<?xmlversion="1.0" encoding="UTF-8"?>version='1.0' encoding='UTF-8'?> <!DOCTYPE rfc [ <!ENTITY nbsp " "> <!ENTITY zwsp "​"> <!ENTITY nbhy "‑"> <!ENTITY wj "⁠"> ]> <rfc xmlns:xi="http://www.w3.org/2001/XInclude" category="std" submissionType="IETF" ipr="trust200902"docName="draft-ietf-ipsecme-ikev2-auth-announce-10"> <?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?> <?rfc toc="yes" ?> <?rfc symrefs="yes" ?> <?rfc sortrefs="no"?> <?rfc iprnotified="no" ?> <?rfc strict="yes" ?>docName="draft-ietf-ipsecme-ikev2-auth-announce-10" number="9593" updates="" obsoletes="" consensus="true" tocInclude="true" symRefs="true" sortRefs="false" version="3" xml:lang="en"> <front> <title abbrev="Announcing Supported Auth Methods">Announcing Supported Authentication Methods inIKEv2</title>the Internet Key Exchange Protocol Version 2 (IKEv2)</title> <seriesInfo name="RFC" value="9593"/> <authorinitials='V.'initials="V." surname="Smyslov"fullname='Valery Smyslov'>fullname="Valery Smyslov"> <organization>ELVIS-PLUS</organization> <address> <postal> <street>PO Box 81</street> <city>Moscow (Zelenograd)</city> <code>124460</code><country>RU</country><country>Russian Federation</country> </postal> <phone>+7 495 276 0211</phone> <email>svan@elvis.ru</email> </address> </author><date/><date month="June" year="2024"/> <area>SEC</area> <workgroup>ipsecme</workgroup> <!--[rfced] Please insert any keywords (beyond those that appear in the title) for use on https://www.rfc-editor.org/search. --> <keyword>example</keyword> <!--[rfced] Please clarify this sentence. What part of the sentence does "to authenticate each other" connect with? Original: This mechanism improves interoperability when IKEv2 partners are configured with multiple credentials of different type to authenticate each other. Perhaps: This mechanism improves interoperability when IKEv2 partners are configured with multiple credentials (of different types) for authenticating each other. --> <abstract> <t> This specification defines a mechanism that allows implementations of the Internet Key ExchangeversionProtocol Version 2 (IKEv2)implementationsto indicate the list of supported authentication methods to their peers while establishing IKEv2 SecurityAssociation (SA).Associations (SAs). This mechanism improves interoperability when IKEv2 partners are configured with multiple credentials of different type to authenticate each other. </t> </abstract> </front> <middle> <sectionanchor="intro" title="Introduction">anchor="intro"> <name>Introduction</name> <t> The Internet Key ExchangeversionProtocol Version 2(IKEv2) protocol,(IKEv2), defined in <xreftarget="RFC7296" />,target="RFC7296"/>, performs authenticated key exchange in IPsec. IKEv2, unlike its predecessor IKEv1, defined in <xreftarget="RFC2409" />,target="RFC2409"/>, doesn't include a mechanism to negotiate an authentication method that the peers would use to authenticate each other. It is assumed that each peer selectswhateverwhichever authentication method it thinks is appropriate, depending on authentication credentials it has. </t> <t> This approach generally works well when there is no ambiguity in selecting authentication credentials. SA establishment failure between peers mayariseoccur when there are several credentials of different types configured on one peer, while only some of them are supported on the other peer. Another problem situation is when a single credential may be used to produce different types of authentication tokens(e.g.(e.g., signatures of different formats). <!--[rfced] Does "could" adequately convey the intent of "it is possible that" here? Also, should "the method" be "a method" (i.e., in this example, is there more than one method that is not supported by the other side)? Original: Since IKEv2 requires that each peer uses exactly one authentication method and doesn't provide means for peers to indicate to the other side which authentication methods they support, it is possible that in these situations the peer that supports wider range of authentication methods (or authentication token formats) improperly selects the method (or format) which is not supported by the other side. Perhaps: Since IKEv2 requires that each peer use exactly one authentication method, and it doesn't provide means for peers to indicate to the other side which authentication methods they support, the peer that supports a wider range of authentication methods (or authentication token formats) could improperly select a method (or format) that is not supported by the other side. --> Since IKEv2 requires that each peer use exactly one authentication method, and it doesn't provide means for peers to indicate to the other side which authentication methods they support, the peer that supports a wider range of authentication methods (or authentication token formats) could improperly select the method (or format) that is not supported by the other side. </t> <t> Emerging post-quantum signature algorithms may bring additional challenges for implementations, especially if so-called hybrid schemes are used(e.g.(e.g., see <xreftarget="I-D.ounsworth-pq-composite-sigs" />).target="I-D.ietf-lamps-pq-composite-sigs"/>). </t> <t> This specification defines an extension to the IKEv2 protocol that allows peers to announce their supported authentication methods, thus decreasing risks of SA establishment failure in situations when there are several ways for the peers to authenticate themselves. </t> </section> <sectionanchor="mustshouldmay" title="Terminologyanchor="mustshouldmay"> <name>Terminology andNotation">Notation</name> <t> The key words"MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY","<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>", "<bcp14>MAY</bcp14>", and"OPTIONAL""<bcp14>OPTIONAL</bcp14>" in this document are to be interpreted as described inBCP 14BCP 14 <xreftarget="RFC2119" />target="RFC2119"/> <xreftarget="RFC8174" />target="RFC8174"/> when, and only when, they appear in all capitals, as shown here. </t> </section> <sectionanchor="protocol" title="Protocol Details">anchor="protocol"> <name>Protocol Details</name> <t>When establishing an IKESASA, each party may send a list to its peer of the authentication methods it supports and is configured touse to its peer.use. For thispurposepurpose, this specification introduces a new Notify Message Type SUPPORTED_AUTH_METHODS. The Notify payload with this Notify Message Type is utilized to convey the supported authentication methods of the party sending it. The sending party may additionally specify that some of the authentication methods are only for use with the particular trust anchors. The receiving party may take this information into consideration when selecting an algorithm for its authentication (i.e., the algorithm used for calculation of the AUTH payload) if several alternatives are available. To simplify the receiver's task of linking the announced authentication methods with the trust anchors, the protocol ensures that the SUPPORTED_AUTH_METHODS notification is always co-located with the CERTREQ payload in the same message. </t> <sectionanchor="exchange" title="Exchanges">anchor="exchange"> <name>Exchanges</name> <t> The initiator starts the IKE_SA_INIT exchange as usual. If the responder is willing to use this extension, it includes a new notification SUPPORTED_AUTH_METHODS in the IKE_SA_INIT response message. This notification contains a list of authentication methods supported by the responder, ordered by their preference. </t> <figurealign="center" anchor="ikesainit" title="Theanchor="ikesainit"> <name>The IKE_SA_INITExchange">Exchange</name> <artwork align="left"><![CDATA[ Initiator Responder ----------- ----------- HDR, SAi1, KEi, Ni --> <-- HDR, SAr1, KEr, Nr, [CERTREQ,] [N(SUPPORTED_AUTH_METHODS)(...)] ]]></artwork> </figure> <t> If the initiator doesn't support this extension, it ignores the received notification as an unknown status notify. </t> <t> Regardless of whether the notification is received, if the initiator supports and is willing to use this extension, it includes the SUPPORTED_AUTH_METHODS notification in the IKE_AUTH request message, with a list of authentication methods supported by the initiator, ordered by their preference. </t> <figurealign="center" anchor="ikeauth" title="Theanchor="ikeauth"> <name>The IKE_AUTHExchange">Exchange</name> <artwork align="left"><![CDATA[ Initiator Responder ----------- ----------- HDR, SK {IDi, [CERT,] [CERTREQ,] [IDr,] AUTH, SAi2, TSi, TSr, [N(SUPPORTED_AUTH_METHODS)(...)] } --> <-- HDR, SK {IDr, [CERT,] AUTH, SAr2, TSi, TSr } ]]></artwork> </figure> <!--[rfced] May this be rephrased as follows for clarity, in particular the phrase "it must take care that the size ... wouldn't grow"? Original: Since the responder sends the SUPPORTED_AUTH_METHODS notification in the IKE_SA_INIT exchange, it must take care that the size of the response message wouldn't grow too much so that IP fragmentation takes place. Perhaps: Because the responder sends the SUPPORTED_AUTH_METHODS notification in the IKE_SA_INIT exchange, it must prevent the size of the response message from growing so much that IP fragmentation occurs. --> <t> Since the responder sends the SUPPORTED_AUTH_METHODS notification in the IKE_SA_INIT exchange, it must take care that the size of the response message wouldn't grow too much so that IP fragmentation takes place. If both of the following conditions are met:<list style="symbols"></t> <ul spacing="normal"> <li> <t>the SUPPORTED_AUTH_METHODS notification to be included is so large, that the responder suspects that IP fragmentation of the resulting IKE_SA_INIT response message may happen;</t> </li> <li> <t>both peers support the IKE_INTERMEDIATE exchange, defined in <xreftarget="RFC9242" /> (i.e.target="RFC9242"/> (i.e., the responder has received and is going to send the INTERMEDIATE_EXCHANGE_SUPPORTED notification);</t></list></li> </ul> <t> then the responderMAY<bcp14>MAY</bcp14> choose not to send an actual list of the supported authentication methods in the IKE_SA_INIT exchange and instead ask the initiator to start the IKE_INTERMEDIATE exchange for the list to be sent in. This would allow using IKE fragmentation <xreftarget="RFC7383" />target="RFC7383"/> for long messages (which cannot be used in the IKE_SA_INIT exchange), thus avoiding IP fragmentation. In thiscasecase, the responder includes a SUPPORTED_AUTH_METHODS notification containing no data in the IKE_SA_INIT response. </t> <t> If the initiator receives the empty SUPPORTED_AUTH_METHODS notification in the IKE_SA_INIT exchange, it means that the responder is going to send the list of the supported authentication methods in the IKE_INTERMEDIATE exchange. If this exchange is to be initiated anyway for some other reason, then the responderMAY<bcp14>MAY</bcp14> use it to send the SUPPORTED_AUTH_METHODS notification. Otherwise, the initiatorMAY<bcp14>MAY</bcp14> start the IKE_INTERMEDIATE exchangejustfor this sole purpose by sending an empty IKE_INTERMEDIATE request. The initiatorMAY<bcp14>MAY</bcp14> also indicate its identity (and possibly the perceived responder's identity too) by including the IDi payload (possibly along with the IDr payload)intoin the IKE_INTERMEDIATE request. This information could help the responder to send back only those authenticationmethods,methods that are configured to be used for authentication of this particular initiator. If these payloads are sent, theyMUST<bcp14>MUST</bcp14> be identical to the IDi/IDr payloads sent later in the IKE_AUTH request. </t> <t>If the responder has sent any CERTREQ payload in the IKE_SA_INIT, then itSHOULD re-send<bcp14>SHOULD</bcp14> resend the same payload(s) in the IKE_INTERMEDIATE response containing the SUPPORTED_AUTH_METHODS notification if any of the included Announcements has a non-zero Cert Link field (see Sections <xref target="ann-3"/>format="counter"/> and <xref target="ann-m"/>).format="counter"/>). This requirement allows peers to have a list of Announcements and a list of CAs in the same message, which simplifies theirlinking (note,linking. (Note that this requirement is always fulfilled for the IKE_SA_INIT and IKE_AUTHexchanges).exchanges.) However, if for any reason the responder doesn'tre-sendresend CERTREQ payload(s) in the IKE_INTERMEDIATE exchange, then the initiatorMUST NOT<bcp14>MUST NOT</bcp14> abort negotiation. Instead, the initiatorMAY<bcp14>MAY</bcp14> either link the Announcements to the CAs received in the IKE_SA_INIT response, orMAYit <bcp14>MAY</bcp14> ignore the Announcements containing links to CAs. </t> <t>If multiple IKE_INTERMEDIATE exchanges take place during IKE SA establishments, it isRECOMMENDED<bcp14>RECOMMENDED</bcp14> that the responder use the last IKE_INTERMEDIATE exchange (the one just before IKE_AUTH) to send the list of supportedauthauthentication methods. However, it is not always possible for the responder to know how many IKE_INTERMEDIATE exchanges the initiator will use. In this case the responderMAY<bcp14>MAY</bcp14> send the list in any IKE_INTERMEDIATE exchange. If the initiator sends IDi/IDr in an IKE_INTERMEDIATE request, then it isRECOMMENDED<bcp14>RECOMMENDED</bcp14> that the responder sends back the list of authentication methods in the response. </t> <figurealign="center" anchor="ikeint" title="Usinganchor="ikeint"> <name>Using the IKE_INTERMEDIATE Exchange forsending auth methods">Sending Authentication Methods</name> <artwork align="left"><![CDATA[ Initiator Responder ----------- ----------- HDR, SAi1, KEi, Ni --> <-- HDR, SAr1, KEr, Nr, [CERTREQ,] [N(SUPPORTED_AUTH_METHODS)()] HDR, SK {..., [IDi, [IDr,]]} --> <-- HDR, SK {..., [CERTREQ,] [N(SUPPORTED_AUTH_METHODS)(...)] } HDR, SK {IDi, [CERT,] [CERTREQ,] [IDr,] AUTH, SAi2, TSi, TSr, [N(SUPPORTED_AUTH_METHODS)(...)] } --> <-- HDR, SK {IDr, [CERT,] AUTH, SAr2, TSi, TSr } ]]></artwork> </figure> <t>Note,Note that sending the SUPPORTED_AUTH_METHODS notification and using information obtained from itisare optional for both the initiator and the responder. If multiple SUPPORTED_AUTH_METHODS notifications are included in a message, all their announcements form a single ordered list, unless overridden by other extension (see <xreftarget="interaction" />).target="interaction"/>). </t> </section> <sectionanchor="format" title="SUPPORTED_AUTH_METHODS Notify">anchor="format"> <name>SUPPORTED_AUTH_METHODS Notify</name> <t> The format of the SUPPORTED_AUTH_METHODS notification is shown below. </t> <figurealign="center" anchor="notify" title="SUPPORTED_AUTH_METHODS Notify">anchor="notify"> <name>SUPPORTED_AUTH_METHODS Notify</name> <artwork align="left"><![CDATA[ 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Payload |C| RESERVED | Payload Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Protocol ID | SPI Size | Notify Message Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ List of Supported Auth Methods Announcements ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ]]></artwork> </figure> <t> The Notify payload format is defined inSection 3.10 of<xref target="RFC7296" section="3.10" sectionFormat="of" />. When a Notify payload of type SUPPORTED_AUTH_METHODS is sent, the Protocol ID field is set to 0, the SPI Size is set to0, meaning0 (meaning there is no SPIfield,field), and the Notify Message Type is set to<TBA by IANA>.16443. </t> <t> Notification data contains the list of supported authentication methods announcements. Each individual announcement is a variable-size datablob, whichblob whose format depends on the announced authentication method. The blob always starts with an octet containing the length of the blob followed by an octet containing the authentication method. Authentication methods are represented as values from the "IKEv2 Authentication Method" registry defined in <xreftarget="IKEV2-IANA" />.target="IKEV2-IANA"/>. The meaning of the remaining octets of the blob, if any, depends on the authentication method.Note, thatNote that, for the currently defined authenticationmethodsmethods, the length octet fully defines both the format and the semantics of the blob. </t> <t> If more authentication methods are defined in the future, the corresponding documents must describe the semantics of the announcements for these methods. ImplementationsMUST<bcp14>MUST</bcp14> ignore announcements whose semantics they don't understand. </t> <sectionanchor="ann-2" title="2-octet Announcement">anchor="ann-2"> <name>2-Octet Announcement</name> <t> If the announcement contains an authentication method that is not concerned with public key cryptography, then the following format is used. </t> <figurealign="center" anchor="authmethod1" title="Supportedanchor="authmethod1"> <name>Supported AuthenticationMethod">Method</name> <artwork align="left"><![CDATA[ 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length (=2) | Auth Method | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ]]></artwork> </figure><list style="symbols"> <t>Length - Length<dl spacing="normal"> <dt>Length:</dt> <dd>Length of the blob inoctets,octets; must be 2 for thiscase.</t> <t>Auth Method - Announcedcase.</dd> <dt>Auth Method:</dt> <dd>Announced authenticationmethod.</t> </list>method.</dd> </dl> <t> This format is applicable for the authentication methods "Shared Key Message Integrity Code" (2) and "NULL Authentication" (13).Note,Note that the authentication method "Generic Secure Password Authentication Method" (12) would also fall in thiscategory, howevercategory; however, it is negotiated separately (see <xreftarget="RFC6467" />)target="RFC6467"/>), and for this reason there is no point to announce it via this mechanism. See also <xreftarget="interaction" />.target="interaction"/>. </t> </section> <sectionanchor="ann-3" title="3-octet Announcement">anchor="ann-3"> <name>3-Octet Announcement</name> <t> If the announcement contains an authentication method that is concerned with public key cryptography, then the following format is used. This format allows linking the announcement with a particular trust anchor from the Certificate Request payload. </t> <figurealign="center" anchor="authmethod2" title="Supportedanchor="authmethod2"> <name>Supported AuthenticationMethod">Method</name> <artwork align="left"><![CDATA[ 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length (=3) | Auth Method | Cert Link | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ]]></artwork> </figure><list style="symbols"> <t>Length - Length<dl spacing="normal"> <dt>Length:</dt> <dd>Length of the blob inoctets,octets; must be 3 for thiscase.</t> <t>Auth Method - Announced authentication method.</t> <t>Cert Link - Linkscase.</dd> <dt>Auth Method:</dt> <dd>Announced authentication method.</dd> <dt>Cert Link:</dt> <dd>Links this announcement with particularCA.</t> </list>CA.</dd> </dl> <t> If the Cert Link field contains a non-zero value N, it means that the announced authentication method is intended to be used only with the N-th trust anchor (CA certificate) from the Certificate Request payload(s) sent by this peer. If it is zero, then this authentication method may be used with any CA. If multiple CERTREQ payloads were sent, the CAs from all of them are treated as a single list for the purpose of the linking. If no Certificate Request payload were received, the content of this fieldMUST<bcp14>MUST</bcp14> be ignored and treated as zero. </t> <t> This format is applicable for the authentication methods "RSA Digital Signature" (1), "DSS Digital Signature" (3), "ECDSA with SHA-256 on the P-256 curve" (9), "ECDSA with SHA-384 on the P-384 curve" (10) and "ECDSA with SHA-512 on the P-521 curve" (11).NoteNote, however, that these authentication methods are currently superseded by the "Digital Signature" (14) authentication method, which has a different announcement format, described below. </t> </section> <sectionanchor="ann-m" title="Multi-octet Announcement">anchor="ann-m"> <name>Multi-octet Announcement</name> <t> The following format is currently used only with the "Digital Signature" (14) authentication method. </t> <figurealign="center" anchor="authmethod3" title="Supportedanchor="authmethod3"> <name>Supported AuthenticationMethod">Method</name> <artwork align="left"><![CDATA[ 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length (>3) | Auth Method | Cert Link | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | ~ AlgorithmIdentifier ASN.1 object ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ]]></artwork> </figure><list style="symbols"> <t>Length - Length<dl spacing="normal"> <dt>Length:</dt> <dd>Length of the blob inoctets,octets; must be greater than 3 for thiscase.</t> <t>Auth Method - Announcedcase.</dd> <dt>Auth Method:</dt> <dd>Announced authenticationmethod, atmethod. At the time of writing thisdocumentdocument, only value 14 ("Digital Signature") isallowed.</t> <t>Cert Link - Linksallowed.</dd> <dt>Cert Link:</dt> <dd>Links this announcement with a particular CA; see <xreftarget="ann-3" />target="ann-3"/> fordetails.</t> <t>AlgorithmIdentifierdetails.</dd> <dt>AlgorithmIdentifier ASN.1object - theobject:</dt> <dd>The AlgorithmIdentifier of PKIX (seeSection 4.1.1.2 of<xref target="RFC5280" section="4.1.1.2" sectionFormat="of" />), encoded usingdistinguished encoding rulesDistinguished Encoding Rules (DER) <xreftarget="X.690" />. </t> </list>target="X.690"/>. </dd> </dl> <t> The "Digital Signature" authentication method, defined in <xreftarget="RFC7427" />,target="RFC7427"/>, supersedes previously defined signature authentication methods. In thiscasecase, the real authentication algorithm is identified via AlgorithmIdentifier ASN.1 object.Appendix A in<xref target="RFC7427"/>section="A" sectionFormat="of"/> contains examples ofCommonly Usedcommonly used ASN.1Objects.objects. </t> </section> </section> </section> <sectiontitle="Interactionanchor="interaction"> <name>Interaction with IKEv2 Extensions concerningAuthentication" anchor="interaction">Authentication</name> <t> Generally in IKEv2 each party independently determines the way it authenticates itself to the peer. In other words, authentication methods selected by the peers need not be the same. However, some IKEv2 extensions break this rule. </t> <!--[rfced] Will the term "PAKE method" (3 instances) be clear to the reader? We see zero instances of this term in RFCs. We see usage of "PAKE scheme" and "PAKE protocol" in RFC 8125. Original: With this framework peers negotiate using one of PAKE methods in the IKE_SA_INIT exchange - the initiator sends a list of supported PAKE methods in the request and the responder picks one of them and sends it back in the response. [...] then the selected PAKE method is used ... --> <t> The prominent example is<xref target="RFC6467" />, (Secure"Secure Password Framework for Internet Key Exchange Version2),2" <xref target="RFC6467"/>, which defines a framework for usingPassword-authenticatedpassword-authenticated key exchanges(PAKE)(PAKEs) in IKEv2. With thisframeworkframework, peers negotiate using one of the PAKE methods in the IKE_SA_INIT exchange--- the initiator sends a list of supported PAKE methods in therequestrequest, and the responder picks one of them and sends it back in the response. </t> <t> If peers negotiate PAKE for authentication, then the selected PAKE method is used by both initiator andresponderresponder, and no other authentication methods are involved. For thisreasonreason, there is no point to announce supported authentication methods in this case. Thus, if the peers choose to go with PAKE, theyMUST NOT<bcp14>MUST NOT</bcp14> send the SUPPORTED_AUTH_METHODS notification. </t> <t> If then peers are going to use Multiple Authentication Exchanges <xreftarget="RFC4739" />,target="RFC4739"/>, then theyMAY<bcp14>MAY</bcp14> include multiple SUPPORTED_AUTH_METHODS notificationsinstead(instead ofone,one), each containing authentication methods appropriate for each authentication round. The notifications are included in the order of the preference of performing authentication rounds. </t> </section> <sectionanchor="sec" title="Security Considerations">anchor="iana"> <name>IANA Considerations</name> <t>This document defines a new type in the "IKEv2 Notify Message Status Types" registry:</t> <table anchor="notify_msg_status_type"> <thead> <tr> <th>Value</th> <th>Notify Message Status Type</th> <th>Reference</th> </tr> </thead> <tbody> <tr> <td>16443</td> <td>SUPPORTED_AUTH_METHODS</td> <td>RFC 9593</td> </tr> </tbody> </table> </section> <section anchor="sec"> <name>Security Considerations</name> <t> Security considerations for the IKEv2 protocol are discussed in <xreftarget="RFC7296" />.target="RFC7296"/>. Security properties of different authentication methodsvaries.vary. Refer to corresponding documents, listed in the "IKEv2 Authentication Method" registry on <xreftarget="IKEV2-IANA" />target="IKEV2-IANA"/> for discussion of security properties of each authentication method. </t> <t> Announcing authentication methods gives an eavesdropper additional information about peers' capabilities. <!--[rfced] FYI, for readability, "attacker on the path" has been changed to "on-path attacker" (2 instances). Please review whether this is correct. --> If a peer advertisesNULL authentication"NULL Authentication" along with other methods, then an active on-path attackeron the pathcan encourage peers to use NULL authentication by removing all other announcements.Note,Note that this is not a real "downgrade" attack, since authentication methods in IKEv2 are notnegotiatednegotiated, and in this case NULL authentication should be allowed by local security policy. </t> <t> Similarly, if an on-path attackeron the pathcan break some of the announced authentication methods online, then the attacker can encourage peers to use one of these weaker methods by removing all other announcements, and if this succeeds, then perform a person-in-the-middle attack. </t> </section><section anchor="iana" title="IANA Considerations"> <t>This document defines a new Notify Message Type in</middle> <back> <displayreference target="I-D.ietf-lamps-pq-composite-sigs" to="COMPOSITE-SIGS"/> <references> <name>References</name> <references> <name>Normative References</name> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7296.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7427.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5280.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9242.xml"/> <!--[rfced] FYI, for [X.690] we have updated the"IKEv2 Notify Message Status Types" registry referencing this RFC:</t> <figure align="center"> <artwork align="left"><![CDATA[ <TBA> SUPPORTED_AUTH_METHODS [RFCXXXX] ]]></artwork> </figure> </section> <section title="Acknowledgments"> <t>The author would likereference from the 2002 tothank Paul Wouters for his valuable comments2021 version because the 2002 is superseded. Please review andproposals. The authorlet us know if this isalso grateful to Daniel Van Geest, who made proposalsacceptable. (Please see https://www.itu.int/rec/T-REC-X.690 forprotocol improvement. Reese Enghardt and Rifaat Shekh-Yusef contributed totheclaritylist ofthe document. </t> </section> </middle> <back> <references title='Normative References'> <?rfc include="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml" ?> <?rfc include="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml" ?> <?rfc include="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7296.xml" ?> <?rfc include="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7427.xml" ?> <?rfc include="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5280.xml" ?> <?rfc include="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.9242.xml" ?> <reference anchor="X.690"> <front> <title>ITU-Tdocuments that are "Superseded" vs. "In force".) Original: [X.690] "ITU-T Recommendation X.690 (2002) | ISO/IEC 8825-1:2002, Information technology – ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules(DER) </title>(DER)", July 2002. Current: [X.690] ITU-T, "Information Technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)", ISO/IEC 8825-1:2021 (E), ITU-T Recommendation X.690, February 2021. --> <reference anchor="X.690"> <front> <title>Information Technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)</title> <author><organization></organization><organization>ITU-T</organization> </author> <datemonth="July" year="2002" />month="February" year="2021"/> </front> <seriesInfo name="ISO/IEC" value="8825-1:2021 (E)"/> <seriesInfo name="ITU-T Recommendation" value="X.690"/> </reference> <reference anchor="IKEV2-IANA"target="https://www.iana.org/assignments/ikev2-parameters/ikev2-parameters.xhtml#ikev2-parameters-12">target="https://www.iana.org/assignments/ikev2-parameters/"> <front> <title>Internet Key Exchange Version 2 (IKEv2) Parameters</title> <author> <organization>IANA</organization> </author> <date/> </front> </reference> </references> <references> <!--[rfced] May we put the references in alphanumeric order (i.e., may we change sortRefs="false" to "true" in the XML file)?--> <name>Informative References</name> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2409.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4739.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6467.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7383.xml"/> <!--[rfced] FYI, draft-ounsworth-pq-composite-sigs was replaced by draft-ietf-lamps-pq-composite-sigs. We have updated the reference accordingly; please review. Original: [I-D.ounsworth-pq-composite-sigs] Ounsworth, M., Gray, J., Pala, M., and J. Klaußner, "Composite ML-DSA for use in Internet PKI", Work in Progress, Internet-Draft, draft-ounsworth-pq-composite- sigs-13, 4 March 2024, <https://datatracker.ietf.org/doc/html/draft-ounsworth-pq- composite-sigs-13>. Current: [COMPOSITE-SIGS] Ounsworth, M., Gray, J., Pala, M., and J. Klaussner, "Composite Signatures For Use In Internet PKI", Work in Progress, Internet-Draft, draft-ietf-lamps-pq-composite- sigs-00, 24 May 2024, <https://datatracker.ietf.org/doc/html/draft-ietf-lamps- pq-composite-sigs-00>. --> <!-- FYI, used the long form so that the author's name matches the header of the I-D (which shows Klaussner not Klaußner). --> <reference anchor="I-D.ietf-lamps-pq-composite-sigs" target="https://datatracker.ietf.org/doc/html/draft-ietf-lamps-pq-composite-sigs-00"> <front> <title>Composite Signatures For Use In Internet PKI</title> <author initials="M." surname="Ounsworth" fullname="Mike Ounsworth"> <organization>Entrust Limited</organization> </author> <author initials="J." surname="Gray" fullname="John Gray"> <organization>Entrust Limited</organization> </author> <author initials="M." surname="Pala" fullname="Massimiliano Pala"> <organization>CableLabs</organization> </author> <author initials="J." surname="Klaußner" fullname="Jan Klaussner"> <organization>D-Trust GmbH</organization> </author> <date month="May" day="24" year="2024" /> </front> <seriesInfo name="Internet-Draft" value="draft-ietf-lamps-pq-composite-sigs-00" /> </reference> </references><references title='Informative References'> <?rfc include="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2409.xml" ?> <?rfc include="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4739.xml" ?> <?rfc include="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6467.xml" ?> <?rfc include="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7383.xml" ?> <?rfc include="https://xml2rfc.ietf.org/public/rfc/bibxml3/reference.I-D.ounsworth-pq-composite-sigs.xml" ?></references> <sectionanchor="examples" title="Examplesanchor="examples"> <name>Examples of Announcing Supported AuthenticationMethods">Methods</name> <t> This appendix shows some examples of announcing authentication methods. This appendix is purely informative; if it disagrees with the body of this document, the other text is considered correct. Note that some payloads that are not relevant to this specification may be omitted for brevity. </t> <sectionanchor="no_intermediate_example" title="Noanchor="no_intermediate_example"> <name>No Need to Use the IKE_INTERMEDIATEExchange" >Exchange</name> <t> This example illustrates the situation when the SUPPORTED_AUTH_METHODS notify fits into the IKE_SA_INITmessagemessage, and thus the IKE_INTERMEDIATE exchange is not needed. In thisscenarioscenario, the responder announces that it supports the "Shared Key Message Integrity Code" and the "NULL Authentication" authentication methods. The initiator informs the responder that it supports only the "Shared Key Message Integrity Code" authentication method.<figure align="center"></t> <artwork align="left"><![CDATA[ Initiator Responder ----------- ----------- IKE_SA_INIT HDR, SAi1, KEi, Ni --> <-- HDR, SAr1, KEr, Nr, N(SUPPORTED_AUTH_METHODS( PSK, NULL)) IKE_AUTH HDR, SK {IDi, AUTH, SAi2, TSi, TSr, N(SUPPORTED_AUTH_METHODS(PSK))} --> <-- HDR, SK {IDr, AUTH, SAr2, TSi, TSr} ]]></artwork></figure> </t></section> <sectionanchor="intermediate_example" title="Withanchor="intermediate_example"> <name>With Use of the IKE_INTERMEDIATEExchange" >Exchange</name> <t>This example illustrates the situation when the IKE_INTERMEDIATE exchange is used. In thisscenarioscenario, the responder announces that it supports the "Digital signature" authentication method using the RSASSA-PSS algorithm with CA1 and CA2 and the same method using the ECDSA algorithm with CA3. The initiator supports only the "Digital signature" authentication method using the RSASSA-PSS algorithm with no link to a particular CA.<figure align="center"></t> <artwork align="left"><![CDATA[ Initiator Responder ----------- ----------- IKE_SA_INIT HDR, SAi1, KEi, Ni, N(SIGNATURE_HASH_ALGORITHMS) --> <-- HDR, SAr1, KEr, Nr, CERTREQ(CA1, CA2, CA3), N(SIGNATURE_HASH_ALGORITHMS), N(SUPPORTED_AUTH_METHODS()) IKE_INTERMEDIATE HDR, SK {..., IDi]} --> <-- HDR, SK {..., CERTREQ(CA1, CA2, CA3), N(SUPPORTED_AUTH_METHODS( SIGNATURE(RSASSA-PSS:1), SIGNATURE(RSASSA-PSS:2), SIGNATURE(ECDSA:3)))} IKE_AUTH HDR, SK {IDi, CERT, CERTREQ(CA2), AUTH, SAi2, TSi, TSr, N(SUPPORTED_AUTH_METHODS( SIGNATURE(RSASSA-PSS:0)))} --> <-- HDR, SK {IDr, CERT, AUTH, SAr2, TSi, TSr} ]]></artwork></figure> </t></section> </section> <section numbered="false"> <name>Acknowledgments</name> <t>The author would like to thank <contact fullname="Paul Wouters" /> for his valuable comments and proposals. The author is also grateful to <contact fullname="Daniel Van Geest"/>, who made proposals for protocol improvement. <contact fullname="Reese Enghardt"/> and <contact fullname="Rifaat Shekh-Yusef"/> contributed to the clarity of the document. </t> </section> <!--[rfced] These terms seem to be used interchangeably. Would you like any instances to be updated for consistency (e.g., change 'notify' to 'notification')? a) SUPPORTED_AUTH_METHODS notification (11 instances) b) SUPPORTED_AUTH_METHODS notify (3 instances; capitalized in titles as needed) (in the titles of Section 3.2 and Figure 4, as well as Appendix A.1: "the SUPPORTED_AUTH_METHODS notify fits into...") c) "a Notify payload of type SUPPORTED_AUTH_METHODS" (1 instance) --> <!-- [rfced] Please review the "Inclusive Language" portion of the online Style Guide <https://www.rfc-editor.org/styleguide/part2/#inclusive_language> and let us know if any changes are needed. Note that our script did not flag any words in particular, but this should still be reviewed as a best practice. --> </back> </rfc>