Internet Engineering Task Force A. MalhotraInternet-Draft S. GoldbergUpdates:5905 (if approved) Boston UniversityIntended status: Standards Track October 3, 2018Expires: April 6, 2019Message Authentication Code for the Network Time Protocoldraft-ietf-ntp-mac-05AbstractRFC 5905 [RFC5905] states that Network Time Protocol (NTP) packets 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 document deprecates MD5-based authentication, which is considered to be too weak, and recommends the use of AES-CMAC [RFC4493] as a replacement.Status of This Memo This Internet-Draft is submitted in full conformance with the provisions ofBCP 78 andBCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is athttps://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on April 6, 2019.Copyright Notice Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject toBCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described inSection 4.e ofMalhotra & Goldberg Expires April 6, 2019 [Page 1]
Internet-Draft MAC for NTP October 2018 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.Table of Contents1. Introduction . . . . . . . . . . . . . . . . . . . . . . . .21.1. Requirements Language . . . . . . . . . . . . . . . . . .22. Deprecating the use of MD5 . . . . . . . . . . . . . . . . .23. Replacement Recommendation . . . . . . . . . . . . . . . . .24. Motivation . . . . . . . . . . . . . . . . . . . . . . . . .35. Test Vectors . . . . . . . . . . . . . . . . . . . . . . . .36. Security Considerations . . . . . . . . . . . . . . . . . . .37. Acknowledgements . . . . . . . . . . . . . . . . . . . . . .38. IANA Considerations . . . . . . . . . . . . . . . . . . . . .49. References . . . . . . . . . . . . . . . . . . . . . . . . .49.1. Normative References . . . . . . . . . . . . . . . . . .49.2. Informative References . . . . . . . . . . . . . . . . .4 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . .51. IntroductionRFC 5905 [RFC5905] states that Network Time Protocol (NTP) packets 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 document deprecates MD5-based authentication, which is considered to be too weak, and recommends the use of AES-CMAC [RFC4493] as a replacement.1.1. Requirements Language 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 inRFC 2119 [RFC2119].2. Deprecating the use of MD5RFC 5905 [RFC5905] defines how the MD5 digest algorithm inRFC 1321 [RFC1321] can be used as a message authentication code (MAC) for authenticating NTP packets. However, as discussed in [BCK] andRFC6151 [RFC6151], this is not a secure MAC and therefore MUST be deprecated.3. Replacement Recommendation If authentication is implemented, then AES-CMAC as specified inRFC4493 [RFC4493] SHOULD be computed over all fields in the NTP header, and any extension fields that are present in the NTP packet as described inRFC 5905 [RFC5905]. The MAC key for NTP MUST be atMalhotra & Goldberg Expires April 6, 2019 [Page 2]
Internet-Draft MAC for NTP October 2018 least 128 bits long AES-128 key and the resulting MAC tag MUST be at least 128 bits long as stated insection 2.4 of RFC 4493 [RFC4493]. NTP makes this transition possible as it supports algorithm agility as described inSection 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 AES-CMAC is recommended for the following reasons: 1. It is an IETF standard that is available in many open source implementations. 2. It is immune to nonce-reuse vulnerabilities (e.g. [Joux]) because it does not use a nonce. 3. It has fine performance in terms of latency and throughput. 4. It benefits from native hardware support, for instance, Intel's New Instruction set.5. Test Vectors For test vectors and their outputs refer toSection 4 of RFC 4493 [RFC4493]6. Security Considerations Refer to the Appendices A, B and C of NIST document [NIST] and Security Considerations Section ofRFC 4493 [RFC4493] for discussion on security guarantees of AES-CMAC.7. Acknowledgements The authors wish to acknowledge useful discussions with Leen Alshenibr, Daniel Franke, Ethan Heilman, Kenny Paterson, Leonid Reyzin, Harlan Stenn, and Mayank Varia.Malhotra & Goldberg Expires April 6, 2019 [Page 3]
Internet-Draft MAC for NTP October 20188. IANA Considerations This memo includes no request to IANA.9. References9.1. 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 Requirement Levels",BCP 14,RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>. [RFC4493] Song, JH., Poovendran, R., Lee, J., and T. Iwata, "The AES-CMAC Algorithm",RFC 4493, DOI 10.17487/RFC4493, June 2006, <https://www.rfc-editor.org/info/rfc4493>. [RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch, "Network Time Protocol Version 4: Protocol and Algorithms Specification",RFC 5905, DOI 10.17487/RFC5905, June 2010, <https://www.rfc-editor.org/info/rfc5905>.9.2. Informative References [BCK] Bellare, M., Canetti, R., and H. Krawczyk, "Keyed Hash Functions and Message Authentication", in Proceedings of Crypto'96, 1996. [Joux] Joux, A., "Authentication Failures in NIST version of GCM", <http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/comments/800-38_Series-Drafts/GCM/Joux_comments.pdf>. [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm",RFC 1321, DOI 10.17487/RFC1321, April 1992, <https://www.rfc-editor.org/info/rfc1321>. [RFC6151] Turner, S. and L. Chen, "Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms",RFC 6151, DOI 10.17487/RFC6151, March 2011, <https://www.rfc-editor.org/info/rfc6151>.Malhotra & Goldberg Expires April 6, 2019 [Page 4]
Internet-Draft MAC for NTP October 2018 [RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm Agility and Selecting Mandatory-to-Implement Algorithms",BCP 201,RFC 7696, DOI 10.17487/RFC7696, November 2015, <https://www.rfc-editor.org/info/rfc7696>.Authors' Addresses Aanchal Malhotra Boston University 111 Cummington St Boston, MA 02215 US Email: aanchal4@bu.edu Sharon Goldberg Boston University 111 Cummington St Boston, MA 02215 US Email: goldbe@cs.bu.eduMalhotra & Goldberg Expires April 6, 2019 [Page 5]
Datatracker
draft-ietf-ntp-mac-05
This is an older version of an Internet-Draft that was ultimately published asRFC 8573.
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| Authors | Aanchal Malhotra,Sharon Goldberg | ||
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