draft-ietf-ntp-mac-05.txt   draft-ietf-ntp-mac-06.txt 
Internet Engineering Task Force A. Malhotra Internet Engineering Task Force A. Malhotra
Internet-Draft S. Goldberg Internet-Draft S. Goldberg
Updates: 5905 (if approved) Boston University Updates: 5905 (if approved) Boston University
Intended status: Standards Track October 3, 2018 Intended status: Standards Track January 4, 2019
Expires: April 6, 2019 Expires: July 8, 2019
Message Authentication Code for the Network Time Protocol Message Authentication Code for the Network Time Protocol
draft-ietf-ntp-mac-05 draft-ietf-ntp-mac-06
Abstract Abstract
RFC 5905 [RFC5905] states that Network Time Protocol (NTP) packets RFC 5905 states that Network Time Protocol (NTP) packets should be
should be authenticated by appending a 128-bit key to the NTP data, authenticated by appending the NTP data to a 128-bit key, and hashing
and hashing the result with MD5 to obtain a 128-bit tag. This the result with MD5 to obtain a 128-bit tag. This document
document deprecates MD5-based authentication, which is considered to deprecates MD5-based authentication, which is considered to be too
be too weak, and recommends the use of AES-CMAC [RFC4493] as a weak, and recommends the use of AES-CMAC as in RFC 4493 as a
replacement. replacement.
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.
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This Internet-Draft will expire on April 6, 2019. This Internet-Draft will expire on July 8, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 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 . . . . . . . . . . . . . . . . . 2 3. Replacement Recommendation . . . . . . . . . . . . . . . . . 3
4. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Test Vectors . . . . . . . . . . . . . . . . . . . . . . . . 3 5. Test Vectors . . . . . . . . . . . . . . . . . . . . . . . . 3
6. Security Considerations . . . . . . . . . . . . . . . . . . . 3 6. Security Considerations . . . . . . . . . . . . . . . . . . . 3
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 3 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
9.1. Normative References . . . . . . . . . . . . . . . . . . 4 9.1. Normative References . . . . . . . . . . . . . . . . . . 4
9.2. Informative References . . . . . . . . . . . . . . . . . 4 9.2. Informative References . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5 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 the NTP data to a 128-bit key,
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.
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", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
document are to be interpreted as described in RFC 2119 [RFC2119]. "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
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 in RFC 1321
[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 NTP authentication is implemented, then AES-CMAC as specified in
4493 [RFC4493] SHOULD be computed over all fields in the NTP header, RFC 4493 [RFC4493] MUST be computed over all fields in the NTP
and any extension fields that are present in the NTP packet as header, and any extension fields that are present in the NTP packet
described in RFC 5905 [RFC5905]. The MAC key for NTP MUST be at as described in RFC 5905 [RFC5905]. The MAC key for NTP MUST be 128
least 128 bits long AES-128 key and the resulting MAC tag MUST be at bits long AES-128 key and the resulting MAC tag MUST be at least 128
least 128 bits long as stated in section 2.4 of RFC 4493 [RFC4493]. bits long as stated in section 2.4 of RFC 4493 [RFC4493]. NTP makes
NTP makes this transition possible as it supports algorithm agility this transition possible as it supports algorithm agility as
as described in Section 2.1 of RFC 7696 [RFC7696]. described in Section 2.1 of RFC 7696 [RFC7696].
The hosts who wish to use NTP authentication share a symmetric key The hosts who 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, AES-CMAC) and the key itself. All three have to
match in order to succesfully authenticate packets between two hosts. match in order to succesfully authenticate packets between two hosts.
Old implementations that don't support AES-CMAC will not accept and Old implementations that don't support AES-CMAC will not accept and
will not send packets authenticated with such a key. will not send packets authenticated with such a key.
4. Motivation 4. Motivation
skipping to change at page 3, line 30 skipping to change at page 3, line 37
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.
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 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 6. Security Considerations
Refer to the Appendices A, B and C of NIST document [NIST] and Refer to the Appendices A, B and C of NIST document on recommendation
Security Considerations Section of RFC 4493 [RFC4493] for discussion for the CMAC mode of authentication [NIST] and Security
on security guarantees of AES-CMAC. Considerations Section of RFC 4493 [RFC4493] for discussion on
security guarantees of AES-CMAC.
7. Acknowledgements 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.
8. IANA Considerations 8. IANA Considerations
This memo includes no request to IANA. This memo includes no request to IANA.
9. References 9. References
9.1. Normative References 9.1. 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",
<https://www.nist.gov/publications recommendation-block- <https://www.nist.gov/publications/recommendation-block-
cipher-modes-operation-cmac-mode-authentication-0>. 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>.
skipping to change at page 4, line 38 skipping to change at page 4, line 44
"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 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.
[GUE] Geuron, S., "Intel Advanced Encryption Standard (AES) New
Instructions Set", <https://www.intel.com/content/dam/doc/
white-paper/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
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
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 US
Email: aanchal4@bu.edu Email: aanchal4@bu.edu
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