of all zero bits when necessary. Only the server sends the AT_KDF_INPUT attribute. The value is sent as specified in [TS-3GPP.24.302] for non-3GPP access networks, and as specified in [TS-3GPP.33.501] for 5G access networks. Per [TS-3GPP.33.402], the server always verifies the authorization of a given access network to use a particular name before sending it to the peer over EAP-AKA'. The value of the AT_KDF_INPUT attribute from the server MUST be non-empty. If it is empty, the peer behaves as if AUTN had been incorrect and authentication fails. See Section 3 and Figure 3 of [RFC4187] for an overview of how authentication failures are handled. Note: Currently, [TS-3GPP.24.302] or [TS-3GPP.33.501] specify separate values. The former specifies what is called "Access Network ID" and the latter specifies what is called "Serving Network Name". However, from an EAP-AKA' perspective both occupy the same field, and need to be distinguishable from each other. Currently specified values are distinguishable, but it would be useful that this be specified explicitly in the 3GPP specifications. In addition, the peer MAY check the received value against its own understanding of the network name. Upon detecting a discrepancy, the peer either warns the user and continues, or fails the authentication process. More specifically, the peer SHOULD have a configurable policy that it can follow under these circumstances. If the policy indicates that it can continue, the peer SHOULD log a warning message or display it to the user. If the peer chooses to proceed, it MUST use the network name as received in the AT_KDF_INPUT attribute. If the policy indicates that the authentication should fail, the peer behaves as if AUTN had been incorrect and authentication fails. The Network Name field contains a UTF-8 string. This string MUST be constructed as specified in [TS-3GPP.24.302] for "Access Network Identity". The string is structured as fields separated by colons Arkko, et al. Expires April 22, 2019 [Page 9] Internet-Draft EAP-AKA' October 2018 (:). The algorithms and mechanisms to construct the identity string depend on the used access technology. On the network side, the network name construction is a configuration issue in an access network and an authorization check in the authentication server. On the peer, the network name is constructed based on the local observations. For instance, the peer knows which access technology it is using on the link, it can see information in a link-layer beacon, and so on. The construction rules specify how this information maps to an access network name. Typically, the network name consists of the name of the access technology, or the name of the access technology followed by some operator identifier that was advertised in a link-layer beacon. In all cases, [TS-3GPP.24.302] is the normative specification for the construction in both the network and peer side. If the peer policy allows running EAP-AKA' over an access technology for which that specification does not provide network name construction rules, the peer SHOULD rely only on the information from the AT_KDF_INPUT attribute and not perform a comparison. If a comparison of the locally determined network name and the one received over EAP-AKA' is performed on the peer, it MUST be done as follows. First, each name is broken down to the fields separated by colons. If one of the names has more colons and fields than the other one, the additional fields are ignored. The remaining sequences of fields are compared, and they match only if they are equal character by character. This algorithm allows a prefix match where the peer would be able to match "", "FOO", and "FOO:BAR" against the value "FOO:BAR" received from the server. This capability is important in order to allow possible updates to the specifications that dictate how the network names are constructed. For instance, if a peer knows that it is running on access technology "FOO", it can use the string "FOO" even if the server uses an additional, more accurate description, e.g., "FOO:BAR", that contains more information. The allocation procedures in [TS-3GPP.24.302] ensure that conflicts potentially arising from using the same name in different types of networks are avoided. The specification also has detailed rules about how a client can determine these based on information available to the client, such as the type of protocol used to attach to the network, beacons sent out by the network, and so on. Information that the client cannot directly observe (such as the type or version of the home network) is not used by this algorithm. The AT_KDF_INPUT attribute MUST be sent and processed as explained above when AT_KDF attribute has the value 1. Future definitions of Arkko, et al. Expires April 22, 2019 [Page 10] Internet-Draft EAP-AKA' October 2018 new AT_KDF values MUST define how this attribute is sent and processed. 3.2. AT_KDF AT_KDF is an attribute that the server uses to reference a specific key derivation function. It offers a negotiation capability that can be useful for future evolution of the key derivation functions. The format of the AT_KDF 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_KDF | Length | Key Derivation Function | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The fields are as follows: AT_KDF This is set to 24. Length The length of the attribute, MUST be set to 1. Key Derivation Function An enumerated value representing the key derivation function that the server (or peer) wishes to use. Value 1 represents the default key derivation function for EAP-AKA', i.e., employing CK' and IK' as defined in Section 3.3. Servers MUST send one or more AT_KDF attributes in the EAP-Request/ AKA'-Challenge message. These attributes represent the desired functions ordered by preference, the most preferred function being the first attribute. Upon receiving a set of these attributes, if the peer supports and is willing to use the key derivation function indicated by the first attribute, the function is taken into use without any further negotiation. However, if the peer does not support this function or is unwilling to use it, it does not process the received EAP-Request/ AKA'-Challenge in any way except by responding with the EAP-Response/ AKA'-Challenge message that contains only one attribute, AT_KDF with the value set to the selected alternative. If there is no suitable Arkko, et al. Expires April 22, 2019 [Page 11] Internet-Draft EAP-AKA' October 2018 alternative, the peer behaves as if AUTN had been incorrect and authentication fails (see Figure 3 of [RFC4187]). The peer fails the authentication also if there are any duplicate values within the list of AT_KDF attributes (except where the duplication is due to a request to change the key derivation function; see below for further information). Upon receiving an EAP-Response/AKA'-Challenge with AT_KDF from the peer, the server checks that the suggested AT_KDF value was one of the alternatives in its offer. The first AT_KDF value in the message from the server is not a valid alternative. If the peer has replied with the first AT_KDF value, the server behaves as if AT_MAC of the response had been incorrect and fails the authentication. For an overview of the failed authentication process in the server side, see Section 3 and Figure 2 of [RFC4187]. Otherwise, the server re-sends the EAP-Response/AKA'-Challenge message, but adds the selected alternative to the beginning of the list of AT_KDF attributes and retains the entire list following it. Note that this means that the selected alternative appears twice in the set of AT_KDF values. Responding to the peer's request to change the key derivation function is the only legal situation where such duplication may occur. When the peer receives the new EAP-Request/AKA'-Challenge message, it MUST check that the requested change, and only the requested change, occurred in the list of AT_KDF attributes. If so, it continues with processing the received EAP-Request/AKA'-Challenge as specified in [RFC4187] and Section 3.1 of this document. If not, it behaves as if AT_MAC had been incorrect and fails the authentication. If the peer receives multiple EAP-Request/AKA'-Challenge messages with differing AT_KDF attributes without having requested negotiation, the peer MUST behave as if AT_MAC had been incorrect and fail the authentication. Note that the peer may also request sequence number resynchronization [RFC4187]. This happens after AT_KDF negotiation has already completed. An AKA'-Synchronization-Failure message is sent as a response to the newly received EAP-Request/AKA'-Challenge (the last message of the AT_KDF negotiation). The AKA'-Synchronization-Failure message MUST contain the AUTS parameter as specified in [RFC4187] and a copy the AT_KDF attributes as they appeared in the last message of the AT_KDF negotiation. If the AT_KDF attributes are found to differ from their earlier values, the peer and server MUST behave as if AT_MAC had been incorrect and fail the authentication. Arkko, et al. Expires April 22, 2019 [Page 12] Internet-Draft EAP-AKA' October 2018 3.3. Key Generation Both the peer and server MUST derive the keys as follows. AT_KDF set to 1 In this case, MK is derived and used as follows: MK = PRF'(IK'|CK',"EAP-AKA'"|Identity) K_encr = MK[0..127] K_aut = MK[128..383] K_re = MK[384..639] MSK = MK[640..1151] EMSK = MK[1152..1663] Here [n..m] denotes the substring from bit n to m. PRF' is a new pseudo-random function specified in Section 3.4. The first 1664 bits from its output are used for K_encr (encryption key, 128 bits), K_aut (authentication key, 256 bits), K_re (re- authentication key, 256 bits), MSK (Master Session Key, 512 bits), and EMSK (Extended Master Session Key, 512 bits). These keys are used by the subsequent EAP-AKA' process. K_encr is used by the AT_ENCR_DATA attribute, and K_aut by the AT_MAC attribute. K_re is used later in this section. MSK and EMSK are outputs from a successful EAP method run [RFC3748]. IK' and CK' are derived as specified in [TS-3GPP.33.402]. The functions that derive IK' and CK' take the following parameters: CK and IK produced by the AKA algorithm, and value of the Network Name field comes from the AT_KDF_INPUT attribute (without length or padding) . The value "EAP-AKA'" is an eight-characters-long ASCII string. It is used as is, without any trailing NUL characters. Identity is the peer identity as specified in Section 7 of [RFC4187]. When the server creates an AKA challenge and corresponding AUTN, CK, CK', IK, and IK' values, it MUST set the Authentication Management Field (AMF) separation bit to 1 in the AKA algorithm [TS-3GPP.33.102]. Similarly, the peer MUST check that the AMF separation bit is set to 1. If the bit is not set to 1, the peer behaves as if the AUTN had been incorrect and fails the authentication. Arkko, et al. Expires April 22, 2019 [Page 13] Internet-Draft EAP-AKA' October 2018 On fast re-authentication, the following keys are calculated: MK = PRF'(K_re,"EAP-AKA' re-auth"|Identity|counter|NONCE_S) MSK = MK[0..511] EMSK = MK[512..1023] MSK and EMSK are the resulting 512-bit keys, taking the first 1024 bits from the result of PRF'. Note that K_encr and K_aut are not re-derived on fast re-authentication. K_re is the re- authentication key from the preceding full authentication and stays unchanged over any fast re-authentication(s) that may happen based on it. The value "EAP-AKA' re-auth" is a sixteen- characters-long ASCII string, again represented without any trailing NUL characters. Identity is the fast re-authentication identity, counter is the value from the AT_COUNTER attribute, NONCE_S is the nonce value from the AT_NONCE_S attribute, all as specified in Section 7 of [RFC4187]. To prevent the use of compromised keys in other places, it is forbidden to change the network name when going from the full to the fast re- authentication process. The peer SHOULD NOT attempt fast re- authentication when it knows that the network name in the current access network is different from the one in the initial, full authentication. Upon seeing a re-authentication request with a changed network name, the server SHOULD behave as if the re- authentication identifier had been unrecognized, and fall back to full authentication. The server observes the change in the name by comparing where the fast re-authentication and full authentication EAP transactions were received at the Authentication, Authorization, and Accounting (AAA) protocol level. AT_KDF has any other value Future variations of key derivation functions may be defined, and they will be represented by new values of AT_KDF. If the peer does not recognize the value, it cannot calculate the keys and behaves as explained in Section 3.2. AT_KDF is missing The peer behaves as if the AUTN had been incorrect and MUST fail the authentication. If the peer supports a given key derivation function but is unwilling to perform it for policy reasons, it refuses to calculate the keys and behaves as explained in Section 3.2. Arkko, et al. Expires April 22, 2019 [Page 14] Internet-Draft EAP-AKA' October 2018 3.4. Hash Functions EAP-AKA' uses SHA-256, not SHA-1 (see [FIPS.180-4]) as in EAP-AKA. This requires a change to the pseudo-random function (PRF) as well as the AT_MAC and AT_CHECKCODE attributes. 3.4.1. PRF' The PRF' construction is the same one IKEv2 uses (see Section 2.13 of [RFC4306]). The function takes two arguments. K is a 256-bit value and S is an octet string of arbitrary length. PRF' is defined as follows: PRF'(K,S) = T1 | T2 | T3 | T4 | ... where: T1 = HMAC-SHA-256 (K, S | 0x01) T2 = HMAC-SHA-256 (K, T1 | S | 0x02) T3 = HMAC-SHA-256 (K, T2 | S | 0x03) T4 = HMAC-SHA-256 (K, T3 | S | 0x04) ... PRF' produces as many bits of output as is needed. HMAC-SHA-256 is the application of HMAC [RFC2104] to SHA-256. 3.4.2. AT_MAC When used within EAP-AKA', the AT_MAC attribute is changed as follows. The MAC algorithm is HMAC-SHA-256-128, a keyed hash value. The HMAC-SHA-256-128 value is obtained from the 32-byte HMAC-SHA-256 value by truncating the output to the first 16 bytes. Hence, the length of the MAC is 16 bytes. Otherwise, the use of AT_MAC in EAP-AKA' follows Section 10.15 of [RFC4187]. 3.4.3. AT_CHECKCODE When used within EAP-AKA', the AT_CHECKCODE attribute is changed as follows. First, a 32-byte value is needed to accommodate a 256-bit hash output: Arkko, et al. Expires April 22, 2019 [Page 15] Internet-Draft EAP-AKA' October 2018 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_CHECKCODE | Length | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Checkcode (0 or 32 bytes) | | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Second, the checkcode is a hash value, calculated with SHA-256 [FIPS.180-4], over the data specified in Section 10.13 of [RFC4187]. 4. Bidding Down Prevention for EAP-AKA As discussed in [RFC3748], negotiation of methods within EAP is insecure. That is, a man-in-the-middle attacker may force the endpoints to use a method that is not the strongest that they both support. This is a problem, as we expect EAP-AKA and EAP-AKA' to be negotiated via EAP. In order to prevent such attacks, this RFC specifies a new mechanism for EAP-AKA that allows the endpoints to securely discover the capabilities of each other. This mechanism comes in the form of the AT_BIDDING attribute. This allows both endpoints to communicate their desire and support for EAP-AKA' when exchanging EAP-AKA messages. This attribute is not included in EAP-AKA' messages as defined in this RFC. It is only included in EAP-AKA messages. This is based on the assumption that EAP-AKA' is always preferable (see Section 7). If during the EAP-AKA authentication process it is discovered that both endpoints would have been able to use EAP-AKA', the authentication process SHOULD be aborted, as a bidding down attack may have happened. The format of the AT_BIDDING 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_BIDDING | Length |D| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The fields are as follows: AT_BIDDING Arkko, et al. Expires April 22, 2019 [Page 16] Internet-Draft EAP-AKA' October 2018 This is set to 136. Length The length of the attribute, MUST be set to 1. D This bit is set to 1 if the sender supports EAP-AKA', is willing to use it, and prefers it over EAP-AKA. Otherwise, it should be set to zero. Reserved This field MUST be set to zero when sent and ignored on receipt. The server sends this attribute in the EAP-Request/AKA-Challenge message. If the peer supports EAP-AKA', it compares the received value to its own capabilities. If it turns out that both the server and peer would have been able to use EAP-AKA' and preferred it over EAP-AKA, the peer behaves as if AUTN had been incorrect and fails the authentication (see Figure 3 of [RFC4187]). A peer not supporting EAP-AKA' will simply ignore this attribute. In all cases, the attribute is protected by the integrity mechanisms of EAP-AKA, so it cannot be removed by a man-in-the-middle attacker. Note that we assume (Section 7) that EAP-AKA' is always stronger than EAP-AKA. As a result, there is no need to prevent bidding "down" attacks in the other direction, i.e., attackers forcing the endpoints to use EAP-AKA'. 5. Peer Identities EAP-AKA' peer identities are as specified in [RFC4187] Section 4.1, with the addition of some requirements specified in this section. EAP-AKA' includes optional identity privacy support that can be used to hide the cleartext permanent identity and thereby make the subscriber's EAP exchanges untraceable to eavesdroppers. EAP-AKA' can also use the privacy friendly identifiers specified for 5G networks. The permanent identity is usually based on the IMSI, which may further help the tracking, because the same identifier may be used in other contexts as well. Identity privacy is based on temporary usernames, or pseudonym usernames. These are similar to but separate from the Temporary Mobile Subscriber Identities (TMSI) that are used on cellular networks. Arkko, et al. Expires April 22, 2019 [Page 17] Internet-Draft EAP-AKA' October 2018 5.1. Username Types in EAP-AKA' Identities Section 220.127.116.11 of [RFC4187] specified that there are three types of usernames: permanent, pseudonym, and fast re-authentication usernames. This specification extends this definition as follows. There are four types of usernames: (1) Regular usernames. These are external names given to EAP- AKA'. The regular usernames are further subdivided into to categories: (a) Permanent usernames, for instance IMSI-based usernames. (b) Privacy-friendly temporary usernames, for instance 5G privacy identifiers (see Section 5.3.2 and Section 18.104.22.168. (2) EAP-AKA' pseudonym usernames. For example, firstname.lastname@example.org might be a valid pseudonym identity. In this example, 2s7ah6n9q is the pseudonym username. (3) EAP-AKA' fast re-authentication usernames. For example, email@example.com might be a valid fast re-authentication identity and 43953754 the fast re-authentication username. The permanent, privacy-friendly temporary, and pseudonym usernames are only used on full authentication, and fast re-authentication usernames only on fast re-authentication. Unlike permanent usernames and pseudonym usernames, privacy friendly temporary usernames and fast re-authentication usernames are one-time identifiers, which are not re-used across EAP exchanges. 5.2. Generating Pseudonyms and Fast Re-Authentication Identities As specified by [RFC4187] Section 22.214.171.124, pseudonym usernames and fast re-authentication identities are generated by the EAP server, in an implementation-dependent manner. RFC 4187 provides some general requirements on how these identities are transported, how they map to the NAI syntax, how they are distinguished from each other, and so on. However, to ensure privacy some additional requirements need to be applied. The pseudonym usernames and fast re-authentication identities MUST be generated in a cryptographically secure way so that that it is computationally infeasible for at attacker to differentiate two identities belonging to the same user from two identities belonging to different users. This can be achieved, for instance, by using Arkko, et al. Expires April 22, 2019 [Page 18] Internet-Draft EAP-AKA' October 2018 random or pseudo-random identifiers such as random byte strings or ciphertexts. Note that the pseudonym and fast re-authentication usernames also MUST NOT include substrings that can be used to relate the username to a particular entity or a particular permanent identity. For instance, the usernames can not include any subscriber-identifying part of an IMSI or other permanent identifier. Similarly, no part of the username can be formed by a fixed mapping that stays the same across multiple different pseudonyms or fast re-authentication identities for the same subscriber. When the identifier used to identify a subscriber in an EAP-AKA' authentication exchange is a privacy-friendly identifier that is used only once, the EAP-AKA' peer MUST NOT use a pseudonym provided in that authentication exchange in subsequent exchanges more than once. To ensure that this does not happen, EAP-AKA' server MAY decline to provide a pseudonym in such authentication exchanges. An important case where such privacy-friendly identifiers are used is in 5G networks (see Section 5.3) 5.3. Identifier Usage in 5G In EAP-AKA', the peer identity may be communicated to the server in one of three ways: o As a part of link layer establishment procedures, externally to EAP. o With the EAP-Response/Identity message in the beginning of the EAP exchange, but before the selection of EAP-AKA'. o Transmitted from the peer to the server using EAP-AKA messages instead of EAP-Response/Identity. In this case, the server includes an identity requesting attribute (AT_ANY_ID_REQ, AT_FULLAUTH_ID_REQ or AT_PERMANENT_ID_REQ) in the EAP-Request/AKA- Identity message; and the peer includes the AT_IDENTITY attribute, which contains the peer's identity, in the EAP-Response/AKA- Identity message. The identity carried above may be a permanent identity, privacy friendly identity, pseudonym identity, or fast re-authentication identity as defined in this RFC. 5G supports the concept of privacy identifiers, and it is important for interoperability that the right type of identifier is used. Arkko, et al. Expires April 22, 2019 [Page 19] Internet-Draft EAP-AKA' October 2018 5G defines the SUbscription Permanent Identifier (SUPI) and SUbscription Concealed Identifier (SUCI) [TS-3GPP.23.501] [TS-3GPP.33.501] [TS-3GPP.23.003]. SUPI is globally unique and allocated to each subscriber. However, it is only used internally in the 5G network, and is privacy sensitive. The SUCI is a privacy preserving identifier containing the concealed SUPI, using public key cryptography to encrypt the SUPI. Given the choice between these two types of identifiers, two areas need further specification in EAP-AKA' to ensure that different implementations understand each other and stay interoperable: o Where identifiers are used within EAP-AKA' -- such as key derivation -- specify what values exactly should be used, to avoid ambiguity. o Where identifiers are carried within EAP-AKA' packets -- such as in the AT_IDENTITY attribute -- specify which identifiers should be filled in. In 5G, the normal mode of operation is that identifiers are only transmitted outside EAP. However, in a system involving terminals from many generations and several connectivity options via 5G and other mechanisms, implementations and the EAP-AKA' specification need to prepare for many different situations, including sometimes having to communicate identities within EAP. The following sections clarify which identifiers are used and how. 5.3.1. Key Derivation In EAP-AKA', the peer identity is used in the Section 3.3 key derivation formula. If the AT_KDF_INPUT parameter contains the prefix "5G:", the AT_KDF parameter has the value 1, and this authentication is not a fast re- authentication, then the peer identity used in the key derivation MUST be the 5G SUPI for the peer. This rule applies to all full EAP- AKA' authentication processes, even if the peer sent some other identifier at a lower layer or as a response to an EAP Identity Request or if no identity was sent. The identity MUST also be represented in the exact correct format for the key derivation formula to produce correct results. For the SUPI, this format is as defined Section 126.96.36.199. In all other cases, the following applies: Arkko, et al. Expires April 22, 2019 [Page 20] Internet-Draft EAP-AKA' October 2018 The identity used in the key derivation formula MUST be exactly the one sent in EAP-AKA' AT_IDENTITY attribute, if one was sent, regardless of the kind of identity that it may have been. If no AT_IDENTITY was sent, the identity MUST be the exactly the one sent in the generic EAP Identity exchange, if one was made. Again, the identity MUST be used exactly as sent. If no identity was communicated inside EAP, then the identity is the one communicated outside EAP in link layer messaging. In this case, the used identity MUST be the identity most recently communicated by the peer to the network, again regardless of what type of identity it may have been. 188.8.131.52. Format of the SUPI A SUPI is either an IMSI or a Network Access Identifier [RFC4282]. When used in EAP-AKA', the format of the SUPI MUST be as specified in [TS-3GPP.23.003] Sections 28.7.2, with the semantics defined in [TS-3GPP.23.003] Section 2.2B. Also, in contrast to [RFC5448], in 5G EAP-AKA' does not use the "0" or "6" prefix in front of the entire IMSI. For instance, if the IMSI is 234150999999999 (MCC = 234, MNC = 15), the NAI format for the SUPI takes the form: firstname.lastname@example.org 5.3.2. EAP Identity Response and EAP-AKA' AT_IDENTITY Attribute The EAP authentication option is only available in 5G when the new 5G core network is also in use. However, in other networks an EAP-AKA' peer may be connecting to other types of networks and existing equipment. When the EAP peer is connecting to a 5G access network and uses the 5G Non-Access Stratum (NAS) protocol [TS-3GPP.24.501], the EAP server is in a 5G network. The EAP identity exchanges are generally not used in this case, as the identity is already made available on previous link layer exchanges. In this situation, the EAP server SHOULD NOT request an additional identity from the peer. If the peer for some reason receives EAP- Request/Identity or EAP-Request/AKA-Identity messages, the peer should behave as follows. Receive EAP-Request/Identity Arkko, et al. Expires April 22, 2019 [Page 21] Internet-Draft EAP-AKA' October 2018 In this case, the peer SHOULD respond with a EAP-Response/Identity containing the privacy-friendly 5G identifier, the SUCI. The SUCI SHOULD be represented as specified in Section 184.108.40.206. EAP-Request/AKA-Identity with AT_PERMANENT_REQ For privacy reasons, the peer should follow a "conservative" policy and terminate the authentication exchange rather than risk revaling its permanent identity. The peer SHOULD respond with EAP-Response/AKA-Client-Error with the client error code 0, "unable to process packet". EAP-Request/AKA-Identity with AT_FULLAUTH_REQ In this case, the peer SHOULD respond with a EAP-Response/AKA- Identity containing the SUCI. The SUCI SHOULD be represented as specified in Section 220.127.116.11. EAP-Request/AKA-Identity with AT_ANY_ID_REQ If the peer supports fast re-authentication and has a fast re- authentication identity available, the peer SHOULD respond with EAP-Response/AKA-Identity containing the fast re-authentication identity. Otherwise the peer SHOULD respond with a EAP-Response/ AKA-Identity containing the SUCI, and SHOULD represent the SUCI as specified in Section 18.104.22.168. Similarly, if the peer is communicating over a non-3GPP network but carrying EAP inside 5G NAS protocol, it MUST assume that the EAP server is in a 5G network, and again employ the SUCI within EAP. Otherwise, the peer SHOULD employ IMSI, SUPI, or a NAI as it is configured to use. 22.214.171.124. Format of the SUCI When used in EAP-AKA', the format of the SUCI MUST be as specified in [TS-3GPP.23.003] Section 28.7.3, with the semantics defined in [TS-3GPP.23.003] Section 2.2B. Also, in contrast to [RFC5448], in 5G EAP-AKA' does not use the "0" or "6" prefix in front of the identifier. For instance, assuming the IMSI 234150999999999, where MCC=234, MNC=15 and MSISN=0999999999, the Routing Indicator 678, and a Home Network Public Key Identifier of 27, the NAI format for the SUCI takes the form: Arkko, et al. Expires April 22, 2019 [Page 22] Internet-Draft EAP-AKA' October 2018 For the null-scheme: email@example.com. mcc234.3gppnetwork.org For the Profile <A> protection scheme: type0.rid678.schid1.hnkey27.ecckey<ECC ephemeral public key>. cip<encryption of 0999999999>.mac<MAC tag value>@nai.5gc. mnc015.mcc234.3gppnetwork.org 6. Exported Parameters The EAP-AKA' Session-Id is the concatenation of the EAP Type Code (50, one octet) with the contents of the RAND field from the AT_RAND attribute, followed by the contents of the AUTN field in the AT_AUTN attribute: Session-Id = 50 || RAND || AUTN When using fast re-authentication, the EAP-AKA' Session-Id is the concatenation of the EAP Type Code (50) with the contents of the NONCE_S field from the AT_NONCE_S attribute, followed by the contents of the MAC field from the AT_MAC attribute from EAP-Request/AKA- Reauthentication: Session-Id = 50 || NONCE_S || MAC The Peer-Id is the contents of the Identity field from the AT_IDENTITY attribute, using only the Actual Identity Length octets from the beginning. Note that the contents are used as they are transmitted, regardless of whether the transmitted identity was a permanent, pseudonym, or fast EAP re-authentication identity. If no AT_IDENTITY attribute was exchanged, the exported Peer-Id is the identity provided from the EAP Identity Response packet. If no EAP Identity Response was provided either, the exported Peer-Id is null string (zero length). The Server-Id is the null string (zero length). 7. Security Considerations A summary of the security properties of EAP-AKA' follows. These properties are very similar to those in EAP-AKA. We assume that SHA-256 is at least as secure as SHA-1. This is called the SHA-256 assumption in the remainder of this section. Under this assumption, EAP-AKA' is at least as secure as EAP-AKA. Arkko, et al. Expires April 22, 2019 [Page 23] Internet-Draft EAP-AKA' October 2018 If the AT_KDF attribute has value 1, then the security properties of EAP-AKA' are as follows: Protected ciphersuite negotiation EAP-AKA' has no ciphersuite negotiation mechanisms. It does have a negotiation mechanism for selecting the key derivation functions. This mechanism is secure against bidding down attacks. The negotiation mechanism allows changing the offered key derivation function, but the change is visible in the final EAP- Request/AKA'-Challenge message that the server sends to the peer. This message is authenticated via the AT_MAC attribute, and carries both the chosen alternative and the initially offered list. The peer refuses to accept a change it did not initiate. As a result, both parties are aware that a change is being made and what the original offer was. Mutual authentication Under the SHA-256 assumption, the properties of EAP-AKA' are at least as good as those of EAP-AKA in this respect. Refer to [RFC4187], Section 12 for further details. Integrity protection Under the SHA-256 assumption, the properties of EAP-AKA' are at least as good (most likely better) as those of EAP-AKA in this respect. Refer to [RFC4187], Section 12 for further details. The only difference is that a stronger hash algorithm, SHA-256, is used instead of SHA-1. Replay protection Under the SHA-256 assumption, the properties of EAP-AKA' are at least as good as those of EAP-AKA in this respect. Refer to [RFC4187], Section 12 for further details. Confidentiality The properties of EAP-AKA' are exactly the same as those of EAP- AKA in this respect. Refer to [RFC4187], Section 12 for further details. Key derivation EAP-AKA' supports key derivation with an effective key strength against brute force attacks equal to the minimum of the length of Arkko, et al. Expires April 22, 2019 [Page 24] Internet-Draft EAP-AKA' October 2018 the derived keys and the length of the AKA base key, i.e., 128 bits or more. The key hierarchy is specified in Section 3.3. The Transient EAP Keys used to protect EAP-AKA packets (K_encr, K_aut, K_re), the MSK, and the EMSK are cryptographically separate. If we make the assumption that SHA-256 behaves as a pseudo-random function, an attacker is incapable of deriving any non-trivial information about any of these keys based on the other keys. An attacker also cannot calculate the pre-shared secret from IK, CK, IK', CK', K_encr, K_aut, K_re, MSK, or EMSK by any practically feasible means. EAP-AKA' adds an additional layer of key derivation functions within itself to protect against the use of compromised keys. This is discussed further in Section 7.4. EAP-AKA' uses a pseudo-random function modeled after the one used in IKEv2 [RFC4306] together with SHA-256. Key strength See above. Dictionary attack resistance Under the SHA-256 assumption, the properties of EAP-AKA' are at least as good as those of EAP-AKA in this respect. Refer to [RFC4187], Section 12 for further details. Fast reconnect Under the SHA-256 assumption, the properties of EAP-AKA' are at least as good as those of EAP-AKA in this respect. Refer to [RFC4187], Section 12 for further details. Note that implementations MUST prevent performing a fast reconnect across method types. Cryptographic binding Note that this term refers to a very specific form of binding, something that is performed between two layers of authentication. It is not the same as the binding to a particular network name. The properties of EAP-AKA' are exactly the same as those of EAP- AKA in this respect, i.e., as it is not a tunnel method, this property is not applicable to it. Refer to [RFC4187], Section 12 for further details. Session independence Arkko, et al. Expires April 22, 2019 [Page 25] Internet-Draft EAP-AKA' October 2018 The properties of EAP-AKA' are exactly the same as those of EAP- AKA in this respect. Refer to [RFC4187], Section 12 for further details. Fragmentation The properties of EAP-AKA' are exactly the same as those of EAP- AKA in this respect. Refer to [RFC4187], Section 12 for further details. Channel binding EAP-AKA', like EAP-AKA, does not provide channel bindings as they're defined in [RFC3748] and [RFC5247]. New skippable attributes can be used to add channel binding support in the future, if required. However, including the Network Name field in the AKA' algorithms (which are also used for other purposes than EAP-AKA') provides a form of cryptographic separation between different network names, which resembles channel bindings. However, the network name does not typically identify the EAP (pass-through) authenticator. See Section 7.4 for more discussion. 7.1. Privacy [RFC6973] suggests that the privacy considerations of IETF protocols be documented. The confidentiality properties of EAP-AKA' itself have been discussed above under "Confidentiality". EAP-AKA' uses several different types of identifiers to identify the authenticating peer. It is strongly RECOMMENDED to use the privacy- friendly temporary or hidden identifiers, i.e., the 5G SUCI, pseudonym usernames, and fast re-authentication usernames. The use of permanent identifiers such as the IMSI or SUPI may lead to an ability to track the peer and/or user associated with the peer. The use of permanent identifiers such as the IMSI or SUPI is strongly NOT RECOMMENDED. As discussed in Section 5.3, when authenticating to a 5G network, only the 5G SUCI identifier should be used. The use of pseudonyms in this situation is at best limited. In fact, the re-use of the same pseudonym multiple times will result in a tracking opportunity for observers that see the pseudonym pass by. To avoid this, the peer and server need to follow the guidelines given in Section 5.2. Arkko, et al. Expires April 22, 2019 [Page 26] Internet-Draft EAP-AKA' October 2018 When authenticating to a 5G network, per Section 5.3.1, both the EAP- AKA' peer and server need employ permanent identifier, SUPI, as an input to key generation. However, this use of the SUPI is only internal and the SUPI need not be communicated in EAP messages. SUCI MUST NOT be communicated in EAP-AKA' when authenticating to a 5G network. While the use of SUCI in 5G networks generally provides identity privacy, this is not true if the null-scheme encryption is used to construct the SUCI (see [TS-3GPP.23.501] Annex C). The use of this scheme turns the use of SUCI equivalent to the use of SUPI or IMSI. The use of the null scheme is NOT RECOMMENDED where identity privacy is important. The use of fast re-authentication identities when authenticating to a 5G network does not have the same problems as the use of pseudonyms, as long as the 5G authentication server generates the fast re- authentication identifiers in a proper manner specified in Section 5.2. Outside 5G, there is a full choice to use permanent, pseudonym, or fast re-authentication identifiers: o A peer that has not yet performed any EAP-AKA' exchanges does not typically have a pseudonym available. If the peer does not have a pseudonym available, then the privacy mechanism cannot be used, and the permanent identity will have to be sent in the clear. The terminal SHOULD store the pseudonym in non-volatile memory so that it can be maintained across reboots. An active attacker that impersonates the network may use the AT_PERMANENT_ID_REQ attribute ([RFC4187] Section 4.1.2) to learn the subscriber's IMSI. However, as discussed in [RFC4187] Section 4.1.2, the terminal can refuse to send the cleartext permanent identity if it believes that the network should be able to recognize the pseudonym. o When pseudonyms and fast re-authentication identities are used, the peer relies on the properly created identifiers by the server. It is essential that an attacker cannot link a privacy-friendly identifier to the user in any way or determine that two identifiers belong to the same user as outlined in Section 5.2. The pseudonym usernames and fast re-authentication identities MUST also not be used for other purposes (e.g. in other protocols). If the peer and server cannot guarantee that 5G SUCI can be used or pseudonyms will available, generated properly, and maintained reliably, and identity privacy is required then additional protection Arkko, et al. Expires April 22, 2019 [Page 27] Internet-Draft EAP-AKA' October 2018 from an external security mechanism such as tunneled EAP methods may be used. The benefits and the security considerations of using an external security mechanism with EAP-AKA are beyond the scope of this document. Finally, as with other EAP methods, even when privacy-friendly identifiers or EAP tunneling is used, typically the domain part of an identifier (e.g., the home operator) is visible to external parties. 7.2. Discovered Vulnerabilities There have been no published attacks that violate the primary secrecy or authentication properties defined for Authentication and Key Agreement (AKA) under the originally assumed trust model. The same is true of EAP-AKA'. However, there have been attacks when a different trust model is in use, with characteristics not originally provided by the design, or when participants in the protocol leak information to outsiders on purpose, and there has been some privacy-related attacks. For instance, the original AKA protocol does not prevent supplying keys by an insider to a third party as done in, e.g., by Mjolsnes and Tsay in [MT2012] where a serving network lets an authentication run succeed, but then misuses the session keys to send traffic on the authenticated user's behalf. This particular attack is not different from any on-path entity (such as a router) pretending to send traffic, but the general issue of insider attacks can be a problem, particularly in a large group of collaborating operators. Another class of attacks is the use of tunneling of traffic from one place to another, e.g., as done by Zhang and Fang in [ZF2005] to leverage security policy differences between different operator networks, for instance. To gain something in such an attack, the attacker needs to trick the user into believing it is in another location where, for instance, it is not required to encrypt all payload traffic after encryption. As an authentication mechanism, EAP-AKA' is not directly affected by most such attacks. EAP-AKA' network name binding can also help alleviate some of the attacks. In any case, it is recommended that EAP-AKA' configuration not be dependent on the location of where a request comes from. Zhang and Fang also looked at Denial-of-Service attacks [ZF2005]. A serving network may request large numbers of authentication runs for a particular subscriber from a home network. While resynchronization process can help recover from this, eventually it is possible to exhaust the sequence number space and render the subscriber's card unusable. This attack is possible for both native AKA and EAP-AKA'. Arkko, et al. Expires April 22, 2019 [Page 28] Internet-Draft EAP-AKA' October 2018 However, it requires the collaboration of a serving network in an attack. It is recommended that EAP-AKA' implementations provide means to track, detect, and limit excessive authentication attempts to combat this problem. There has also been attacks related to the use of AKA without the generated session keys (e.g., [BT2013]). Some of those attacks relate to the use of originally man-in-the-middle vulnerable HTTP Digest AKAv1 [RFC3310]. This has since then been corrected in [RFC4169]. The EAP-AKA' protocol uses session keys and provides channel binding, and as such, is resistant to the above attacks except where the protocol participants leak information to outsiders. Basin et al [Basin2018] have performed formal analysis and concluded that the AKA protocol would have benefited from additional security requirements, such as key confirmation. In the context of pervasive monitoring revelations, there were also reports of compromised long term pre-shared keys used in SIM and AKA [Heist2015]. While no protocol can survive the theft of key material associated with its credentials, there are some things that alleviate the impacts in such situations. These are discussed further in Section 7.3. Arapinis et al ([Arapinis2012]) describe an attack that uses the AKA resynchronization protocol to attempt to detect whether a particular subscriber is on a given area. This attack depends on the ability of the attacker to have a false base station on the given area, and the subscriber performing at least one authentication between the time the attack is set up and run. Finally, while this is not a problem with the protocol itself, bad implementations may not produce pseudonym usernames or fast re- authentication identities in a manner that is sufficiently secure. Recommendations from Section 5.2 need to be followed to avoid this. 7.3. Pervasive Monitoring As required by [RFC7258], work on IETF protocols needs to consider the effects of pervasive monitoring and mitigate them when possible. As described Section 7.2, after the publication of RFC 5448, new information has come to light regarding the use of pervasive monitoring techniques against many security technologies, including AKA-based authentication. For AKA, these attacks relate to theft of the long-term shared secret key material stored on the cards. Such attacks are conceivable, for Arkko, et al. Expires April 22, 2019 [Page 29] Internet-Draft EAP-AKA' October 2018 instance, during the manufacturing process of cards, through coercion of the card manufacturers, or during the transfer of cards and associated information to an operator. Since the publication of reports about such attacks, manufacturing and provisioning processes have gained much scrutiny and have improved. In particular, it is crucial that manufacturers limit access to the secret information and the cards only to necessary systems and personnel. It is also crucial that secure mechanisms be used to communicate the secrets between the manufacturer and the operator that adopts those cards for their customers. Beyond these operational considerations, there are also technical means to improve resistance to these attacks. One approach is to provide Perfect Forwards Secrecy (PFS). This would prevent any passive attacks merely based on the long-term secrets and observation of traffic. Such a mechanism can be defined as an backwards- compatible extension of EAP-AKA', and is pursued separately from this specification [I-D.arkko-eap-aka-pfs]. Alternatively, EAP-AKA' authentication can be run inside a PFS-capable tunneled authentication method. In any case, the use of some PFS-capable mechanism is recommended. 7.4. Security Properties of Binding Network Names The ability of EAP-AKA' to bind the network name into the used keys provides some additional protection against key leakage to inappropriate parties. The keys used in the protocol are specific to a particular network name. If key leakage occurs due to an accident, access node compromise, or another attack, the leaked keys are only useful when providing access with that name. For instance, a malicious access point cannot claim to be network Y if it has stolen keys from network X. Obviously, if an access point is compromised, the malicious node can still represent the compromised node. As a result, neither EAP-AKA' nor any other extension can prevent such attacks; however, the binding to a particular name limits the attacker's choices, allows better tracking of attacks, makes it possible to identify compromised networks, and applies good cryptographic hygiene. The server receives the EAP transaction from a given access network, and verifies that the claim from the access network corresponds to the name that this access network should be using. It becomes impossible for an access network to claim over AAA that it is another access network. In addition, if the peer checks that the information it has received locally over the network-access link layer matches with the information the server has given it via EAP-AKA', it becomes impossible for the access network to tell one story to the AAA Arkko, et al. Expires April 22, 2019 [Page 30] Internet-Draft EAP-AKA' October 2018 network and another one to the peer. These checks prevent some "lying NAS" (Network Access Server) attacks. For instance, a roaming partner, R, might claim that it is the home network H in an effort to lure peers to connect to itself. Such an attack would be beneficial for the roaming partner if it can attract more users, and damaging for the users if their access costs in R are higher than those in other alternative networks, such as H. Any attacker who gets hold of the keys CK and IK, produced by the AKA algorithm, can compute the keys CK' and IK' and, hence, the Master Key (MK) according to the rules in Section 3.3. The attacker could then act as a lying NAS. In 3GPP systems in general, the keys CK and IK have been distributed to, for instance, nodes in a visited access network where they may be vulnerable. In order to reduce this risk, the AKA algorithm MUST be computed with the AMF separation bit set to 1, and the peer MUST check that this is indeed the case whenever it runs EAP-AKA'. Furthermore, [TS-3GPP.33.402] requires that no CK or IK keys computed in this way ever leave the home subscriber system. The additional security benefits obtained from the binding depend obviously on the way names are assigned to different access networks. This is specified in [TS-3GPP.24.302]. See also [TS-3GPP.23.003]. Ideally, the names allow separating each different access technology, each different access network, and each different NAS within a domain. If this is not possible, the full benefits may not be achieved. For instance, if the names identify just an access technology, use of compromised keys in a different technology can be prevented, but it is not possible to prevent their use by other domains or devices using the same technology. 8. IANA Considerations 8.1. Type Value EAP-AKA' has the EAP Type value 50 in the Extensible Authentication Protocol (EAP) Registry under Method Types. Per Section 6.2 of [RFC3748], this allocation can be made with Designated Expert and Specification Required. 8.2. Attribute Type Values EAP-AKA' shares its attribute space and subtypes with EAP-SIM [RFC4186] and EAP-AKA [RFC4187]. No new registries are needed. However, a new Attribute Type value (23) in the non-skippable range has been assigned for AT_KDF_INPUT (Section 3.1) in the EAP-AKA and EAP-SIM Parameters registry under Attribute Types. Arkko, et al. Expires April 22, 2019 [Page 31] Internet-Draft EAP-AKA' October 2018 Also, a new Attribute Type value (24) in the non-skippable range has been assigned for AT_KDF (Section 3.2). Finally, a new Attribute Type value (136) in the skippable range has been assigned for AT_BIDDING (Section 4). 8.3. Key Derivation Function Namespace IANA has also created a new namespace for EAP-AKA' AT_KDF Key Derivation Function Values. This namespace exists under the EAP-AKA and EAP-SIM Parameters registry. The initial contents of this namespace are given below; new values can be created through the Specification Required policy [RFC8126]. Value Description Reference --------- ---------------------- ------------------------------- 0 Reserved [RFC Editor: Refer to this RFC] 1 EAP-AKA' with CK'/IK' [RFC Editor: Refer to this RFC] 2-65535 Unassigned 9. References 9.1. Normative References [TS-3GPP.23.003] 3GPP, "3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Numbering, addressing and identification (Release 15)", 3GPP Draft Technical Specification 23.003, September 2018. [TS-3GPP.23.501] 3GPP, "3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; 3G Security; Security architecture and procedures for 5G System; (Release 15)", 3GPP Technical Specification 23.501, September 2018. [TS-3GPP.24.302] 3GPP, "3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Access to the 3GPP Evolved Packet Core (EPC) via non-3GPP access networks; Stage 3; (Release 15)", 3GPP Draft Technical Specification 24.302, September 2018. Arkko, et al. Expires April 22, 2019 [Page 32] Internet-Draft EAP-AKA' October 2018 [TS-3GPP.24.501] 3GPP, "3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Access to the 3GPP Evolved Packet Core (EPC) via non-3GPP access networks; Stage 3; (Release 15)", 3GPP Draft Technical Specification 24.501, September 2018. [TS-3GPP.33.102] 3GPP, "3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; 3G Security; Security architecture (Release 15)", 3GPP Draft Technical Specification 33.102, June 2018. [TS-3GPP.33.402] 3GPP, "3GPP System Architecture Evolution (SAE); Security aspects of non-3GPP accesses (Release 15)", 3GPP Draft Technical Specification 33.402, June 2018. [TS-3GPP.33.501] 3GPP, "3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; 3G Security; Security architecture and procedures for 5G System (Release 15)", 3GPP Draft Technical Specification 33.501, September 2018. [FIPS.180-4] National Institute of Standards and Technology, "Secure Hash Standard", FIPS PUB 180-4, August 2015, <https://nvlpubs.nist.gov/nistpubs/FIPS/ NIST.FIPS.180-4.pdf>. [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- Hashing for Message Authentication", RFC 2104, DOI 10.17487/RFC2104, February 1997, <https://www.rfc- editor.org/info/rfc2104>. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc- editor.org/info/rfc2119>. [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. Levkowetz, Ed., "Extensible Authentication Protocol (EAP)", RFC 3748, DOI 10.17487/RFC3748, June 2004, <https://www.rfc-editor.org/info/rfc3748>. Arkko, et al. Expires April 22, 2019 [Page 33] Internet-Draft EAP-AKA' October 2018 [RFC4187] Arkko, J. and H. Haverinen, "Extensible Authentication Protocol Method for 3rd Generation Authentication and Key Agreement (EAP-AKA)", RFC 4187, DOI 10.17487/RFC4187, January 2006, <https://www.rfc-editor.org/info/rfc4187>. [RFC4282] Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The Network Access Identifier", RFC 4282, DOI 10.17487/RFC4282, December 2005, <https://www.rfc- editor.org/info/rfc4282>. [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, <https://www.rfc-editor.org/info/rfc8126>. [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/info/rfc8174>. 9.2. Informative References [TS-3GPP.35.208] 3GPP, "3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; 3G Security; Specification of the MILENAGE Algorithm Set: An example algorithm set for the 3GPP authentication and key generation functions f1, f1*, f2, f3, f4, f5 and f5*; Document 4: Design Conformance Test Data (Release 14)", 3GPP Technical Specification 35.208, March 2017. [FIPS.180-1] National Institute of Standards and Technology, "Secure Hash Standard", FIPS PUB 180-1, April 1995, <http://www.itl.nist.gov/fipspubs/fip180-1.htm>. [FIPS.180-2] National Institute of Standards and Technology, "Secure Hash Standard", FIPS PUB 180-2, August 2002, <http://csrc.nist.gov/publications/fips/fips180-2/ fips180-2.pdf>. [RFC3310] Niemi, A., Arkko, J., and V. Torvinen, "Hypertext Transfer Protocol (HTTP) Digest Authentication Using Authentication and Key Agreement (AKA)", RFC 3310, DOI 10.17487/RFC3310, September 2002, <https://www.rfc-editor.org/info/rfc3310>. Arkko, et al. Expires April 22, 2019 [Page 34] Internet-Draft EAP-AKA' October 2018 [RFC4169] Torvinen, V., Arkko, J., and M. Naslund, "Hypertext Transfer Protocol (HTTP) Digest Authentication Using Authentication and Key Agreement (AKA) Version-2", RFC 4169, DOI 10.17487/RFC4169, November 2005, <https://www.rfc-editor.org/info/rfc4169>. [RFC4186] Haverinen, H., Ed. and J. Salowey, Ed., "Extensible Authentication Protocol Method for Global System for Mobile Communications (GSM) Subscriber Identity Modules (EAP-SIM)", RFC 4186, DOI 10.17487/RFC4186, January 2006, <https://www.rfc-editor.org/info/rfc4186>. [RFC4284] Adrangi, F., Lortz, V., Bari, F., and P. Eronen, "Identity Selection Hints for the Extensible Authentication Protocol (EAP)", RFC 4284, DOI 10.17487/RFC4284, January 2006, <https://www.rfc-editor.org/info/rfc4284>. [RFC4306] Kaufman, C., Ed., "Internet Key Exchange (IKEv2) Protocol", RFC 4306, DOI 10.17487/RFC4306, December 2005, <https://www.rfc-editor.org/info/rfc4306>. [RFC5113] Arkko, J., Aboba, B., Korhonen, J., Ed., and F. Bari, "Network Discovery and Selection Problem", RFC 5113, DOI 10.17487/RFC5113, January 2008, <https://www.rfc- editor.org/info/rfc5113>. [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 5226, DOI 10.17487/RFC5226, May 2008, <https://www.rfc- editor.org/info/rfc5226>. [RFC5247] Aboba, B., Simon, D., and P. Eronen, "Extensible Authentication Protocol (EAP) Key Management Framework", RFC 5247, DOI 10.17487/RFC5247, August 2008, <https://www.rfc-editor.org/info/rfc5247>. [RFC5448] Arkko, J., Lehtovirta, V., and P. Eronen, "Improved Extensible Authentication Protocol Method for 3rd Generation Authentication and Key Agreement (EAP-AKA')", RFC 5448, DOI 10.17487/RFC5448, May 2009, <https://www.rfc-editor.org/info/rfc5448>. [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., Morris, J., Hansen, M., and R. Smith, "Privacy Considerations for Internet Protocols", RFC 6973, DOI 10.17487/RFC6973, July 2013, <https://www.rfc- editor.org/info/rfc6973>. Arkko, et al. Expires April 22, 2019 [Page 35] Internet-Draft EAP-AKA' October 2018 [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May 2014, <https://www.rfc-editor.org/info/rfc7258>. [I-D.arkko-eap-aka-pfs] Arkko, J., Norrman, K., and V. Torvinen, "Perfect-Forward Secrecy for the Extensible Authentication Protocol Method for Authentication and Key Agreement (EAP-AKA' PFS)", draft-arkko-eap-aka-pfs-02 (work in progress), July 2018. [Heist2015] Scahill, J. and J. Begley, "The great SIM heist", February 2015, in https://firstlook.org/theintercept/2015/02/19/ great-sim-heist/ . [MT2012] Mjolsnes, S. and J-K. Tsay, "A vulnerability in the UMTS and LTE authentication and key agreement protocols", October 2012, in Proceedings of the 6th international conference on Mathematical Methods, Models and Architectures for Computer Network Security: computer network security. [BT2013] Beekman, J. and C. Thompson, "Breaking Cell Phone Authentication: Vulnerabilities in AKA, IMS and Android", August 2013, in 7th USENIX Workshop on Offensive Technologies, WOOT '13. [ZF2005] Zhang, M. and Y. Fang, "Breaking Cell Phone Authentication: Vulnerabilities in AKA, IMS and Android", March 2005, IEEE Transactions on Wireless Communications, Vol. 4, No. 2. [Basin2018] Basin, D., Dreier, J., Hirsch, L., Radomirovic, S., Sasse, R., and V. Stettle, "A Formal Analysis of 5G Authentication", August 2018, arXiv:1806.10360. [Arapinis2012] Arapinis, M., Mancini, L., Ritter, E., Ryan, M., Golde, N., and R. Borgaonkar, "New Privacy Issues in Mobile Telephony: Fix and Verification", October 2012, CCS'12, Raleigh, North Carolina, USA. Appendix A. Changes from RFC 5448 The changes consist first of all, referring to a newer version of [TS-3GPP.24.302]. The new version includes an updated definition of the Network Name field, to include 5G. Arkko, et al. Expires April 22, 2019 [Page 36] Internet-Draft EAP-AKA' October 2018 Secondly, identifier usage for 5G has been specified in Section 5.3. Also, the requirements on generating pseudonym usernames and fast re- authentication identities have been updated from the original definition in RFC 5448, which referenced RFC 4187. See Section 5. Thirdly, exported parameters for EAP-AKA' have been defined in Section 6, as required by [RFC5247], including the definition of those parameters for both full authentication and fast re- authentication. The security, privacy, and pervasive monitoring considerations have been updated or added. See Section 7. Finally, the references to [RFC2119], [RFC5226], [FIPS.180-1] and [FIPS.180-2] have been updated to their most recent versions and language in this document changed accordingly. Similarly, references to all 3GPP technical specifications have been updated to their 5G (Release 15) versions or otherwise most recent version when there has not been a 5G-related update. Appendix B. Changes from RFC 4187 to RFC 5448 The changes to RFC 4187 relate only to the bidding down prevention support defined in Section 4. In particular, this document does not change how the Master Key (MK) is calculated in RFC 4187 (it uses CK and IK, not CK' and IK'); neither is any processing of the AMF bit added to RFC 4187. Appendix C. Changes from Previous Version of This Draft RFC Editor: Please delete this section at the time of publication. The -00 version of the working group draft is merely a republication of an earlier individual draft. The -01 version of the working group draft clarifies updates relationship to RFC 4187, clarifies language relating to obsoleting RFC 5448, clarifies when the 3GPP references are expected to be stable, updates several past references to their more recently published versions, specifies what identifiers should be used in key derivation formula for 5G, specifies how to construct the network name in manner that is compatible with both 5G and previous versions, and has some minor editorial changes. The -02 version of the working group draft added specification of peer identity usage in EAP-AKA', added requirements on the generation of pseudonym and fast re-authentication identifiers, specified the format of 5G-identifiers when they are used within EAP-AKA', defined Arkko, et al. Expires April 22, 2019 [Page 37] Internet-Draft EAP-AKA' October 2018 privacy and pervasive surveillance considerations, clarified when 5G- related procedures apply, specified what Peer-Id value is exported when no AT_IDENTITY is exchanged within EAP-AKA', and made a number of other clarifications and editorial improvements. The security considerations section also includes a summary of vulnerabilities brought up in the context of AKA or EAP-AKA', and discusses their applicability and impacts in EAP-AKA'. The -03 version of the working group draft corrected some typos, referred to the 3GPP specifications for the SUPI and SUCI formats, updated some of the references to newer versions, and reduced the strength of some of the recommendations in the security considerations section from keyword level to normal language (as they are just deployment recommendations). Appendix D. Importance of Explicit Negotiation Choosing between the traditional and revised AKA key derivation functions is easy when their use is unambiguously tied to a particular radio access network, e.g., Long Term Evolution (LTE) as defined by 3GPP or evolved High Rate Packet Data (eHRPD) as defined by 3GPP2. There is no possibility for interoperability problems if this radio access network is always used in conjunction with new protocols that cannot be mixed with the old ones; clients will always know whether they are connecting to the old or new system. However, using the new key derivation functions over EAP introduces several degrees of separation, making the choice of the correct key derivation functions much harder. Many different types of networks employ EAP. Most of these networks have no means to carry any information about what is expected from the authentication process. EAP itself is severely limited in carrying any additional information, as noted in [RFC4284] and [RFC5113]. Even if these networks or EAP were extended to carry additional information, it would not affect millions of deployed access networks and clients attaching to them. Simply changing the key derivation functions that EAP-AKA [RFC4187] uses would cause interoperability problems with all of the existing implementations. Perhaps it would be possible to employ strict separation into domain names that should be used by the new clients and networks. Only these new devices would then employ the new key derivation mechanism. While this can be made to work for specific cases, it would be an extremely brittle mechanism, ripe to result in problems whenever client configuration, routing of authentication requests, or server configuration does not match expectations. It also does not help to assume that the EAP client and server are running a particular release of 3GPP network specifications. Network Arkko, et al. Expires April 22, 2019 [Page 38] Internet-Draft EAP-AKA' October 2018 vendors often provide features from future releases early or do not provide all features of the current release. And obviously, there are many EAP and even some EAP-AKA implementations that are not bundled with the 3GPP network offerings. In general, these approaches are expected to lead to hard-to-diagnose problems and increased support calls. Appendix E. Test Vectors Test vectors are provided below for four different cases. The test vectors may be useful for testing implementations. In the first two cases, we employ the MILENAGE algorithm and the algorithm configuration parameters (the subscriber key K and operator algorithm variant configuration value OP) from test set 19 in [TS-3GPP.35.208]. The last two cases use artificial values as the output of AKA, and is useful only for testing the computation of values within EAP-AKA', not AKA itself. Arkko, et al. Expires April 22, 2019 [Page 39] Internet-Draft EAP-AKA' October 2018 Case 1 The parameters for the AKA run are as follows: Identity: "0555444333222111" Network name: "WLAN" RAND: 81e9 2b6c 0ee0 e12e bceb a8d9 2a99 dfa5 AUTN: bb52 e91c 747a c3ab 2a5c 23d1 5ee3 51d5 IK: 9744 871a d32b f9bb d1dd 5ce5 4e3e 2e5a CK: 5349 fbe0 9864 9f94 8f5d 2e97 3a81 c00f RES: 28d7 b0f2 a2ec 3de5 Then the derived keys are generated as follows: CK': 0093 962d 0dd8 4aa5 684b 045c 9edf fa04 IK': ccfc 230c a74f cc96 c0a5 d611 64f5 a76c K_encr: 766f a0a6 c317 174b 812d 52fb cd11 a179 K_aut: 0842 ea72 2ff6 835b fa20 3249 9fc3 ec23 c2f0 e388 b4f0 7543 ffc6 77f1 696d 71ea K_re: cf83 aa8b c7e0 aced 892a cc98 e76a 9b20 95b5 58c7 795c 7094 715c b339 3aa7 d17a MSK: 67c4 2d9a a56c 1b79 e295 e345 9fc3 d187 d42b e0bf 818d 3070 e362 c5e9 67a4 d544 e8ec fe19 358a b303 9aff 03b7 c930 588c 055b abee 58a0 2650 b067 ec4e 9347 c75a EMSK: f861 703c d775 590e 16c7 679e a387 4ada 8663 11de 2907 64d7 60cf 76df 647e a01c 313f 6992 4bdd 7650 ca9b ac14 1ea0 75c4 ef9e 8029 c0e2 90cd bad5 638b 63bc 23fb Arkko, et al. Expires April 22, 2019 [Page 40] Internet-Draft EAP-AKA' October 2018 Case 2 The parameters for the AKA run are as follows: Identity: "0555444333222111" Network name: "HRPD" RAND: 81e9 2b6c 0ee0 e12e bceb a8d9 2a99 dfa5 AUTN: bb52 e91c 747a c3ab 2a5c 23d1 5ee3 51d5 IK: 9744 871a d32b f9bb d1dd 5ce5 4e3e 2e5a CK: 5349 fbe0 9864 9f94 8f5d 2e97 3a81 c00f RES: 28d7 b0f2 a2ec 3de5 Then the derived keys are generated as follows: CK': 3820 f027 7fa5 f777 32b1 fb1d 90c1 a0da IK': db94 a0ab 557e f6c9 ab48 619c a05b 9a9f K_encr: 05ad 73ac 915f ce89 ac77 e152 0d82 187b K_aut: 5b4a caef 62c6 ebb8 882b 2f3d 534c 4b35 2773 37a0 0184 f20f f25d 224c 04be 2afd K_re: 3f90 bf5c 6e5e f325 ff04 eb5e f653 9fa8 cca8 3981 94fb d00b e425 b3f4 0dba 10ac MSK: 87b3 2157 0117 cd6c 95ab 6c43 6fb5 073f f15c f855 05d2 bc5b b735 5fc2 1ea8 a757 57e8 f86a 2b13 8002 e057 5291 3bb4 3b82 f868 a961 17e9 1a2d 95f5 2667 7d57 2900 EMSK: c891 d5f2 0f14 8a10 0755 3e2d ea55 5c9c b672 e967 5f4a 66b4 bafa 0273 79f9 3aee 539a 5979 d0a0 042b 9d2a e28b ed3b 17a3 1dc8 ab75 072b 80bd 0c1d a612 466e 402c Arkko, et al. Expires April 22, 2019 [Page 41] Internet-Draft EAP-AKA' October 2018 Case 3 The parameters for the AKA run are as follows: Identity: "0555444333222111" Network name: "WLAN" RAND: e0e0 e0e0 e0e0 e0e0 e0e0 e0e0 e0e0 e0e0 AUTN: a0a0 a0a0 a0a0 a0a0 a0a0 a0a0 a0a0 a0a0 IK: b0b0 b0b0 b0b0 b0b0 b0b0 b0b0 b0b0 b0b0 CK: c0c0 c0c0 c0c0 c0c0 c0c0 c0c0 c0c0 c0c0 RES: d0d0 d0d0 d0d0 d0d0 d0d0 d0d0 d0d0 d0d0 Then the derived keys are generated as follows: CK': cd4c 8e5c 68f5 7dd1 d7d7 dfd0 c538 e577 IK': 3ece 6b70 5dbb f7df c459 a112 80c6 5524 K_encr: 897d 302f a284 7416 488c 28e2 0dcb 7be4 K_aut: c407 00e7 7224 83ae 3dc7 139e b0b8 8bb5 58cb 3081 eccd 057f 9207 d128 6ee7 dd53 K_re: 0a59 1a22 dd8b 5b1c f29e 3d50 8c91 dbbd b4ae e230 5189 2c42 b6a2 de66 ea50 4473 MSK: 9f7d ca9e 37bb 2202 9ed9 86e7 cd09 d4a7 0d1a c76d 9553 5c5c ac40 a750 4699 bb89 61a2 9ef6 f3e9 0f18 3de5 861a d1be dc81 ce99 1639 1b40 1aa0 06c9 8785 a575 6df7 EMSK: 724d e00b db9e 5681 87be 3fe7 4611 4557 d501 8779 537e e37f 4d3c 6c73 8cb9 7b9d c651 bc19 bfad c344 ffe2 b52c a78b d831 6b51 dacc 5f2b 1440 cb95 1552 1cc7 ba23 Arkko, et al. Expires April 22, 2019 [Page 42] Internet-Draft EAP-AKA' October 2018 Case 4 The parameters for the AKA run are as follows: Identity: "0555444333222111" Network name: "HRPD" RAND: e0e0 e0e0 e0e0 e0e0 e0e0 e0e0 e0e0 e0e0 AUTN: a0a0 a0a0 a0a0 a0a0 a0a0 a0a0 a0a0 a0a0 IK: b0b0 b0b0 b0b0 b0b0 b0b0 b0b0 b0b0 b0b0 CK: c0c0 c0c0 c0c0 c0c0 c0c0 c0c0 c0c0 c0c0 RES: d0d0 d0d0 d0d0 d0d0 d0d0 d0d0 d0d0 d0d0 Then the derived keys are generated as follows: CK': 8310 a71c e6f7 5488 9613 da8f 64d5 fb46 IK': 5adf 1436 0ae8 3819 2db2 3f6f cb7f 8c76 K_encr: 745e 7439 ba23 8f50 fcac 4d15 d47c d1d9 K_aut: 3e1d 2aa4 e677 025c fd86 2a4b e183 61a1 3a64 5765 5714 63df 833a 9759 e809 9879 K_re: 99da 835e 2ae8 2462 576f e651 6fad 1f80 2f0f a119 1655 dd0a 273d a96d 04e0 fcd3 MSK: c6d3 a6e0 ceea 951e b20d 74f3 2c30 61d0 680a 04b0 b086 ee87 00ac e3e0 b95f a026 83c2 87be ee44 4322 94ff 98af 26d2 cc78 3bac e75c 4b0a f7fd feb5 511b a8e4 cbd0 EMSK: 7fb5 6813 838a dafa 99d1 40c2 f198 f6da cebf b6af ee44 4961 1054 02b5 08c7 f363 352c b291 9644 b504 63e6 a693 5415 0147 ae09 cbc5 4b8a 651d 8787 a689 3ed8 536d Appendix F. Contributors The test vectors in Appendix C were provided by Yogendra Pal and Jouni Malinen, based on two independent implementations of this specification. Arkko, et al. Expires April 22, 2019 [Page 43] Internet-Draft EAP-AKA' October 2018 Jouni Malinen provided suggested text for Section 6. John Mattsson provided much of the text for Section 7.1. Karl Norrman was the source of much of the information in Section 7.2. Appendix G. Acknowledgments The authors would like to thank Guenther Horn, Joe Salowey, Mats Naslund, Adrian Escott, Brian Rosenberg, Laksminath Dondeti, Ahmad Muhanna, Stefan Rommer, Miguel Garcia, Jan Kall, Ankur Agarwal, Jouni Malinen, John Mattsson, Jesus De Gregorio, Brian Weis, Russ Housley, Alfred Hoenes, Anand Palanigounder, and Mohit Sethi for their in- depth reviews and interesting discussions in this problem space. Authors' Addresses Jari Arkko Ericsson Jorvas 02420 Finland Email: firstname.lastname@example.org Vesa Lehtovirta Ericsson Jorvas 02420 Finland Email: email@example.com Vesa Torvinen Ericsson Jorvas 02420 Finland Email: firstname.lastname@example.org Pasi Eronen Nokia Research Center P.O. Box 407 FIN-00045 Nokia Group Finland Email: email@example.com Arkko, et al. Expires April 22, 2019 [Page 44]