< draft-ietf-ipsecme-ikev2-intermediate-07.txt   draft-ietf-ipsecme-ikev2-intermediate-08.txt >
Network Working Group V. Smyslov Network Working Group V. Smyslov
Internet-Draft ELVIS-PLUS Internet-Draft ELVIS-PLUS
Intended status: Standards Track August 3, 2021 Intended status: Standards Track February 2, 2022
Expires: February 4, 2022 Expires: August 6, 2022
Intermediate Exchange in the IKEv2 Protocol Intermediate Exchange in the IKEv2 Protocol
draft-ietf-ipsecme-ikev2-intermediate-07 draft-ietf-ipsecme-ikev2-intermediate-08
Abstract Abstract
This documents defines a new exchange, called Intermediate Exchange, This documents defines a new exchange, called Intermediate Exchange,
for the Internet Key Exchange protocol Version 2 (IKEv2). This for the Internet Key Exchange protocol Version 2 (IKEv2). This
exchange can be used for transferring large amount of data in the exchange can be used for transferring large amounts of data in the
process of IKEv2 Security Association (SA) establishment. process of IKEv2 Security Association (SA) establishment.
Introducing Intermediate Exchange allows re-using existing IKE Introducing the Intermediate Exchange allows re-using the existing
fragmentation mechanism, that helps to avoid IP fragmentation of IKE fragmentation mechanism, that helps to avoid IP fragmentation of
large IKE messages, but cannot be used in the initial IKEv2 exchange. large IKE messages, but cannot be used in the initial IKEv2 exchange.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 4, 2022. This Internet-Draft will expire on August 6, 2022.
Copyright Notice Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the Copyright (c) 2022 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
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carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
skipping to change at page 2, line 19 skipping to change at page 2, line 19
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology and Notation . . . . . . . . . . . . . . . . . . 3 2. Terminology and Notation . . . . . . . . . . . . . . . . . . 3
3. Intermediate Exchange Details . . . . . . . . . . . . . . . . 3 3. Intermediate Exchange Details . . . . . . . . . . . . . . . . 3
3.1. Support for Intermediate Exchange Negotiation . . . . . . 3 3.1. Support for Intermediate Exchange Negotiation . . . . . . 3
3.2. Using Intermediate Exchange . . . . . . . . . . . . . . . 4 3.2. Using Intermediate Exchange . . . . . . . . . . . . . . . 4
3.3. The IKE_INTERMEDIATE Exchange Protection and 3.3. The IKE_INTERMEDIATE Exchange Protection and
Authentication . . . . . . . . . . . . . . . . . . . . . 5 Authentication . . . . . . . . . . . . . . . . . . . . . 5
3.3.1. Protection of the IKE_INTERMEDIATE Messages . . . . . 5 3.3.1. Protection of the IKE_INTERMEDIATE Messages . . . . . 5
3.3.2. Authentication of the IKE_INTERMEDIATE Exchanges . . 5 3.3.2. Authentication of the IKE_INTERMEDIATE Exchanges . . 5
3.4. Error Handling in the IKE_INTERMEDIATE Exchange . . . . . 9 3.4. Error Handling in the IKE_INTERMEDIATE Exchange . . . . . 9
4. Interaction with other IKEv2 Extensions . . . . . . . . . . . 9 4. Interaction with other IKEv2 Extensions . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7. Implementation Status . . . . . . . . . . . . . . . . . . . . 10 7. Implementation Status . . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
9.1. Normative References . . . . . . . . . . . . . . . . . . 11 9.1. Normative References . . . . . . . . . . . . . . . . . . 12
9.2. Informative References . . . . . . . . . . . . . . . . . 11 9.2. Informative References . . . . . . . . . . . . . . . . . 12
Appendix A. Example of IKE_INTERMEDIATE exchange . . . . . . . . 11 Appendix A. Example of IKE_INTERMEDIATE exchange . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 13 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction 1. Introduction
The Internet Key Exchange protocol version 2 (IKEv2) defined in The Internet Key Exchange protocol version 2 (IKEv2) defined in
[RFC7296] uses UDP as a transport for its messages. If size of a [RFC7296] uses UDP as a transport for its messages. If size of a
message is large enough, IP fragmentation takes place, that may message is large enough, IP fragmentation takes place, that may
interfere badly with some network devices. The problem is described interfere badly with some network devices. The problem is described
in more detail in [RFC7383], which also defines an extension to the in more detail in [RFC7383], which also defines an extension to IKEv2
IKEv2 called IKE fragmentation. This extension allows IKE messages called IKE fragmentation. This extension allows IKE messages to be
to be fragmented at IKE level, eliminating possible issues caused by fragmented at the IKE level, eliminating possible issues caused by IP
IP fragmentation. However, the IKE fragmentation cannot be used in fragmentation. However, IKE fragmentation cannot be used in the
the initial IKEv2 exchange (IKE_SA_INIT). This limitation in most initial IKEv2 exchange (IKE_SA_INIT). This limitation in most cases
cases is not a problem, since the IKE_SA_INIT messages used to be is not a problem, since the IKE_SA_INIT messages are usually small
small enough not to cause IP fragmentation. enough not to cause IP fragmentation.
However, the situation has been changing recently. One example of However, the situation has been changing recently. One example of
the need to transfer large amount of data before IKE SA is created is the need to transfer large amount of data before an IKE SA is created
using Quantum Computer resistant key exchange methods in IKEv2. is using Quantum Computer resistant key exchange methods in IKEv2.
Recent progress in Quantum Computing has brought a concern that Recent progress in Quantum Computing has brought a concern that
classical Diffie-Hellman key exchange methods will become insecure in classical Diffie-Hellman key exchange methods will become insecure in
a relatively near future and should be replaced with Quantum Computer a relatively near future and should be replaced with Quantum Computer
(QC) resistant ones. Currently most of QC-resistant key exchange (QC) resistant ones. Currently most QC-resistant key exchange
methods have large public keys. If these keys are exchanged in the methods have large public keys. If these keys are exchanged in the
IKE_SA_INIT, then most probably IP fragmentation will take place, IKE_SA_INIT, then most probably IP fragmentation will take place,
therefore all the problems caused by it will become inevitable. therefore all the problems caused by it will become inevitable.
A possible solution to the problem would be to use TCP as a transport A possible solution to the problem would be to use TCP as a transport
for IKEv2, as defined in [RFC8229]. However this approach has for IKEv2, as defined in [RFC8229]. However this approach has
significant drawbacks and is intended to be a "last resort" when UDP significant drawbacks and is intended to be a "last resort" when UDP
transport is completely blocked by intermediate network devices. transport is completely blocked by intermediate network devices.
This specification describes a way to transfer large amount of data This specification describes a way to transfer a large amount of data
in IKEv2 using UDP transport. For this purpose the document defines in IKEv2 using UDP transport. For this purpose the document defines
a new exchange for the IKEv2 protocol, called Intermediate Exchange a new exchange for the IKEv2 protocol, called Intermediate Exchange
or IKE_INTERMEDIATE. One or more these exchanges may take place or IKE_INTERMEDIATE. One or more these exchanges may take place
right after the IKE_SA_INIT exchange and prior to the IKE_AUTH right after the IKE_SA_INIT exchange and prior to the IKE_AUTH
exchange. The IKE_INTERMEDIATE exchange messages can be fragmented exchange. The IKE_INTERMEDIATE exchange messages can be fragmented
using IKE fragmentation mechanism, so these exchanges may be used to using the IKE fragmentation mechanism, so these exchanges may be used
transfer large amounts of data which don't fit into the IKE_SA_INIT to transfer large amounts of data which don't fit into the
exchange without causing IP fragmentation. IKE_SA_INIT exchange without causing IP fragmentation.
The Intermediate Exchange can be used to transfer large public keys The Intermediate Exchange can be used to transfer large public keys
of QC-resistant key exchange methods, but its application is not of QC-resistant key exchange methods, but its application is not
limited to this use case. This exchange can also be used whenever limited to this use case. This exchange can also be used whenever
some data need to be transferred before the IKE_AUTH exchange and for some data need to be transferred before the IKE_AUTH exchange and for
some reason the IKE_SA_INIT exchange is not suited for this purpose. some reason the IKE_SA_INIT exchange is not suited for this purpose.
This document defines the IKE_INTERMEDIATE exchange without tying it This document defines the IKE_INTERMEDIATE exchange without tying it
to any specific use case. It is expected that separate to any specific use case. It is expected that separate
specifications will define for which purposes and how the specifications will define for which purposes and how the
IKE_INTERMEDIATE exchange is used in the IKEv2. IKE_INTERMEDIATE exchange is used in IKEv2.
2. Terminology and Notation 2. Terminology and Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
It is expected that readers are familiar with the terms used in the It is expected that readers are familiar with the terms used in the
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Initiator Responder Initiator Responder
----------- ----------- ----------- -----------
HDR, SAi1, KEi, Ni, HDR, SAi1, KEi, Ni,
[N(INTERMEDIATE_EXCHANGE_SUPPORTED)] --> [N(INTERMEDIATE_EXCHANGE_SUPPORTED)] -->
<-- HDR, SAr1, KEr, Nr, [CERTREQ], <-- HDR, SAr1, KEr, Nr, [CERTREQ],
[N(INTERMEDIATE_EXCHANGE_SUPPORTED)] [N(INTERMEDIATE_EXCHANGE_SUPPORTED)]
The INTERMEDIATE_EXCHANGE_SUPPORTED is a Status Type IKEv2 The INTERMEDIATE_EXCHANGE_SUPPORTED is a Status Type IKEv2
notification. Its Notify Message Type is 16438, Protocol ID and SPI notification. Its Notify Message Type is 16438, Protocol ID and SPI
Size are both set to 0. This specification doesn't define any data Size are both set to 0. This specification doesn't define any data
this notification may contain, so the Notification Data is left that this notification may contain, so the Notification Data is left
empty. However, future enhancements of this specification may empty. However, future enhancements to this specification may
override this. Implementations MUST ignore the non-empty override this. Implementations MUST ignore non-empty Notification
Notification Data if they don't understand its purpose. Data if they don't understand its purpose.
3.2. Using Intermediate Exchange 3.2. Using Intermediate Exchange
If both peers indicated their support for the Intermediate Exchange, If both peers indicated their support for the Intermediate Exchange,
the initiator may use one or more these exchanges to transfer the initiator may use one or more these exchanges to transfer
additional data. Using the Intermediate Exchange is optional, the additional data. Using the Intermediate Exchange is optional; the
initiator may find it unnecessary even when support for this initiator may find it unnecessary even when support for this
exchanged has been already negotiated. exchanged has been negotiated.
The Intermediate Exchange is denoted as IKE_INTERMEDIATE, its The Intermediate Exchange is denoted as IKE_INTERMEDIATE, its
Exchange Type is 43. Exchange Type is 43.
Initiator Responder Initiator Responder
----------- ----------- ----------- -----------
HDR, ..., SK {...} --> HDR, ..., SK {...} -->
<-- HDR, ..., SK {...} <-- HDR, ..., SK {...}
The initiator may use several IKE_INTERMEDIATE exchanges if The initiator may use several IKE_INTERMEDIATE exchanges if
necessary. Since window size is initially set to one for both peers necessary. Since window size is initially set to one for both peers
(Section 2.3 of [RFC7296]), these exchanges MUST follow each other (Section 2.3 of [RFC7296]), these exchanges MUST follow each other
and MUST all be completed before the IKE_AUTH exchange is initiated. and MUST all be completed before the IKE_AUTH exchange is initiated.
The IKE SA MUST NOT be considered as established until the IKE_AUTH The IKE SA MUST NOT be considered as established until the IKE_AUTH
exchange is successfully completed. exchange is successfully completed.
The Message IDs for IKE_INTERMEDIATE exchanges MUST be chosen The Message IDs for IKE_INTERMEDIATE exchanges MUST be chosen
according to the standard IKEv2 rule, described in the Section 2.2. according to the standard IKEv2 rule, described in the Section 2.2.
of [RFC7296], i.e. it is set to 1 for the first IKE_INTERMEDIATE of [RFC7296], i.e. it is set to 1 for the first IKE_INTERMEDIATE
exchange, 2 for the next (if any) and so on. The Message ID for the exchange, 2 for the next (if any) and so on. Implementations MUST
first pair of the IKE_AUTH messages is one more than the value used verify that Message IDs in the IKE_INTERMEDIATE messages they receive
in the last IKE_INTERMEDIATE exchange. actually follow this rule. The Message ID for the first pair of the
IKE_AUTH messages is one more than the value used in the last
IKE_INTERMEDIATE exchange.
If the presence of NAT is detected in the IKE_SA_INIT exchange via If the presence of NAT is detected in the IKE_SA_INIT exchange via
NAT_DETECTION_SOURCE_IP and NAT_DETECTION_DESTINATION_IP NAT_DETECTION_SOURCE_IP and NAT_DETECTION_DESTINATION_IP
notifications, then the peers MUST switch to port 4500 and send all notifications, then the peers switch to port 4500 in the first
IKE_INTERMEDIATE exchanges using port 4500. IKE_INTERMEDIATE exchange and use this port for all subsequent
exchanges, as described in Section 2.23 of [RFC7296].
The content of the IKE_INTERMEDIATE exchange messages depends on the The content of the IKE_INTERMEDIATE exchange messages depends on the
data being transferred and will be defined by specifications data being transferred and will be defined by specifications
utilizing this exchange. However, since the main motivation for the utilizing this exchange. However, since the main motivation for the
IKE_INTERMEDIATE exchange is to avoid IP fragmentation when large IKE_INTERMEDIATE exchange is to avoid IP fragmentation when large
amount of data need to be transferred prior to IKE_AUTH, the amounts of data need to be transferred prior to IKE_AUTH, the
Encrypted payload MUST be present in the IKE_INTERMEDIATE exchange Encrypted payload MUST be present in the IKE_INTERMEDIATE exchange
messages and payloads containing large data MUST be placed inside it. messages and payloads containing large data MUST be placed inside it.
This will allow IKE fragmentation [RFC7383] to take place, provided This will allow IKE fragmentation [RFC7383] to take place, provided
it is supported by the peers and negotiated in the initial exchange. it is supported by the peers and negotiated in the initial exchange.
Appendix A contains an example of using IKE_INTERMEDIATE exchange in Appendix A contains an example of using an IKE_INTERMEDIATE exchange
creating IKE SA. in creating an IKE SA.
3.3. The IKE_INTERMEDIATE Exchange Protection and Authentication 3.3. The IKE_INTERMEDIATE Exchange Protection and Authentication
3.3.1. Protection of the IKE_INTERMEDIATE Messages 3.3.1. Protection of the IKE_INTERMEDIATE Messages
The keys SK_e[i/r] and SK_a[i/r] for the IKE_INTERMEDIATE exchanges The keys SK_e[i/r] and SK_a[i/r] for the IKE_INTERMEDIATE exchanges
protection are computed in a standard fashion, as defined in the protection are computed in the standard fashion, as defined in the
Section 2.14 of [RFC7296]. Section 2.14 of [RFC7296].
Every subsequent IKE_INTERMEDIATE exchange uses the most recently Every subsequent IKE_INTERMEDIATE exchange uses the most recently
calculated IKE SA keys before this exchange is started. So, the calculated IKE SA keys before this exchange is started. So, the
first IKE_INTERMEDIATE exchange always uses SK_e[i/r] and SK_a[i/r] first IKE_INTERMEDIATE exchange always uses SK_e[i/r] and SK_a[i/r]
keys that were computed as a result of the IKE_SA_INIT exchange. If keys that were computed as a result of the IKE_SA_INIT exchange. If
additional key exchange is performed in the first IKE_INTERMEDIATE additional key exchange is performed in the first IKE_INTERMEDIATE
exchange resulting in the update of SK_e[i/r] and SK_a[i/r], then exchange, resulting in the update of SK_e[i/r] and SK_a[i/r], then
these updated keys are used for protection of the second these updated keys are used for protection of the second
IKE_INTERMEDIATE exchange, otherwise the original SK_e[i/r] and IKE_INTERMEDIATE exchange. Otherwise, the original SK_e[i/r] and
SK_a[i/r] keys are used again, and so on. SK_a[i/r] keys are used again, and so on.
Once all the IKE_INTERMEDIATE exchanges are completed, the most Once all the IKE_INTERMEDIATE exchanges are completed, the most
recently calculated SK_e[i/r] and SK_a[i/r] keys are used for recently calculated SK_e[i/r] and SK_a[i/r] keys are used for
protection of the IKE_AUTH and all the subsequent exchanges. protection of the IKE_AUTH and all the subsequent exchanges.
3.3.2. Authentication of the IKE_INTERMEDIATE Exchanges 3.3.2. Authentication of the IKE_INTERMEDIATE Exchanges
The IKE_INTERMEDIATE messages must be authenticated in the IKE_AUTH The IKE_INTERMEDIATE messages must be authenticated in the IKE_AUTH
exchange, which is performed by adding their content into the AUTH exchange, which is performed by adding their content into the AUTH
payload calculation. It is anticipated that in many use cases payload calculation. It is anticipated that in many use cases
IKE_INTERMEDIATE messages will be fragmented using IKE fragmentation IKE_INTERMEDIATE messages will be fragmented using IKE fragmentation
[RFC7383] mechanism. According to [RFC7383], when IKE fragmentation [RFC7383] mechanism. According to [RFC7383], when IKE fragmentation
is negotiated, initiator may first send request message in is negotiated, the initiator may first send a request message in
unfragmented form, but later turn IKE fragmentation on and re-send it unfragmented form, but later turn on IKE fragmentation and re-send it
fragmented if no response is received after few retransmissions. In fragmented if no response is received after a few retransmissions.
addition, peers may re-send fragmented message using different In addition, peers may re-send fragmented message using different
fragment sizes to perform simple PMTU discovery. fragment sizes to perform simple PMTU discovery.
The requirement to support this behavior makes authentication The requirement to support this behavior makes authentication
challenging: it is not appropriate to add on-the-wire content of the challenging: it is not appropriate to add on-the-wire content of the
IKE_INTERMEDIATE messages into the AUTH payload calculation, because IKE_INTERMEDIATE messages into the AUTH payload calculation, because
peers generally are unaware in which form other side has received peers generally are unaware in which form other side has received
them. Instead, a more complex scheme is used - authentication is them. Instead, a more complex scheme is used -- authentication is
performed by adding content of these messages before their encryption performed by adding content of these messages before their encryption
and possible fragmentation, so that data to be authenticated doesn't and possible fragmentation, so that data to be authenticated doesn't
depend on the form the messages are delivered in. depend on the form the messages are delivered in.
If any IKE_INTERMEDIATE exchange took place, the definition of the If any IKE_INTERMEDIATE exchange took place, the definition of the
blob to be signed (or MAC'ed) from the Section 2.15 of [RFC7296] is blob to be signed (or MAC'ed) from the Section 2.15 of [RFC7296] is
modified as follows: modified as follows:
InitiatorSignedOctets = RealMsg1 | NonceRData | MACedIDForI | IntAuth InitiatorSignedOctets = RealMsg1 | NonceRData | MACedIDForI | IntAuth
ResponderSignedOctets = RealMsg2 | NonceIData | MACedIDForR | IntAuth ResponderSignedOctets = RealMsg2 | NonceIData | MACedIDForR | IntAuth
IntAuth = IntAuth_1 [| IntAuth_2 [| IntAuth_3 ... ]] IntAuth = IntAuth_iN | IntAuth_rN | IKE_AUTH_MID
IntAuth_1 = IntAuth_1_I | IntAuth_1_R IntAuth_i1 = prf(SK_pi1, IntAuth_i1A [| IntAuth_i1P])
IntAuth_2 = IntAuth_2_I | IntAuth_2_R IntAuth_i2 = prf(SK_pi2, IntAuth_i1 | IntAuth_i2A [| IntAuth_i2P])
IntAuth_3 = IntAuth_3_I | IntAuth_3_R IntAuth_i3 = prf(SK_pi3, IntAuth_i2 | IntAuth_i3A [| IntAuth_i3P])
... ...
IntAuth_iN = prf(SK_piN, IntAuth_iN-1 | IntAuth_iNA [| IntAuth_iNP])
IntAuth_1_I = prf(SK_pi_1, IntAuth_1_I_A [| IntAuth_1_I_P]) IntAuth_r1 = prf(SK_pr1, IntAuth_r1A [| IntAuth_r1P])
IntAuth_2_I = prf(SK_pi_2, IntAuth_2_I_A [| IntAuth_2_I_P]) IntAuth_r2 = prf(SK_pr2, IntAuth_r1 | IntAuth_r2A [| IntAuth_r2P])
IntAuth_3_I = prf(SK_pi_3, IntAuth_3_I_A [| IntAuth_3_I_P]) IntAuth_r3 = prf(SK_pr3, IntAuth_r2 | IntAuth_r3A [| IntAuth_r3P])
... ...
IntAuth_rN = prf(SK_prN, IntAuth_rN-1 | IntAuth_rNA [| IntAuth_rNP])
IntAuth_1_R = prf(SK_pr_1, IntAuth_1_R_A [| IntAuth_1_R_P]) The essence of this modification is that a new chunk called IntAuth
IntAuth_2_R = prf(SK_pr_2, IntAuth_2_R_A [| IntAuth_2_R_P]) is appended to the string of octets that is signed (or MAC'ed) by the
IntAuth_3_R = prf(SK_pr_3, IntAuth_3_R_A [| IntAuth_3_R_P]) peers. IntAuth consists of three parts: IntAuth_iN, IntAuth_rN, and
... IKE_AUTH_MID.
IntAuth_1_I/IntAuth_1_R, IntAuth_2_I/IntAuth_2_R, IntAuth_3_I/ The IKE_AUTH_MID chunk is a value of the Message ID field from the
IntAuth_3_R, etc. represent the results of applying the negotiated IKE Header of the first round of the IKE_AUTH exchange. It is
prf to the content of the IKE_INTERMEDIATE messages sent by the represented as a four octet integer in network byte order (in other
initiator (IntAuth_*_I) and by the responder (IntAuth_*_R) in an words, exactly as it appears on the wire).
order of increasing their Message IDs (i.e. in an order the
IKE_INTERMEDIATE exchanges took place). The prf is applied to the The IntAuth_iN and IntAuth_rN chunks each represent the cumulative
the concatenation of two chunks of data: mandatory IntAuth_*_[I/R]_A result of applying the negotiated prf to all IKE_INTERMEDIATE
optionally followed by IntAuth_*_[I/R]_P. The IntAuth_*_[I/R]_A exchange messages sent during IKE SA establishing by the initiator
chunk lasts from the first octet of the IKE Header (not including and the responder respectively. After the first IKE_INTERMEDIATE
prepended four octets of zeros, if port 4500 is used) to the last exchange is completed peers calculate the IntAuth_i1 value by
octet of the Encrypted payload header. The IntAuth_*_[I/R]_P chunk applying the negotiated prf to the content of the request message
is present if the Encrypted payload is not empty. It consists of the from this exchange and calculate the IntAuth_r1 value by applying the
content of the Encrypted payload that is fully formed, but not yet negotiated prf to the content of the response message. For every
encrypted. The Initialization Vector, the Padding, the Pad Length following IKE_INTERMEDIATE exchange (if any) peers re-calculate these
and the Integrity Checksum Data fields (see Section 3.14 of values as follows. After n-th exchange is completed they compute
[RFC7296]) are not included into the calculation. In other words, IntAuth_[i/r]n by applying the negotiated prf to the concatenation of
the IntAuth_*_[I/R]_P chunk is the inner payloads of the Encrypted IntAuth_[i/r](n-1) (computed for the previous IKE_INTERMEDIATE
payload in plaintext form. exchange) and the content of the request (for IntAuth_in) or response
(for IntAuth_rn) messages from this exchange. After all
IKE_INTERMEDIATE exchanges are over the resulted IntAuth_[i/r]N
values (assuming N exchanges took place) are used in the computing
the AUTH payload.
For the purpose of calculating the IntAuth_[i/r]* values the content
of the IKE_INTERMEDIATE messages is represented as two chunks of
data: mandatory IntAuth_[i/r]*A optionally followed by IntAuth_[i/
r]*P.
The IntAuth_[i/r]*A chunk lasts from the first octet of the IKE
Header (not including prepended four octets of zeros, if UDP
encapsulation or TCP encapsulation of ESP packets is used) to the
last octet of the generic header of the Encrypted payload. The scope
of IntAuth_[i/r]*A is identical to the scope of Associated Data
defined for use of AEAD algorithms in IKEv2 (see Section 5.1 of
[RFC5282]), which is stressed by using "A" suffix in its name. Note,
that calculation of IntAuth_[i/r]*A doesn't depend on whether an AEAD
algorithm or a plain cipher is used in IKE SA.
The IntAuth_[i/r]*P chunk is present if the Encrypted payload is not
empty. It consists of the content of the Encrypted payload that is
fully formed, but not yet encrypted. The Initialization Vector, the
Padding, the Pad Length and the Integrity Checksum Data fields (see
Section 3.14 of [RFC7296]) are not included into the calculation. In
other words, the IntAuth_[i/r]*P chunk is the inner payloads of the
Encrypted payload in plaintext form, which is stressed by using "P"
suffix in its name.
1 2 3 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ^ ^ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ^ ^
| IKE SA Initiator's SPI | | | | IKE SA Initiator's SPI | | |
| | | | | | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ I | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ I |
| IKE SA Responder's SPI | K | | IKE SA Responder's SPI | K |
| | E | | | E |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
skipping to change at page 8, line 5 skipping to change at page 8, line 44
| Padding (0-255 octets) | Pad Length | d | Padding (0-255 octets) | Pad Length | d
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | | | | |
~ Integrity Checksum Data ~ | ~ Integrity Checksum Data ~ |
| | | | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ v +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ v
Figure 1: Data to Authenticate in the IKE_INTERMEDIATE Exchange Figure 1: Data to Authenticate in the IKE_INTERMEDIATE Exchange
Messages Messages
Figure 1 illustrates the layout of the IntAuth_*_[I/R]_P (denoted as Figure 1 illustrates the layout of the IntAuth_[i/r]*A (denoted as A)
P) and the IntAuth_*_[I/R]_A (denoted as A) chunks in case the and the IntAuth_[i/r]*P (denoted as P) chunks in case the Encrypted
Encrypted payload is not empty. payload is not empty.
For the purpose of prf calculation the Length field in the IKE header For the purpose of prf calculation the Length field in the IKE Header
and the Payload Length field in the Encrypted payload header are and the Payload Length field in the Encrypted payload header are
adjusted so that they don't count the lengths of Initialization adjusted so that they don't count the lengths of Initialization
Vector, Integrity Checksum Data, Padding and Pad Length fields. In Vector, Integrity Checksum Data, Padding and Pad Length fields. In
other words, the Length field in the IKE header (denoted as Adjusted other words, the Length field in the IKE Header (denoted as Adjusted
Length in Figure 1) is set to the sum of the lengths of IntAuth_*_[I/ Length in Figure 1) is set to the sum of the lengths of IntAuth_[i/
R]_A and IntAuth_*_[I/R]_P, and the Payload Length field in the r]*A and IntAuth_[i/r]*P, and the Payload Length field in the
Encrypted payload header (denoted as Adjusted Payload Length in Encrypted payload header (denoted as Adjusted Payload Length in
Figure 1) is set to the length of IntAuth_*_[I/R]_P plus the size of Figure 1) is set to the length of IntAuth_[i/r]*P plus the size of
the Encrypted payload header (four octets). the Encrypted payload header (four octets).
The prf calculations MUST be applied to whole messages only, before The prf calculations MUST be applied to whole messages only, before
possible IKE fragmentation. This ensures that the IntAuth will be possible IKE fragmentation. This ensures that the IntAuth will be
the same regardless of whether IKE fragmentation takes place or not. the same regardless of whether IKE fragmentation takes place or not.
If the message was received in fragmented form, it MUST be If the message was received in fragmented form, it MUST be
reconstructed before calculating prf as if it were received reconstructed before calculating the prf as if it were received
unfragmented. While reconstructing, the RESERVED field in the unfragmented. While reconstructing, the RESERVED field in the
reconstructed Encrypted payload header MUST be set to the value of reconstructed Encrypted payload header MUST be set to the value of
the RESERVED field in the Encrypted Fragment payload header from the the RESERVED field in the Encrypted Fragment payload header from the
first fragment (with Fragment Number field set to 1). first fragment (with Fragment Number field set to 1).
Note that it is possible to avoid actual reconstruction of the Note that it is possible to avoid actual reconstruction of the
message by incrementally calculating prf on decrypted (or ready to be message by incrementally calculating prf on decrypted (or ready to be
encrypted) fragments. However care must be taken to properly replace encrypted) fragments. However care must be taken to properly replace
the content of the Next Header and the Length fields so that the the content of the Next Header and the Length fields so that the
result of computing prf is the same as if it were computed on result of computing the prf is the same as if it were computed on the
reconstructed message. reconstructed message.
Each calculation of IntAuth_*_[I/R] uses its own keys SK_p[i/r]_*, Each calculation of IntAuth_[i/r]* uses its own keys SK_p[i/r]*,
which are the most recently updated SK_p[i/r] keys available before which are the most recently updated SK_p[i/r] keys available before
the corresponded IKE_INTERMEDIATE exchange is started. The first the corresponded IKE_INTERMEDIATE exchange is started. The first
IKE_INTERMEDIATE exchange always uses SK_p[i/r] keys that were IKE_INTERMEDIATE exchange always uses the SK_p[i/r] keys that were
computed in the IKE_SA_INIT as SK_p[i/r]_1. If the first computed in the IKE_SA_INIT as SK_p[i/r]1. If the first
IKE_INTERMEDIATE exchange performs additional key exchange resulting IKE_INTERMEDIATE exchange performs additional key exchange resulting
in SK_p[i/r] update, then this updated SK_p[i/r] are used as SK_p[i/ in SK_p[i/r] update, then this updated SK_p[i/r] are used as SK_p[i/
r]_2, otherwise the original SK_p[i/r] are used, and so on. Note, r]2, otherwise the original SK_p[i/r] are used, and so on. Note that
that if keys are updated then for any given IKE_INTERMEDIATE exchange if keys are updated, then for any given IKE_INTERMEDIATE exchange the
the keys SK_e[i/r] and SK_a[i/r] used for its messages protection keys SK_e[i/r] and SK_a[i/r] used for its messages protection (see
(see Section 3.3.1) and the keys SK_p[i/r] for its authentication are Section 3.3.1) and the keys SK_p[i/r] for its authentication are
always from the same generation. always from the same generation.
3.4. Error Handling in the IKE_INTERMEDIATE Exchange 3.4. Error Handling in the IKE_INTERMEDIATE Exchange
Since messages of the IKE_INTERMEDIATE exchange are not authenticated Since messages of the IKE_INTERMEDIATE exchange are not authenticated
until the IKE_AUTH exchange successfully completes, possible errors until the IKE_AUTH exchange successfully completes, possible errors
need to be handled with care. There is a trade-off between providing need to be handled with care. There is a trade-off between providing
a better diagnostics of the problem and a risk to become a part of better diagnostics of the problem and risk of becoming part of DoS
DoS attack. See Section 2.21.1 and 2.21.2 of [RFC7296] describe how attack. Section 2.21.1 and 2.21.2 of [RFC7296] describe how errors
errors are handled in initial IKEv2 exchanges, these considerations are handled in initial IKEv2 exchanges; these considerations are also
are also applied to the IKE_INTERMEDIATE exchange. applied to the IKE_INTERMEDIATE exchange with a qualification, that
not all error notifications may ever appear in the IKE_INTERMEDIATE
exchange (for example, errors concerning authentication are generally
only applicable to the IKE_AUTH exchange).
4. Interaction with other IKEv2 Extensions 4. Interaction with other IKEv2 Extensions
The IKE_INTERMEDIATE exchanges MAY be used during the IKEv2 Session The IKE_INTERMEDIATE exchanges MAY be used during the IKEv2 Session
Resumption [RFC5723] between the IKE_SESSION_RESUME and the IKE_AUTH Resumption [RFC5723] between the IKE_SESSION_RESUME and the IKE_AUTH
exchanges. To be able to use it peers MUST negotiate support for exchanges. To be able to use it peers MUST negotiate support for
intermediate exchange by including INTERMEDIATE_EXCHANGE_SUPPORTED intermediate exchange by including INTERMEDIATE_EXCHANGE_SUPPORTED
notifications in the IKE_SESSION_RESUME messages. Note, that a flag notifications in the IKE_SESSION_RESUME messages. Note, that a flag
whether peers supported the IKE_INTERMEDIATE exchange is not stored whether peers supported the IKE_INTERMEDIATE exchange is not stored
in the resumption ticket and is determined each time from the in the resumption ticket and is determined each time from the
IKE_SESSION_RESUME exchange. IKE_SESSION_RESUME exchange.
5. Security Considerations 5. Security Considerations
The data that is transferred by means of the IKE_INTERMEDIATE The data that is transferred by means of the IKE_INTERMEDIATE
exchanges is not authenticated until the subsequent IKE_AUTH exchange exchanges is not authenticated until the subsequent IKE_AUTH exchange
is completed. However, if the data is placed inside the Encrypted is completed. However, if the data is placed inside the Encrypted
payload, then it is protected from passive eavesdroppers. In payload, then it is protected from passive eavesdroppers. In
addition the peers can be certain that they receives messages from addition, the peers can be certain that they receives messages from
the party they performed the IKE_SA_INIT with if they can the party they performed the IKE_SA_INIT with if they can
successfully verify the Integrity Checksum Data of the Encrypted successfully verify the Integrity Checksum Data of the Encrypted
payload. payload.
The main application for Intermediate Exchange is to transfer large The main application for the Intermediate Exchange is to transfer
amount of data before IKE SA is set up without causing IP large amounts of data before an IKE SA is set up, without causing IP
fragmentation. For that reason it is expected that in most cases IKE fragmentation. For that reason it is expected that in most cases IKE
fragmentation will be employed in the IKE_INTERMEDIATE exchanges. fragmentation will be employed in the IKE_INTERMEDIATE exchanges.
Section 5 of [RFC7383] contains security considerations for IKE Section 5 of [RFC7383] contains security considerations for IKE
fragmentation. fragmentation.
Note, that if an attacker was able to break key exchange in real time Since authentication of the peers occurs only in the IKE_AUTH
(e.g. by means of Quantum Computer), then the security of the exchange, malicious initiator may use the Intermediate Exchange to
mount Denial of Service attack on responder. In this case it starts
creating IKE SA, negotiates using the Intermediate Exchanges and
transfers a lot of data to the responder that may also require some
computationally expensive processing. Then it aborts the SA
establishment before the IKE_AUTH exchange. Specifications utilizing
the Intermediate Exchange MUST NOT allow unlimited number of these
exchanges to take place on initiator's discretion. It is RECOMMENDED
that these specifications are defined in such a way, that the
responder would know (possibly via negotiation with the initiator)
the exact number of these exchanges that need to take place. In
other words: it is preferred that both the initiator and the
responder know after the IKE_SA_INIT is completed the exact number of
the IKE_INTERMEDIATE exchanges they have to perform; it is allowed
that some IKE_INTERMEDIATE exchanges are optional and are performed
on the initiator's discretion, but in this case the maximum number of
optional exchanges must be hard capped by the corresponding
specification. In addition, [RFC8019] provides guidelines for the
responder of how to deal with DoS attacks during IKE SA
establishment.
Note that if an attacker was able to break the key exchange in real
time (e.g. by means of a Quantum Computer), then the security of the
IKE_INTERMEDIATE exchange would degrade. In particular, such an IKE_INTERMEDIATE exchange would degrade. In particular, such an
attacker would be able both to read data contained in the Encrypted attacker would be able both to read data contained in the Encrypted
payload and to forge it. The forgery would become evident in the payload and to forge it. The forgery would become evident in the
IKE_AUTH exchange (provided the attacker cannot break employed IKE_AUTH exchange (provided the attacker cannot break the employed
authentication mechanism), but the ability to inject forged the authentication mechanism), but the ability to inject forged
IKE_INTERMEDIATE exchange messages with valid ICV would allow the IKE_INTERMEDIATE exchange messages with valid ICV would allow the
attacker to mount Denial-of-Service attack. Moreover, if in this attacker to mount a Denial-of-Service attack. Moreover, if in this
situation the negotiated prf was not secure against preimage attack situation the negotiated prf was not secure against second preimage
with known key, then the attacker could forge the IKE_INTERMEDIATE attack with known key, then the attacker could forge the
exchange messages without later being detected in the IKE_AUTH IKE_INTERMEDIATE exchange messages without later being detected in
exchange. To do this the attacker should find the same the IKE_AUTH exchange. To do this the attacker would find the same
IntAuth_*_[I|R] value for the forged message as for original. IntAuth_[i/r]* value for the forged message as for original.
6. IANA Considerations 6. IANA Considerations
This document defines a new Exchange Type in the "IKEv2 Exchange This document defines a new Exchange Type in the "IKEv2 Exchange
Types" registry: Types" registry:
43 IKE_INTERMEDIATE 43 IKE_INTERMEDIATE
This document also defines a new Notify Message Type in the "Notify This document also defines a new Notify Message Type in the "Notify
Message Types - Status Types" registry: Message Types - Status Types" registry:
skipping to change at page 10, line 44 skipping to change at page 12, line 12
o libreswan (only one IKE_INTERMEDIATE exchange is supported) o libreswan (only one IKE_INTERMEDIATE exchange is supported)
8. Acknowledgements 8. Acknowledgements
The idea to use an intermediate exchange between IKE_SA_INIT and The idea to use an intermediate exchange between IKE_SA_INIT and
IKE_AUTH was first suggested by Tero Kivinen. He also helped with IKE_AUTH was first suggested by Tero Kivinen. He also helped with
writing an example of using IKE_INTERMEDIATE exchange (shown in writing an example of using IKE_INTERMEDIATE exchange (shown in
Appendix A). Scott Fluhrer and Daniel Van Geest identified a Appendix A). Scott Fluhrer and Daniel Van Geest identified a
possible problem with authentication of the IKE_INTERMEDIATE exchange possible problem with authentication of the IKE_INTERMEDIATE exchange
and helped to resolve it. Author is also grateful to Tobias Brunner and helped to resolve it. Author is grateful to Tobias Brunner who
for raising good points concerning authentication of the raised good questions concerning authentication of the
IKE_INTERMEDIATE exchange and to Paul Wouters who suggested text IKE_INTERMEDIATE exchange and proposed how to make the size of
improvements for the document. authentication chunk constant regadless of the number of exchanges.
Author is also grateful to Paul Wouters and to Benjamin Kaduk who
suggested a lot of text improvements for the document.
9. References 9. References
9.1. Normative References 9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
skipping to change at page 11, line 30 skipping to change at page 12, line 44
(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>.
[RFC7383] Smyslov, V., "Internet Key Exchange Protocol Version 2 [RFC7383] Smyslov, V., "Internet Key Exchange Protocol Version 2
(IKEv2) Message Fragmentation", RFC 7383, (IKEv2) Message Fragmentation", RFC 7383,
DOI 10.17487/RFC7383, November 2014, DOI 10.17487/RFC7383, November 2014,
<https://www.rfc-editor.org/info/rfc7383>. <https://www.rfc-editor.org/info/rfc7383>.
9.2. Informative References 9.2. Informative References
[RFC8229] Pauly, T., Touati, S., and R. Mantha, "TCP Encapsulation [RFC5282] Black, D. and D. McGrew, "Using Authenticated Encryption
of IKE and IPsec Packets", RFC 8229, DOI 10.17487/RFC8229, Algorithms with the Encrypted Payload of the Internet Key
August 2017, <https://www.rfc-editor.org/info/rfc8229>. Exchange version 2 (IKEv2) Protocol", RFC 5282,
DOI 10.17487/RFC5282, August 2008,
<https://www.rfc-editor.org/info/rfc5282>.
[RFC5723] Sheffer, Y. and H. Tschofenig, "Internet Key Exchange [RFC5723] Sheffer, Y. and H. Tschofenig, "Internet Key Exchange
Protocol Version 2 (IKEv2) Session Resumption", RFC 5723, Protocol Version 2 (IKEv2) Session Resumption", RFC 5723,
DOI 10.17487/RFC5723, January 2010, DOI 10.17487/RFC5723, January 2010,
<https://www.rfc-editor.org/info/rfc5723>. <https://www.rfc-editor.org/info/rfc5723>.
[RFC8019] Nir, Y. and V. Smyslov, "Protecting Internet Key Exchange
Protocol Version 2 (IKEv2) Implementations from
Distributed Denial-of-Service Attacks", RFC 8019,
DOI 10.17487/RFC8019, November 2016,
<https://www.rfc-editor.org/info/rfc8019>.
[RFC8229] Pauly, T., Touati, S., and R. Mantha, "TCP Encapsulation
of IKE and IPsec Packets", RFC 8229, DOI 10.17487/RFC8229,
August 2017, <https://www.rfc-editor.org/info/rfc8229>.
Appendix A. Example of IKE_INTERMEDIATE exchange Appendix A. Example of IKE_INTERMEDIATE exchange
This appendix contains an example of the messages using This appendix contains an example of the messages using
IKE_INTERMEDIATE exchange. This appendix is purely informative; if IKE_INTERMEDIATE exchanges. This appendix is purely informative; if
it disagrees with the body of this document, the other text is it disagrees with the body of this document, the other text is
considered correct. considered correct.
In this example there is one IKE_SA_INIT exchange, two In this example there is one IKE_SA_INIT exchange and two
IKE_INTERMEDIATE exchanges followed by the IKE_AUTH exchange to IKE_INTERMEDIATE exchanges, followed by the IKE_AUTH exchange to
authenticate all initial exchanges. The xxx in the HDR(xxx,MID=yyy) authenticate all initial exchanges. The xxx in the HDR(xxx,MID=yyy)
indicates the exchange type, and yyy tells the message id used for indicates the exchange type, and yyy tells the message id used for
that exchange. The keys used for each SK {} payload are indicated in that exchange. The keys used for each SK {} payload are indicated in
the parenthesis after the SK. Otherwise payload notation is same as the parenthesis after the SK. Otherwise, the payload notation is the
is used in [RFC7296]. same as is used in [RFC7296].
Initiator Responder Initiator Responder
----------- ----------- ----------- -----------
HDR(IKE_SA_INIT,MID=0), HDR(IKE_SA_INIT,MID=0),
SAi1, KEi, Ni, SAi1, KEi, Ni,
N(INTERMEDIATE_EXCHANGE_SUPPORTED) --> N(INTERMEDIATE_EXCHANGE_SUPPORTED) -->
<-- HDR(IKE_SA_INIT,MID=0), <-- HDR(IKE_SA_INIT,MID=0),
SAr1, KEr, Nr, [CERTREQ], SAr1, KEr, Nr, [CERTREQ],
N(INTERMEDIATE_EXCHANGE_SUPPORTED) N(INTERMEDIATE_EXCHANGE_SUPPORTED)
At this point peers calculate SK_* and store them as SK_*_1. SK_e[i/ At this point peers calculate SK_* and store them as SK_*1. SK_e[i/
r]_1 and SK_a[i/r]_1 will be used to protect the first r]1 and SK_a[i/r]1 will be used to protect the first IKE_INTERMEDIATE
IKE_INTERMEDIATE exchange and SK_p[i/r]_1 will be used for its exchange and SK_p[i/r]1 will be used for its authentication.
authentication.
Initiator Responder Initiator Responder
----------- ----------- ----------- -----------
HDR(IKE_INTERMEDIATE,MID=1), HDR(IKE_INTERMEDIATE,MID=1),
SK(SK_ei_1,SK_ai_1) {...} --> SK(SK_ei1,SK_ai1) {...} -->
<Calculate IntAuth_1_I = prf(SK_pi_1, ...)> <Calculate IntAuth_i1 = prf(SK_pi1, ...)>
<-- HDR(IKE_INTERMEDIATE,MID=1), <-- HDR(IKE_INTERMEDIATE,MID=1),
SK(SK_er_1,SK_ar_1) {...} SK(SK_er1,SK_ar1) {...}
<Calculate IntAuth_1_R = prf(SK_pr_1, ...)> <Calculate IntAuth_r1 = prf(SK_pr1, ...)>
If after completing this IKE_INTERMEDIATE exchange SK_*_1 keys are If after completing this IKE_INTERMEDIATE exchange the SK_*1 keys are
updated (e.g., as a result of a new key exchange), then peers store updated (e.g., as a result of a new key exchange), then the peers
updated keys as SK_*_2, otherwise they use SK_*_1 as SK_*_2. SK_e[i/ store the updated keys as SK_*2, otherwise they use SK_*1 as SK_*2.
r]_2 and SK_a[i/r]_2 will be used to protect the second SK_e[i/r]2 and SK_a[i/r]2 will be used to protect the second
IKE_INTERMEDIATE exchange and SK_p[i/r]_2 will be used for its IKE_INTERMEDIATE exchange and SK_p[i/r]2 will be used for its
authentication. authentication.
Initiator Responder Initiator Responder
----------- ----------- ----------- -----------
HDR(IKE_INTERMEDIATE,MID=2), HDR(IKE_INTERMEDIATE,MID=2),
SK(SK_ei_2,SK_ai_2) {...} --> SK(SK_ei2,SK_ai2) {...} -->
<Calculate IntAuth_2_I = prf(SK_pi_2, ...)> <Calculate IntAuth_i2 = prf(SK_pi2, ...)>
<-- HDR(IKE_INTERMEDIATE,MID=2), <-- HDR(IKE_INTERMEDIATE,MID=2),
SK(SK_er_2,SK_ar_2) {...} SK(SK_er2,SK_ar2) {...}
<Calculate IntAuth_2_R = prf(SK_pr_2, ...)> <Calculate IntAuth_r2 = prf(SK_pr2, ...)>
If after completing the second IKE_INTERMEDIATE exchange SK_*_2 keys If after completing the second IKE_INTERMEDIATE exchange the SK_*2
are updated (e.g., as a result of a new key exchange), then peers keys are updated (e.g., as a result of a new key exchange), then the
store updated keys as SK_*_3, otherwise they use SK_*_2 as SK_*_3. peers store the updated keys as SK_*3, otherwise they use SK_*2 as
SK_e[i/r]_3 and SK_a[i/r]_3 will be used to protect the IKE_AUTH SK_*3. SK_e[i/r]3 and SK_a[i/r]3 will be used to protect the
exchange, SK_p[i/r]_3 will be used for authentication and SK_d_3 will IKE_AUTH exchange, SK_p[i/r]3 will be used for authentication, and
be used for derivation of other keys (e.g. for Child SAs). SK_d3 will be used for derivation of other keys (e.g. for Child SAs).
Initiator Responder Initiator Responder
----------- ----------- ----------- -----------
HDR(IKE_AUTH,MID=3), HDR(IKE_AUTH,MID=3),
SK(SK_ei_3,SK_ai_3) SK(SK_ei3,SK_ai3)
{IDi, [CERT,] [CERTREQ,] {IDi, [CERT,] [CERTREQ,]
[IDr,] AUTH, SAi2, TSi, TSr} --> [IDr,] AUTH, SAi2, TSi, TSr} -->
<-- HDR(IKE_AUTH,MID=3), <-- HDR(IKE_AUTH,MID=3),
SK(SK_er_3,SK_ar_3) SK(SK_er3,SK_ar3)
{IDr, [CERT,] AUTH, SAr2, TSi, TSr} {IDr, [CERT,] AUTH, SAr2, TSi, TSr}
In this example two IKE_INTERMEDIATE exchanges took place, therefore In this example two IKE_INTERMEDIATE exchanges took place, therefore
SK_*_3 keys would be used as SK_* keys for further cryptographic SK_*3 keys would be used as SK_* keys for further cryptographic
operations in the context of the created IKE SA, as defined in operations in the context of the created IKE SA, as defined in
[RFC7296]. [RFC7296].
Author's Address Author's Address
Valery Smyslov Valery Smyslov
ELVIS-PLUS ELVIS-PLUS
PO Box 81 PO Box 81
Moscow (Zelenograd) 124460 Moscow (Zelenograd) 124460
RU RU
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