draft-ietf-ntp-mac-06.txt   rfc8573.txt 
Internet Engineering Task Force A. Malhotra Internet Engineering Task Force (IETF) A. Malhotra
Internet-Draft S. Goldberg Request for Comments: 8573 S. Goldberg
Updates: 5905 (if approved) Boston University Updates: 5905 Boston University
Intended status: Standards Track January 4, 2019 Category: Standards Track June 2019
Expires: July 8, 2019 ISSN: 2070-1721
Message Authentication Code for the Network Time Protocol Message Authentication Code for the Network Time Protocol
draft-ietf-ntp-mac-06
Abstract Abstract
RFC 5905 states that Network Time Protocol (NTP) packets should be The Network Time Protocol (NTP), as described in RFC 5905, states
authenticated by appending the NTP data to a 128-bit key, and hashing that NTP packets should be authenticated by appending NTP data to a
the result with MD5 to obtain a 128-bit tag. This document 128-bit key and hashing the result with MD5 to obtain a 128-bit tag.
deprecates MD5-based authentication, which is considered to be too This document deprecates MD5-based authentication, which is
weak, and recommends the use of AES-CMAC as in RFC 4493 as a considered too weak, and recommends the use of AES-CMAC as described
replacement. in RFC 4493 as a replacement.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on July 8, 2019. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8573.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
2. Deprecating the use of MD5 . . . . . . . . . . . . . . . . . 2 2. Deprecating the Use of MD5 . . . . . . . . . . . . . . . . . 2
3. Replacement Recommendation . . . . . . . . . . . . . . . . . 3 3. Replacement Recommendation . . . . . . . . . . . . . . . . . 2
4. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Test Vectors . . . . . . . . . . . . . . . . . . . . . . . . 3 5. Test Vectors . . . . . . . . . . . . . . . . . . . . . . . . 3
6. Security Considerations . . . . . . . . . . . . . . . . . . . 3 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4 7. Security Considerations . . . . . . . . . . . . . . . . . . . 3
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 8.1. Normative References . . . . . . . . . . . . . . . . . . 4
9.1. Normative References . . . . . . . . . . . . . . . . . . 4 8.2. Informative References . . . . . . . . . . . . . . . . . 4
9.2. Informative References . . . . . . . . . . . . . . . . . 4 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction 1. Introduction
RFC 5905 [RFC5905] states that Network Time Protocol (NTP) packets The Network Time Protocol [RFC5905] states that NTP packets should be
should be authenticated by appending the NTP data to a 128-bit key, authenticated by appending NTP data to a 128-bit key and hashing the
and hashing the result with MD5 to obtain a 128-bit tag. This result with MD5 to obtain a 128-bit tag. This document deprecates
document deprecates MD5-based authentication, which is considered to MD5-based authentication, which is considered too weak, and
be too weak, and recommends the use of AES-CMAC [RFC4493] as a recommends the use of AES-CMAC [RFC4493] as a replacement.
replacement.
1.1. Requirements Language 1.1. Requirements Language
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
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
2. Deprecating the use of MD5 2. Deprecating the Use of MD5
RFC 5905 [RFC5905] defines how the MD5 digest algorithm in RFC 1321 RFC 5905 [RFC5905] defines how the MD5 digest algorithm described in
[RFC1321] can be used as a message authentication code (MAC) for RFC 1321 [RFC1321] can be used as a Message Authentication Code (MAC)
authenticating NTP packets. However, as discussed in [BCK] and RFC for authenticating NTP packets. However, as discussed in [BCK] and
6151 [RFC6151], this is not a secure MAC and therefore MUST be RFC 6151 [RFC6151], this is not a secure MAC and therefore MUST be
deprecated. deprecated.
3. Replacement Recommendation 3. Replacement Recommendation
If NTP authentication is implemented, then AES-CMAC as specified in If NTP authentication is implemented, then AES-CMAC as specified in
RFC 4493 [RFC4493] MUST be computed over all fields in the NTP RFC 4493 [RFC4493] MUST be computed over all fields in the NTP header
header, and any extension fields that are present in the NTP packet and any extension fields that are present in the NTP packet as
as described in RFC 5905 [RFC5905]. The MAC key for NTP MUST be 128 described in RFC 5905 [RFC5905]. The MAC key for NTP MUST be an
bits long AES-128 key and the resulting MAC tag MUST be at least 128 AES-128 key that is 128 bits in length, and the resulting MAC tag
bits long as stated in section 2.4 of RFC 4493 [RFC4493]. NTP makes MUST be at least 128 bits in length, as stated in Section 2.4 of RFC
this transition possible as it supports algorithm agility as 4493 [RFC4493]. NTP makes this transition possible as it supports
described in Section 2.1 of RFC 7696 [RFC7696]. algorithm agility as described in Section 2.1 of RFC 7696 [RFC7696].
The hosts who wish to use NTP authentication share a symmetric key The hosts that wish to use NTP authentication share a symmetric key
out-of-band. So they MUST implement AES-CMAC and share the out of band. So they MUST implement AES-CMAC and share the
corresponding symmetric key. A symmetric key is a triplet of ID, 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 type (e.g., MD5 and AES-CMAC) and the key itself. All three have to
match in order to succesfully authenticate packets between two hosts. match in order to successfully authenticate packets between two
Old implementations that don't support AES-CMAC will not accept and hosts. Old implementations that don't support AES-CMAC will not
will not send packets authenticated with such a key. 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 specification that is supported 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.
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 GUE [GUE]. New Instruction set GUE [GUE].
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. Security Considerations
Refer to the Appendices A, B and C of NIST document on recommendation
for the CMAC mode of authentication [NIST] and Security
Considerations Section of RFC 4493 [RFC4493] for discussion on
security guarantees of AES-CMAC.
7. Acknowledgements 6. IANA Considerations
The authors wish to acknowledge useful discussions with Leen This document has no IANA actions.
Alshenibr, Daniel Franke, Ethan Heilman, Kenny Paterson, Leonid
Reyzin, Harlan Stenn, and Mayank Varia.
8. IANA Considerations 7. Security Considerations
This memo includes no request to IANA. Refer to Appendices A, B, and C of the NIST document [NIST] for a
recommendation for the CMAC mode of authentication; see the Security
Considerations of RFC 4493 [RFC4493] for discussion on security
guarantees of AES-CMAC.
9. References 8. References
9.1. Normative References 8.1. Normative References
[NIST] Dworkin, M., "Recommendation for Block Cipher Modes of [NIST] Dworkin, M., "Recommendation for Block Cipher Modes of
Operation: The CMAC Mode for Authentication", Operation: The CMAC Mode for Authentication", NIST Special
<https://www.nist.gov/publications/recommendation-block- Publication 800-38B, DOI 10.6028/NIST.SP.800-38B, October
cipher-modes-operation-cmac-mode-authentication-0>. 2016, <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>.
9.2. Informative References [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[BCK] Bellare, M., Canetti, R., and H. Krawczyk, "Keyed Hash 8.2. Informative References
Functions and Message Authentication", in Proceedings of
Crypto'96, 1996. [BCK] Bellare, M., Canetti, R., and H. Krawczyk, "Keying Hash
Functions and Message Authentication", Advances in
Cryptology - Crypto 96 Proceedings, Lecture Notes in
Computer Science, Vol. 1109, N. Koblitz ed, Springer-
Verlag, 1996.
[GUE] Geuron, S., "Intel Advanced Encryption Standard (AES) New [GUE] Geuron, S., "Intel Advanced Encryption Standard (AES) New
Instructions Set", <https://www.intel.com/content/dam/doc/ Instructions Set", May 2010,
white-paper/advanced-encryption-standard-new-instructions- <https://www.intel.com/content/dam/doc/white-paper/
set-paper.pdf>. advanced-encryption-standard-new-instructions-set-
paper.pdf>.
[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>.
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
DOI 10.17487/RFC1321, April 1992, DOI 10.17487/RFC1321, April 1992,
<https://www.rfc-editor.org/info/rfc1321>. <https://www.rfc-editor.org/info/rfc1321>.
[RFC6151] Turner, S. and L. Chen, "Updated Security Considerations [RFC6151] Turner, S. and L. Chen, "Updated Security Considerations
for the MD5 Message-Digest and the HMAC-MD5 Algorithms", for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
RFC 6151, DOI 10.17487/RFC6151, March 2011, RFC 6151, DOI 10.17487/RFC6151, March 2011,
<https://www.rfc-editor.org/info/rfc6151>. <https://www.rfc-editor.org/info/rfc6151>.
[RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm [RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm
Agility and Selecting Mandatory-to-Implement Algorithms", Agility and Selecting Mandatory-to-Implement Algorithms",
BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015, BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015,
<https://www.rfc-editor.org/info/rfc7696>. <https://www.rfc-editor.org/info/rfc7696>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC Acknowledgements
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. The authors wish to acknowledge useful discussions with Leen
Alshenibr, Daniel Franke, Ethan Heilman, Kenny Paterson, Leonid
Reyzin, Harlan Stenn, and Mayank Varia.
Authors' Addresses Authors' Addresses
Aanchal Malhotra Aanchal Malhotra
Boston University Boston University
111 Cummington St 111 Cummington St
Boston, MA 02215 Boston, MA 02215
US United States of America
Email: aanchal4@bu.edu Email: aanchal4@bu.edu
Sharon Goldberg Sharon Goldberg
Boston University Boston University
111 Cummington St 111 Cummington St
Boston, MA 02215 Boston, MA 02215
US United States of America
Email: goldbe@cs.bu.edu Email: goldbe@cs.bu.edu
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