--- 1/draft-ietf-ipsecme-qr-ikev2-09.txt 2019-12-26 23:13:13.028014256 -0800 +++ 2/draft-ietf-ipsecme-qr-ikev2-10.txt 2019-12-26 23:13:13.068015279 -0800 @@ -1,51 +1,51 @@ Internet Engineering Task Force S. Fluhrer Internet-Draft D. McGrew Intended status: Standards Track P. Kampanakis -Expires: May 30, 2020 Cisco Systems +Expires: June 29, 2020 Cisco Systems V. Smyslov ELVIS-PLUS - November 27, 2019 + December 27, 2019 - Postquantum Preshared Keys for IKEv2 - draft-ietf-ipsecme-qr-ikev2-09 + Mixing Preshared Keys in IKEv2 for Post-quantum Resistance + draft-ietf-ipsecme-qr-ikev2-10 Abstract - The possibility of Quantum Computers poses a serious challenge to + The possibility of quantum computers poses a serious challenge to cryptographic algorithms deployed widely today. 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 + quantum computer is available. It is anticipated that IKEv2 will be extended to support quantum-secure key exchange algorithms; however 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 Quantum Computer, by using preshared + allow it to be resistant to a quantum computer, by using preshared keys. 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 https://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 May 30, 2020. + This Internet-Draft will expire on June 29, 2020. Copyright Notice Copyright (c) 2019 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 (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -73,39 +73,39 @@ 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 8.1. Normative References . . . . . . . . . . . . . . . . . . 17 8.2. Informational References . . . . . . . . . . . . . . . . 17 Appendix A. Discussion and Rationale . . . . . . . . . . . . . . 18 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 1. Introduction - Recent achievements in developing Quantum Computers demonstrate that + Recent achievements in developing quantum computers demonstrate that it is probably feasible to build a cryptographically significant one. 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 solve DH and ECDH problems in + quantum computer would be able to solve DH and ECDH problems in polynomial time [I-D.hoffman-c2pq], and this would imply that the security of existing IKEv2 [RFC7296] systems would be compromised. IKEv1 [RFC2409], when used with strong preshared keys, is not vulnerable to quantum attacks, because those keys are one of the inputs to the key derivation function. If the preshared key has sufficient entropy and the PRF, encryption and authentication transforms are quantum-secure, then the resulting system is believed to be quantum resistant, that is, invulnerable to an attacker with a - Quantum Computer. + quantum computer. This document describes a way to extend IKEv2 to have a similar property; assuming that the two end systems share a long secret key, - then the resulting exchange is quantum resistant. By bringing - postquantum security to IKEv2, this note removes the need to use an + then the resulting exchange is quantum resistant. By bringing post- + quantum security to IKEv2, this note removes the need to use an obsolete version of the Internet Key Exchange in order to achieve that security goal. 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 @@ -117,36 +117,40 @@ authentication if configured). This document does not replace the authentication checks that the protocol does; instead, it is done as a parallel check. 1.1. Changes RFC EDITOR PLEASE DELETE THIS SECTION. Changes in this draft in each version iterations. + draft-ietf-ipsecme-qr-ikev2-10 + + o Addresses issues raised during IETF LC. + draft-ietf-ipsecme-qr-ikev2-09 o Addresses issues raised in AD review. draft-ietf-ipsecme-qr-ikev2-08 o Editorial changes. draft-ietf-ipsecme-qr-ikev2-07 o Editorial changes. - draft-ietf-ipsecme-qr-ikev2-06 - o Editorial changes. + draft-ietf-ipsecme-qr-ikev2-05 + o Addressed comments received during WGLC. draft-ietf-ipsecme-qr-ikev2-04 o Using Group PPK is clarified based on comment from Quynh Dang. draft-ietf-ipsecme-qr-ikev2-03 o Editorial changes and minor text nit fixes. @@ -175,22 +179,20 @@ o Clarified using PPK in case of EAP authentication. o PPK_SUPPORT notification is changed to USE_PPK to better reflect its purpose. draft-ietf-ipsecme-qr-ikev2-00 o Migrated from draft-fluhrer-qr-ikev2-05 to draft-ietf-ipsecme-qr- ikev2-00 that is a WG item. - draft-fluhrer-qr-ikev2-05 - o Nits and editorial fixes. o Made PPK_ID format and PPK Distributions subsection of the PPK section. Also added an Operational Considerations section. o Added comment about Child SA rekey in the Security Considerations section. o Added NO_PPK_AUTH to solve the cases where a PPK_ID is not configured for a responder. @@ -204,26 +206,26 @@ o Modified how we stir the PPK into the IKEv2 secret state. o Modified how the use of PPKs is negotiated. draft-fluhrer-qr-ikev2-02 o 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 + that point); it does mean that someone with a quantum computer can recover the initial IKE negotiation. o Removed positive endorsements of various algorithms. Retained - warnings about algorithms known to be weak against a Quantum - Computer. + warnings about algorithms known to be weak against a quantum + computer. draft-fluhrer-qr-ikev2-01 o Added explicit guidance as to what IKE and IPsec algorithms are quantum resistant. draft-fluhrer-qr-ikev2-00 o We switched from using vendor ID's to transmit the additional data to notifications. @@ -244,58 +246,59 @@ 1.2. 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. 2. Assumptions - We assume that each IKE peer has a list of Postquantum Preshared Keys - (PPK) 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 this postquantum preshared key is mandatory. This PPK is + We assume that each IKE peer has a list of Post-quantum Preshared + Keys (PPK) 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 this post-quantum preshared key 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 key derivation, and thus doesn't protect against - Quantum Computers). The PPK specific configuration that is assumed + quantum computers). The PPK specific configuration that is assumed to be on each node consists of the following tuple: Peer, PPK, PPK_ID, mandatory_or_not 3. Exchanges - If the initiator is configured to use a postquantum preshared key + If the initiator is configured to use a post-quantum preshared key with the responder (whether or not the use of the PPK is mandatory), then it will include a notification USE_PPK in the IKE_SA_INIT request message as follows: Initiator Responder ------------------------------------------------------------------ HDR, SAi1, KEi, Ni, N(USE_PPK) ---> N(USE_PPK) is a status notification payload with the type 16435; it has a protocol ID of 0, no SPI and no notification data associated with it. If the initiator needs to resend this initial message with a cookie (because the responder response included a COOKIE notification), then the resend would include the USE_PPK notification if the original message did. If the responder does not support this specification or does not have - any PPK configured, then it ignores the received notification and - continues with the IKEv2 protocol as normal. Otherwise the responder - replies with the IKE_SA_INIT message including a USE_PPK notification - in the response: + any PPK configured, then it ignores the received notification (as + defined in [RFC7296] for unknown status notifications) and continues + with the IKEv2 protocol as normal. Otherwise the responder replies + with the IKE_SA_INIT message including a USE_PPK notification in the + response: Initiator Responder ------------------------------------------------------------------ <--- HDR, SAr1, KEr, Nr, [CERTREQ,] N(USE_PPK) When the initiator receives this reply, it checks whether the responder included the USE_PPK notification. If the responder did not and the flag mandatory_or_not indicates that using PPKs is mandatory for communication with this responder, then the initiator MUST abort the exchange. This situation may happen in case of @@ -516,22 +519,22 @@ both peers have been upgraded, but the responder isn't yet configured with the PPK for the initiator, then the responder could do standard IKEv2 protocol if the initiator sent 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 be quantum-secure. As an optional second step, after all nodes have been upgraded, then the administrator should then go back through the nodes, and mark the use of PPK as mandatory. This will not affect the strength against a - passive attacker; it would mean that an attacker with a Quantum - Computer (which is sufficiently fast to be able to break the (EC)DH + passive attacker; it would mean that an attacker with a quantum + computer (which is sufficiently fast to be able to break the (EC)DH in real time) would not be able to perform a downgrade attack. 5. PPK 5.1. PPK_ID format 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_ID @@ -589,71 +592,73 @@ This document doesn't explicitly require that PPK is unique for each pair of peers. If it is the case, then this solution provides full peer authentication, but it also means that each host must have as many independent PPKs as the peers it is going to communicate with. As the number of peers grows the PPKs will not scale. It is possible to use a single PPK for a group of users. Since each peer uses classical public key cryptography in addition to PPK for key exchange and authentication, members of the group can neither impersonate each other nor read other's traffic, unless they use - Quantum Computers to break public key operations. However group + quantum computers to break public key operations. However 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. + quantum computer. 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 + equipped with a quantum computer gets access to a group PPK, all communications inside the group are revealed. For these reasons using group PPK is NOT RECOMMENDED. 5.2.3. PPK-only Authentication - If Quantum Computers become a reality, classical public key + 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 to PPKs only. Combining group PPK and PPK-only authentication is NOT RECOMMENDED, since in this case any member of the group can impersonate any other - member even without help of Quantum Computers. + member even without help of quantum computers. PPK-only authentication can be achieved in IKEv2 if the NULL Authentication method [RFC7619] is employed. Without PPK the NULL Authentication method provides no authentication of the peers, 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 PPKs MUST be mandatory for the peers if they advertise support for PPK in IKE_SA_INIT and use NULL Authentication. Addtionally, since the peers are authenticated via PPK, the ID Type in the IDi/IDr payloads SHOULD NOT be ID_NULL, despite using the NULL Authentication method. 6. Security Considerations - Quantum computers are able to perform Grover's algorithm; that - effectively halves the size of a symmetric key. Because of this, the - user SHOULD ensure that the postquantum preshared key used has at - least 256 bits of entropy, in order to provide 128 bits of security. + Quantum computers are able to perform Grover's algorithm [GROVER]; + that effectively halves the size of a symmetric key. Because of + this, the user SHOULD ensure that the post-quantum preshared key used + has at least 256 bits of entropy, in order to provide 128 bits of + post-quantum security. That provides security equivalent to Level 5 + as defined in the NIST PQ Project Call For Proposals [NISTPQCFP]. With this protocol, the computed SK_d is a function of the PPK. Assuming that the PPK has sufficient entropy (for example, at least 2^256 possible values), then even 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 + 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 Child SAs keys and all keys for subsequent IKE SAs (created when the initial IKE SA is rekeyed), are also quantum resistant (assuming that the PPK was of high enough entropy, and that all the subkeys are sufficiently long). - An attacker with a Quantum Computer that can decrypt the initial IKE + 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, configuration parameters and all negotiated IPsec SAs information (including traffic selectors), with the exception of the cryptographic keys used by the IPsec SAs which are protected by the PPK. Deployments that treat this information as sensitive or that send other sensitive data (like cryptographic keys) over IKE SA MUST 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 @@ -662,22 +667,22 @@ SA that is not protected by a PPK. Some information related to IKE SA, that is sent in the IKE_AUTH exchange, such as peer identities, feature notifications, Vendor ID's etc. cannot be hidden from the attack described above, even if the additional IKE SA rekey is performed. In addition, the policy SHOULD be set to negotiate only quantum- resistant 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 not to be - quantum resistant + IPsec algorithms that should not be used, as they are known to + provide less than 128 bits of post-quantum security o Any IKEv2 Encryption algorithm, PRF or Integrity algorithm with key size less than 256 bits. o Any ESP Transform with key size less than 256 bits. o PRF_AES128_XCBC and PRF_AES128_CBC; even though they are defined to be able to use an arbitrary key size, they convert it into a 128-bit key internally. @@ -691,21 +696,21 @@ IKE SA with a high enough rate, then the responder may consider it as a Denial-of-Service attack and take protection measures (see [RFC8019] for more detail). In this situation, it is RECOMMENDED that the initiator caches the negative result of the negotiation for some time and doesn't make attempts to create it again for some time, because this is a result of misconfiguration and probably some re- configuration of the peers is needed. 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 + equipped with a quantum computer capable of breaking public key operations in real time, is able to mount downgrade attack by removing 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 or PSK is used for authentication, then the attack will be detected and the SA won't be created. If using PPKs is mandatory for the initiator, then an attacker able to eavesdrop and to inject packets into the network can prevent creating an IKE SA by mounting the following attack. The attacker @@ -715,44 +720,45 @@ response, then the initiator would abort the exchange. To thwart this kind of attack it is RECOMMENDED, that if using PPKs is mandatory for the initiator and the received response doesn't contain the USE_PPK notification, then the initiator doesn't abort the exchange immediately, but instead waits some time for more responses (possibly retransmitting the request). If all the received responses contain no USE_PPK, then the exchange is aborted. If using PPK is optional for both peers, then in case of misconfiguration (e.g. mismatched PPK_ID) the IKE SA will be created - without protection against Quantum Computers. It is advised that if + without protection against quantum computers. It is advised that if PPK was configured, but was not used for a particular IKE SA, then implementations SHOULD audit this event. 7. IANA Considerations This document defines three new Notify Message Types in the "Notify Message Types - Status Types" registry: - 16435 USE_PPK - 16436 PPK_IDENTITY - 16437 NO_PPK_AUTH - - This document also creates a new IANA registry for the PPK_ID types. - The initial values of this registry are: + 16435 USE_PPK [THIS RFC] + 16436 PPK_IDENTITY [THIS RFC] + 16437 NO_PPK_AUTH [THIS RFC] - PPK_ID Type Value - ----------- ----- - Reserved 0 - PPK_ID_OPAQUE 1 - PPK_ID_FIXED 2 - Unassigned 3-127 - Reserved for private use 128-255 + This document also creates a new IANA registry "IKEv2 Post-quantum + Preshared Key ID Types" in IKEv2 IANA registry + (https://www.iana.org/assignments/ikev2-parameters/) for the PPK_ID + types. The initial values of the new registry are: + 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] + Reserved for private use 128-255 [THIS RFC] Changes and additions to this registry are by Expert Review [RFC8126]. 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, @@ -762,31 +768,39 @@ Kivinen, "Internet Key Exchange Protocol Version 2 (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October 2014, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 8.2. Informational References + [GROVER] Grover, L., "A Fast Quantum Mechanical Algorithm for + Database Search", Proc. of the Twenty-Eighth Annual ACM + Symposium on the Theory of Computing (STOC 1996), 1996. + [I-D.hoffman-c2pq] Hoffman, P., "The Transition from Classical to Post- - Quantum Cryptography", draft-hoffman-c2pq-05 (work in - progress), May 2019. + Quantum Cryptography", draft-hoffman-c2pq-06 (work in + progress), November 2019. [IKEV2-IANA-PRFS] "Internet Key Exchange Version 2 (IKEv2) Parameters, Transform Type 2 - Pseudorandom Function Transform IDs", . + [NISTPQCFP] + NIST, "NIST Post-Quantum Cryptography Call for Proposals", + 2016. + [RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)", RFC 2409, DOI 10.17487/RFC2409, November 1998, . [RFC6023] Nir, Y., Tschofenig, H., Deng, H., and R. Singh, "A Childless Initiation of the Internet Key Exchange Version 2 (IKEv2) Security Association (SA)", RFC 6023, DOI 10.17487/RFC6023, October 2010, . @@ -805,34 +819,34 @@ DOI 10.17487/RFC8019, November 2016, . [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, . Appendix A. Discussion and Rationale - The idea behind this document is that while a Quantum Computer can + The idea behind this document is that while a quantum computer can easily reconstruct the shared secret of an (EC)DH exchange, they cannot as easily recover a secret from a symmetric exchange. This document makes the SK_d, and hence the IPsec KEYMAT and any child SA's SKEYSEED, depend on both the symmetric PPK, and also the Diffie- Hellman exchange. If we assume that the attacker knows everything except the PPK during the key exchange, and there are 2^n plausible - PPKs, then a Quantum Computer (using Grover's algorithm) would take + PPKs, then a quantum computer (using Grover's algorithm) would take O(2^(n/2)) 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_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 + 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. Another goal of this protocol is to minimize the number of changes within the IKEv2 protocol, and in particular, within the cryptography of IKEv2. By limiting our changes to notifications, and only adjusting the SK_d, SK_pi, SK_pr, it is hoped that this would be implementable, even on systems that perform most of the IKEv2 processing in hardware.