draft-ietf-ipsecme-qr-ikev2-09.txt   draft-ietf-ipsecme-qr-ikev2-10.txt 
Internet Engineering Task Force S. Fluhrer Internet Engineering Task Force S. Fluhrer
Internet-Draft D. McGrew Internet-Draft D. McGrew
Intended status: Standards Track P. Kampanakis Intended status: Standards Track P. Kampanakis
Expires: May 30, 2020 Cisco Systems Expires: June 29, 2020 Cisco Systems
V. Smyslov V. Smyslov
ELVIS-PLUS ELVIS-PLUS
November 27, 2019 December 27, 2019
Postquantum Preshared Keys for IKEv2 Mixing Preshared Keys in IKEv2 for Post-quantum Resistance
draft-ietf-ipsecme-qr-ikev2-09 draft-ietf-ipsecme-qr-ikev2-10
Abstract 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 cryptographic algorithms deployed widely today. IKEv2 is one example
of a cryptosystem that could be broken; someone storing VPN of a cryptosystem that could be broken; someone storing VPN
communications today could decrypt them at a later time when a 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 extended to support quantum-secure key exchange algorithms; however
that is not likely to happen in the near term. To address this that is not likely to happen in the near term. To address this
problem before then, this document describes an extension of IKEv2 to 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. keys.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." 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 Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
8.1. Normative References . . . . . . . . . . . . . . . . . . 17 8.1. Normative References . . . . . . . . . . . . . . . . . . 17
8.2. Informational References . . . . . . . . . . . . . . . . 17 8.2. Informational References . . . . . . . . . . . . . . . . 17
Appendix A. Discussion and Rationale . . . . . . . . . . . . . . 18 Appendix A. Discussion and Rationale . . . . . . . . . . . . . . 18
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 19 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction 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. it is probably feasible to build a cryptographically significant one.
If such a computer is implemented, many of the cryptographic If such a computer is implemented, many of the cryptographic
algorithms and protocols currently in use would be insecure. A 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 polynomial time [I-D.hoffman-c2pq], and this would imply that the
security of existing IKEv2 [RFC7296] systems would be compromised. security of existing IKEv2 [RFC7296] systems would be compromised.
IKEv1 [RFC2409], when used with strong preshared keys, is not IKEv1 [RFC2409], when used with strong preshared keys, is not
vulnerable to quantum attacks, because those keys are one of the vulnerable to quantum attacks, because those keys are one of the
inputs to the key derivation function. If the preshared key has inputs to the key derivation function. If the preshared key has
sufficient entropy and the PRF, encryption and authentication sufficient entropy and the PRF, encryption and authentication
transforms are quantum-secure, then the resulting system is believed transforms are quantum-secure, then the resulting system is believed
to be quantum resistant, that is, invulnerable to an attacker with a 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 This document describes a way to extend IKEv2 to have a similar
property; assuming that the two end systems share a long secret key, property; assuming that the two end systems share a long secret key,
then the resulting exchange is quantum resistant. By bringing then the resulting exchange is quantum resistant. By bringing post-
postquantum security to IKEv2, this note removes the need to use an quantum security to IKEv2, this note removes the need to use an
obsolete version of the Internet Key Exchange in order to achieve obsolete version of the Internet Key Exchange in order to achieve
that security goal. that security goal.
The general idea is that we add an additional secret that is shared The general idea is that we add an additional secret that is shared
between the initiator and the responder; this secret is in addition between the initiator and the responder; this secret is in addition
to the authentication method that is already provided within IKEv2. to the authentication method that is already provided within IKEv2.
We stir this secret into the SK_d value, which is used to generate 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 the key material (KEYMAT) and the SKEYSEED for the child SAs; this
secret provides quantum resistance to the IPsec SAs (and any child 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 IKE SAs). We also stir the secret into the SK_pi, SK_pr values; this
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authentication if configured). This document does not replace the authentication if configured). This document does not replace the
authentication checks that the protocol does; instead, it is done as authentication checks that the protocol does; instead, it is done as
a parallel check. a parallel check.
1.1. Changes 1.1. Changes
RFC EDITOR PLEASE DELETE THIS SECTION. RFC EDITOR PLEASE DELETE THIS SECTION.
Changes in this draft in each version iterations. 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 draft-ietf-ipsecme-qr-ikev2-09
o Addresses issues raised in AD review. o Addresses issues raised in AD review.
draft-ietf-ipsecme-qr-ikev2-08 draft-ietf-ipsecme-qr-ikev2-08
o Editorial changes. o Editorial changes.
draft-ietf-ipsecme-qr-ikev2-07 draft-ietf-ipsecme-qr-ikev2-07
o Editorial changes. o Editorial changes.
draft-ietf-ipsecme-qr-ikev2-06
o Editorial changes. o Editorial changes.
draft-ietf-ipsecme-qr-ikev2-05
o Addressed comments received during WGLC. o Addressed comments received during WGLC.
draft-ietf-ipsecme-qr-ikev2-04 draft-ietf-ipsecme-qr-ikev2-04
o Using Group PPK is clarified based on comment from Quynh Dang. o Using Group PPK is clarified based on comment from Quynh Dang.
draft-ietf-ipsecme-qr-ikev2-03 draft-ietf-ipsecme-qr-ikev2-03
o Editorial changes and minor text nit fixes. o Editorial changes and minor text nit fixes.
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o Clarified using PPK in case of EAP authentication. o Clarified using PPK in case of EAP authentication.
o PPK_SUPPORT notification is changed to USE_PPK to better reflect o PPK_SUPPORT notification is changed to USE_PPK to better reflect
its purpose. its purpose.
draft-ietf-ipsecme-qr-ikev2-00 draft-ietf-ipsecme-qr-ikev2-00
o Migrated from draft-fluhrer-qr-ikev2-05 to draft-ietf-ipsecme-qr- o Migrated from draft-fluhrer-qr-ikev2-05 to draft-ietf-ipsecme-qr-
ikev2-00 that is a WG item. ikev2-00 that is a WG item.
draft-fluhrer-qr-ikev2-05
o Nits and editorial fixes. o Nits and editorial fixes.
o Made PPK_ID format and PPK Distributions subsection of the PPK o Made PPK_ID format and PPK Distributions subsection of the PPK
section. Also added an Operational Considerations section. section. Also added an Operational Considerations section.
o Added comment about Child SA rekey in the Security Considerations o Added comment about Child SA rekey in the Security Considerations
section. section.
o Added NO_PPK_AUTH to solve the cases where a PPK_ID is not o Added NO_PPK_AUTH to solve the cases where a PPK_ID is not
configured for a responder. configured for a responder.
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o Modified how we stir the PPK into the IKEv2 secret state. o Modified how we stir the PPK into the IKEv2 secret state.
o Modified how the use of PPKs is negotiated. o Modified how the use of PPKs is negotiated.
draft-fluhrer-qr-ikev2-02 draft-fluhrer-qr-ikev2-02
o Simplified the protocol by stirring in the preshared key into the o Simplified the protocol by stirring in the preshared key into the
child SAs; this avoids the problem of having the responder decide child SAs; this avoids the problem of having the responder decide
which preshared key to use (as it knows the initiator identity at 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. recover the initial IKE negotiation.
o Removed positive endorsements of various algorithms. Retained o Removed positive endorsements of various algorithms. Retained
warnings about algorithms known to be weak against a Quantum warnings about algorithms known to be weak against a quantum
Computer. computer.
draft-fluhrer-qr-ikev2-01 draft-fluhrer-qr-ikev2-01
o Added explicit guidance as to what IKE and IPsec algorithms are o Added explicit guidance as to what IKE and IPsec algorithms are
quantum resistant. quantum resistant.
draft-fluhrer-qr-ikev2-00 draft-fluhrer-qr-ikev2-00
o We switched from using vendor ID's to transmit the additional data o We switched from using vendor ID's to transmit the additional data
to notifications. to notifications.
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1.2. Requirements Language 1.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
2. Assumptions 2. Assumptions
We assume that each IKE peer has a list of Postquantum Preshared Keys We assume that each IKE peer has a list of Post-quantum Preshared
(PPK) along with their identifiers (PPK_ID), and any potential IKE Keys (PPK) along with their identifiers (PPK_ID), and any potential
initiator selects which PPK to use with any specific responder. In IKE initiator selects which PPK to use with any specific responder.
addition, implementations have a configurable flag that determines In addition, implementations have a configurable flag that determines
whether this postquantum preshared key is mandatory. This PPK is whether this post-quantum preshared key is mandatory. This PPK is
independent of the preshared key (if any) that the IKEv2 protocol independent of the preshared key (if any) that the IKEv2 protocol
uses to perform authentication (because the preshared key in IKEv2 is uses to perform authentication (because the preshared key in IKEv2 is
not used for any key derivation, and thus doesn't protect against 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: to be on each node consists of the following tuple:
Peer, PPK, PPK_ID, mandatory_or_not Peer, PPK, PPK_ID, mandatory_or_not
3. Exchanges 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), 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 then it will include a notification USE_PPK in the IKE_SA_INIT
request message as follows: request message as follows:
Initiator Responder Initiator Responder
------------------------------------------------------------------ ------------------------------------------------------------------
HDR, SAi1, KEi, Ni, N(USE_PPK) ---> HDR, SAi1, KEi, Ni, N(USE_PPK) --->
N(USE_PPK) is a status notification payload with the type 16435; it 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 has a protocol ID of 0, no SPI and no notification data associated
with it. with it.
If the initiator needs to resend this initial message with a cookie If the initiator needs to resend this initial message with a cookie
(because the responder response included a COOKIE notification), then (because the responder response included a COOKIE notification), then
the resend would include the USE_PPK notification if the original the resend would include the USE_PPK notification if the original
message did. message did.
If the responder does not support this specification or does not have If the responder does not support this specification or does not have
any PPK configured, then it ignores the received notification and any PPK configured, then it ignores the received notification (as
continues with the IKEv2 protocol as normal. Otherwise the responder defined in [RFC7296] for unknown status notifications) and continues
replies with the IKE_SA_INIT message including a USE_PPK notification with the IKEv2 protocol as normal. Otherwise the responder replies
in the response: with the IKE_SA_INIT message including a USE_PPK notification in the
response:
Initiator Responder Initiator Responder
------------------------------------------------------------------ ------------------------------------------------------------------
<--- HDR, SAr1, KEr, Nr, [CERTREQ,] N(USE_PPK) <--- HDR, SAr1, KEr, Nr, [CERTREQ,] N(USE_PPK)
When the initiator receives this reply, it checks whether the When the initiator receives this reply, it checks whether the
responder included the USE_PPK notification. If the responder did responder included the USE_PPK notification. If the responder did
not and the flag mandatory_or_not indicates that using PPKs is not and the flag mandatory_or_not indicates that using PPKs is
mandatory for communication with this responder, then the initiator mandatory for communication with this responder, then the initiator
MUST abort the exchange. This situation may happen in case of MUST abort the exchange. This situation may happen in case of
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both peers have been upgraded, but the responder isn't yet configured both peers have been upgraded, but the responder isn't yet configured
with the PPK for the initiator, then the responder could do standard with the PPK for the initiator, then the responder could do standard
IKEv2 protocol if the initiator sent NO_PPK_AUTH notification. If IKEv2 protocol if the initiator sent NO_PPK_AUTH notification. If
both the responder and initiator have been upgraded and properly both the responder and initiator have been upgraded and properly
configured, they will both realize it, and the Child SAs will be configured, they will both realize it, and the Child SAs will be
quantum-secure. quantum-secure.
As an optional second step, after all nodes have been upgraded, then As an optional second step, after all nodes have been upgraded, then
the administrator should then go back through the nodes, and mark the 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 use of PPK as mandatory. This will not affect the strength against a
passive attacker; it would mean that an attacker with a Quantum passive attacker; it would mean that an attacker with a quantum
Computer (which is sufficiently fast to be able to break the (EC)DH 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. in real time) would not be able to perform a downgrade attack.
5. PPK 5. PPK
5.1. PPK_ID format 5.1. PPK_ID format
This standard requires that both the initiator and the responder have This standard requires that both the initiator and the responder have
a secret PPK value, with the responder selecting the PPK based on the a secret PPK value, with the responder selecting the PPK based on the
PPK_ID that the initiator sends. In this standard, both the PPK_ID that the initiator sends. In this standard, both the
initiator and the responder are configured with fixed PPK and PPK_ID initiator and the responder are configured with fixed PPK and PPK_ID
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This document doesn't explicitly require that PPK is unique for each 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 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 peer authentication, but it also means that each host must have as
many independent PPKs as the peers it is going to communicate with. many independent PPKs as the peers it is going to communicate with.
As the number of peers grows the PPKs will not scale. 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 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 peer uses classical public key cryptography in addition to PPK for
key exchange and authentication, members of the group can neither key exchange and authentication, members of the group can neither
impersonate each other nor read other's traffic, unless they use 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 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 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) 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 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. communications inside the group are revealed.
For these reasons using group PPK is NOT RECOMMENDED. For these reasons using group PPK is NOT RECOMMENDED.
5.2.3. PPK-only Authentication 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 cryptography will provide little security, so administrators may find
it attractive not to use it at all for authentication. This will it attractive not to use it at all for authentication. This will
reduce the number of credentials they need to maintain to PPKs only. reduce the number of credentials they need to maintain to PPKs only.
Combining group PPK and PPK-only authentication is NOT RECOMMENDED, Combining group PPK and PPK-only authentication is NOT RECOMMENDED,
since in this case any member of the group can impersonate any other 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 PPK-only authentication can be achieved in IKEv2 if the NULL
Authentication method [RFC7619] is employed. Without PPK the NULL Authentication method [RFC7619] is employed. Without PPK the NULL
Authentication method provides no authentication of the peers, Authentication method provides no authentication of the peers,
however since a PPK is stirred into the SK_pi and the SK_pr, the 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 peers become authenticated if a PPK is in use. Using PPKs MUST be
mandatory for the peers if they advertise support for PPK in mandatory for the peers if they advertise support for PPK in
IKE_SA_INIT and use NULL Authentication. Addtionally, since the IKE_SA_INIT and use NULL Authentication. Addtionally, since the
peers are authenticated via PPK, the ID Type in the IDi/IDr payloads peers are authenticated via PPK, the ID Type in the IDi/IDr payloads
SHOULD NOT be ID_NULL, despite using the NULL Authentication method. SHOULD NOT be ID_NULL, despite using the NULL Authentication method.
6. Security Considerations 6. Security Considerations
Quantum computers are able to perform Grover's algorithm; that Quantum computers are able to perform Grover's algorithm [GROVER];
effectively halves the size of a symmetric key. Because of this, the that effectively halves the size of a symmetric key. Because of
user SHOULD ensure that the postquantum preshared key used has at this, the user SHOULD ensure that the post-quantum preshared key used
least 256 bits of entropy, in order to provide 128 bits of security. 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. With this protocol, the computed SK_d is a function of the PPK.
Assuming that the PPK has sufficient entropy (for example, at least Assuming that the PPK has sufficient entropy (for example, at least
2^256 possible values), then even if an attacker was able to recover 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 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 value. Similarly, all keys that are a function of SK_d, which
include all Child SAs keys and all keys for subsequent IKE SAs include all Child SAs keys and all keys for subsequent IKE SAs
(created when the initial IKE SA is rekeyed), are also quantum (created when the initial IKE SA is rekeyed), are also quantum
resistant (assuming that the PPK was of high enough entropy, and that resistant (assuming that the PPK was of high enough entropy, and that
all the subkeys are sufficiently long). 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 SA has access to all the information exchanged over it, such as
identities of the peers, configuration parameters and all negotiated identities of the peers, configuration parameters and all negotiated
IPsec SAs information (including traffic selectors), with the IPsec SAs information (including traffic selectors), with the
exception of the cryptographic keys used by the IPsec SAs which are exception of the cryptographic keys used by the IPsec SAs which are
protected by the PPK. protected by the PPK.
Deployments that treat this information as sensitive or that send Deployments that treat this information as sensitive or that send
other sensitive data (like cryptographic keys) over IKE SA MUST rekey other sensitive data (like cryptographic keys) over IKE SA MUST rekey
the IKE SA before the sensitive information is sent to ensure this the IKE SA before the sensitive information is sent to ensure this
information is protected by the PPK. It is possible to create a information is protected by the PPK. It is possible to create a
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SA that is not protected by a PPK. Some information related to IKE 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, SA, that is sent in the IKE_AUTH exchange, such as peer identities,
feature notifications, Vendor ID's etc. cannot be hidden from the feature notifications, Vendor ID's etc. cannot be hidden from the
attack described above, even if the additional IKE SA rekey is attack described above, even if the additional IKE SA rekey is
performed. performed.
In addition, the policy SHOULD be set to negotiate only quantum- In addition, the policy SHOULD be set to negotiate only quantum-
resistant symmetric algorithms; while this RFC doesn't claim to give resistant symmetric algorithms; while this RFC doesn't claim to give
advice as to what algorithms are secure (as that may change based on advice as to what algorithms are secure (as that may change based on
future cryptographical results), below is a list of defined IKEv2 and 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 IPsec algorithms that should not be used, as they are known to
quantum resistant provide less than 128 bits of post-quantum security
o Any IKEv2 Encryption algorithm, PRF or Integrity algorithm with o Any IKEv2 Encryption algorithm, PRF or Integrity algorithm with
key size less than 256 bits. key size less than 256 bits.
o Any ESP Transform 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 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 to be able to use an arbitrary key size, they convert it into a
128-bit key internally. 128-bit key internally.
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IKE SA with a high enough rate, then the responder may consider it as IKE SA with a high enough rate, then the responder may consider it as
a Denial-of-Service attack and take protection measures (see a Denial-of-Service attack and take protection measures (see
[RFC8019] for more detail). In this situation, it is RECOMMENDED [RFC8019] for more detail). In this situation, it is RECOMMENDED
that the initiator caches the negative result of the negotiation for 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, 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- because this is a result of misconfiguration and probably some re-
configuration of the peers is needed. configuration of the peers is needed.
If using PPKs is optional for both peers and they authenticate If using PPKs is optional for both peers and they authenticate
themselves using digital signatures, then an attacker in between, 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 operations in real time, is able to mount downgrade attack by
removing USE_PPK notification from the IKE_SA_INIT and forging removing USE_PPK notification from the IKE_SA_INIT and forging
digital signatures in the subsequent exchange. If using PPKs is digital signatures in the subsequent exchange. If using PPKs is
mandatory for at least one of the peers or PSK is used for 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 authentication, then the attack will be detected and the SA won't be
created. created.
If using PPKs is mandatory for the initiator, then an attacker able If using PPKs is mandatory for the initiator, then an attacker able
to eavesdrop and to inject packets into the network can prevent to eavesdrop and to inject packets into the network can prevent
creating an IKE SA by mounting the following attack. The attacker creating an IKE SA by mounting the following attack. The attacker
skipping to change at page 16, line 23 skipping to change at page 16, line 25
response, then the initiator would abort the exchange. To thwart response, then the initiator would abort the exchange. To thwart
this kind of attack it is RECOMMENDED, that if using PPKs is this kind of attack it is RECOMMENDED, that if using PPKs is
mandatory for the initiator and the received response doesn't contain mandatory for the initiator and the received response doesn't contain
the USE_PPK notification, then the initiator doesn't abort the the USE_PPK notification, then the initiator doesn't abort the
exchange immediately, but instead waits some time for more responses exchange immediately, but instead waits some time for more responses
(possibly retransmitting the request). If all the received responses (possibly retransmitting the request). If all the received responses
contain no USE_PPK, then the exchange is aborted. contain no USE_PPK, then the exchange is aborted.
If using PPK is optional for both peers, then in case of If using PPK is optional for both peers, then in case of
misconfiguration (e.g. mismatched PPK_ID) the IKE SA will be created 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 PPK was configured, but was not used for a particular IKE SA, then
implementations SHOULD audit this event. implementations SHOULD audit this event.
7. IANA Considerations 7. IANA Considerations
This document defines three new Notify Message Types in the "Notify This document defines three new Notify Message Types in the "Notify
Message Types - Status Types" registry: Message Types - Status Types" registry:
16435 USE_PPK 16435 USE_PPK [THIS RFC]
16436 PPK_IDENTITY 16436 PPK_IDENTITY [THIS RFC]
16437 NO_PPK_AUTH 16437 NO_PPK_AUTH [THIS RFC]
This document also creates a new IANA registry for the PPK_ID types.
The initial values of this registry are:
PPK_ID Type Value This document also creates a new IANA registry "IKEv2 Post-quantum
----------- ----- Preshared Key ID Types" in IKEv2 IANA registry
Reserved 0 (https://www.iana.org/assignments/ikev2-parameters/) for the PPK_ID
PPK_ID_OPAQUE 1 types. The initial values of the new registry are:
PPK_ID_FIXED 2
Unassigned 3-127
Reserved for private use 128-255
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 Changes and additions to this registry are by Expert Review
[RFC8126]. [RFC8126].
8. References 8. References
8.1. Normative References 8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
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Kivinen, "Internet Key Exchange Protocol Version 2 Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <https://www.rfc-editor.org/info/rfc7296>. 2014, <https://www.rfc-editor.org/info/rfc7296>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
8.2. Informational References 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] [I-D.hoffman-c2pq]
Hoffman, P., "The Transition from Classical to Post- Hoffman, P., "The Transition from Classical to Post-
Quantum Cryptography", draft-hoffman-c2pq-05 (work in Quantum Cryptography", draft-hoffman-c2pq-06 (work in
progress), May 2019. progress), November 2019.
[IKEV2-IANA-PRFS] [IKEV2-IANA-PRFS]
"Internet Key Exchange Version 2 (IKEv2) Parameters, "Internet Key Exchange Version 2 (IKEv2) Parameters,
Transform Type 2 - Pseudorandom Function Transform IDs", Transform Type 2 - Pseudorandom Function Transform IDs",
<https://www.iana.org/assignments/ikev2-parameters/ <https://www.iana.org/assignments/ikev2-parameters/
ikev2-parameters.xhtml#ikev2-parameters-6>. ikev2-parameters.xhtml#ikev2-parameters-6>.
[NISTPQCFP]
NIST, "NIST Post-Quantum Cryptography Call for Proposals",
2016.
[RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange [RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange
(IKE)", RFC 2409, DOI 10.17487/RFC2409, November 1998, (IKE)", RFC 2409, DOI 10.17487/RFC2409, November 1998,
<https://www.rfc-editor.org/info/rfc2409>. <https://www.rfc-editor.org/info/rfc2409>.
[RFC6023] Nir, Y., Tschofenig, H., Deng, H., and R. Singh, "A [RFC6023] Nir, Y., Tschofenig, H., Deng, H., and R. Singh, "A
Childless Initiation of the Internet Key Exchange Version Childless Initiation of the Internet Key Exchange Version
2 (IKEv2) Security Association (SA)", RFC 6023, 2 (IKEv2) Security Association (SA)", RFC 6023,
DOI 10.17487/RFC6023, October 2010, DOI 10.17487/RFC6023, October 2010,
<https://www.rfc-editor.org/info/rfc6023>. <https://www.rfc-editor.org/info/rfc6023>.
skipping to change at page 18, line 23 skipping to change at page 18, line 33
DOI 10.17487/RFC8019, November 2016, DOI 10.17487/RFC8019, November 2016,
<https://www.rfc-editor.org/info/rfc8019>. <https://www.rfc-editor.org/info/rfc8019>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
Appendix A. Discussion and Rationale 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 easily reconstruct the shared secret of an (EC)DH exchange, they
cannot as easily recover a secret from a symmetric exchange. This cannot as easily recover a secret from a symmetric exchange. This
document makes the SK_d, and hence the IPsec KEYMAT and any child 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- SA's SKEYSEED, depend on both the symmetric PPK, and also the Diffie-
Hellman exchange. If we assume that the attacker knows everything Hellman exchange. If we assume that the attacker knows everything
except the PPK during the key exchange, and there are 2^n plausible 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 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 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 (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 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 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 material for the initial IKE SA; this was a compromise to allow the
responder to select the correct PPK quickly. responder to select the correct PPK quickly.
Another goal of this protocol is to minimize the number of changes Another goal of this protocol is to minimize the number of changes
within the IKEv2 protocol, and in particular, within the cryptography within the IKEv2 protocol, and in particular, within the cryptography
of IKEv2. By limiting our changes to notifications, and only 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 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 implementable, even on systems that perform most of the IKEv2
processing in hardware. processing in hardware.
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