draft-ietf-ntp-mac-03.txt   draft-ietf-ntp-mac-04.txt 
Internet Engineering Task Force A. Malhotra Internet Engineering Task Force A. Malhotra
Internet-Draft S. Goldberg Internet-Draft S. Goldberg
Intended status: Standards Track Boston University Intended status: Standards Track Boston University
Expires: May 3, 2018 October 30, 2017 Expires: September 6, 2018 March 5, 2018
Message Authentication Code for the Network Time Protocol Message Authentication Code for the Network Time Protocol
draft-ietf-ntp-mac-03 draft-ietf-ntp-mac-04
Abstract Abstract
RFC 5905 [RFC5905] states that Network Time Protocol (NTP) packets RFC 5905 [RFC5905] states that Network Time Protocol (NTP) packets
should be authenticated by appending a 128-bit key to the NTP data, should be authenticated by appending a 128-bit key to the NTP data,
and hashing the result with MD5 to obtain a 128-bit tag. This and hashing the result with MD5 to obtain a 128-bit tag. This
document deprecates MD5-based authentication, which is considered to document deprecates MD5-based authentication, which is considered to
be too weak, and recommends the use of AES-CMAC [RFC4493] as a be too weak, and recommends the use of AES-CMAC [RFC4493] as a
replacement. replacement.
skipping to change at page 1, line 35 skipping to change at page 1, line 35
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 May 3, 2018. This Internet-Draft will expire on September 6, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
2. Deprecating MD5 . . . . . . . . . . . . . . . . . . . . . . . 2 2. Deprecating MD5 . . . . . . . . . . . . . . . . . . . . . . . 2
3. Replacement Recommendation . . . . . . . . . . . . . . . . . 2 3. Replacement Recommendation . . . . . . . . . . . . . . . . . 2
4. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Test Vectors . . . . . . . . . . . . . . . . . . . . . . . . 3 5. Test Vectors . . . . . . . . . . . . . . . . . . . . . . . . 3
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 3 6. Security Considerations . . . . . . . . . . . . . . . . . . . 3
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 3
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 3 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
8.1. Normative References . . . . . . . . . . . . . . . . . . 3 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
8.2. Informative References . . . . . . . . . . . . . . . . . 4 9.1. Normative References . . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 4 9.2. Informative References . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction 1. Introduction
RFC 5905 [RFC5905] states that Network Time Protocol (NTP) packets RFC 5905 [RFC5905] states that Network Time Protocol (NTP) packets
should be authenticated by appending a 128-bit key to the NTP data, should be authenticated by appending a 128-bit key to the NTP data,
and hashing the result with MD5 to obtain a 128-bit tag. This and hashing the result with MD5 to obtain a 128-bit tag. This
document deprecates MD5-based authentication, which is considered to document deprecates MD5-based authentication, which is considered to
be too weak, and recommends the use of AES-CMAC [RFC4493] as a be too weak, and recommends the use of AES-CMAC [RFC4493] as a
replacement. replacement.
skipping to change at page 2, line 50 skipping to change at page 2, line 51
[RFC1321] can be used as a message authentication code (MAC) for [RFC1321] can be used as a message authentication code (MAC) for
authenticating NTP packets. However, as discussed in [BCK] and RFC authenticating NTP packets. However, as discussed in [BCK] and RFC
6151 [RFC6151], this is not a secure MAC and therefore MUST be 6151 [RFC6151], this is not a secure MAC and therefore MUST be
deprecated. deprecated.
3. Replacement Recommendation 3. Replacement Recommendation
If authentication is implemented, then AES-CMAC as specified in RFC If authentication is implemented, then AES-CMAC as specified in RFC
4493 [RFC4493] SHOULD be computed over all fields in the NTP header, 4493 [RFC4493] SHOULD be computed over all fields in the NTP header,
and any extension fields that are present in the NTP packet as and any extension fields that are present in the NTP packet as
described in RFC 5905 [RFC5905]. The MAC key for NTP SHOULD be 128 described in RFC 5905 [RFC5905]. The MAC key for NTP MUST be at
bits long AES-128 key and the resulting MAC tag SHOULD be 128 bits least 128 bits long AES-128 key and the resulting MAC tag MUST be at
long as stated in section 2.4 of RFC 4493 [RFC4493]. NTP makes this least 128 bits long as stated in section 2.4 of RFC 4493 [RFC4493].
transition possible as it supports algorithm agility as described in NTP makes this transition possible as it supports algorithm agility
Section 2.1 of RFC 7696 [RFC7696]. as described in Section 2.1 of RFC 7696 [RFC7696].
The hosts who wish to use NTP authentication share a symmetric key
out-of-band. So they MUST implement AES-CMAC and share the
corresponding symmetric key. A symmetric key is a triplet of ID,
type (e.g. MD5, AES-CMAC) and the key itself. All three have to
match in order to succesfully authenticate packets between two hosts.
Old implementations that don't support AES-CMAC will not accept and
will not send packets authenticated with such a key.
4. Motivation 4. Motivation
AES-CMAC is recommended for the following reasons: AES-CMAC is recommended for the following reasons:
1. It is an IETF standard that is available in many open source 1. It is an IETF standard that is available in many open source
implementations. implementations.
2. It is immune to nonce-reuse vulnerabilities (e.g. [Joux]) 2. It is immune to nonce-reuse vulnerabilities (e.g. [Joux])
because it does not use a nonce. because it does not use a nonce.
skipping to change at page 3, line 28 skipping to change at page 3, line 37
3. It has fine performance in terms of latency and throughput. 3. It has fine performance in terms of latency and throughput.
4. It benefits from native hardware support, for instance, Intel's 4. It benefits from native hardware support, for instance, Intel's
New Instruction set. New Instruction set.
5. Test Vectors 5. Test Vectors
For test vectors and their outputs refer to Section 4 of RFC 4493 For test vectors and their outputs refer to Section 4 of RFC 4493
[RFC4493] [RFC4493]
6. Acknowledgements 6. Security Considerations
Refer to the Appendices A, B and C of NIST document [NIST] and
Security Considerations Section of RFC 4493 [RFC4493] for discussion
on security guarantees of AES-CMAC.
7. Acknowledgements
The authors wish to acknowledge useful discussions with Leen The authors wish to acknowledge useful discussions with Leen
Alshenibr, Daniel Franke, Ethan Heilman, Kenny Paterson, Leonid Alshenibr, Daniel Franke, Ethan Heilman, Kenny Paterson, Leonid
Reyzin, Harlan Stenn, and Mayank Varia. Reyzin, Harlan Stenn, and Mayank Varia.
7. IANA Considerations 8. IANA Considerations
This memo includes no request to IANA. This memo includes no request to IANA.
8. References 9. References
8.1. Normative References 9.1. Normative References
[NIST] Dworkin, M., "Recommendation for Block Cipher Modes of
Operation: The CMAC Mode for Authentication",
<https://www.nist.gov/publications recommendation-block-
cipher-modes-operation-cmac-mode-authentication-0>.
[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>.
[RFC4493] Song, JH., Poovendran, R., Lee, J., and T. Iwata, "The [RFC4493] Song, JH., Poovendran, R., Lee, J., and T. Iwata, "The
AES-CMAC Algorithm", RFC 4493, DOI 10.17487/RFC4493, June AES-CMAC Algorithm", RFC 4493, DOI 10.17487/RFC4493, June
2006, <https://www.rfc-editor.org/info/rfc4493>. 2006, <https://www.rfc-editor.org/info/rfc4493>.
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch, [RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms "Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010, Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<https://www.rfc-editor.org/info/rfc5905>. <https://www.rfc-editor.org/info/rfc5905>.
8.2. Informative References 9.2. Informative References
[BCK] Bellare, M., Canetti, R., and H. Krawczyk, "Keyed Hash [BCK] Bellare, M., Canetti, R., and H. Krawczyk, "Keyed Hash
Functions and Message Authentication", in Proceedings of Functions and Message Authentication", in Proceedings of
Crypto'96, 1996. Crypto'96, 1996.
[Joux] Joux, A., "Authentication Failures in NIST version of [Joux] Joux, A., "Authentication Failures in NIST version of
GCM", GCM",
<http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/ <http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/
comments/800-38_Series-Drafts/GCM/Joux_comments.pdf>. comments/800-38_Series-Drafts/GCM/Joux_comments.pdf>.
 End of changes. 11 change blocks. 
20 lines changed or deleted 40 lines changed or added

This html diff was produced by rfcdiff 1.46. The latest version is available from http://tools.ietf.org/tools/rfcdiff/