IPSECME D. Migault, Ed.
Internet-Draft Ericsson
Intended status: Standards Track T. Guggemos, Ed.
Expires: December 11, 2016 LMU Munich
Y. Nir
Check Point
June 9, 2016
Implicit IV for Counter-based Ciphers in IPsec
draft-mglt-ipsecme-implicit-iv-00.txt
Abstract
IPsec ESP sends an initialization vector (IV) or nonce in each
packet, adding 8 or 16 octets. Some algorithms such as AES-GCM, AES-
CCM, AES-CTR and ChaCha20-Poly1305 require a unique nonce but do not
require an unpredictable nonce. When using such algorithms the
packet counter value can be used to generate a nonce, saving 8 octets
per packet. This document describes how to do this.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on December 11, 2016.
Copyright Notice
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document authors. All rights reserved.
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to this document. Code Components extracted from this document must
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Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Implicit IV . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Implicit IV Agreement . . . . . . . . . . . . . . . . . . . . 4
6. Initiator Behavior . . . . . . . . . . . . . . . . . . . . . 5
7. Responder Behavior . . . . . . . . . . . . . . . . . . . . . 5
8. Security Consideration . . . . . . . . . . . . . . . . . . . 5
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
10. Normative References . . . . . . . . . . . . . . . . . . . . 5
Appendix A. Document Change Log . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Introduction
Counter-based AES modes of operation such as AES-CTR ([RFC3686]),
AES-CCM ([RFC4309]), and AES-GCM ([RFC4104]) require the
specification of an nonce for each ESP packet. The same applies for
ChaCha20-Poly1305 ([RFC7634]. Currently this nonce is sent in each
ESP packet ([RFC4303]). This practice is designated in this document
as "explicit nonce".
In some context, such as IoT, it may be preferable to avoid carrying
the extra bytes associated to the IV and instead compute it locally
on each peer. The local generation of the nonce is designated in
this document as "implicit IV".
The size of this nonce depends on the specific algorithm, but all of
the algorithms mentioned above take an 8-octet nonce.
This document defines how to compute the nonce locally when it is
implicit. It also specifies how to negotiate this behavior within
the Internet Key Exchange version 2 (IKEv2 - [RFC7296]).
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This document limits its scope to the algorithms mentioned above.
Other algorithms with similar properties may later be defined to use
this extension.
This document does not consider AES-CBC ([RFC3602])as AES-CBC
requires the IV to be unpredictable. Deriving it directly from the
packet counter as described below is insecure.
3. Terminology
o IoT: Internet of Things
o IV: Initialization Vector. Although security requirements vary,
the common usage of this term implies that the value is
unpredictable.
o Nonce: a fixed-size octet string used only once. This is similar
to IV, except that in common usage there is no implication of non-
predictability.
4. Implicit IV
With the algorithms listed in Section 2, the 8 byte nonce MUST NOT
repeat. The binding between a ESP packet and its nonce is provided
using the Sequence Number or the Extended Sequence Number. Figure 1
and Figure 2 represent the IV with a regular 4-byte Sequence Number
and with an 8-byte Extended Sequence Number respectively.
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Implicit IV with a 4 byte Sequence Number
o Sequence Number: the 4 byte Sequence Number carried in the ESP
packet.
o Zero: a 4 byte array with all bits set to zero.
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0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended |
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Implicit IV with an 8 byte Extended Sequence Number
o Extended Sequence Number: the 8 byte Extended Sequence Number of
the Security Association. The 4 byte low order bytes are carried
in the ESP packet.
5. Implicit IV Agreement
NOTE: THIS SECTION SHOWS SEVERAL WAYS TO DO THE SAME THING.
OBVIOUSLY THIS DOCUMENT WILL NOT BE PUBLISHED LIKE THAT. WE EXPECT
WG DISCUSSION TO PARE THIS DOWN TO JUST ONE WAY OF NEGOTIATING THE
USE OF IMPLICIT IV (IIV).
Negotiation of the use of implicit IV can be done in 3 different
ways:
o An IMPLICIT IV Transform Type. A proposal that contains this
transform type requires (if accepted) that IPsec use the implicit
IV and not include an explicit IV in the packets. To facilitate
backward compatibility with non-supporting implementations the
Initiator SHOULD add another proposal that does not include this
transform type as well as cryptographic suite the Initiator does
not support the implicit IV.
o An IMPLICIT IV Transform ID. This doubles the number of ENCR
transform IDs by creating an ENCR_AES_CCM_16_IIV for each
ENCR_AES_CCM_16.
o An IMPLICIT IV Transform Attribute, which would be associated to a
Transform Type ID, specifying the use of an implicit IV. marks a
particular ENCR transform as using implicit IVs. To facilitate
backward compatibility with non-supporting implementations the
Initiator SHOULD add another ENCR transform for each algorithm so
marked. In other words, for each ENCR_AES_CCM_16 with
keylength=256 and IIV=1, there will need to be an ENCR_AES_CCM_16
with keylength=256 and no IIV attribute.
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6. Initiator Behavior
An initiator supporting this feature SHOULD propose implicit IV for
all relevant algorithms. To facilitate backward compatibility with
non-supporting peers the initiator SHOULD also include those same
algorithms without IIV. Depending on the method chosen in Section 5
this may require extra proposals or extra transforms.
7. Responder Behavior
An responder supporting this feature SHOULD accept implicit IV for
all relevant algorithms. It MUST NOT accept implicit IV for
algorithms not specified to be safe for IIV in this or subsequent
documents. It SHOULD accept non-IIV proposals for all algorithms if
IIV proposals were not included.
The rules of SA payload processing ensure that the responder will
never send an SA payload containing the IIV indicator to an initiator
that does not support IIV.
8. Security Consideration
Nonce generation for these algorithms has not been explicitly
defined. It has been left to the implementation as long as certain
security requirements are met. This document provides an explicit
and normative way to generate IVs. The mechanism described in this
document meets the IV security requirements of all relevant
algorithms.
9. IANA Considerations
TBD: The content of this section depends on our decisions about
Section 5.
The following Transform Type is requested: IMPLICIT_IV Transform Type
Values associated to IMPLICIT Transform Type are:
False: 0 ===> Do we really need a negative value???
True: 1
10. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
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[RFC3602] Frankel, S., Glenn, R., and S. Kelly, "The AES-CBC Cipher
Algorithm and Its Use with IPsec", RFC 3602,
DOI 10.17487/RFC3602, September 2003,
<http://www.rfc-editor.org/info/rfc3602>.
[RFC3686] Housley, R., "Using Advanced Encryption Standard (AES)
Counter Mode With IPsec Encapsulating Security Payload
(ESP)", RFC 3686, DOI 10.17487/RFC3686, January 2004,
<http://www.rfc-editor.org/info/rfc3686>.
[RFC4104] Pana, M., Ed., Reyes, A., Barba, A., Moron, D., and M.
Brunner, "Policy Core Extension Lightweight Directory
Access Protocol Schema (PCELS)", RFC 4104,
DOI 10.17487/RFC4104, June 2005,
<http://www.rfc-editor.org/info/rfc4104>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<http://www.rfc-editor.org/info/rfc4303>.
[RFC4309] Housley, R., "Using Advanced Encryption Standard (AES) CCM
Mode with IPsec Encapsulating Security Payload (ESP)",
RFC 4309, DOI 10.17487/RFC4309, December 2005,
<http://www.rfc-editor.org/info/rfc4309>.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <http://www.rfc-editor.org/info/rfc7296>.
[RFC7634] Nir, Y., "ChaCha20, Poly1305, and Their Use in the
Internet Key Exchange Protocol (IKE) and IPsec", RFC 7634,
DOI 10.17487/RFC7634, August 2015,
<http://www.rfc-editor.org/info/rfc7634>.
Appendix A. Document Change Log
Authors' Addresses
Daniel Migault (editor)
Ericsson
8400 boulevard Decarie
Montreal, QC H4P 2N2
Canada
Email: daniel.migault@ericsson.com
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Tobias Guggemos (editor)
LMU Munich
Am Osteroesch 9
87637 Seeg, Bavaria
Germany
Email: tobias.guggemos@gmail.com
Yoav Nir
Check Point Software Technologies Ltd.
5 Hasolelim st.
Tel Aviv 6789735
Israel
Email: ynir.ietf@gmail.com
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