draft-ietf-ipsecme-qr-ikev2-08.txt   draft-ietf-ipsecme-qr-ikev2-09.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: September 29, 2019 Cisco Systems Expires: May 30, 2020 Cisco Systems
V. Smyslov V. Smyslov
ELVIS-PLUS ELVIS-PLUS
March 28, 2019 November 27, 2019
Postquantum Preshared Keys for IKEv2 Postquantum Preshared Keys for IKEv2
draft-ietf-ipsecme-qr-ikev2-08 draft-ietf-ipsecme-qr-ikev2-09
Abstract Abstract
The possibility of Quantum Computers pose a serious challenge to The possibility of Quantum Computers poses a serious challenge to
cryptography 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 http://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 September 29, 2019. This Internet-Draft will expire on May 30, 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
(http://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
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
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Changes . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Changes . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 5 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 6
2. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Exchanges . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Exchanges . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Upgrade procedure . . . . . . . . . . . . . . . . . . . . . . 10 4. Upgrade procedure . . . . . . . . . . . . . . . . . . . . . . 11
5. PPK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 5. PPK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.1. PPK_ID format . . . . . . . . . . . . . . . . . . . . . . 11 5.1. PPK_ID format . . . . . . . . . . . . . . . . . . . . . . 12
5.2. Operational Considerations . . . . . . . . . . . . . . . 12 5.2. Operational Considerations . . . . . . . . . . . . . . . 13
5.2.1. PPK Distribution . . . . . . . . . . . . . . . . . . 12 5.2.1. PPK Distribution . . . . . . . . . . . . . . . . . . 13
5.2.2. Group PPK . . . . . . . . . . . . . . . . . . . . . . 12 5.2.2. Group PPK . . . . . . . . . . . . . . . . . . . . . . 13
5.2.3. PPK-only Authentication . . . . . . . . . . . . . . . 13 5.2.3. PPK-only Authentication . . . . . . . . . . . . . . . 14
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 6. Security Considerations . . . . . . . . . . . . . . . . . . . 14
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
8.1. Normative References . . . . . . . . . . . . . . . . . . 16 8.1. Normative References . . . . . . . . . . . . . . . . . . 17
8.2. Informational References . . . . . . . . . . . . . . . . 16 8.2. Informational References . . . . . . . . . . . . . . . . 17
Appendix A. Discussion and Rationale . . . . . . . . . . . . . . 17 Appendix A. Discussion and Rationale . . . . . . . . . . . . . . 18
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 18 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction 1. Introduction
It is an open question whether or not it is feasible to build a Recent achievements in developing Quantum Computers demonstrate that
Quantum Computer (and if so, when one might be implemented), but if it is probably feasible to build a cryptographically significant one.
it is, many of the cryptographic algorithms and protocols currently If such a computer is implemented, many of the cryptographic
in use would be insecure. A Quantum Computer would be able to solve algorithms and protocols currently in use would be insecure. A
DH and ECDH problems in polynomial time [I-D.hoffman-c2pq], and this Quantum Computer would be able to solve DH and ECDH problems in
would imply that the security of existing IKEv2 [RFC7296] systems polynomial time [I-D.hoffman-c2pq], and this would imply that the
would be compromised. IKEv1 [RFC2409], when used with strong security of existing IKEv2 [RFC7296] systems would be compromised.
preshared keys, is not vulnerable to quantum attacks, because those IKEv1 [RFC2409], when used with strong preshared keys, is not
keys are one of the inputs to the key derivation function. If the vulnerable to quantum attacks, because those keys are one of the
preshared key has sufficient entropy and the PRF, encryption and inputs to the key derivation function. If the preshared key has
authentication transforms are postquantum secure, then the resulting sufficient entropy and the PRF, encryption and authentication
system is believed to be quantum resistant, that is, invulnerable to transforms are quantum-secure, then the resulting system is believed
an attacker with a Quantum Computer. to be quantum resistant, that is, invulnerable to an attacker 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 then the resulting exchange is quantum resistant. By bringing
postquantum security to IKEv2, this note removes the need to use an postquantum 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
skipping to change at page 3, line 34 skipping to change at page 3, line 36
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-ikev2-05 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.
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.
skipping to change at page 5, line 5 skipping to change at page 5, line 25
o Expanded Security Considerations section to describe some security o Expanded Security Considerations section to describe some security
concerns and how they should be addressed. concerns and how they should be addressed.
draft-fluhrer-qr-ikev2-03 draft-fluhrer-qr-ikev2-03
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
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.
skipping to change at page 5, line 42 skipping to change at page 6, line 16
the server to make a trade-off between the efficiency for the the server to make a trade-off between the efficiency for the
search of the clients PPK, and the anonymity of the client. search of the clients PPK, and the anonymity of the client.
o We now use the negotiated PRF (rather than a fixed HMAC-SHA256) to o We now use the negotiated PRF (rather than a fixed HMAC-SHA256) to
transform the nonces during the KDF. transform the nonces during the KDF.
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 RFC "OPTIONAL" in this document are to be interpreted as described in BCP
2119 [RFC2119]. 14 [RFC2119] [RFC8174] when, and only when, they appear in all
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 Postquantum Preshared Keys
(PPK) along with their identifiers (PPK_ID), and any potential IKE (PPK) along with their identifiers (PPK_ID), and any potential IKE
initiator has a selection of which PPK to use with any specific initiator selects which PPK to use with any specific responder. In
responder. In addition, implementations have a configurable flag addition, implementations have a configurable flag that determines
that determines whether this postquantum preshared key is mandatory. whether this postquantum preshared key is mandatory. This PPK is
This PPK is independent of the preshared key (if any) that the IKEv2 independent of the preshared key (if any) that the IKEv2 protocol
protocol uses to perform authentication. The PPK specific uses to perform authentication (because the preshared key in IKEv2 is
configuration that is assumed on each peer consists of the following not used for any key derivation, and thus doesn't protect against
tuple: 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 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 postquantum 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 he 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 she ignores the received notification and any PPK configured, then it ignores the received notification and
continues with the IKEv2 protocol as normal. Otherwise the responder continues with the IKEv2 protocol as normal. Otherwise the responder
checks if she has a PPK configured, and if she does, then the replies with the IKE_SA_INIT message including a USE_PPK notification
responder replies with the IKE_SA_INIT message including a USE_PPK in the response:
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, he 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 he 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, she 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:
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')
skipping to change at page 8, line 11 skipping to change at page 8, line 31
HDR, SK {IDi, [CERT,] [CERTREQ,] HDR, SK {IDi, [CERT,] [CERTREQ,]
[IDr,] AUTH, SAi2, [IDr,] AUTH, SAi2,
TSi, TSr, N(PPK_IDENTITY, PPK_ID), [N(NO_PPK_AUTH)]} ---> TSi, TSr, N(PPK_IDENTITY, PPK_ID), [N(NO_PPK_AUTH)]} --->
PPK_IDENTITY is a status notification with the type 16436; it has a PPK_IDENTITY is a status notification with the type 16436; it has a
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, she cannot the responder cannot continue with PPK (in particular, it cannot
authenticate the initiator), but she could be able to continue with authenticate the initiator), but the responder could be able to
normal IKEv2 protocol if the initiator provided its authentication continue with normal IKEv2 protocol if the initiator provided its
data computed as in normal IKEv2, without using PPKs. For this authentication data computed as in normal IKEv2, without using PPKs.
purpose, if using PPKs for communication with this responder is For this purpose, if using PPKs for communication with this responder
optional for the initiator, then the initiator MAY include a is optional for the initiator, then the initiator MAY include a
notification NO_PPK_AUTH in the above message. notification NO_PPK_AUTH in the above message.
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, she 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 )
She then uses the SK_ei/SK_ai values to decrypt/check the message and The responder then uses the SK_ei/SK_ai values to decrypt/check the
then scans through the payloads for the PPK_ID attached to the message and then scans through the payloads for the PPK_ID attached
PPK_IDENTITY notification. If no PPK_IDENTITY notification is found to the PPK_IDENTITY notification. If no PPK_IDENTITY notification is
and the peers successfully exchanged USE_PPK notifications in the found and the peers successfully exchanged USE_PPK notifications in
IKE_SA_INIT exchange, then the responder MUST send back the IKE_SA_INIT exchange, then the responder MUST send back
AUTHENTICATION_FAILED notification and then fail the negotiation. AUTHENTICATION_FAILED notification and then fail the negotiation.
If the PPK_IDENTITY notification contains PPK_ID that is not known to If the PPK_IDENTITY notification contains a PPK_ID that is not known
the responder or is not configured for use for the identity from IDi to the responder or is not configured for use for the identity from
payload, then the responder checks whether using PPKs for this IDi payload, then the responder checks whether using PPKs for this
initiator is mandatory and whether the initiator included NO_PPK_AUTH initiator is mandatory and whether the initiator included NO_PPK_AUTH
notification in the message. If using PPKs is mandatory or no notification in the message. If using PPKs is mandatory or no
NO_PPK_AUTH notification found, then then the responder MUST send NO_PPK_AUTH notification is found, then then the responder MUST send
back AUTHENTICATION_FAILED notification and then fail the back AUTHENTICATION_FAILED notification and then fail the
negotiation. Otherwise (when PPK is optional and the initiator negotiation. Otherwise (when PPK is optional and the initiator
included NO_PPK_AUTH notification) the responder MAY continue regular included NO_PPK_AUTH notification) the responder MAY continue regular
IKEv2 protocol, except that she uses the data from the NO_PPK_AUTH IKEv2 protocol, except that it uses the data from the NO_PPK_AUTH
notification as the authentication data (which usually resides in the notification as the authentication data (which usually resides in the
AUTH payload), for the purpose of the initiator authentication. AUTH payload), for the purpose of the initiator authentication.
Note, that Authentication Method is still indicated in the AUTH Note, that Authentication Method is still indicated in the AUTH
payload. payload.
This table summarizes the above logic for the responder: This table summarizes the above logic for the responder:
Received Received Configured PPK is Received Received Configured PPK is
USE_PPK NO_PPK_AUTH with PPK Mandatory Action USE_PPK NO_PPK_AUTH with PPK Mandatory Action
--------------------------------------------------------------------- ---------------------------------------------------------------------
skipping to change at page 9, line 43 skipping to change at page 10, line 16
the AUTH payload that the initiator included) as usual and sends back the AUTH payload that the initiator included) as usual and sends back
a response, which includes the PPK_IDENTITY notification with no data a response, which includes the PPK_IDENTITY notification with no data
to indicate that the PPK is used in the exchange: to indicate that the PPK is used in the exchange:
Initiator Responder Initiator Responder
------------------------------------------------------------------ ------------------------------------------------------------------
<-- HDR, SK {IDr, [CERT,] <-- HDR, SK {IDr, [CERT,]
AUTH, SAr2, AUTH, SAr2,
TSi, TSr, N(PPK_IDENTITY)} TSi, TSr, N(PPK_IDENTITY)}
When the initiator receives the response, then he checks for the When the initiator receives the response, then it checks for the
presence of the PPK_IDENTITY notification. If he receives one, he presence of the PPK_IDENTITY notification. If it receives one, it
marks the SA as using the configured PPK to generate SK_d, SK_pi, marks the SA as using the configured PPK to generate SK_d, SK_pi,
SK_pr (as shown above); the content of the received PPK_IDENTITY (if SK_pr (as shown above); the content of the received PPK_IDENTITY (if
any) MUST be ignored. If the initiator does not receive the any) MUST be ignored. If the initiator does not receive the
PPK_IDENTITY, he MUST either fail the IKE SA negotiation sending the PPK_IDENTITY, it MUST either fail the IKE SA negotiation sending the
AUTHENTICATION_FAILED notification in the Informational exchange (if AUTHENTICATION_FAILED notification in the Informational exchange (if
the PPK was configured as mandatory), or continue without using the the PPK was configured as mandatory), or continue without using the
PPK (if the PPK was not configured as mandatory and the initiator PPK (if the PPK was not configured as mandatory and the initiator
included the NO_PPK_AUTH notification in the request). included the NO_PPK_AUTH notification in the request).
If EAP is used in the IKE_AUTH exchange, then the initiator doesn't If EAP is used in the IKE_AUTH exchange, then the initiator doesn't
include AUTH payload in the first request message, however the include AUTH payload in the first request message, however the
responder sends back AUTH payload in the first reply. The peers then responder sends back AUTH payload in the first reply. The peers then
exchange AUTH payloads after EAP is successfully completed. As a exchange AUTH payloads after EAP is successfully completed. As a
result, the responder sends AUTH payload twice - in the first result, the responder sends AUTH payload twice - in the first
skipping to change at page 10, line 23 skipping to change at page 10, line 43
AUTH payload only in the last IKE_AUTH request. See more details AUTH payload only in the last IKE_AUTH request. See more details
about EAP authentication in IKEv2 in Section 2.16 of [RFC7296]. about EAP authentication in IKEv2 in Section 2.16 of [RFC7296].
The general rule for using PPK in the IKE_AUTH exchange, which covers The general rule for using PPK in the IKE_AUTH exchange, which covers
EAP authentication case too, is that the initiator includes EAP authentication case too, is that the initiator includes
PPK_IDENTITY (and optionally NO_PPK_AUTH) notification in the request PPK_IDENTITY (and optionally NO_PPK_AUTH) notification in the request
message containing AUTH payload. Therefore, in case of EAP the message containing AUTH payload. Therefore, in case of EAP the
responder always computes the AUTH payload in the first IKE_AUTH responder always computes the AUTH payload in the first IKE_AUTH
reply message without using PPK (by means of SK_pr'), since PPK_ID is reply message without using PPK (by means of SK_pr'), since PPK_ID is
not yet known to the responder. Once the IKE_AUTH request message not yet known to the responder. Once the IKE_AUTH request message
containing PPK_IDENTITY notification is received, the responder containing the PPK_IDENTITY notification is received, the responder
follows rules described above for non-EAP authentication case. follows the rules described above for the non-EAP authentication
case.
Initiator Responder Initiator Responder
---------------------------------------------------------------- ----------------------------------------------------------------
HDR, SK {IDi, [CERTREQ,] HDR, SK {IDi, [CERTREQ,]
[IDr,] SAi2, [IDr,] SAi2,
TSi, TSr} --> TSi, TSr} -->
<-- HDR, SK {IDr, [CERT,] AUTH, <-- HDR, SK {IDr, [CERT,] AUTH,
EAP} EAP}
HDR, SK {EAP} --> HDR, SK {EAP} -->
<-- HDR, SK {EAP (success)} <-- HDR, SK {EAP (success)}
HDR, SK {AUTH, HDR, SK {AUTH,
N(PPK_IDENTITY, PPK_ID) N(PPK_IDENTITY, PPK_ID)
[, N(NO_PPK_AUTH)]} --> [, N(NO_PPK_AUTH)]} -->
<-- HDR, SK {AUTH, SAr2, TSi, TSr <-- HDR, SK {AUTH, SAr2, TSi, TSr
[, N(PPK_IDENTITY)]} [, N(PPK_IDENTITY)]}
Note, that the IKE_SA_INIT exchange in case of PPK is as described Note that the diagram above shows both the cases when the responder
above (including exchange of the USE_PPK notifications), regardless uses PPK and when it chooses not to use it (provided the initiator
whether EAP is employed in the IKE_AUTH or not. has included NO_PPK_AUTH notification), and thus the responder's
PPK_IDENTITY notification is marked as optional. Also, note that the
IKE_SA_INIT exchange in case of PPK is as described above (including
exchange of the USE_PPK notifications), regardless whether EAP is
employed in the IKE_AUTH or not.
4. Upgrade procedure 4. Upgrade procedure
This algorithm was designed so that someone can introduce PPKs into This algorithm was designed so that someone can introduce PPKs into
an existing IKE network without causing network disruption. an existing IKE network without causing network disruption.
In the initial phase of the network upgrade, the network In the initial phase of the network upgrade, the network
administrator would visit each IKE node, and configure: administrator would visit each IKE node, and configure:
o The set of PPKs (and corresponding PPK_IDs) that this node would o The set of PPKs (and corresponding PPK_IDs) that this node would
need to know. need to know.
o For each peer that this node would initiate to, which PPK will be o For each peer that this node would initiate to, which PPK will be
used. used.
o That the use of PPK is currently not mandatory. o That the use of PPK is currently not mandatory.
With this configuration, the node will continue to operate with nodes With this configuration, the node will continue to operate with nodes
that have not yet been upgraded. This is due to the USE_PPK notify that have not yet been upgraded. This is due to the USE_PPK
and the NO_PPK_AUTH notify; if the initiator has not been upgraded, notification and the NO_PPK_AUTH notification; if the initiator has
he will not send the USE_PPK notify (and so the responder will know not been upgraded, it will not send the USE_PPK notification (and so
that we will not use a PPK). If the responder has not been upgraded, the responder will know that the peers will not use a PPK). If the
she will not send the USE_PPK notify (and so the initiator will know responder has not been upgraded, it will not send the USE_PPK
to not use a PPK). If both peers have been upgraded, but the notification (and so the initiator will know to not use a PPK). If
responder isn't yet configured with the PPK for the initiator, then both peers have been upgraded, but the responder isn't yet configured
the responder could do standard IKEv2 protocol if the initiator sent with the PPK for the initiator, then the responder could do standard
NO_PPK_AUTH notification. If both the responder and initiator have IKEv2 protocol if the initiator sent NO_PPK_AUTH notification. If
been upgraded and properly configured, they will both realize it, and both the responder and initiator have been upgraded and properly
in that case, the link will be quantum secure. 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 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
skipping to change at page 12, line 9 skipping to change at page 12, line 40
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 to do a look initiator and the responder. The responder can use the PPK_ID to
up the passed PPK_ID value to determine the corresponding PPK look up the corresponding PPK value. Not all implementations are
value. Not all implementations are able to configure arbitrary able to configure arbitrary octet strings; to improve the
octet strings; to improve the potential interoperability, it is potential interoperability, it is recommended that, in the
recommended that, in the PPK_ID_FIXED case, both the PPK and the PPK_ID_FIXED case, both the PPK and the PPK_ID strings be limited
PPK_ID strings be limited to the base64 character set, namely the to the base64 character set, namely the 64 characters 0-9, A-Z,
64 characters 0-9, A-Z, a-z, + and /. a-z, + and /.
The PPK_ID type value 0 is reserved; values 3-127 are reserved for 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 IANA; values 128-255 are for private use among mutually consenting
parties. 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.
5.2.1. PPK Distribution 5.2.1. PPK Distribution
PPK_IDs of the type PPK_ID_FIXED (and the corresponding PPKs) are PPK_IDs of the type PPK_ID_FIXED (and the corresponding PPKs) are
assumed to be configured within the IKE device in an out-of-band assumed to be configured within the IKE device in an out-of-band
fashion. While the method of distribution is a local matter and out fashion. While the method of distribution is a local matter and out
of scope of this document or IKEv2, [RFC6030] describes a format for of scope of this document or IKEv2, [RFC6030] describes a format for
symmetric key exchange. That format could be reused with the Key Id for the transport and provisioning of symmetric keys. That format
field being the PPK_ID (without the PPK_ID Type octet for a could be reused using the PIN profile (defined in Section 10.2 of
PPK_ID_FIXED), the PPK being the secret, and algorithm [RFC6030]) with the "Id" attribute of the <Key> element being the
("Algorithm=urn:ietf:params:xml:ns:keyprov:pskc:pin") as the PIN. PPK_ID (without the PPK_ID Type octet for a PPK_ID_FIXED) and the
<Secret> element containing the PPK.
5.2.2. Group PPK 5.2.2. Group PPK
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 other members' traffic and decrypt it later, when members can record any traffic they have access to that comes from
they get access to a Quantum Computer. other group members and decrypt it later, when they get access to a
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 got 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 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; that
effectively halves the size of a symmetric key. Because of this, the effectively halves the size of a symmetric key. Because of this, the
user SHOULD ensure that the postquantum preshared key used has at user SHOULD ensure that the postquantum preshared key used has at
least 256 bits of entropy, in order to provide 128-bit security least 256 bits of entropy, in order to provide 128 bits of security.
level.
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
skipping to change at page 14, line 43 skipping to change at page 15, line 30
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.
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 might 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 the USE_PPK notification in the response. In this situation, when
initiator aborts negotiation he leaves 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 attack and take protection measures (see
[RFC8019] for more detail). It is RECOMMENDED that implementations [RFC8019] for more detail). In this situation, it is RECOMMENDED
in this situation cache the negative result of negotiation for some that the initiator caches the negative result of the negotiation for
time and don'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 If using PPKs is mandatory for the initiator, then an attacker able
capable to eavesdrop and to inject packets into the network can to eavesdrop and to inject packets into the network can prevent
prevent creating IKE SA by mounting the following attack. The creating an IKE SA by mounting the following attack. The attacker
attacker intercepts the initial request containing the USE_PPK intercepts the initial request containing the USE_PPK notification
notification and injects the forget response containing no USE_PPK. and injects a forged response containing no USE_PPK. If the attacker
If the attacker manages to inject this packet before the responder manages to inject this packet before the responder sends a genuine
sends a genuine response, then the initiator would abort the response, then the initiator would abort the exchange. To thwart
exchange. To thwart this kind of attack it is RECOMMENDED, that if this kind of attack it is RECOMMENDED, that if using PPKs is
using PPKs is mandatory for the initiator and the received response mandatory for the initiator and the received response doesn't contain
doesn't contain the USE_PPK notification, then the initiator doesn't the USE_PPK notification, then the initiator doesn't abort the
abort the exchange immediately, but instead waits some time for more exchange immediately, but instead waits some time for more responses
responses (possibly retransmitting the request). If all the received (possibly retransmitting the request). If all the received responses
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
misconfiguration (e.g. mismatched PPK_ID) the IKE SA will be created
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 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
16436 PPK_IDENTITY 16436 PPK_IDENTITY
16437 NO_PPK_AUTH 16437 NO_PPK_AUTH
This document also creates a new IANA registry for the PPK_ID types. This document also creates a new IANA registry for the PPK_ID types.
The initial values of this registry are: The initial values of this registry are:
PPK_ID Type Value PPK_ID Type Value
----------- ----- ----------- -----
Reserved 0 Reserved 0
PPK_ID_OPAQUE 1 PPK_ID_OPAQUE 1
PPK_ID_FIXED 2 PPK_ID_FIXED 2
Unassigned 3-127 Unassigned 3-127
Reserved for private use 128-255 Reserved for private use 128-255
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, <https://www.rfc- DOI 10.17487/RFC2119, March 1997,
editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T. [RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
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
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
8.2. Informational References 8.2. Informational References
[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-04 (work in Quantum Cryptography", draft-hoffman-c2pq-05 (work in
progress), August 2018. progress), May 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>.
[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, <https://www.rfc- DOI 10.17487/RFC6023, October 2010,
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>.
[RFC7619] Smyslov, V. and P. Wouters, "The NULL Authentication [RFC7619] Smyslov, V. and P. Wouters, "The NULL Authentication
Method in the Internet Key Exchange Protocol Version 2 Method in the Internet Key Exchange Protocol Version 2
(IKEv2)", RFC 7619, DOI 10.17487/RFC7619, August 2015, (IKEv2)", RFC 7619, DOI 10.17487/RFC7619, August 2015,
<https://www.rfc-editor.org/info/rfc7619>. <https://www.rfc-editor.org/info/rfc7619>.
[RFC8019] Nir, Y. and V. Smyslov, "Protecting Internet Key Exchange [RFC8019] Nir, Y. and V. Smyslov, "Protecting Internet Key Exchange
Protocol Version 2 (IKEv2) Implementations from Protocol Version 2 (IKEv2) Implementations from
Distributed Denial-of-Service Attacks", RFC 8019, Distributed Denial-of-Service Attacks", RFC 8019,
DOI 10.17487/RFC8019, November 2016, <https://www.rfc- DOI 10.17487/RFC8019, November 2016,
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
makes the SK_d, and hence the IPsec KEYMAT and any child SA's document makes the SK_d, and hence the IPsec KEYMAT and any child
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, SK_ar values for the initial IKE (except for the SK_ei, SK_er, SK_ai and SK_ar values for the initial
exchange) unless they can find the PPK, which is too difficult if the IKE exchange) unless they can find the PPK, which is too difficult if
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 adjusting of IKEv2. By limiting our changes to notifications, and only
the SK_d, SK_pi, SK_pr, it is hoped that this would be implementable, adjusting the SK_d, SK_pi, SK_pr, it is hoped that this would be
even on systems that perform most of the IKEv2 processing in implementable, even on systems that perform most of the IKEv2
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 resistant 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 goals of A fourth goal was to avoid violating any of the security properties
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
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