< draft-ietf-ipsecme-qr-ikev2-02.txt   draft-ietf-ipsecme-qr-ikev2-03.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: August 31, 2018 Cisco Systems Expires: December 20, 2018 Cisco Systems
V. Smyslov V. Smyslov
ELVIS-PLUS ELVIS-PLUS
February 27, 2018 June 18, 2018
Postquantum Preshared Keys for IKEv2 Postquantum Preshared Keys for IKEv2
draft-ietf-ipsecme-qr-ikev2-02 draft-ietf-ipsecme-qr-ikev2-03
Abstract Abstract
The possibility of Quantum Computers pose a serious challenge to The possibility of Quantum Computers pose a serious challenge to
cryptography algorithms deployed widely today. IKEv2 is one example cryptography 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
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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 August 31, 2018. This Internet-Draft will expire on December 20, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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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 . . . . . . . . . . . . . . . . . . 5
2. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Exchanges . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Exchanges . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Upgrade procedure . . . . . . . . . . . . . . . . . . . . . . 10 4. Upgrade procedure . . . . . . . . . . . . . . . . . . . . . . 10
5. PPK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 5. PPK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1. PPK_ID format . . . . . . . . . . . . . . . . . . . . . . 11 5.1. PPK_ID format . . . . . . . . . . . . . . . . . . . . . . 11
5.2. Operational Considerations . . . . . . . . . . . . . . . 12 5.2. Operational Considerations . . . . . . . . . . . . . . . 12
5.2.1. PPK Distribution . . . . . . . . . . . . . . . . . . 12 5.2.1. PPK Distribution . . . . . . . . . . . . . . . . . . 12
5.2.2. Group PPK . . . . . . . . . . . . . . . . . . . . . . 12 5.2.2. Group PPK . . . . . . . . . . . . . . . . . . . . . . 12
5.2.3. PPK-only Authentication . . . . . . . . . . . . . . . 13 5.2.3. PPK-only Authentication . . . . . . . . . . . . . . . 13
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
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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
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) keys and the SKEYSEED for the child SAs; the key material (KEYMAT) and the SKEYSEED for the child SAs; this
this secret provides quantum resistance to the IPsec SAs (and any secret provides quantum resistance to the IPsec SAs (and any child
child IKE SAs). We also stir the secret into the SK_pi, SK_pr IKE SAs). We also stir the secret into the SK_pi, SK_pr values; this
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 a 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, 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-ikev2-03
o Editorial changes and minor text nit fixes.
o Integrated Tommy P. text suggestions.
draft-ietf-ipsecme-qr-ikev2-02 draft-ietf-ipsecme-qr-ikev2-02
o Added note that the PPK is stirred in the initial IKE SA setup o Added note that the PPK is stirred in the initial IKE SA setup
only. only.
o Added note about the initiator ignoring any content in the o Added note about the initiator ignoring any content in the
PPK_IDENTITY notification from the responder. PPK_IDENTITY notification from the responder.
o fixed Tero's suggestions from 2/6/1028 o fixed Tero's suggestions from 2/6/1028
o Added IANA assigned message types where necessary. o Added IANA assigned message types where necessary.
o fixed minor text nits o fixed minor text nits
draft-ietf-ipsecme-qr-ikev2-01
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 draft-ietf-ipsecme-qr-ikev2-00
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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 he 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 If the responder did not include the USE_PPK notification and using a
PPKs for this responder is optional, then the initiator continues PPK for this particular responder is optional, then the initiator
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, she
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')
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 subkeys SK_d, SK_pi, SK_pr are run through the prf+ again,
this time using the PPK as the key. Using prf+ construction ensures this time using the PPK as the key. Using prf+ construction ensures
that it is always possible to get the resulting keys of the same size that it is always possible to get the resulting keys of the same size
as the initial ones, even if the underlying prf has output size as the initial ones, even if the underlying PRF has output size
different from its key size. Note, that at the time this document different from its key size. Note, that at the time this document
was written, all prfs defined for use in IKEv2 [IKEV2-IANA-PRFS] had 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 output size equal to the (preferred) key size. For such PRFs only
the first iteration of prf+ is needed: 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.
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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, she cannot
authenticate the initiator), but she could be able to continue with authenticate the initiator), but she could be able to continue with
normal IKEv2 protocol if the initiator provided its authentication normal IKEv2 protocol if the initiator provided its authentication
data computed as in normal IKEv2, without using PPKs. For this data computed as in normal IKEv2, without using PPKs. For this
purpose, if using PPKs for communication with this responder is purpose, if using PPKs for communication with this responder is
optional for the initiator, then the initiator MAY include a 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. A notification data consists of the protocol ID of 0 and no SPI. The Notification Data field contains
initiator's authentication data computed using SK_pi' (i.e. the data the initiator's authentication data computed using SK_pi', which has
that computed without using PPKs and would normally be placed in the been computed without using PPKs. This is the same data that would
AUTH payload). Authentication Method for computing the normally be placed in the Authentication Data field of an AUTH
authentication data MUST be the same as indicated in the AUTH payload payload. Since the Auth Method field is not present in the
and is not included in the notification. Note that if the initiator notification, the authentication method used for computing the
decides to include NO_PPK_AUTH notification, then it means that the authentication data MUST be the same as method indicated in the AUTH
initiator needs to perform authentication data computation twice that payload. Note that if the initiator decides to include the
may consume substantial computation power (e.g. if digital signatures NO_PPK_AUTH notification, the initiator needs to perform
are involved). authentication data computation twice, which may consume computation
power (e.g. if digital signatures are involved).
When the responder receives this encrypted exchange, she first When the responder receives this encrypted exchange, she 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 She then uses the SK_ei/SK_ai values to decrypt/check the message and
then scans through the payloads for the PPK_ID attached to the then scans through the payloads for the PPK_ID attached to the
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NO_PPK_AUTH notification found, then then the responder MUST send NO_PPK_AUTH notification 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 she 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 by the responder: This table summarizes the above logic for the responder:
Received Received Have PPK Received Received Have PPK
USE_PPK NO_PPK_AUTH PPK Mandatory Action USE_PPK NO_PPK_AUTH PPK Mandatory Action
------------------------------------------------------------------ -----------------------------------------------------------------
No * No * Standard IKEv2 protocol No * No * Standard IKEv2 protocol
No * Yes No Standard IKEv2 protocol No * Yes No Standard IKEv2 protocol
No * Yes Yes Abort negotiation No * Yes Yes Abort negotiation
Yes No No * Abort negotiation Yes No No * Abort negotiation
Yes Yes No Yes Abort negotiation Yes Yes No Yes Abort negotiation
Yes Yes No No Standard IKEv2 protocol Yes Yes No No Standard IKEv2 protocol
Yes * Yes * Use PPK Yes * Yes * Use PPK
If PPK is in use, then the responder extracts corresponding PPK and If PPK is in use, then the responder extracts the corresponding PPK
computes the following values: and computes the following values:
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')
The responder then continues with the IKE_AUTH exchange (validating The responder then continues with the IKE_AUTH exchange (validating
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:
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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 PPK_IDENTITY notification is received, the responder
follows rules described above for non-EAP authentication case. follows rules described above for 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 IKE_SA_INIT exchange in case of PPK is as described
above (including exchange of the USE_PPK notifications), regardless above (including exchange of the USE_PPK notifications), regardless
whether EAP is employed in the IKE_AUTH or not. 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.
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the responder could do standard IKEv2 protocol if the initiator sent the responder could do standard IKEv2 protocol if the initiator sent
NO_PPK_AUTH notification. If both the responder and initiator have NO_PPK_AUTH notification. If both the responder and initiator have
been upgraded and properly configured, they will both realize it, and been upgraded and properly configured, they will both realize it, and
in that case, the link will be quantum secure. in that case, the link 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 may then go back through the nodes, and mark the the administrator may then go back through the nodes, and mark the
use of PPK as mandatory. This will not affect the strength against a use of PPK as mandatory. This will not affect the strength against a
passive attacker; it would mean that an attacker with a Quantum passive attacker; it would mean that an attacker with a Quantum
Computer (which is sufficiently fast to be able to break the (EC)DH Computer (which is sufficiently fast to be able to break the (EC)DH
in real time would not be able to perform a downgrade attack). in real time) would not be able to perform a downgrade attack.
5. PPK 5. PPK
5.1. PPK_ID format 5.1. PPK_ID format
This standard requires that both the initiator and the responder have This standard requires that both the initiator and the responder have
a secret PPK value, with the responder selecting the PPK based on the a secret PPK value, with the responder selecting the PPK based on the
PPK_ID that the initiator sends. In this standard, both the PPK_ID that the initiator sends. In this standard, both the
initiator and the responder are configured with fixed PPK and PPK_ID initiator and the responder are configured with fixed PPK and PPK_ID
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
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PPK_ID strings be limited to the base64 character set, namely the PPK_ID strings be limited to the base64 character set, namely the
64 characters 0-9, A-Z, a-z, + and /. 64 characters 0-9, A-Z, 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 security administrators job, and can can significantly complicate a security administrator's job, and can
potentially slow down widespread adoption of this solution. It is potentially slow down widespread adoption of this specification. It
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 symmetric key exchange. That format could be reused with the Key Id
field being the PPK_ID (without the PPK_ID Type octet for a field being the PPK_ID (without the PPK_ID Type octet for a
PPK_ID_FIXED), the PPK being the secret, and the algorithm PPK_ID_FIXED), the PPK being the secret, and algorithm
("Algorithm=urn:ietf:params:xml:ns:keyprov:pskc:pin") as PIN. ("Algorithm=urn:ietf:params:xml:ns:keyprov:pskc:pin") as the PIN.
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 that peer authentication, but it also means that each host must have as
many independent PPKs, how many peers it is going to communicate many independent PPKs as the peers it is going to communicate with.
with. As the number of hosts grows this will scale badly. As the number of peers grows the PPKs will not scale.
Even though it is NOT RECOMMENDED, it is possible to use a single PPK Even though it is NOT RECOMMENDED, it is possible to use a single PPK
for a group of users. Since each peer uses classical public key for a group of users. Since each peer uses classical public key
cryptography in addition to PPK for key exchange and authentication, cryptography in addition to PPK for key exchange and authentication,
members of the group can neither impersonate each other nor read members of the group can neither impersonate each other nor read
other's traffic, unless they use Quantum Computers to break public other's traffic, unless they use Quantum Computers to break public
key operations. key operations.
Although it's probably safe to use group PPK in short term, the fact, Although it's probably safe to use group PPK, the fact that the PPK
that the PPK is known to a (potentially large) group of users makes is known to a (potentially large) group of users makes it more
it more susceptible to theft. If an attacker equipped with a Quantum susceptible to theft. If an attacker equipped with a Quantum
Computer got access to a group PPK, then all the communications Computer got access to a group PPK, then all communications inside
inside the group are revealed. the group are revealed.
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 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 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 a 128-bit security least 256 bits of entropy, in order to provide 128-bit security
level. level.
With this protocol, the computed SK_d is a function of the PPK, and 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, every child SA key is a function of SK_d, hence value. Similarly, every child SA key is a function of SK_d, hence
all the keys for all the child SAs are also quantum resistant all the keys for all the child SAs are also quantum resistant
(assuming that the PPK was high entropy and secret, and that all the (assuming that the PPK was of high enough entropy, and that all the
subkeys are sufficiently long). subkeys are sufficiently long).
Although this protocol preserves all the security properties of IKEv2 Although this protocol preserves all the security properties of IKEv2
against adversaries with conventional computers, it allows an against adversaries with conventional computers, it allows an
adversary with a Quantum Computer to decrypt all traffic encrypted adversary with a Quantum Computer to decrypt all traffic encrypted
with the initial IKE SA. In particular, it allows the adversary to with the initial IKE SA. In particular, it allows the adversary to
recover the identities of both sides. If there is IKE traffic other recover the identities of both sides. If there is IKE traffic other
than the identities that need to be protected against such an than the identities that need to be protected against such an
adversary, implementations MAY rekey the initial IKE SA immediately adversary, implementations MAY rekey the initial IKE SA immediately
after negotiating it to generate a new SKEYSEED from the postquantum after negotiating it to generate a new SKEYSEED from the postquantum
SK_d. This would reduce the amount of data available to an attacker SK_d. This would reduce the amount of data available to an attacker
with a Quantum Computer. with a Quantum Computer.
If sensitive information (like keys) is to be transferred over IKE
SA, then implementations MUST rekey the initial IKE SA before sending
this information to get protection against Quantum Computers.
Alternatively, an initial IKE SA (which is used to exchange Alternatively, an initial IKE SA (which is used to exchange
identities) can take place, perhaps by using the protocol documented identities) can take place, perhaps by using the protocol documented
in [RFC6023]. After the childless IKE SA is created, implementations in [RFC6023]. After the childless IKE SA is created, implementations
would immediately create a new IKE SA (which is used to exchange would immediately create a new IKE SA (which is used to exchange
everything else) by using a rekey mechanism for IKE SAs. Because the everything else) by using a rekey mechanism for IKE SAs. Because the
rekeyed IKE SA keys are a function of SK_d, which is a function of rekeyed IKE SA keys are a function of SK_d, which is a function of
the PPK (among other things), traffic protected by that IKE SA is the PPK (among other things), traffic protected by that IKE SA is
secure against Quantum capable adversaries. secure against Quantum capable adversaries.
If some sensitive information (like keys) is to be transferred over
IKE SA, then implementations MUST rekey the initial IKE SA before
sending this information to get protection against Quantum Computers.
In addition, the policy SHOULD be set to negotiate only quantum- In addition, the policy SHOULD be set to negotiate only quantum-
resistant symmetric algorithms; while this RFC doesn't claim to give resistant symmetric algorithms; while this RFC doesn't claim to give
advise as to what algorithms are secure (as that may change based on advice as to what algorithms are secure (as that may change based on
future cryptographical results), below is a list of defined IKEv2 and future cryptographical results), below is a list of defined IKEv2 and
IPsec algorithms that should NOT be used, as they are known not to be IPsec algorithms that should NOT be used, as they are known not to be
quantum resistant quantum resistant
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 didn't include the using PPKs is mandatory for it, but the responder might not include
USE_PPK notification in the response. In this situation when the the USE_PPK notification in the response. In this situation when the
initiator aborts negotiation he leaves half-open IKE SA on the initiator aborts negotiation he leaves half-open IKE SA on the
responder (because IKE_SA_INIT completes successfully from 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 some measures (see [RFC8019] for a Denial-of-Service attack and take protection measures (see
more detail). It is RECOMMENDED that implementations in this [RFC8019] for more detail). It is RECOMMENDED that implementations
situation cache the negative result of negotiation for some time and in this situation cache the negative result of negotiation for some
don't make attempts to create it again for some time, because this is time and don't make attempts to create it again for some time,
a result of misconfiguration and probably some re-configuration of because this is a result of misconfiguration and probably some re-
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
capable to eavesdrop and to inject packets into the network can capable to eavesdrop and to inject packets into the network can
prevent creating IKE SA by mounting the following attack. The prevent creating IKE SA by mounting the following attack. The
attacker intercepts the the initial request containing the USE_PPK attacker intercepts the initial request containing the USE_PPK
notification and injects the forget response containing no USE_PPK. notification and injects the forget response containing no USE_PPK.
If the attacker manages to inject this packet before the responder If the attacker manages to inject this packet before the responder
sends a genuine response, then the initiator would abort the sends a genuine response, then the initiator would abort the
exchange. To thwart this kind of attack it is RECOMMENDED, that if exchange. To thwart this kind of attack it is RECOMMENDED, that if
using PPKs is mandatory for the initiator and the received response using PPKs is mandatory for the initiator and the received response
doesn't contain the USE_PPK notification, then the initiator doesn't doesn't contain the USE_PPK notification, then the initiator doesn't
abort exchange immediately, but instead waits some time for more abort the exchange immediately, but instead waits some time for more
responses (possibly retransmitting the request). If all the received responses (possibly retransmitting the request). If all the received
responses contain no USE_PPK, then the exchange is aborted. responses contain no USE_PPK, then the exchange is aborted.
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
skipping to change at page 16, line 20 skipping to change at page 16, line 20
[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>.
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-02 (work in Quantum Cryptography", draft-hoffman-c2pq-03 (work in
progress), August 2017. progress), February 2018.
[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>.
skipping to change at page 17, line 34 skipping to change at page 17, line 34
exchange) unless they can find the PPK, which is too difficult if the exchange) unless they can find the PPK, which is too difficult if the
PPK has enough entropy (for example, 256 bits). Note that we do 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 adjusting
the SK_d, SK_pi, SK_pr, it is hoped that this would be implementable, the SK_d, SK_pi, SK_pr, it is hoped that this would be implementable,
even on systems that perform much of the IKEv2 processing is in even on systems that perform most of the IKEv2 processing in
hardware. 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 goals of
IKEv2. 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,
and the rest of the IPSecME Working Group for their feedback and Tommy Pauly and the rest of the IPSecME Working Group for their
suggestions for the scheme. 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 David McGrew
Cisco Systems Cisco Systems
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