<?xmlversion="1.0" encoding="US-ASCII"?> <!-- This template is for creating an Internet Draft using xml2rfc, which is available here: http://xml.resource.org. -->version='1.0' encoding='utf-8'?> <!DOCTYPE rfc SYSTEM"rfc2629.dtd" [ <!-- One method to get references from the online citation libraries. There has to be one entity for each item to be referenced. 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(Here they are set differently than their defaults in xml2rfc v1.32) --> <?rfc strict="yes" ?> <!-- give errors regarding ID-nits and DTD validation --> <!-- control the table of contents (ToC) --> <?rfc toc="yes"?> <!-- generate a ToC --> <?rfc tocdepth="4"?> <!-- the number of levels of subsections in ToC. default: 3 --> <!-- control references --> <?rfc symrefs="yes"?> <!-- use symbolic references tags, i.e, [RFC2119] instead of [1] --> <?rfc sortrefs="yes" ?> <!-- sort the reference entries alphabetically --> <!-- control vertical white space (using these PIs as follows is recommended by the RFC Editor) --> <?rfc compact="yes" ?> <!-- do not start each main section on a new page --> <?rfc subcompact="no" ?> <!-- keep one blank line between list items --> <!-- end of list of popular I-D processing instructions -->"rfc2629-xhtml.ent"> <rfc xmlns:xi="http://www.w3.org/2001/XInclude" category="std" docName="draft-ietf-ipsecme-qr-ikev2-11"ipr="trust200902"> <!-- category values: std, bcp, info, exp, and historic ipr values: full3667, noModification3667, noDerivatives3667 you can add the attributes updates="NNNN" and obsoletes="NNNN" they will automatically be output with "(if approved)" -->number="8784" ipr="trust200902" obsoletes="" updates="" submissionType="IETF" xml:lang="en" tocInclude="true" tocDepth="4" symRefs="true" sortRefs="true" consensus="true" version="3"> <!--***** FRONT MATTER *****xml2rfc v2v3 conversion 2.41.0 --> <front><!-- The abbreviated title is used in the page header - it is only necessary if the full title is longer than 39 characters --><title abbrev="MixingPSKPSKs in IKEv2 for PQResistance">MixingSecurity">Mixing Preshared Keys inIKEv2the Internet Key Exchange Protocol Version 2 (IKEv2) for Post-quantum Security</title><!-- add 'role="editor"' below for the editors if appropriate --> <!-- Another author who claims to be an editor --><seriesInfo name="RFC" value="8784"/> <author fullname="Scott Fluhrer"initials="S.F."initials="S." surname="Fluhrer"> <organization>Cisco Systems</organization> <address> <email>sfluhrer@cisco.com</email> </address> </author> <author fullname="Panos Kampanakis"initials="P.K."initials="P." surname="Kampanakis"> <organization>Cisco Systems</organization> <address> <email>pkampana@cisco.com</email> </address> </author> <author fullname="David McGrew"initials="D.M."initials="D." surname="McGrew"> <organization>Cisco Systems</organization> <address> <email>mcgrew@cisco.com</email> </address> </author> <author fullname="Valery Smyslov"initials="V.S."initials="V." surname="Smyslov"> <organization>ELVIS-PLUS</organization> <address> <phone>+7 495 276 0211</phone> <email>svan@elvis.ru</email> </address> </author> <date/> <!-- Meta-data Declarations -->month="June" year="2020"/> <area>Security</area> <workgroup>Internet Engineering Task Force</workgroup><!-- WG name at the upperleft corner of the doc, IETF is fine for individual submissions. If this element is not present, the default is "Network Working Group", which is used by the RFC Editor as a nod to the history of the IETF. --><keyword>internet key exchange</keyword> <keyword>quantum computer</keyword> <keyword>post quantum</keyword> <keyword>post-quantum</keyword> <keyword>quantum safe</keyword> <keyword>quantum secure</keyword> <keyword>quantum resistant</keyword><!-- Keywords will be incorporated into HTML output files in a meta tag but they have no effect on text or nroff output. If you submit your draft to the RFC Editor, the keywords will be used for the search engine. --><abstract> <t>The possibility of quantum computers poses a serious challenge to cryptographic algorithms deployed widely today.IKEv2The Internet Key Exchange Protocol Version 2 (IKEv2) is one example of a cryptosystem that could be broken; someone storing VPN communications today could decrypt them at a later time when a quantum computer is available. It is anticipated that IKEv2 will be extended to support quantum-secure key exchange algorithms;howeverhowever, that is not likely to happen in the near term. To address this problem before then, this document describes an extension of IKEv2 to allow it to be resistant to a quantumcomputer,computer by using preshared keys.</t> </abstract> </front> <middle> <sectiontitle="Introduction">numbered="true" toc="default"> <name>Introduction</name> <t>Recent achievements in developing quantum computers demonstrate that it is probably feasible to buildaone that is cryptographicallysignificant one.significant. If such a computer is implemented, many of the cryptographic algorithms and protocols currently in use would be insecure. A quantum computer would be able to solveDHDiffie-Hellman (DH) andECDHElliptic Curve Diffie-Hellman (ECDH) problems in polynomial time <xreftarget="I-D.hoffman-c2pq"/>,target="I-D.hoffman-c2pq" format="default"/>, and this would imply that the security of existing IKEv2 <xreftarget="RFC7296"/>target="RFC7296" format="default"/> systems would be compromised. IKEv1 <xreftarget="RFC2409"/>,target="RFC2409" format="default"/>, when used with strong preshared keys, is not vulnerable to quantumattacks,attacks because those keys are one of the inputs to the key derivation function. If the preshared key has sufficient entropy and thePRF, encryption andPseudorandom Function (PRF), encryption, and authentication transforms arequantum-secure,quantum secure, then the resulting system is believed to bequantum-secure,quantum secure -- that is, secure against classical attackers of today or future attackers with a quantum computer.</t> <t>This document describes a way to extend IKEv2 to have a similar property; assuming that the two end systems share a long secretkey, then the resulting exchange is quantum-secure. By bringing post-quantum security to IKEv2, this document removes the need to use an obsolete version of the Internet Key Exchange in order to achieve that security goal.</t> <t>The general idea is that we add an additional secret that is shared between the initiator and the responder; this secret is in addition to the authentication method that is already provided within IKEv2. We stir this secret into the SK_d value, which is used to generate the key material (KEYMAT) and the SKEYSEED for the child SAs; this secret provides quantum resistance to the IPsec SAs (and any child IKE SAs). We also stir the secret into the SK_pi, SK_pr values; this allows both sides to detect a secret mismatch cleanly.</t> <t>It was considered important to minimize the changes to IKEv2. The existing mechanisms to do authentication and key exchange remain in place (that is, we continue to do (EC)DH, and potentially PKI authentication if configured). This document does not replace the authentication checks that the protocol does; instead, they are strengthened by using an additional secret key.</t> <section title="Changes"> <t>RFC EDITOR PLEASE DELETE THIS SECTION.</t> <t>Changes in this draft in each version iterations.</t> <t>draft-ietf-ipsecme-qr-ikev2-11 <list style="symbols"> <t>Updates the IANA section based on Eric V.'s IESG Review.</t> <t>Updates based on IESG Reviews (Alissa, Adam, Barry, Alexey, Mijra, Roman, Martin.</t> </list></t> <t>draft-ietf-ipsecme-qr-ikev2-10 <list style="symbols"> <t>Addresses issues raised during IETF LC.</t> </list></t> <t>draft-ietf-ipsecme-qr-ikev2-09 <list style="symbols"> <t>Addresses issues raised in AD review.</t> </list></t> <t>draft-ietf-ipsecme-qr-ikev2-08 <list style="symbols"> <t>Editorial changes.</t> </list></t> <t>draft-ietf-ipsecme-qr-ikev2-07 <list style="symbols"> <t>Editorial changes.</t> </list></t> <t>draft-ietf-ipsecme-qr-ikev2-06 <list style="symbols"> <t>Editorial changes.</t> </list></t> <t>draft-ietf-ipsecme-qr-ikev2-05 <list style="symbols"> <t>Addressed comments received during WGLC.</t> </list></t> <t>draft-ietf-ipsecme-qr-ikev2-04 <list style="symbols"> <t>Using Group PPK is clarified based on comment from Quynh Dang.</t> </list></t> <t>draft-ietf-ipsecme-qr-ikev2-03 <list style="symbols"> <t>Editorial changes and minor text nit fixes.</t> <t>Integrated Tommy P. text suggestions.</t> </list></t> <t>draft-ietf-ipsecme-qr-ikev2-02 <list style="symbols"> <t>Added note that the PPK is stirred in the initial IKE SA setup only. </t> <t>Added note about the initiator ignoring any content in the PPK_IDENTITY notification from the responder.</t> <t>fixed Tero's suggestions from 2/6/1028</t> <t>Added IANA assigned message types where necessary.</t> <t>fixed minor text nits </t> </list></t> <t>draft-ietf-ipsecme-qr-ikev2-01 <list style="symbols"> <t>Nits and minor fixes. </t> <t>prf is replaced with prf+ for the SK_d and SK_pi/r calculations.</t> <t>Clarified using PPK in case of EAP authentication.</t> <t>PPK_SUPPORT notification is changed to USE_PPK to better reflect its purpose.</t> </list></t> <t>draft-ietf-ipsecme-qr-ikev2-00 <list style="symbols"> <t>Migrated from draft-fluhrer-qr-ikev2-05 to draft-ietf-ipsecme-qr-ikev2-00 that is a WG item.</t> </list></t> <t>draft-fluhrer-qr-ikev2-05 <list style="symbols"> <t>Nits and editorial fixes.</t> <t>Made PPK_ID format and PPK Distributions subsection of the PPK section. Also added an Operational Considerations section.</t> <t>Added comment about Child SA rekey in the Security Considerations section.</t> <t>Added NO_PPK_AUTH to solve the cases where a PPK_ID is not configured for a responder.</t> <t>Various text changes and clarifications.</t> <t>Expanded Security Considerations section to describe some security concerns and how they should be addressed.</t> </list></t> <t>draft-fluhrer-qr-ikev2-03 <list style="symbols"> <t>Modified how we stir the PPK into the IKEv2 secret state.</t> <t>Modified how the use of PPKs is negotiated.</t> </list></t> <t>draft-fluhrer-qr-ikev2-02 <list style="symbols"> <t>Simplified the protocol by stirring in the preshared key into the child SAs; this avoids the problem of having the responder decide which preshared key to use (as it knows the initiator identity at that point); it does mean that someone with a quantum computer can recover the initial IKE negotiation.</t> <t>Removed positive endorsements of various algorithms. Retained warnings about algorithms known to be weak against a quantum computer.</t> </list></t> <t>draft-fluhrer-qr-ikev2-01 <list style="symbols"> <t>Added explicit guidance as to what IKE and IPsec algorithms are quantum resistant.</t> </list></t> <t>draft-fluhrer-qr-ikev2-00 <list style="symbols"> <t>We switched from using vendor ID's to transmit the additional data to notifications.</t> <t>We added a mandatory cookie exchange to allow the server to communicate to the client before the initial exchange.</t> <t>We added algorithm agility by havingkey, then theserver tellresulting exchange is quantum secure. By bringing post-quantum security to IKEv2, this document removes theclient what algorithmneed to use an obsolete version of IKE in order to achieve that security goal.</t> <t>The general idea is that we add an additional secret that is shared between thecookie exchange.</t> <t>We haveinitiator and theserver specifyresponder; this secret is in addition to thePPK Indicator Input, which allowsauthentication method that is already provided within IKEv2. We stir this secret into theserverSK_d value, which is used tomake a trade-off betweengenerate theefficiencykey material (KEYMAT) for thesearch of the clients PPK,Child Security Associations (SAs) and theanonymitySKEYSEED for the IKE SAs created as a result of theclient.</t> <t>We now useinitial IKE SA rekey. This secret provides quantum resistance to thenegotiated PRF (rather thanIPsec SAs and any subsequent IKE SAs. We also stir the secret into the SK_pi and SK_pr values; this allows both sides to detect afixed HMAC-SHA256)secret mismatch cleanly.</t> <t>It was considered important totransformminimize thenonces duringchanges to IKEv2. The existing mechanisms to perform authentication and key exchange remain in place (that is, we continue to perform (EC)DH and potentially PKI authentication if configured). This document does not replace theKDF.</t> </list></t> </section>authentication checks that the protocol does; instead, they are strengthened by using an additional secret key.</t> <sectiontitle="Requirements Language">numbered="true" toc="default"> <name>Requirements Language</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 shownhere.</t>here. </t> </section> </section> <sectiontitle="Assumptions"> <t>Wenumbered="true" toc="default"> <name>Assumptions</name> <t> We assume that each IKE peer has a list of Post-quantum Preshared Keys(PPK)(PPKs) along with their identifiers (PPK_ID), and any potential IKE initiator selects which PPK to use with any specific responder. In addition, implementations have a configurable flag that determines whether thispost-quantum preshared keyPPK is mandatory. This PPK is independent of the preshared key (if any) that the IKEv2 protocol uses to perform authentication (because the preshared key in IKEv2 is not used for any keyderivation,derivation and thus doesn't protect against quantum computers). ThePPK specificPPK-specific configuration that is assumed to be on each node consists of the following tuple:</t><figure align="center"><artworkalign="left"><![CDATA[align="left" name="" type="" alt=""><![CDATA[ Peer, PPK, PPK_ID, mandatory_or_not ]]></artwork></figure><t>We assume the reader is familiar with the payload notation defined in <xref target="RFC7296" sectionFormat="of" section="1.2"/>.</t> </section> <section anchor="Exchanges"title="Exchanges">numbered="true" toc="default"> <name>Exchanges</name> <t>If the initiator is configured to use apost-quantum preshared keyPPK with the responder (whether or not the use of the PPK is mandatory), then itMUST<bcp14>MUST</bcp14> include a notification USE_PPK in the IKE_SA_INIT request message as follows:</t><figure align="center"><artworkalign="left"><![CDATA[align="left" name="" type="" alt=""><![CDATA[ Initiator Responder ------------------------------------------------------------------ HDR, SAi1, KEi, Ni, N(USE_PPK) ---> ]]></artwork></figure><t>N(USE_PPK) is a status notification payload with the type 16435; it has a protocol ID of 0, noSPISecurity Parameter Index (SPI), and no notification data associated with it.</t> <t>If the initiator needs to resend this initial message with a COOKIE notification, then the resend would include the USE_PPK notification if the original message did (seeSection 2.6 of<xref target="RFC7296"/>).</t>sectionFormat="of" section="2.6"/>).</t> <t>If the responder does not support this specification or does not have any PPK configured, then it ignores the received notification (as defined in <xref target="RFC7296"/>format="default"/> for unknown status notifications) and continues with the IKEv2 protocol as normal.OtherwiseOtherwise, the responder replies with the IKE_SA_INITmessagemessage, including a USE_PPK notification in the response:</t><figure align="center"><artworkalign="left"><![CDATA[align="left" name="" type="" alt=""><![CDATA[ Initiator Responder ------------------------------------------------------------------ <--- HDR, SAr1, KEr, Nr, [CERTREQ,] N(USE_PPK) ]]></artwork></figure><t>When the initiator receives this reply, it checks whether the responder included the USE_PPK notification. If the responder did not include the USE_PPK notification and the flag mandatory_or_not indicates that using PPKs is mandatory for communication with this responder, then the initiatorMUST<bcp14>MUST</bcp14> abort the exchange. This situation may happen in case of misconfiguration, i.e., when the initiator believes it has a mandatory-to-use PPK for theresponder, whileresponder and the responder either doesn't support PPKs at all or doesn't have any PPK configured for the initiator. See <xreftarget="Security"/>target="Security" format="default"/> for discussion of the possible impacts of this situation.</t> <t>If the responder did not include the USE_PPK notification and using a PPK for this particular responder is optional, then the initiator continues with the IKEv2 protocol as normal, without using PPKs.</t> <t>If the responder did include the USE_PPK notification, then the initiator selects a PPK, along with its identifier PPK_ID. Then, it computes this modification of the standard IKEv2 key derivation fromSection 2.14 of<xref target="RFC7296"/>:</t> <figure align="center"> <artwork align="left"><![CDATA[sectionFormat="of" section="2.14"/>:</t> <sourcecode name="" type="pseudocode"><![CDATA[ SKEYSEED = prf(Ni | Nr, g^ir) {SK_d' | SK_ai | SK_ar | SK_ei | SK_er | SK_pi' |SK_pr' )SK_pr'} = prf+ (SKEYSEED, Ni | Nr | SPIi |SPIr }SPIr) SK_d = prf+ (PPK, SK_d') SK_pi = prf+ (PPK, SK_pi') SK_pr = prf+ (PPK, SK_pr')]]></artwork> </figure>]]></sourcecode> <t> That is, we use the standard IKEv2 key derivationprocessprocess, except that the three resulting subkeys SK_d, SK_pi, and SK_pr (marked with primes in the formula above) are then run through the prf+ again, this time using the PPK as the key. The result is the unprimed versions of thesekeyskeys, which are then used as inputs to subsequent steps of the IKEv2 exchange.</t> <t> Using a prf+ construction ensures that it is always possible to get the resulting keys of the same size as the initial ones, even if the underlying PRF has an output size different from its key size.Note,Note that at the time of this writing, all PRFs defined for use in IKEv2 (see the "Transform Type 2 - Pseudorandom Function Transform IDs" subregistry <xreftarget="IKEV2-IANA-PRFS" /> hadtarget="IANA-IKEV2" format="default"/>) have an output size equal to the (preferred) key size. For suchPRFsPRFs, only the first iteration of prf+ is needed: </t><figure align="center"> <artwork align="left"><![CDATA[<sourcecode name="" type="pseudocode"><![CDATA[ SK_d = prf (PPK, SK_d' | 0x01) SK_pi = prf (PPK, SK_pi' | 0x01) SK_pr = prf (PPK, SK_pr' | 0x01)]]></artwork> </figure>]]></sourcecode> <t>Note that the PPK is used in SK_d,SK_piSK_pi, and SK_prcalculationcalculations only during the initial IKE SA setup. ItMUST NOT<bcp14>MUST NOT</bcp14> be used when these subkeys are calculated as result of IKE SA rekey,resumptionresumption, or other similaroperation.</t>operations.</t> <t>The initiator then sends the IKE_AUTH request message, including the PPK_ID value as follows:</t><figure align="center"><artworkalign="left"><![CDATA[align="left" name="" type="" alt=""><![CDATA[ Initiator Responder ------------------------------------------------------------------ HDR, SK {IDi, [CERT,] [CERTREQ,] [IDr,] AUTH, SAi2, TSi, TSr, N(PPK_IDENTITY, PPK_ID), [N(NO_PPK_AUTH)]} ---> ]]></artwork></figure><t>PPK_IDENTITY is a status notification with the type 16436; it has a protocol ID of 0, noSPISPI, andanotification data that consists of the identifier PPK_ID.</t> <t>A situation may happen when the responder has somePPKs,PPKs but doesn't have a PPK with the PPK_ID received from the initiator. In thiscasecase, the responder cannot continue with the PPK (in particular, it cannot authenticate the initiator), but the responder could be able to continue with the normal IKEv2 protocol if the initiator provided its authentication data computed as in the normalIKEv2,IKEv2 without using PPKs. For this purpose, if using PPKs for communication with this responder is optional for the initiator (based on the mandatory_or_not flag), then the initiatorMUST<bcp14>MUST</bcp14> include a NO_PPK_AUTH notification in the above message. This notification informs the responder thatPPK isPPKs are optional and allows for authenticating the initiator without usingPPK.</t>PPKs.</t> <t>NO_PPK_AUTH is a status notification with the type 16437; it has a protocol ID of 0 and no SPI. The Notification Data field contains the initiator's authentication data computed using SK_pi', which has been computed without using PPKs. This is the same data that would normally be placed in the Authentication Data field of an AUTH payload. Since the Auth Method field is not present in the notification, the authentication method used for computing the authentication dataMUST<bcp14>MUST</bcp14> be the same as the method indicated in the AUTH payload. Note that if the initiator decides to include the NO_PPK_AUTH notification, the initiator needs to perform authentication data computation twice, which may consume computation power (e.g., if digital signatures are involved).</t> <t>When the responder receives this encrypted exchange, it first computes the values:</t><figure align="center"> <artwork align="left"><![CDATA[<sourcecode name="" type="pseudocode"><![CDATA[ SKEYSEED = prf(Ni | Nr, g^ir) {SK_d' | SK_ai | SK_ar | SK_ei | SK_er | SK_pi' |SK_pr' }SK_pr'} = prf+ (SKEYSEED, Ni | Nr | SPIi |SPIr ) ]]></artwork> </figure>SPIr) ]]></sourcecode> <t>The responder then uses the SK_ei/SK_ai values to decrypt/check the message and then scans through the payloads for the PPK_ID attached to the PPK_IDENTITY notification. If no PPK_IDENTITY notification is found and the peers successfully exchanged USE_PPK notifications in the IKE_SA_INIT exchange, then the responderMUST<bcp14>MUST</bcp14> send back an AUTHENTICATION_FAILED notification and then fail the negotiation.</t> <t>If the PPK_IDENTITY notification contains a PPK_ID that is not known to the responder or is not configured for use for the identity from the IDi payload, then the responder checks whether using PPKs for this initiator is mandatory and whether the initiator included a NO_PPK_AUTH notification in the message. If using PPKs is mandatory or no NO_PPK_AUTH notification is found, thenthenthe responderMUST<bcp14>MUST</bcp14> send back an AUTHENTICATION_FAILED notification and then fail the negotiation. Otherwise (when a PPK is optional and the initiator included a NO_PPK_AUTHnotification)notification), the responderMAY<bcp14>MAY</bcp14> continue the regular IKEv2 protocol, except that it uses the data from the NO_PPK_AUTH notification as the authentication data (which usually resides in the AUTHpayload),payload) for the purpose of the initiator authentication.Note,Note thatAuthentication Methodthe authentication method is still indicated in the AUTH payload.</t><t>This table<t><xref target="table1"/> summarizes the above logic for the responder:</t><figure align="center"> <artwork align="left"><![CDATA[ Received Received Configured PPK is USE_PPK NO_PPK_AUTH with PPK Mandatory Action --------------------------------------------------------------------- No * No * Standard<table align="left" anchor="table1"> <thead> <tr> <th align="left">Received USE_PPK</th> <th align="left">Received NO_PPK_AUTH</th> <th align="left">Configured with PPK</th> <th align="left">PPK is Mandatory</th> <th align="left">Action</th> </tr> </thead> <tbody> <tr> <td align="left">No</td> <td align="left">*</td> <td align="left">No</td> <td align="left">*</td> <td align="left">Standard IKEv2protocol No * Yes No Standardprotocol</td> </tr> <tr> <td align="left">No</td> <td align="left">*</td> <td align="left">Yes</td> <td align="left">No</td> <td align="left">Standard IKEv2protocol No * Yes Yes Abort negotiation Yes No No * Abort negotiation Yes Yes No Yes Abort negotiation Yes Yes No No Standardprotocol</td> </tr> <tr> <td align="left">No</td> <td align="left">*</td> <td align="left">Yes</td> <td align="left">Yes</td> <td align="left">Abort negotiation</td> </tr> <tr> <td align="left">Yes</td> <td align="left">No</td> <td align="left">No</td> <td align="left">*</td> <td align="left">Abort negotiation</td> </tr> <tr> <td align="left">Yes</td> <td align="left">Yes</td> <td align="left">No</td> <td align="left">Yes</td> <td align="left">Abort negotiation</td> </tr> <tr> <td align="left">Yes</td> <td align="left">Yes</td> <td align="left">No</td> <td align="left">No</td> <td align="left">Standard IKEv2protocol Yes * Yes * Use PPK ]]></artwork> </figure>protocol</td> </tr> <tr> <td align="left">Yes</td> <td align="left">*</td> <td align="left">Yes</td> <td align="left">*</td> <td align="left">Use PPK</td> </tr> </tbody> </table> <t>If a PPK is in use, then the responder extracts the corresponding PPK and computes the following values:</t><figure align="center"> <artwork align="left"><![CDATA[<sourcecode name="" type="pseudocode"><![CDATA[ SK_d = prf+ (PPK, SK_d') SK_pi = prf+ (PPK, SK_pi') SK_pr = prf+ (PPK, SK_pr')]]></artwork> </figure>]]></sourcecode> <t>The responder then continues with the IKE_AUTH exchange (validating the AUTH payload that the initiator included) as usual and sends back a response, which includes the PPK_IDENTITY notification with no data to indicate that the PPK is used in the exchange:</t><figure align="center"><artworkalign="left"><![CDATA[align="left" name="" type="" alt=""><![CDATA[ Initiator Responder ------------------------------------------------------------------ <-- HDR, SK {IDr, [CERT,] AUTH, SAr2, TSi, TSr, N(PPK_IDENTITY)} ]]></artwork></figure><t>When the initiator receives the response,thenit checks for the presence of the PPK_IDENTITY notification. If it receives one, it marks the SA as using the configured PPK to generate SK_d, SK_pi, and SK_pr (as shown above); the content of the received PPK_IDENTITY (if any)MUST<bcp14>MUST</bcp14> be ignored. If the initiator does not receive the PPK_IDENTITY, itMUST<bcp14>MUST</bcp14> either fail the IKE SA negotiation sending the AUTHENTICATION_FAILED notification in theInformationalINFORMATIONAL exchange (if the PPK was configured asmandatory),mandatory) or continue without using the PPK (if the PPK was not configured as mandatory and the initiator included the NO_PPK_AUTH notification in the request).</t> <t>IfEAPthe Extensible Authentication Protocol (EAP) is used in the IKE_AUTH exchange, then the initiator doesn't include the AUTH payload in the first requestmessage, howevermessage; however, the responder sends back the AUTH payload in the first reply. The peers then exchange AUTH payloads after EAP is successfully completed. As a result, the responder sends the AUTH payload twice--- in the first and last IKE_AUTH reply messageand in the last one,-- while the initiator sends the AUTH payload only in the last IKE_AUTH request. See more details about EAP authentication in IKEv2 inSection 2.16 of<xref target="RFC7296"/>.</t>sectionFormat="of" section="2.16"/>.</t> <t>The general rule for using a PPK in the IKE_AUTH exchange, which covers the EAP authentication case too, is that the initiator includes a PPK_IDENTITY (and optionally a NO_PPK_AUTH) notification in the request message containing the AUTH payload. Therefore, in case ofEAPEAP, the responder always computes the AUTH payload in the first IKE_AUTH reply message without using a PPK (by means of SK_pr'), since PPK_ID is not yet known to the responder. Once the IKE_AUTH request message containing the PPK_IDENTITY notification is received, the responder follows the rules described above for the non-EAP authentication case. </t><figure align="center"><artworkalign="left"><![CDATA[align="left" name="" type="" alt=""><![CDATA[ Initiator Responder ---------------------------------------------------------------- HDR, SK {IDi, [CERTREQ,] [IDr,] SAi2, TSi, TSr} --> <-- HDR, SK {IDr, [CERT,] AUTH, EAP} HDR, SK {EAP} --> <-- HDR, SK {EAP (success)} HDR, SK {AUTH, N(PPK_IDENTITY, PPK_ID) [, N(NO_PPK_AUTH)]} --> <-- HDR, SK {AUTH, SAr2, TSi, TSr [, N(PPK_IDENTITY)]} ]]></artwork></figure><t>Note that the diagram above shows both the cases when the responder uses a PPK and when it chooses not to use it (provided the initiator has included the NO_PPK_AUTHnotification), and thusnotification); thus, the responder's PPK_IDENTITY notification is marked as optional. Also, note that the IKE_SA_INIT exchangein case ofusing a PPK is as described above (including exchange of the USE_PPK notifications), regardless of whether or not EAP is employed in theIKE_AUTH or not.</t>IKE_AUTH.</t> </section> <sectiontitle="Upgrade procedure">numbered="true" toc="default"> <name>Upgrade Procedure</name> <t>This algorithm was designed so that someone can introduce PPKs into an existing IKE network without causing network disruption.</t> <t>In the initial phase of the network upgrade, the network administrator would visit each IKEnode,node and configure:<list style="symbols"> <t>The</t> <ul spacing="normal"> <li>The set of PPKs (and corresponding PPK_IDs) that this node would need toknow.</t> <t>Forknow.</li> <li>The PPK that will be used for each peer that this node would initiateto, which PPK will be used.</t> <t>Thatto.</li> <li>The value "false" for the mandatory_or_not flag for each peer that this node would initiate to (thus indicating that the use ofPPKPPKs iscurrentlynotmandatory.</t> </list></t>mandatory).</li> </ul> <t>With this configuration, the node will continue to operate with nodes that have not yet been upgraded. This is due to the USE_PPK notification and the NO_PPK_AUTH notification; if the initiator has not been upgraded, it will not send the USE_PPK notification (and so the responder will know that the peers will not use a PPK). If the responder has not been upgraded, it will not send the USE_PPK notification (and so the initiator will know to not use a PPK). If both peers have beenupgraded,upgraded but the responder isn't yet configured with the PPK for the initiator, then the responder coulddocontinue with the standard IKEv2 protocol if the initiator sent a NO_PPK_AUTH notification. If both the responder and initiator have been upgraded and properly configured, they will both realize it, and the Child SAs will bequantum-secure.</t>quantum secure.</t> <t>As an optional second step, after all nodes have been upgraded,thenthe administrator should then go back through thenodes,nodes and mark the use of a PPK as mandatory. This will not affect the strength against a passive attacker, but it would mean that an active attacker with a quantum computer (which is sufficiently fast to be able to break the (EC)DH inreal-time)real time) would not be able to perform a downgrade attack.</t> </section> <sectiontitle="PPK">numbered="true" toc="default"> <name>PPK</name> <sectiontitle="PPK_ID format">numbered="true" toc="default"> <name>PPK_ID Format</name> <t>This standard requires that both the initiator and the responder have a secret PPK value, with the responder selecting the PPK based on the PPK_ID that the initiator sends. In this standard, both the initiator and the responder are configured with fixed PPK and PPK_IDvalues,values anddoperform thelook uplookup based on the PPK_ID value. It is anticipated that later specifications will extend this technique to allow dynamically changing PPK values. To facilitate such an extension, we specify that the PPK_ID the initiator sends will have its first octet be the PPK_IDTypetype value. This document defines two values for the PPK_IDType: <list style="symbols"> <t>PPK_ID_OPAQUEtype: </t> <ul spacing="normal"> <li>PPK_ID_OPAQUE (1) -forFor thistypetype, the format of the PPK_ID (and the PPK itself) is not specified by this document; it is assumed to be mutually intelligible by bothbythe initiator and the responder. This PPK_ID type is intended for those implementations that choose not to disclose the type of PPK to activeattackers.</t> <t>PPK_ID_FIXEDattackers.</li> <li>PPK_ID_FIXED (2) -inIn thiscasecase, the format of the PPK_ID and the PPK are fixed octet strings; the remaining bytes of the PPK_ID are a configured value. We assume that there is a fixed mapping between PPK_ID and PPK, which is configured locally to both the initiator and the responder. The responder can use the PPK_ID to look up the corresponding PPK value. Not all implementations are able to configure arbitrary octet strings; to improve the potential interoperability, it is recommended that, in the PPK_ID_FIXED case, both the PPK and the PPK_ID strings be limited to theBase64base64 character set <xreftarget="RFC4648"/>.</t> </list></t>target="RFC4648" format="default"/>.</li> </ul> </section> <sectiontitle="Operational Considerations">numbered="true" toc="default"> <name>Operational Considerations</name> <t>The need to maintain several independent sets of security credentials can significantly complicate a security administrator'sjob,job and can potentially slow down widespread adoption of this specification. It isanticipated,anticipated that administrators will try to simplify their job by decreasing the number of credentials they need to maintain. This section describes some of the considerations for PPK management.</t> <sectiontitle="PPK Distribution">numbered="true" toc="default"> <name>PPK Distribution</name> <t>PPK_IDs of the type PPK_ID_FIXED (and the corresponding PPKs) are assumed to be configured within the IKE device in an out-of-band fashion. While the method of distribution is a local matter and is out of scope of this document or IKEv2, <xreftarget="RFC6030"/>target="RFC6030" format="default"/> describes a format forforthe transport and provisioning of symmetric keys. That format could be reused using the PIN profile (defined inSection 10.2 of<xreftarget="RFC6030"/>)target="RFC6030" sectionFormat="of" section="10.2"/>) with the "Id" attribute of the <Key> element being the PPK_ID (without the PPK_IDTypetype octet for a PPK_ID_FIXED) and the <Secret> element containing the PPK.</t> </section> <sectiontitle="Group PPK">numbered="true" toc="default"> <name>Group PPK</name> <t>This document doesn't explicitly require that the PPKisbe unique for each pair of peers. Ifitthis is the case, then this solution provides full peer authentication, but it also means that each host must have as many independent PPKs asthepeers it is going to communicate with. As the number of peersgrowsgrows, the PPKs will not scale.</t> <t>It is possible to use a single PPK for a group of users. Since each peer uses classical public key cryptography in addition to a PPK for key exchange and authentication, members of the group can neither impersonate each other nor read each other'straffic,traffic unless they use quantum computers to break public key operations.HoweverHowever, group members can record any traffic they have access to that comes from other group members and decrypt it later, when they get access to a quantum computer.</t> <t>In addition, the fact that the PPK is known to a (potentially large) group of users makes it more susceptible to theft. When an attacker equipped with a quantum computer gets access to a group PPK, all communications inside the group are revealed.</t> <t>For thesereasonsreasons, using a group PPK isNOT RECOMMENDED.</t><bcp14>NOT RECOMMENDED</bcp14>.</t> </section> <sectiontitle="PPK-only Authentication">numbered="true" toc="default"> <name>PPK-Only Authentication</name> <t>If quantum computers become a reality, classical public key cryptography will provide little security, so administrators may find it attractive not to use it at all for authentication. This will reduce the number of credentials they need to maintain because they only need toPPKs only.maintain PPK credentials. Combining group PPK and PPK-only authentication isNOT RECOMMENDED, since<bcp14>NOT RECOMMENDED</bcp14> since, in thiscasecase, any member of the group can impersonate any othermembermember, even without the help of quantum computers.</t> <t>PPK-only authentication can be achieved in IKEv2 if the NULL Authentication method <xreftarget="RFC7619"/>target="RFC7619" format="default"/> is employed. WithoutPPKPPK, the NULL Authentication method provides no authentication of thepeers, howeverpeers; however, since a PPK is stirred into the SK_pi and the SK_pr, the peers become authenticated if a PPK is in use. Using PPKsMUST<bcp14>MUST</bcp14> be mandatory for the peers if they advertise support forPPKPPKs in IKE_SA_INIT and use NULL Authentication. Additionally, since the peers are authenticated viaPPK,PPKs, the ID Type in the IDi/IDr payloadsSHOULD NOT<bcp14>SHOULD NOT</bcp14> be ID_NULL, despite using the NULL Authentication method.</t> </section> </section> </section> <section anchor="Security"title="Security Considerations"> <t>Quantumnumbered="true" toc="default"> <name>Security Considerations</name> <t>A critical consideration is how to ensure the randomness of this post-quantum preshared key. Quantum computers are able to perform Grover's algorithm <xreftarget="GROVER"/>;target="GROVER" format="default"/>; that effectively halves the size of a symmetric key.Because of this,In addition, an adversary impersonating theuser SHOULDserver, even with a conventional computer, can perform a dictionary search over plausible post-quantum preshared key values. The strongest practice is to ensure thattheany post-quantum preshared keyused hascontains at least 256 bits ofentropy, in order toentropy; this will provide 128 bits of post-quantumsecurity.security, while providing security against conventional dictionary attacks. That provides the security equivalent toLevelCategory 5 as defined in the NISTPQ ProjectPost-Quantum Cryptography CallForfor Proposals <xreftarget="NISTPQCFP"/>. </t>target="NISTPQCFP" format="default"/>. Deriving a post-quantum preshared key from a password, name, or other low-entropy source is not secure because of these known attacks.</t> <t>With this protocol, the computed SK_d is a function of the PPK. Assuming that the PPK has sufficient entropy (for example, at least2^2562<sup>256</sup> possible values),theneven if an attacker was able to recover the rest of the inputs to the PRF function, it would be infeasible to use Grover's algorithm with a quantum computer to recover the SK_d value. Similarly, all keys that are a function of SK_d, which include all ChildSAsSA keys and all keys for subsequent IKE SAs (created when the initial IKE SA is rekeyed), are alsoquantum-securequantum secure (assuming that the PPK was of high enoughentropy,entropy and that all the subkeys are sufficiently long). </t> <t>An attacker with a quantum computer that can decrypt the initial IKE SA has access to all the information exchanged over it, such as identities of the peers, configurationparametersparameters, and all negotiated IPsecSAsSA information (including traffic selectors), with the exception of the cryptographic keys used by the IPsecSAsSAs, which are protected by the PPK. </t> <t>Deployments that treat this information as sensitive or that send other sensitive data (like cryptographic keys) over IKESA MUSTSAs <bcp14>MUST</bcp14> rekey the IKE SA before the sensitive information is sent to ensure this information is protected by the PPK. It is possible to create a childless IKE SA as specified in <xreftarget="RFC6023"/>.target="RFC6023" format="default"/>. This prevents Child SA configuration information from being transmitted in the original IKE SA that is not protected by a PPK. Some information related to IKESA,SA that is sent in the IKE_AUTH exchange, such as peer identities, feature notifications,Vendor ID's etc.vendor IDs, etc., cannot be hidden from the attack described above, even if the additional IKE SA rekey is performed. </t> <t>In addition, the policySHOULD<bcp14>SHOULD</bcp14> be set to negotiate only quantum-secure symmetric algorithms; while this RFC doesn't claim to give advice as to what algorithms are secure (as that may change based on future cryptographical results), below is a list of defined IKEv2 and IPsec algorithms that should not be used, as they are known to provide less than 128 bits of post-quantumsecurity <list style="symbols"> <t>Anysecurity: </t> <ul spacing="normal"> <li>Any IKEv2Encryptionencryption algorithm,PRFPRF, orIntegrityintegrity algorithm with a key size less than 256bits.</t> <t>Anybits.</li> <li>Any ESPTransformtransform with a key size less than 256bits.</t> <t>PRF_AES128_XCBCbits.</li> <li>PRF_AES128_XCBC andPRF_AES128_CBC;PRF_AES128_CBC: even though theyare defined to be able tocan usean arbitraryas input a key of arbitrary size,they convert itsuch input keys are converted into a 128-bit keyinternally.</t> </list></t>for internal use.</li> </ul> <t><xref target="Exchanges"/>format="default"/> requires the initiator to abort the initial exchange if using PPKs is mandatory forit,it but the responder does not include the USE_PPK notification in the response. In this situation, when the initiator abortsnegotiationthe negotiation, it leaves a half-open IKE SA on the responder (because IKE_SA_INIT completes successfully from the responder's point of view). This half-open SA will eventually expire and be deleted, but if the initiator continues its attempts to create IKE SA with a high enough rate, then the responder may consider itasaDenial-of-Servicedenial-of-service (DoS) attack and takeprotectionprotective measures (see <xref target="RFC8019"/>format="default"/> for moredetail).details). In this situation, it isRECOMMENDED<bcp14>RECOMMENDED</bcp14> that the initiatorcachescache the negative result of the negotiation anddoesn't make attemptsnot attempt to create it again for some time. This period of time may vary, but it is believed that waiting for at least few minutes will not cause the responder to treat it as a DoS attack.Note,Note that this situation would most likely be a result ofmisconfigurationmisconfiguration, and somere-configurationreconfiguration of the peers would probably be needed.</t> <t>If using PPKs is optional for both peers and they authenticate themselves using digital signatures, then an attacker in between, equipped with a quantum computer capable of breaking public key operations in real time, is able to mount a downgrade attack by removing the USE_PPK notification from the IKE_SA_INIT and forging digital signatures in the subsequent exchange. If using PPKs is mandatory for at least one of the peers orPSKif a preshared key mode is used for authentication, then the attack will be detected and the SA won't be created.</t> <t>If using PPKs is mandatory for the initiator, then an attacker able to eavesdrop andtoinject packets into the network can preventcreatingcreation of an IKE SA by mounting the following attack. The attacker intercepts the initial request containing the USE_PPK notification and injects a forged response containing no USE_PPK. If the attacker manages to inject this packet before the responder sends a genuine response, then the initiator would abort the exchange. To thwart this kind ofattackattack, it isRECOMMENDED, that<bcp14>RECOMMENDED</bcp14> that, if using PPKs is mandatory for the initiator and the received response doesn't contain the USE_PPK notification,thenthe initiatordoesn'tnot abort the exchange immediately.InsteadInstead, it waits for more responsemessagesmessages, retransmitting the request as if no responses were received at all, until either the received message contains the USE_PPK notification or the exchange times out (seesection 2.4 of<xreftarget="RFC7296"/>target="RFC7296" format="default" sectionFormat="of" section="2.4"/> for more details about retransmission timers in IKEv2). Ifneithernone of the received responses contains USE_PPK, then the exchange is aborted.</t> <t>If using a PPK is optional for both peers, then in case of misconfiguration (e.g., mismatchedPPK_ID)PPK_ID), the IKE SA will be created without protection against quantum computers. It is advised that if a PPK wasconfigured,configured but was not used for a particular IKE SA, then implementationsSHOULD<bcp14>SHOULD</bcp14> audit this event. </t> </section> <sectiontitle="IANA Considerations">numbered="true" toc="default"> <name>IANA Considerations</name> <t>This document defines three new Notify Message Types in the"Notify"IKEv2 Notify Message Types - Status Types" subregistry under the "Internet Key Exchange Version 2 (IKEv2) Parameters" registry(https://www.iana.org/assignments/ikev2-parameters/ikev2-parameters.xhtml#ikev2-parameters-16):</t> <figure<xref target="IANA-IKEV2" format="default"/>:</t> <table anchor="table2" align="center"><artwork align="left"><![CDATA[ 16435 USE_PPK [THIS RFC] 16436 PPK_IDENTITY [THIS RFC] 16437 NO_PPK_AUTH [THIS RFC] ]]></artwork> </figure> <t>This document also creates<tbody> <tr> <th align="left">Value</th> <th align="left">NOTIFY MESSAGES - STATUS TYPES</th> <th align="left">Reference</th> </tr> <tr> <td align="left">16435</td> <td align="left">USE_PPK</td> <td align="left">RFC 8784</td> </tr> <tr> <td align="left">16436</td> <td align="left">PPK_IDENTITY</td> <td align="left">RFC 8784</td> </tr> <tr> <td align="left">16437</td> <td align="left">NO_PPK_AUTH</td> <td align="left">RFC 8784</td> </tr> </tbody> </table> <t>Per this document, IANA has created a newIANA registrysubregistry titled "IKEv2 Post-quantum Preshared Key ID Types"in IKEv2 IANAunder the "Internet Key Exchange Version 2 (IKEv2) Parameters" registry(https://www.iana.org/assignments/ikev2-parameters/)<xref target="IANA-IKEV2" format="default"/>. This new subregistry is for the PPK_ID types used in the PPK_IDENTITY notification defined in this specification. The initialvaluescontents of the newregistry are:</t> <figuresubregistry are as follows: </t> <table anchor="table3" align="center"><artwork align="left"><![CDATA[ PPK_ID Type Value Reference ----------- ----- --------- Reserved 0 [THIS RFC] PPK_ID_OPAQUE 1 [THIS RFC] PPK_ID_FIXED 2 [THIS RFC] Unassigned 3-127 [THIS RFC]<thead> <tr> <th align="left">Value</th> <th align="left">PPK_ID Type</th> <th align="left">Reference</th> </tr> </thead> <tbody> <tr> <td align="left">0</td> <td align="left">Reserved</td> <td align="left">RFC 8784</td> </tr> <tr> <td align="left">1</td> <td align="left">PPK_ID_OPAQUE</td> <td align="left">RFC 8784</td> </tr> <tr> <td align="left">2</td> <td align="left">PPK_ID_FIXED</td> <td align="left">RFC 8784</td> </tr> <tr> <td align="left">3-127</td> <td align="left">Unassigned</td> <td align="left">RFC 8784</td> </tr> <tr> <td align="left">128-255</td> <td align="left">Reserved for PrivateUse 128-255 [THIS RFC] ]]></artwork> </figure>Use</td> <td align="left">RFC 8784</td> </tr> </tbody> </table> <t>The PPK_ID type value 0 is reserved; values 3-127 are to be assigned by IANA; and values 128-255 are for private use among mutually consenting parties. To register new PPK_IDs in theunassignedUnassigned range, aTypetype name, aValuevalue between 3 and127127, and aReferencereference specification need to be defined. Changes and additions to theunassignedUnassigned range of this registry arebymade using the Expert ReviewPolicypolicy <xref target="RFC8126"/>.format="default"/>. Changes and additions to theprivate useReserved for Private Use range of this registry arebymade using the Private UsePolicypolicy <xref target="RFC8126"/>.</t>format="default"/>.</t> </section> </middle><!-- *****BACK MATTER ***** --><back><!-- References split into informative and normative --> <references title="Normative References"> &RFC2119; &RFC8174; &RFC7296;<displayreference target="I-D.hoffman-c2pq" to="C2PQ"/> <references> <name>References</name> <references> <name>Normative References</name> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7296.xml"/> </references><references title="Informational References"><references> <name>Informative References</name> <referenceanchor="GROVER"><front>anchor="GROVER"> <front> <title>A Fast Quantum Mechanical Algorithm for Database Search</title> <seriesInfo name="DOI" value="10.1145/237814.237866"/> <author fullname="L. Grover" initials="L." surname="Grover"> </author> <date month="July" year="1996"/> </front><seriesInfo name="Proc." value="of<refcontent>STOC '96: Proceedings of the Twenty-Eighth Annual ACM Symposium on the Theory ofComputing (STOC 1996)"/>Computing, pp. 212-219"</refcontent> </reference> <reference anchor="NISTPQCFP"target="https://csrc.nist.gov/CSRC/media/Projects/Post-Quantum-Cryptography/documents/call-for-proposals-final-dec-2016.pdf"><front> <title>NISTtarget="https://csrc.nist.gov/CSRC/media/Projects/Post-Quantum-Cryptography/documents/call-for-proposals-final-dec-2016.pdf"> <front> <title>Submission Requirements and Evaluation Criteria for the Post-Quantum CryptographyCall for Proposals</title> <author fullname="NIST" surname="NIST">Standardization Process</title> <author><organization>NIST</organization> </author> <date month="December" year="2016"/> </front> </reference>&RFC2409; &RFC4648; &RFC6023; &RFC6030; &RFC7619; &RFC8019; &RFC8126; <?rfc include="https://xml2rfc.ietf.org/public/rfc/bibxml3/reference.I-D.hoffman-c2pq.xml"?><xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2409.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4648.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6023.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6030.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7619.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8019.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8126.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml3/reference.I-D.hoffman-c2pq.xml"/> <referenceanchor="IKEV2-IANA-PRFS" target="https://www.iana.org/assignments/ikev2-parameters/ikev2-parameters.xhtml#ikev2-parameters-6">anchor="IANA-IKEV2" target="https://www.iana.org/assignments/ikev2-parameters/"> <front> <title>Internet Key Exchange Version 2 (IKEv2)Parameters, Transform Type 2 - Pseudorandom Function Transform IDs</title> <author initials="" surname="" fullname=""> <organization />Parameters</title> <author><organization>IANA </organization> </author><date /></front> </reference> </references> </references> <section anchor="app-additional"title="Discussionnumbered="true" toc="default"> <name>Discussion andRationale">Rationale</name> <t>The primary goal of this document is to augment the IKEv2 protocol to provide protection against quantum computers without requiring novel cryptographic algorithms. The idea behind this document is that while a quantum computer can easily reconstruct the shared secret of an (EC)DH exchange,theyit cannot as easily recover a secret from a symmetric exchange. This document makes theSK_d, and henceSK_d (and thus also the IPsec KEYMAT and anychildsubsequent IKE SA'sSKEYSEED,SKEYSEED) depend on both the symmetricPPK,PPK andalsothe Diffie-Hellman exchange. If we assume that the attacker knows everything except the PPK during the keyexchange,exchange and there are2^n2<sup>n</sup> plausible PPKs, then a quantum computer (using Grover's algorithm) would takeO(2^(n/2))O(2<sup>n/2</sup>) time to recover the PPK. So, even if the (EC)DH can be trivially solved, the attacker still can't recover any key material (except for the SK_ei, SK_er,SK_aiSK_ai, and SK_ar values for the initial IKE exchange) unless they can find the PPK, which is too difficult if the PPK has enough entropy (for example, 256 bits). Note that we do allow an attacker with a quantum computer to rederive the keying material for the initial IKE SA; this was a compromise to allow the responder to select the correct PPK quickly. </t> <t>Another goal of this protocol is to minimize the number of changes within the IKEv2 protocol,andin particular, within the cryptography of IKEv2. By limiting our changes tonotifications,notifications and only adjusting the SK_d, SK_pi, and SK_pr, it is hoped that this would be implementable, even on systems that perform most of the IKEv2 processing in hardware.</t> <t>A third goalwasis to be friendly to incremental deployment in operationalnetworks,networks for which we might not want to have a global sharedkey,key or for which quantum-secure IKEv2 is rolled out incrementally. This is why we specifically try to allow the PPK to be dependent on thepeer,peer and why we allow the PPK to be configured as optional.</t> <t>A fourth goalwasis to avoid violating any of the security properties provided by IKEv2.</t> </section> <section anchor="Acknowledgements"title="Acknowledgements">numbered="false" toc="default"> <name>Acknowledgements</name> <t>We would like to thankTero Kivinen, Paul Wouters, Graham Bartlett, Tommy Pauly, Quynh Dang<contact fullname="Tero Kivinen"/>, <contact fullname="Paul Wouters"/>, <contact fullname="Graham Bartlett"/>, <contact fullname="Tommy Pauly"/>, <contact fullname="Quynh Dang"/>, and the rest of theIPSecMEIPSECME Working Group for their feedback and suggestions for the scheme.</t> </section> </back> </rfc>