Mixing Preshared Keys in the Internet Key Exchange Protocol Version 2 (IKEv2) for Post-quantum SecurityCisco Systemssfluhrer@cisco.comCisco Systemspkampana@cisco.comCisco Systemsmcgrew@cisco.comELVIS-PLUS+7 495 276 0211svan@elvis.ru
Security
Internet Engineering Task Forceinternet key exchangequantum computerpost quantumpost-quantumquantum safequantum securequantum resistantThe possibility of quantum computers poses a serious challenge to
cryptographic algorithms deployed widely today. The Internet Key Exchange
Protocol Version 2 (IKEv2) is one example of a cryptosystem that could
be broken; someone storing VPN communications today could decrypt them
at a later time when a quantum computer is available. It is anticipated
that IKEv2 will be extended to support quantum-secure key exchange
algorithms; however, that is not likely to happen in the near term. To
address this problem before then, this document describes an extension
of IKEv2 to allow it to be resistant to a quantum computer by using
preshared keys.Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by
the Internet Engineering Steering Group (IESG). Further
information on Internet Standards is available in Section 2 of
RFC 7841.
Information about the current status of this document, any
errata, and how to provide feedback on it may be obtained at
.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
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Provisions Relating to IETF Documents
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Table of Contents
. Introduction
. Requirements Language
. Assumptions
. Exchanges
. Upgrade Procedure
. PPK
. PPK_ID Format
. Operational Considerations
. PPK Distribution
. Group PPK
. PPK-Only Authentication
. Security Considerations
. IANA Considerations
. References
. Normative References
. Informative References
. Discussion and Rationale
Acknowledgements
Authors' Addresses
IntroductionRecent achievements in developing quantum computers demonstrate that
it is probably feasible to build one that is cryptographically significant. If
such a computer is implemented, many of the cryptographic algorithms and
protocols currently in use would be insecure. A quantum computer would
be able to solve Diffie-Hellman (DH) and Elliptic Curve Diffie-Hellman
(ECDH) problems in polynomial time , and this would imply that the security of existing
IKEv2 systems would be
compromised. IKEv1 , when used with strong preshared
keys, is not vulnerable to quantum attacks because those keys are one of
the inputs to the key derivation function. If the preshared key has
sufficient entropy and the Pseudorandom Function (PRF), encryption, and authentication
transforms are quantum secure, then the resulting system is believed to
be quantum secure -- that is, secure against classical attackers of
today or future attackers with a quantum computer.This document describes a way to extend IKEv2 to have a similar
property; assuming that the two end systems share a long secret key,
then the
resulting exchange is quantum secure.
By bringing post-quantum security to IKEv2, this document removes the need
to use an obsolete version of IKE in order to achieve
that security goal.The general idea is that we add an additional secret that is shared
between the initiator and the responder; this secret is in addition to
the authentication method that is already provided within IKEv2. We
stir this secret into the SK_d value, which is used to generate the key
material (KEYMAT) for the Child Security Associations (SAs) and the
SKEYSEED for the IKE SAs created as a result
of the initial IKE SA rekey. This secret provides quantum resistance to
the IPsec SAs and any subsequent IKE SAs. We also stir the secret into the SK_pi and SK_pr values;
this allows both sides to detect a secret mismatch cleanly.It was considered important to minimize the changes to IKEv2.
The existing mechanisms to perform authentication and key exchange remain
in place (that is, we continue to perform (EC)DH and potentially PKI
authentication if configured). This document does not replace the authentication
checks that the protocol does; instead, they are
strengthened by using an additional secret key.Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED",
"MAY", and "OPTIONAL" in this document are to be interpreted as
described in BCP 14
when, and only when, they appear in all capitals, as shown here.
Assumptions We assume that each IKE peer has a list of Post-quantum Preshared
Keys (PPKs) along with their identifiers (PPK_ID), and any potential IKE
initiator selects which PPK to use with any specific responder. In
addition, implementations have a configurable flag that determines
whether this PPK is mandatory. This PPK is
independent of the preshared key (if any) that the IKEv2 protocol uses
to perform authentication (because the preshared key in IKEv2 is not
used for any key derivation and thus doesn't protect against quantum
computers). The PPK-specific configuration that is assumed to be on
each node consists of the following tuple:
Peer, PPK, PPK_ID, mandatory_or_not
We assume the reader is familiar with the payload notation defined in
.ExchangesIf the initiator is configured to use a PPK with the responder (whether or not
the use of the PPK is mandatory), then it MUST include a
notification USE_PPK in the IKE_SA_INIT request message as follows:
Initiator Responder
------------------------------------------------------------------
HDR, SAi1, KEi, Ni, N(USE_PPK) --->
N(USE_PPK) is a status notification payload with the type 16435;
it has a protocol ID of 0, no Security Parameter Index (SPI), and no notification data associated with it.If the initiator needs to resend this initial message with a COOKIE notification, then the resend would include the USE_PPK notification
if the original message did (see ).If the responder does not support this specification or does not have any PPK configured,
then it ignores the received notification (as defined in for unknown status notifications)
and continues with the IKEv2 protocol as normal.
Otherwise, the responder replies with the IKE_SA_INIT message, including a USE_PPK notification in the response:
Initiator Responder
------------------------------------------------------------------
<--- HDR, SAr1, KEr, Nr, [CERTREQ,] N(USE_PPK)
When the initiator receives this reply, it checks whether the responder included the USE_PPK notification.
If the responder did not include the USE_PPK notification and the flag mandatory_or_not indicates that using PPKs is mandatory for communication with this responder,
then the initiator MUST abort the exchange. This
situation may happen in case of misconfiguration, i.e., when the
initiator believes it has a mandatory-to-use PPK for the responder and the responder either doesn't support
PPKs at all or doesn't have any PPK configured for the initiator. See for discussion
of the possible impacts of this situation.If the responder did not include the USE_PPK notification and using a PPK for this particular responder is optional,
then the initiator continues with the IKEv2 protocol as normal, without using PPKs.If the responder did include the USE_PPK notification, then the initiator selects a PPK, along with its
identifier PPK_ID. Then, it computes this modification of the standard
IKEv2 key derivation from :
SKEYSEED = prf(Ni | Nr, g^ir)
{SK_d' | SK_ai | SK_ar | SK_ei | SK_er | SK_pi' | SK_pr'}
= prf+ (SKEYSEED, Ni | Nr | SPIi | SPIr)
SK_d = prf+ (PPK, SK_d')
SK_pi = prf+ (PPK, SK_pi')
SK_pr = prf+ (PPK, SK_pr')
That is, we use the standard IKEv2 key derivation process, except
that the three resulting subkeys SK_d, SK_pi, and SK_pr
(marked with primes in the formula above) are then run through the prf+ again, this time using the PPK as the key.
The result is the unprimed versions of these keys, which are then used as inputs to subsequent steps of the
IKEv2 exchange. Using a prf+ construction ensures that it is always possible to get
the resulting keys of the same size as the initial ones, even if the
underlying PRF has an output size different from its key size. Note that
at the time of this writing, all PRFs defined for use in IKEv2 (see the
"Transform Type 2 - Pseudorandom Function Transform IDs" subregistry
) have an output size equal to the (preferred) key size. For such PRFs, only the first
iteration of prf+ is needed:
SK_d = prf (PPK, SK_d' | 0x01)
SK_pi = prf (PPK, SK_pi' | 0x01)
SK_pr = prf (PPK, SK_pr' | 0x01)
Note that the PPK is used in SK_d, SK_pi, and SK_pr calculations only
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 similar
operations.The initiator then sends the IKE_AUTH request message, including the PPK_ID value as follows:
Initiator Responder
------------------------------------------------------------------
HDR, SK {IDi, [CERT,] [CERTREQ,]
[IDr,] AUTH, SAi2,
TSi, TSr, N(PPK_IDENTITY, PPK_ID), [N(NO_PPK_AUTH)]} --->
PPK_IDENTITY is a status notification with the type 16436;
it has a protocol ID of 0, no SPI, and notification data that consists of the identifier PPK_ID.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, the responder cannot continue with the
PPK (in particular, it cannot
authenticate the initiator), but the responder could be able to continue
with the normal IKEv2 protocol if the initiator
provided its authentication data computed as in the normal IKEv2 without using PPKs. For this purpose,
if using PPKs for communication with this responder is optional for the initiator (based on the mandatory_or_not flag),
then the initiator MUST include a NO_PPK_AUTH notification in the above message. This notification informs the responder
that PPKs are optional and allows for authenticating the initiator
without using PPKs.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
the initiator's authentication data computed using SK_pi', which has
been computed without using PPKs. This is the same data that would
normally be placed in the Authentication Data field of an AUTH payload.
Since the Auth Method field is not present in the notification, the
authentication method used for computing the authentication data MUST
be the same as the method indicated in the AUTH payload. Note that if the
initiator decides to include the NO_PPK_AUTH notification, the initiator
needs to perform authentication data computation twice, which may
consume computation power (e.g., if digital signatures are involved).When the responder receives this encrypted exchange, it first computes the values:
SKEYSEED = prf(Ni | Nr, g^ir)
{SK_d' | SK_ai | SK_ar | SK_ei | SK_er | SK_pi' | SK_pr'}
= prf+ (SKEYSEED, Ni | Nr | SPIi | SPIr)
The responder then uses the SK_ei/SK_ai values to decrypt/check the message and then scans through the payloads for the PPK_ID
attached to the PPK_IDENTITY notification. If no PPK_IDENTITY notification is found and the peers successfully
exchanged USE_PPK notifications in the IKE_SA_INIT exchange, then the
responder MUST send back an AUTHENTICATION_FAILED
notification and then fail the negotiation.If the PPK_IDENTITY notification contains a PPK_ID that is not known to the responder or is not configured
for use for the identity from the IDi payload, then the responder checks whether using PPKs for this initiator is mandatory
and whether the initiator included a NO_PPK_AUTH notification in the message. If using PPKs is mandatory or no NO_PPK_AUTH
notification is found, then the responder MUST send
back an AUTHENTICATION_FAILED notification and then fail the negotiation.
Otherwise (when a PPK is optional and the initiator included a NO_PPK_AUTH notification), the responder MAY
continue the regular IKEv2 protocol, except that it uses the data from the NO_PPK_AUTH notification as the
authentication data (which usually resides in the AUTH payload) for the purpose of the initiator authentication.
Note that the authentication method is still indicated in the AUTH payload. summarizes the above logic for the responder:
Received USE_PPK
Received NO_PPK_AUTH
Configured with PPK
PPK is Mandatory
Action
No
*
No
*
Standard IKEv2 protocol
No
*
Yes
No
Standard IKEv2 protocol
No
*
Yes
Yes
Abort negotiation
Yes
No
No
*
Abort negotiation
Yes
Yes
No
Yes
Abort negotiation
Yes
Yes
No
No
Standard IKEv2 protocol
Yes
*
Yes
*
Use PPK
If a PPK is in use, then the responder extracts the corresponding PPK and computes the following values:
SK_d = prf+ (PPK, SK_d')
SK_pi = prf+ (PPK, SK_pi')
SK_pr = prf+ (PPK, SK_pr')
The responder then continues with the IKE_AUTH exchange (validating the AUTH payload that the initiator included) as usual
and sends back a response, which includes the PPK_IDENTITY notification with no data to indicate that the PPK is
used in the exchange:
Initiator Responder
------------------------------------------------------------------
<-- HDR, SK {IDr, [CERT,]
AUTH, SAr2,
TSi, TSr, N(PPK_IDENTITY)}
When the initiator receives the response, it checks for the
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, and
SK_pr (as shown above); the content of the received PPK_IDENTITY (if
any) MUST be ignored. If the initiator does not receive the
PPK_IDENTITY, it MUST either fail the IKE SA negotiation sending the
AUTHENTICATION_FAILED notification in the INFORMATIONAL exchange (if
the PPK was configured as mandatory) or continue without using the
PPK (if the PPK was not configured as mandatory and the initiator
included the NO_PPK_AUTH notification in the request).If the Extensible Authentication Protocol (EAP) is used in the IKE_AUTH exchange, then the initiator doesn't
include the AUTH payload
in the first request message; however, the responder sends back the AUTH payload in the first reply.
The peers then exchange AUTH payloads after EAP is successfully completed.
As a result, the responder sends the AUTH payload twice -- in the first
and last IKE_AUTH reply message -- while the initiator sends the AUTH payload only in the last IKE_AUTH request.
See more details about EAP authentication in IKEv2 in .The general rule for using a PPK in the IKE_AUTH exchange, which
covers the EAP authentication case too, is that the initiator includes a
PPK_IDENTITY (and optionally a NO_PPK_AUTH) notification in the request
message containing the AUTH payload. Therefore, in case of EAP, the
responder always computes the AUTH payload in the first IKE_AUTH reply
message without using a PPK (by means of SK_pr'), since PPK_ID is not
yet known to the responder. Once the IKE_AUTH request message containing
the PPK_IDENTITY notification is received, the responder follows the
rules described above for the non-EAP authentication case.
Initiator Responder
----------------------------------------------------------------
HDR, SK {IDi, [CERTREQ,]
[IDr,] SAi2,
TSi, TSr} -->
<-- HDR, SK {IDr, [CERT,] AUTH,
EAP}
HDR, SK {EAP} -->
<-- HDR, SK {EAP (success)}
HDR, SK {AUTH,
N(PPK_IDENTITY, PPK_ID)
[, N(NO_PPK_AUTH)]} -->
<-- HDR, SK {AUTH, SAr2, TSi, TSr
[, N(PPK_IDENTITY)]}
Note that the diagram above shows both the cases when the responder
uses a PPK and when it chooses not to use it (provided the initiator has
included the NO_PPK_AUTH notification); thus, the responder's
PPK_IDENTITY notification is marked as optional. Also, note that the
IKE_SA_INIT exchange using a PPK is as described above (including
exchange of the USE_PPK notifications), regardless of whether or not EAP is
employed in the IKE_AUTH.Upgrade ProcedureThis algorithm was designed so that someone can introduce PPKs into an existing IKE network
without causing network disruption.In the initial phase of the network upgrade, the network administrator would visit each IKE node and configure:
The set of PPKs (and corresponding PPK_IDs) that this node would need to know.
The PPK that will be used for each peer that this node would
initiate to.
The value "false" for the mandatory_or_not flag for each peer
that this node would initiate to (thus indicating that the use of PPKs
is not mandatory).
With this configuration, the node will continue to operate with nodes that have not yet been upgraded.
This is due to the USE_PPK notification and the NO_PPK_AUTH notification; if the initiator has not been upgraded, it will not send the USE_PPK
notification (and so the responder will know that the peers will not use a PPK). If the responder has not been upgraded, it
will not send the USE_PPK notification (and so the initiator will know to not use a PPK). If both peers
have been upgraded but the responder isn't yet configured with the PPK for the initiator, then the responder
could continue with the standard IKEv2 protocol if the initiator sent a NO_PPK_AUTH notification.
If both the responder and initiator have been upgraded and properly configured, they will both realize it, and the Child SAs will be quantum secure.As an optional second step, after all nodes have been upgraded, the administrator should then go back through
the nodes and mark the use of a PPK as mandatory. This will not affect the strength against a passive attacker, but
it would mean that an active attacker with a quantum computer (which is sufficiently fast to be able to break the (EC)DH
in real time) would not be able to perform a downgrade attack.PPKPPK_ID FormatThis standard requires that both the initiator and the responder
have a secret PPK value, with the responder selecting the PPK based on
the PPK_ID that the initiator sends. In this standard, both the
initiator and the responder are configured with fixed PPK and PPK_ID
values and perform the lookup based on the PPK_ID value. It is anticipated
that later specifications will extend this technique to allow
dynamically changing PPK values. To facilitate such an extension, we
specify that the PPK_ID the initiator sends will have its first octet
be the PPK_ID type value. This document defines two values for the
PPK_ID type:
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 to
be mutually intelligible by both the initiator and the responder.
This PPK_ID type is intended for those implementations that choose
not to disclose the type of PPK to active attackers.
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 a configured value. We assume that there is a fixed mapping
between PPK_ID and PPK, which is configured locally to both the
initiator and the responder. The responder can use the PPK_ID to
look up the corresponding PPK value. Not all implementations are
able to configure arbitrary octet strings; to improve the potential
interoperability, it is recommended that, in the PPK_ID_FIXED case,
both the PPK and the PPK_ID strings be limited to the base64
character set .
Operational ConsiderationsThe need to maintain several independent sets of security credentials can significantly complicate a security administrator's job
and can potentially slow down widespread adoption of this specification. It is anticipated that administrators will try to simplify their job
by decreasing the number of credentials they need to maintain. This section describes some of the considerations for PPK management.PPK DistributionPPK_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 fashion.
While the method of distribution is a local matter and is out of scope of this document or IKEv2, describes a format for the transport and provisioning of symmetric keys. That format
could be reused using the PIN profile (defined in )
with the "Id" attribute of the <Key> element being the PPK_ID (without the PPK_ID type octet for a PPK_ID_FIXED) and the <Secret> element containing the PPK.Group PPKThis document doesn't explicitly require that the PPK be unique for each pair of peers. If this is the case, then this solution provides full
peer authentication, but it also means that each host must have as many independent PPKs as peers it is going to communicate with.
As the number of peers grows, the PPKs will not scale.It is possible to use a single PPK for a group of users. Since
each peer uses classical public key cryptography in addition to a
PPK for key exchange and authentication, members of the group can
neither impersonate each other nor read each other's traffic unless
they use quantum computers to break public key operations. However,
group members can record any traffic they have access to that comes
from other group members and decrypt it later, when they get access
to a quantum computer.In addition, the fact that the PPK is known to a (potentially large) group of users makes it more susceptible to theft.
When an attacker equipped with a quantum computer gets access to a group PPK, all communications inside the group are revealed.For these reasons, using a group PPK is NOT RECOMMENDED.PPK-Only AuthenticationIf quantum computers become a reality, classical public key cryptography will provide little security, so administrators may find it attractive
not to use it at all for authentication.
This will reduce the number of credentials they need to maintain because they
only need to maintain PPK credentials. Combining group PPK and
PPK-only authentication is NOT RECOMMENDED since, in
this case, any member of the group can impersonate any other member,
even without the help
of quantum computers.PPK-only authentication can be achieved in IKEv2 if the NULL
Authentication method is
employed. Without PPK, the NULL Authentication method provides no
authentication of the peers; however, since a PPK is stirred into
the SK_pi and the SK_pr, the peers become authenticated if a PPK is
in use. Using PPKs MUST be mandatory for the peers if
they advertise support for PPKs in IKE_SA_INIT and use NULL
Authentication. Additionally, since the peers are authenticated via
PPKs, the ID Type in the IDi/IDr payloads SHOULD NOT
be ID_NULL, despite using the NULL Authentication method.Security ConsiderationsA critical consideration is how to ensure the randomness of this
post-quantum preshared key. Quantum computers are able to perform Grover's
algorithm ; that effectively halves the size of
a symmetric key. In addition, an adversary impersonating the server,
even with a conventional computer, can perform a dictionary search over
plausible post-quantum preshared key values. The strongest practice is
to ensure that any post-quantum preshared key contains at least 256 bits of
entropy; this will provide 128 bits of post-quantum security, while
providing security against conventional dictionary attacks. That provides the security
equivalent to Category 5 as defined in the NIST Post-Quantum Cryptography
Call for Proposals . Deriving
a post-quantum preshared key from a password, name, or other low-entropy
source is not secure because of these known attacks.With this protocol, the computed SK_d is a function of the
PPK. Assuming that the PPK has sufficient entropy (for example, at least
2256 possible values), even if an attacker was able to recover the
rest of the inputs to the PRF function, it would be infeasible to use
Grover's algorithm with a quantum computer to recover the SK_d value.
Similarly, all keys that are a function of SK_d, which include all Child
SA keys and all keys for subsequent IKE SAs (created when the initial
IKE SA is rekeyed), are also quantum secure (assuming that the PPK was
of high enough entropy and that all the subkeys are sufficiently long).
An attacker with a quantum computer that can decrypt the initial IKE
SA has access to all the information exchanged over it, such as
identities of the peers, configuration parameters, and all negotiated
IPsec SA information (including traffic selectors), with the exception
of the cryptographic keys used by the IPsec SAs, which are protected by
the PPK.
Deployments that treat this information as sensitive or that send other sensitive data (like cryptographic keys)
over IKE SAs MUST rekey the IKE SA before the sensitive information is sent to ensure this information is protected by the PPK.
It is possible to create a childless IKE SA as specified in . This prevents Child SA
configuration information from being transmitted in the original IKE SA that is not protected by a PPK.
Some information related to IKE SA that is sent in the IKE_AUTH exchange, such as peer identities, feature notifications,
vendor IDs, etc., cannot be hidden from the attack described above, even if the additional IKE SA rekey is performed.
In addition, the policy SHOULD be set to negotiate only quantum-secure
symmetric algorithms; while this RFC doesn't claim to give
advice as to what algorithms are secure (as that may change
based on future cryptographical results), below is a list of defined IKEv2 and
IPsec algorithms that should not be used, as they are known to provide less than 128 bits of post-quantum security:
Any IKEv2 encryption algorithm, PRF, or integrity algorithm with a
key size less than 256 bits.
Any ESP transform with a key size less than 256 bits.
PRF_AES128_XCBC and PRF_AES128_CBC: even though they can use as
input a key of arbitrary size, such input keys are converted into a 128-bit key for internal use.
requires the initiator to
abort the initial exchange if using PPKs is mandatory for it but the
responder does not include the USE_PPK notification in the response. In
this situation, when the initiator aborts the negotiation, it leaves a
half-open IKE SA on the responder (because IKE_SA_INIT completes
successfully from the responder's point of view). This half-open SA will
eventually expire 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 a denial-of-service (DoS) attack and take protective
measures (see for more
details). In this situation, it is RECOMMENDED that the
initiator cache the negative result of the negotiation and not attempt
to create it again for some time. This period of time may vary, but it
is believed that waiting for at least few minutes will not cause the
responder to treat it as a DoS attack. Note that this situation would
most likely be a result of misconfiguration, and some reconfiguration of
the peers would probably be needed.If using PPKs is optional for both peers and they authenticate themselves using digital signatures, then
an attacker in between, equipped with a quantum computer capable of breaking public key operations
in real time, is able to mount a downgrade attack by removing the USE_PPK notification from the IKE_SA_INIT
and forging digital signatures in the subsequent exchange. If using PPKs is mandatory for at least one of the peers
or if a preshared key mode is used for authentication, then the attack will be detected
and the SA won't be created.If using PPKs is mandatory for the initiator, then an attacker able
to eavesdrop and inject packets into the network can prevent creation of an
IKE SA by mounting the following attack. The attacker intercepts the
initial request containing the USE_PPK notification and injects a forged
response containing no USE_PPK. If the attacker manages to inject this
packet before the responder sends a genuine response, then the initiator
would abort the exchange. To thwart this kind of attack, it is
RECOMMENDED that, if using PPKs is mandatory for the
initiator and the received response doesn't contain the USE_PPK
notification, the initiator not abort the exchange
immediately. Instead, it waits for more response messages,
retransmitting the request as if no responses were received at all, until
either the received message contains the USE_PPK notification or the exchange times
out (see for more details about retransmission timers in
IKEv2). If none of the received responses contains USE_PPK, then the
exchange is aborted.If using a 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 a PPK was configured but
was not used for a particular IKE SA, then implementations SHOULD audit this event.
IANA ConsiderationsThis document defines three new Notify Message Types in the
"IKEv2 Notify Message Types - Status Types" subregistry under the
"Internet Key Exchange Version 2 (IKEv2) Parameters" registry
:
Value
NOTIFY MESSAGES - STATUS TYPES
Reference
16435
USE_PPK
RFC 8784
16436
PPK_IDENTITY
RFC 8784
16437
NO_PPK_AUTH
RFC 8784
Per this document, IANA has created a new subregistry titled "IKEv2
Post-quantum Preshared Key ID Types" under the "Internet Key Exchange
Version 2 (IKEv2) Parameters" registry . This new subregistry is for the PPK_ID types used in
the PPK_IDENTITY notification defined in this specification. The initial
contents of the new subregistry are as follows:
Value
PPK_ID Type
Reference
0
Reserved
RFC 8784
1
PPK_ID_OPAQUE
RFC 8784
2
PPK_ID_FIXED
RFC 8784
3-127
Unassigned
RFC 8784
128-255
Reserved for Private Use
RFC 8784
The PPK_ID type value 0 is reserved; values 3-127 are to be assigned
by IANA; and values 128-255 are for private use among mutually consenting
parties. To register new PPK_IDs in the Unassigned range, a type name, a
value between 3 and 127, and a reference specification need to be
defined. Changes and additions to the Unassigned range of this registry
are made using the Expert Review policy . Changes and additions to the Reserved for Private Use range of
this registry are made using the Private Use policy .ReferencesNormative ReferencesKey words for use in RFCs to Indicate Requirement LevelsIn many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.Internet Key Exchange Protocol Version 2 (IKEv2)This document describes version 2 of the Internet Key Exchange (IKE) protocol. IKE is a component of IPsec used for performing mutual authentication and establishing and maintaining Security Associations (SAs). This document obsoletes RFC 5996, and includes all of the errata for it. It advances IKEv2 to be an Internet Standard.Ambiguity of Uppercase vs Lowercase in RFC 2119 Key WordsRFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.Informative ReferencesThe Transition from Classical to Post-Quantum CryptographyQuantum computing is the study of computers that use quantum features in calculations. For over 20 years, it has been known that if very large, specialized quantum computers could be built, they could have a devastating effect on asymmetric classical cryptographic algorithms such as RSA and elliptic curve signatures and key exchange, as well as (but in smaller scale) on symmetric cryptographic algorithms such as block ciphers, MACs, and hash functions. There has already been a great deal of study on how to create algorithms that will resist large, specialized quantum computers, but so far, the properties of those algorithms make them onerous to adopt before they are needed. Small quantum computers are being built today, but it is still far from clear when large, specialized quantum computers will be built that can recover private or secret keys in classical algorithms at the key sizes commonly used today. It is important to be able to predict when large, specialized quantum computers usable for cryptanalysis will be possible so that organization can change to post-quantum cryptographic algorithms well before they are needed. This document describes quantum computing, how it might be used to attack classical cryptographic algorithms, and possibly how to predict when large, specialized quantum computers will become feasible.Work in ProgressA Fast Quantum Mechanical Algorithm for Database SearchSTOC '96: Proceedings of the Twenty-Eighth Annual ACM Symposium
on the Theory of Computing, pp. 212-219"Internet Key Exchange Version 2 (IKEv2) ParametersIANASubmission Requirements and Evaluation Criteria for the Post-Quantum Cryptography Standardization ProcessNISTThe Internet Key Exchange (IKE)This memo describes a hybrid protocol. The purpose is to negotiate, and provide authenticated keying material for, security associations in a protected manner. [STANDARDS-TRACK]The Base16, Base32, and Base64 Data EncodingsThis document describes the commonly used base 64, base 32, and base 16 encoding schemes. It also discusses the use of line-feeds in encoded data, use of padding in encoded data, use of non-alphabet characters in encoded data, use of different encoding alphabets, and canonical encodings. [STANDARDS-TRACK]A Childless Initiation of the Internet Key Exchange Version 2 (IKEv2) Security Association (SA)This document describes an extension to the Internet Key Exchange version 2 (IKEv2) protocol that allows an IKEv2 Security Association (SA) to be created and authenticated without generating a Child SA. This document is not an Internet Standards Track specification; it is published for examination, experimental implementation, and evaluation.Portable Symmetric Key Container (PSKC)This document specifies a symmetric key format for the transport and provisioning of symmetric keys to different types of crypto modules. For example, One-Time Password (OTP) shared secrets or symmetric cryptographic keys to strong authentication devices. A standard key transport format enables enterprises to deploy best-of-breed solutions combining components from different vendors into the same infrastructure. [STANDARDS-TRACK]The NULL Authentication Method in the Internet Key Exchange Protocol Version 2 (IKEv2)This document specifies the NULL Authentication method and the ID_NULL Identification Payload ID Type for Internet Key Exchange Protocol version 2 (IKEv2). This allows two IKE peers to establish single-side authenticated or mutual unauthenticated IKE sessions for those use cases where a peer is unwilling or unable to authenticate or identify itself. This ensures IKEv2 can be used for Opportunistic Security (also known as Opportunistic Encryption) to defend against Pervasive Monitoring attacks without the need to sacrifice anonymity.Protecting Internet Key Exchange Protocol Version 2 (IKEv2) Implementations from Distributed Denial-of-Service AttacksThis document recommends implementation and configuration best practices for Internet Key Exchange Protocol version 2 (IKEv2) Responders, to allow them to resist Denial-of-Service and Distributed Denial-of-Service attacks. Additionally, the document introduces a new mechanism called "Client Puzzles" that helps accomplish this task.Guidelines for Writing an IANA Considerations Section in RFCsMany protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA).To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry.This is the third edition of this document; it obsoletes RFC 5226.Discussion and RationaleThe primary goal of this document is to augment the IKEv2 protocol to
provide protection against
quantum computers without requiring novel cryptographic algorithms. The idea behind this document is that while a quantum computer can easily
reconstruct the shared secret of an (EC)DH exchange, it cannot as
easily recover a secret from a symmetric exchange. This document makes the
SK_d (and thus also the IPsec KEYMAT and any subsequent IKE SA's SKEYSEED) depend
on both the symmetric PPK and the Diffie-Hellman exchange.
If we assume that the attacker knows everything except the
PPK during the key exchange and there are 2n plausible PPKs, then
a quantum computer (using Grover's algorithm) would take O(2n/2)
time to recover the PPK. So, even if the (EC)DH can be trivially
solved, the attacker still can't recover any key material
(except for the SK_ei, SK_er, SK_ai, and SK_ar values for the initial IKE exchange) unless they
can find the PPK, which is too difficult if the PPK has enough
entropy (for example, 256 bits).
Note that we do allow an attacker with a quantum computer to
rederive the keying material for the initial IKE SA; this was
a compromise to allow the responder to select the correct PPK quickly. Another goal of this protocol is to minimize the number of changes
within the IKEv2 protocol, in particular, within the cryptography
of IKEv2. By limiting our changes to notifications and only adjusting the
SK_d, SK_pi, and SK_pr, it is hoped that this would be implementable, even
on systems that perform most of the IKEv2 processing in hardware.A third goal is to be friendly to incremental deployment in
operational networks for which we might not want to have a global
shared key or for which quantum-secure IKEv2 is rolled out incrementally. 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.A fourth goal is to avoid violating any of the security properties
provided by IKEv2.AcknowledgementsWe would like to thank , , ,
, , and
the rest of the IPSECME Working Group for their feedback and suggestions
for the scheme.Authors' AddressesCisco Systemssfluhrer@cisco.comCisco Systemspkampana@cisco.comCisco Systemsmcgrew@cisco.comELVIS-PLUS+7 495 276 0211svan@elvis.ru