draft-ietf-ipsecme-qr-ikev2-10.txt   draft-ietf-ipsecme-qr-ikev2-11.txt 
Internet Engineering Task Force S. Fluhrer Internet Engineering Task Force S. Fluhrer
Internet-Draft D. McGrew Internet-Draft P. Kampanakis
Intended status: Standards Track P. Kampanakis Intended status: Standards Track D. McGrew
Expires: June 29, 2020 Cisco Systems Expires: July 17, 2020 Cisco Systems
V. Smyslov V. Smyslov
ELVIS-PLUS ELVIS-PLUS
December 27, 2019 January 14, 2020
Mixing Preshared Keys in IKEv2 for Post-quantum Resistance Mixing Preshared Keys in IKEv2 for Post-quantum Security
draft-ietf-ipsecme-qr-ikev2-10 draft-ietf-ipsecme-qr-ikev2-11
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
skipping to change at page 1, line 42 skipping to change at page 1, line 42
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 June 29, 2020. This Internet-Draft will expire on July 17, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2020 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
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publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
skipping to change at page 2, line 33 skipping to change at page 2, line 33
5. PPK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 5. PPK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.1. PPK_ID format . . . . . . . . . . . . . . . . . . . . . . 12 5.1. PPK_ID format . . . . . . . . . . . . . . . . . . . . . . 12
5.2. Operational Considerations . . . . . . . . . . . . . . . 13 5.2. Operational Considerations . . . . . . . . . . . . . . . 13
5.2.1. PPK Distribution . . . . . . . . . . . . . . . . . . 13 5.2.1. PPK Distribution . . . . . . . . . . . . . . . . . . 13
5.2.2. Group PPK . . . . . . . . . . . . . . . . . . . . . . 13 5.2.2. Group PPK . . . . . . . . . . . . . . . . . . . . . . 13
5.2.3. PPK-only Authentication . . . . . . . . . . . . . . . 14 5.2.3. PPK-only Authentication . . . . . . . . . . . . . . . 14
6. Security Considerations . . . . . . . . . . . . . . . . . . . 14 6. Security Considerations . . . . . . . . . . . . . . . . . . . 14
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 . . . . . . . . . . . . . . . . 18
Appendix A. Discussion and Rationale . . . . . . . . . . . . . . 18 Appendix A. Discussion and Rationale . . . . . . . . . . . . . . 19
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 19 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
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-secure, that is, secure against classical attackers of
quantum computer. today or future attackers with a 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 post- then the resulting exchange is quantum-secure. By bringing post-
quantum security to IKEv2, this note removes the need to use an quantum security to IKEv2, this document 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
allows both sides to detect a secret mismatch cleanly. allows both sides to detect a secret mismatch cleanly.
It was considered important to minimize the changes to IKEv2. The It was considered important to minimize the changes to IKEv2. The
existing mechanisms to do authentication and key exchange remain in existing mechanisms to do authentication and key exchange remain in
place (that is, we continue to do (EC)DH, and potentially PKI place (that is, we continue to do (EC)DH, and potentially PKI
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, they are
a parallel check. strengthened by using an additional secret key.
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-ikev2-11
o Updates the IANA section based on Eric V.'s IESG Review.
o Updates based on IESG Reviews (Alissa, Adam, Barry, Alexey, Mijra,
Roman, Martin.
draft-ietf-ipsecme-qr-ikev2-10 draft-ietf-ipsecme-qr-ikev2-10
o Addresses issues raised during IETF LC. 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 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.
skipping to change at page 4, line 46 skipping to change at page 5, line 5
o Nits and minor fixes. o Nits and minor fixes.
o prf is replaced with prf+ for the SK_d and SK_pi/r calculations. o prf is replaced with prf+ for the SK_d and SK_pi/r calculations.
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
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.
skipping to change at page 6, line 42 skipping to change at page 6, line 47
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 post-quantum 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 MUST 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 notification, then the resend would include the USE_PPK notification
the resend would include the USE_PPK notification if the original if the original message did (see Section 2.6 of [RFC7296]).
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 (as any PPK configured, then it ignores the received notification (as
defined in [RFC7296] for unknown status notifications) and continues defined in [RFC7296] for unknown status notifications) and continues
with the IKEv2 protocol as normal. Otherwise the responder replies with the IKEv2 protocol as normal. Otherwise the responder replies
with the IKE_SA_INIT message including a USE_PPK notification in the with the IKE_SA_INIT message including a USE_PPK notification in the
response: 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
misconfiguration, when the initiator believes it has a mandatory to misconfiguration, when the initiator believes it has a mandatory-to-
use PPK for the responder, while the responder either doesn't support use PPK for the responder, while the responder either doesn't support
PPKs at all or doesn't have any PPK configured for the initiator. PPKs at all or doesn't have any PPK configured for the initiator.
See Section 6 for discussion of the possible impacts of this See Section 6 for discussion of the possible impacts of this
situation. situation.
If the responder did not include the USE_PPK notification and using a If the responder did not include the USE_PPK notification and using a
PPK for this particular responder is optional, then the initiator PPK for this particular responder is optional, then the initiator
continues with the IKEv2 protocol as normal, without using PPKs. continues with the IKEv2 protocol as normal, without using PPKs.
If the responder did include the USE_PPK notification, then the If the responder did include the USE_PPK notification, then the
initiator selects a PPK, along with its identifier PPK_ID. Then, it initiator selects a PPK, along with its identifier PPK_ID. Then, it
computes this modification of the standard IKEv2 key derivation: computes this modification of the standard IKEv2 key derivation from
Section 2.14 of [RFC7296]:
SKEYSEED = prf(Ni | Nr, g^ir) SKEYSEED = prf(Ni | Nr, g^ir)
{SK_d' | SK_ai | SK_ar | SK_ei | SK_er | SK_pi' | SK_pr' ) {SK_d' | SK_ai | SK_ar | SK_ei | SK_er | SK_pi' | SK_pr' )
= prf+ (SKEYSEED, Ni | Nr | SPIi | SPIr } = prf+ (SKEYSEED, Ni | Nr | SPIi | SPIr }
SK_d = prf+ (PPK, SK_d') SK_d = prf+ (PPK, SK_d')
SK_pi = prf+ (PPK, SK_pi') SK_pi = prf+ (PPK, SK_pi')
SK_pr = prf+ (PPK, SK_pr') SK_pr = prf+ (PPK, SK_pr')
That is, we use the standard IKEv2 key derivation process except that That is, we use the standard IKEv2 key derivation process except that
the three subkeys SK_d, SK_pi, SK_pr are run through the prf+ again, the three resulting subkeys SK_d, SK_pi, SK_pr (marked with primes in
this time using the PPK as the key. Using prf+ construction ensures the formula above) are then run through the prf+ again, this time
that it is always possible to get the resulting keys of the same size using the PPK as the key. The result is the unprimed versions of
as the initial ones, even if the underlying PRF has output size these keys which are then used as inputs to subsequent steps of the
different from its key size. Note, that at the time this document IKEv2 exchange.
was written, all PRFs defined for use in IKEv2 [IKEV2-IANA-PRFS] had
output size equal to the (preferred) key size. For such PRFs only Using a prf+ construction ensures that it is always possible to get
the first iteration of prf+ is needed: the resulting keys of the same size as the initial ones, even if the
underlying PRF has output size different from its key size. Note,
that at the time of this writing, all PRFs defined for use in IKEv2
[IKEV2-IANA-PRFS] had output size equal to the (preferred) key size.
For such PRFs only the first iteration of prf+ is needed:
SK_d = prf (PPK, SK_d' | 0x01) SK_d = prf (PPK, SK_d' | 0x01)
SK_pi = prf (PPK, SK_pi' | 0x01) SK_pi = prf (PPK, SK_pi' | 0x01)
SK_pr = prf (PPK, SK_pr' | 0x01) SK_pr = prf (PPK, SK_pr' | 0x01)
Note that the PPK is used in SK_d, SK_pi and SK_pr calculation only Note that the PPK is used in SK_d, SK_pi and SK_pr calculation only
during the initial IKE SA setup. It MUST NOT be used when these during the initial IKE SA setup. It MUST NOT be used when these
subkeys are calculated as result of IKE SA rekey, resumption or other subkeys are calculated as result of IKE SA rekey, resumption or other
similar operation. similar operation.
skipping to change at page 8, line 38 skipping to change at page 9, line 7
protocol ID of 0, no SPI and a notification data that consists of the protocol ID of 0, no SPI and a notification data that consists of the
identifier PPK_ID. identifier PPK_ID.
A situation may happen when the responder has some PPKs, but doesn't A situation may happen when the responder has some PPKs, but doesn't
have a PPK with the PPK_ID received from the initiator. In this case have a PPK with the PPK_ID received from the initiator. In this case
the responder cannot continue with PPK (in particular, it cannot the responder cannot continue with PPK (in particular, it cannot
authenticate the initiator), but the responder could be able to authenticate the initiator), but the responder could be able to
continue with normal IKEv2 protocol if the initiator provided its continue with normal IKEv2 protocol if the initiator provided its
authentication data computed as in normal IKEv2, without using PPKs. authentication data computed as in normal IKEv2, without using PPKs.
For this purpose, if using PPKs for communication with this responder For this purpose, if using PPKs for communication with this responder
is optional for the initiator, then the initiator MAY include a is optional for the initiator (based on the mandatory_or_not flag),
notification NO_PPK_AUTH in the above message. then the initiator MUST include a NO_PPK_AUTH notification in the
above message. This notification informs the responder that PPK is
optional and allows for authenticating the initiator without using
PPK.
NO_PPK_AUTH is a status notification with the type 16437; it has a 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 protocol ID of 0 and no SPI. The Notification Data field contains
the initiator's authentication data computed using SK_pi', which has the initiator's authentication data computed using SK_pi', which has
been computed without using PPKs. This is the same data that would been computed without using PPKs. This is the same data that would
normally be placed in the Authentication Data field of an AUTH normally be placed in the Authentication Data field of an AUTH
payload. Since the Auth Method field is not present in the payload. Since the Auth Method field is not present in the
notification, the authentication method used for computing the notification, the authentication method used for computing the
authentication data MUST be the same as method indicated in the AUTH authentication data MUST be the same as method indicated in the AUTH
payload. Note that if the initiator decides to include the payload. Note that if the initiator decides to include the
NO_PPK_AUTH notification, the initiator needs to perform NO_PPK_AUTH notification, the initiator needs to perform
authentication data computation twice, which may consume computation authentication data computation twice, which may consume computation
power (e.g. if digital signatures are involved). power (e.g., if digital signatures are involved).
When the responder receives this encrypted exchange, it first When the responder receives this encrypted exchange, it first
computes the values: computes the values:
SKEYSEED = prf(Ni | Nr, g^ir) SKEYSEED = prf(Ni | Nr, g^ir)
{SK_d' | SK_ai | SK_ar | SK_ei | SK_er | SK_pi' | SK_pr' } {SK_d' | SK_ai | SK_ar | SK_ei | SK_er | SK_pi' | SK_pr' }
= prf+ (SKEYSEED, Ni | Nr | SPIi | SPIr ) = prf+ (SKEYSEED, Ni | Nr | SPIi | SPIr )
The responder then uses the SK_ei/SK_ai values to decrypt/check the 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 message and then scans through the payloads for the PPK_ID attached
skipping to change at page 12, line 12 skipping to change at page 12, line 30
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, but it would mean that an active attacker with a
computer (which is sufficiently fast to be able to break the (EC)DH quantum computer (which is sufficiently fast to be able to break the
in real time) would not be able to perform a downgrade attack. (EC)DH 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
values, and do the look up based on PPK_ID value. It is anticipated values, and do the look up based on PPK_ID value. It is anticipated
that later standards will extend this technique to allow dynamically that later specifications will extend this technique to allow
changing PPK values. To facilitate such an extension, we specify dynamically changing PPK values. To facilitate such an extension, we
that the PPK_ID the initiator sends will have its first octet be the specify that the PPK_ID the initiator sends will have its first octet
PPK_ID Type value. This document defines two values for PPK_ID Type: be the PPK_ID Type value. This document defines two values for
PPK_ID Type:
o PPK_ID_OPAQUE (1) - for this type the format of the PPK_ID (and o PPK_ID_OPAQUE (1) - for this type the format of the PPK_ID (and
the PPK itself) is not specified by this document; it is assumed the PPK itself) is not specified by this document; it is assumed
to be mutually intelligible by both by initiator and the to be mutually intelligible by both by initiator and the
responder. This PPK_ID type is intended for those implementations responder. This PPK_ID type is intended for those implementations
that choose not to disclose the type of PPK to active attackers. that choose not to disclose the type of PPK to active attackers.
o PPK_ID_FIXED (2) - in this case the format of the PPK_ID and the o PPK_ID_FIXED (2) - in this case the format of the PPK_ID and the
PPK are fixed octet strings; the remaining bytes of the PPK_ID are PPK are fixed octet strings; the remaining bytes of the PPK_ID are
a configured value. We assume that there is a fixed mapping a configured value. We assume that there is a fixed mapping
between PPK_ID and PPK, which is configured locally to both the between PPK_ID and PPK, which is configured locally to both the
initiator and the responder. The responder can use the PPK_ID to initiator and the responder. The responder can use the PPK_ID to
look up the corresponding PPK value. Not all implementations are look up the corresponding PPK value. Not all implementations are
able to configure arbitrary octet strings; to improve the able to configure arbitrary octet strings; to improve the
potential interoperability, it is recommended that, in the potential interoperability, it is recommended that, in the
PPK_ID_FIXED case, both the PPK and the PPK_ID strings be limited PPK_ID_FIXED case, both the PPK and the PPK_ID strings be limited
to the base64 character set, namely the 64 characters 0-9, A-Z, to the Base64 character set [RFC4648].
a-z, + and /.
The PPK_ID type value 0 is reserved; values 3-127 are reserved for
IANA; values 128-255 are for private use among mutually consenting
parties.
5.2. Operational Considerations 5.2. Operational Considerations
The need to maintain several independent sets of security credentials The need to maintain several independent sets of security credentials
can significantly complicate a security administrator's job, and can can significantly complicate a security administrator's job, and can
potentially slow down widespread adoption of this specification. It potentially slow down widespread adoption of this specification. It
is anticipated, that administrators will try to simplify their job by is anticipated, that administrators will try to simplify their job by
decreasing the number of credentials they need to maintain. This decreasing the number of credentials they need to maintain. This
section describes some of the considerations for PPK management. section describes some of the considerations for PPK management.
skipping to change at page 14, line 21 skipping to change at page 14, line 31
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. Additionally, 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 [GROVER]; Quantum computers are able to perform Grover's algorithm [GROVER];
that effectively halves the size of a symmetric key. Because of that effectively halves the size of a symmetric key. Because of
this, the user SHOULD ensure that the post-quantum preshared key used 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 has at least 256 bits of entropy, in order to provide 128 bits of
post-quantum security. That provides security equivalent to Level 5 post-quantum security. That provides security equivalent to Level 5
as defined in the NIST PQ Project Call For Proposals [NISTPQCFP]. 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-secure
resistant (assuming that the PPK was of high enough entropy, and that (assuming that the PPK was of high enough entropy, and that all the
all the subkeys are sufficiently long). 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
childless IKE SA as specified in [RFC6023]. This prevents Child SA childless IKE SA as specified in [RFC6023]. This prevents Child SA
configuration information from being transmited in the original IKE configuration information from being transmitted in the original IKE
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 secure 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 to IPsec algorithms that should not be used, as they are known to
provide less than 128 bits of post-quantum security 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.
skipping to change at page 15, line 41 skipping to change at page 15, line 50
128-bit key internally. 128-bit key internally.
Section 3 requires the initiator to abort the initial exchange if Section 3 requires the initiator to abort the initial exchange if
using PPKs is mandatory for it, but the responder does not include using PPKs is mandatory for it, but the responder does not include
the USE_PPK notification in the response. In this situation, when the USE_PPK notification in the response. In this situation, when
the initiator aborts negotiation it leaves a half-open IKE SA on the the initiator aborts negotiation it leaves a half-open IKE SA on the
responder (because IKE_SA_INIT completes successfully from the responder (because IKE_SA_INIT completes successfully from the
responder's point of view). This half-open SA will eventually expire responder's point of view). This half-open SA will eventually expire
and be deleted, but if the initiator continues its attempts to create and be deleted, but if the initiator continues its attempts to create
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 (DoS) 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 and
some time and doesn't make attempts to create it again for some time, doesn't make attempts to create it again for some time. This period
because this is a result of misconfiguration and probably some re- of time may vary, but it is believed that waiting for at least few
configuration of the peers is needed. minutes will not cause the responder to treat it as DoS attack.
Note, that this situation would most likely be a result of
misconfiguration and some re-configuration of the peers would
probably be 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.
skipping to change at page 16, line 19 skipping to change at page 16, line 32
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
intercepts the initial request containing the USE_PPK notification intercepts the initial request containing the USE_PPK notification
and injects a forged response containing no USE_PPK. If the attacker and injects a forged response containing no USE_PPK. If the attacker
manages to inject this packet before the responder sends a genuine manages to inject this packet before the responder sends a genuine
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. Instead it waits for more response messages
(possibly retransmitting the request). If all the received responses retransmitting the request as if no responses were received at all,
contain no USE_PPK, then the exchange is aborted. until either the received message contains the USE_PPK or the
exchange times out (see section 2.4 of [RFC7296] for more details
about retransmission timers in IKEv2). If neither of the received
responses contains 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
(https://www.iana.org/assignments/ikev2-parameters/
ikev2-parameters.xhtml#ikev2-parameters-16):
16435 USE_PPK [THIS RFC] 16435 USE_PPK [THIS RFC]
16436 PPK_IDENTITY [THIS RFC] 16436 PPK_IDENTITY [THIS RFC]
16437 NO_PPK_AUTH [THIS RFC] 16437 NO_PPK_AUTH [THIS RFC]
This document also creates a new IANA registry "IKEv2 Post-quantum This document also creates a new IANA registry "IKEv2 Post-quantum
Preshared Key ID Types" in IKEv2 IANA registry Preshared Key ID Types" in IKEv2 IANA registry
(https://www.iana.org/assignments/ikev2-parameters/) for the PPK_ID (https://www.iana.org/assignments/ikev2-parameters/) for the PPK_ID
types. The initial values of the new registry are: types used in the PPK_IDENTITY notification defined in this
specification. The initial values of the new registry are:
PPK_ID Type Value Reference PPK_ID Type Value Reference
----------- ----- --------- ----------- ----- ---------
Reserved 0 [THIS RFC] Reserved 0 [THIS RFC]
PPK_ID_OPAQUE 1 [THIS RFC] PPK_ID_OPAQUE 1 [THIS RFC]
PPK_ID_FIXED 2 [THIS RFC] PPK_ID_FIXED 2 [THIS RFC]
Unassigned 3-127 [THIS RFC] Unassigned 3-127 [THIS RFC]
Reserved for private use 128-255 [THIS RFC] Private Use 128-255 [THIS RFC]
Changes and additions to this registry are by Expert Review
[RFC8126]. The PPK_ID type value 0 is reserved; values 3-127 are to be assigned
by IANA; values 128-255 are for private use among mutually consenting
parties. To register new PPK_IDs in the unassigned range, a Type
name, a Value between 3 and 127 and a Reference specification need to
be defined. Changes and additions to the unassigned range of this
registry are by the Expert Review Policy [RFC8126]. Changes and
additions to the private use range of this registry are by the
Private Use Policy [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,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
skipping to change at page 17, line 44 skipping to change at page 18, line 24
progress), November 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] [NISTPQCFP]
NIST, "NIST Post-Quantum Cryptography Call for Proposals", NIST, "NIST Post-Quantum Cryptography Call for Proposals",
2016. 2016, <https://csrc.nist.gov/CSRC/media/Projects/Post-
Quantum-Cryptography/documents/call-for-proposals-final-
dec-2016.pdf>.
[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>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.
[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>.
[RFC6030] Hoyer, P., Pei, M., and S. Machani, "Portable Symmetric [RFC6030] Hoyer, P., Pei, M., and S. Machani, "Portable Symmetric
Key Container (PSKC)", RFC 6030, DOI 10.17487/RFC6030, Key Container (PSKC)", RFC 6030, DOI 10.17487/RFC6030,
October 2010, <https://www.rfc-editor.org/info/rfc6030>. October 2010, <https://www.rfc-editor.org/info/rfc6030>.
skipping to change at page 19, line 10 skipping to change at page 19, line 44
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.
A third goal was to be friendly to incremental deployment in A third goal was to be friendly to incremental deployment in
operational networks, for which we might not want to have a global operational networks, for which we might not want to have a global
shared key, or quantum resistant IKEv2 is rolled out incrementally. shared key, or quantum-secure IKEv2 is rolled out incrementally.
This is why we specifically try to allow the PPK to be dependent on This is why we specifically try to allow the PPK to be dependent on
the peer, and why we allow the PPK to be configured as optional. the peer, and why we allow the PPK to be configured as optional.
A fourth goal was to avoid violating any of the security properties A fourth goal was to avoid violating any of the security properties
provided by IKEv2. provided by IKEv2.
Appendix B. Acknowledgements Appendix B. Acknowledgements
We would like to thank Tero Kivinen, Paul Wouters, Graham Bartlett, We would like to thank Tero Kivinen, Paul Wouters, Graham Bartlett,
Tommy Pauly, Quynh Dang and the rest of the IPSecME Working Group for Tommy Pauly, Quynh Dang and the rest of the IPSecME Working Group for
their feedback and suggestions for the scheme. their feedback and suggestions for the scheme.
Authors' Addresses Authors' Addresses
Scott Fluhrer Scott Fluhrer
Cisco Systems Cisco Systems
Email: sfluhrer@cisco.com Email: sfluhrer@cisco.com
David McGrew Panos Kampanakis
Cisco Systems Cisco Systems
Email: mcgrew@cisco.com Email: pkampana@cisco.com
Panos Kampanakis David McGrew
Cisco Systems Cisco Systems
Email: pkampana@cisco.com Email: mcgrew@cisco.com
Valery Smyslov Valery Smyslov
ELVIS-PLUS ELVIS-PLUS
Phone: +7 495 276 0211 Phone: +7 495 276 0211
Email: svan@elvis.ru Email: svan@elvis.ru
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