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Whited 3 Internet-Draft 10 March 2021 4 Updates: 5802, 8446 (if approved) 5 Intended status: Standards Track 6 Expires: 11 September 2021 8 Channel Bindings for TLS 1.3 9 draft-ietf-kitten-tls-channel-bindings-for-tls13-02 11 Abstract 13 This document defines a channel binding type, tls-exporter, that is 14 compatible with TLS 1.3 in accordance with RFC 5056, On Channel 15 Binding. 17 Status of This Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at https://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on 11 September 2021. 34 Copyright Notice 36 Copyright (c) 2021 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 41 license-info) in effect on the date of publication of this document. 42 Please review these documents carefully, as they describe your rights 43 and restrictions with respect to this document. Code Components 44 extracted from this document must include Simplified BSD License text 45 as described in Section 4.e of the Trust Legal Provisions and are 46 provided without warranty as described in the Simplified BSD License. 48 Table of Contents 50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 51 1.1. Conventions and Terminology . . . . . . . . . . . . . . . 2 52 2. The 'tls-exporter' Channel Binding Type . . . . . . . . . . . 2 53 3. Security Considerations . . . . . . . . . . . . . . . . . . . 3 54 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3 55 4.1. Registration of Channel Binding Type . . . . . . . . . . 3 56 4.2. Registration of Channel Binding TLS Exporter Label . . . 4 57 5. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 58 5.1. Normative References . . . . . . . . . . . . . . . . . . 4 59 5.2. Informative References . . . . . . . . . . . . . . . . . 4 60 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5 62 1. Introduction 64 The "unique" channel binding types defined in [RFC5929] were found to 65 be vulnerable to the "triple handshake vulnerability" 66 [TRIPLE-HANDSHAKE] without the extended master secret extension 67 defined in [RFC7627]. Because of this they were not defined for TLS 68 1.3 (see [RFC8446] section C.5). To facilitate channel binding with 69 TLS 1.3, a new channel binding type is needed. 71 1.1. Conventions and Terminology 73 Throughout this document the acronym "EKM" is used to refer to 74 Exported Keying Material as defined in [RFC5705]. 76 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 77 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 78 "OPTIONAL" in this document are to be interpreted as described in BCP 79 14 [RFC2119] [RFC8174] when, and only when, they appear in all 80 capitals, as shown here. 82 2. The 'tls-exporter' Channel Binding Type 84 Channel binding mechanisms are not useful until TLS implementations 85 expose the required data. To facilitate this, "tls-exporter" uses 86 exported keying material (EKM) which is already widely exposed by TLS 87 implementations. The EKM is obtained using the keying material 88 exporters for TLS as defined in [RFC5705] and [RFC8446] section 7.5 89 by supplying the following inputs: 91 Label: The ASCII string "EXPORTER-Channel-Binding" with no 92 terminating NUL. 94 Context value: Empty context value. 96 Length: 32 bytes. 98 When TLS renegotiation is enabled (pre TLS 1.3) the "tls-exporter" 99 channel binding type is not defined and implementations MUST NOT 100 support it. 102 3. Security Considerations 104 While it is possible to use this channel binding mechanism with TLS 105 versions below 1.3, extra precaution must be taken to ensure that the 106 chosen cipher suites always result in unique master secrets. For 107 more information see the Security Considerations section of 108 [RFC5705]. 110 The Security Considerations sections of [RFC5056], [RFC5705], and 111 [RFC8446] apply to this document. 113 4. IANA Considerations 115 4.1. Registration of Channel Binding Type 117 This document adds the following registration in the "Channel-Binding 118 Types" registry: 120 Subject: Registration of channel binding tls-exporter 122 Channel binding unique prefix: tls-exporter 124 Channel binding type: unique 126 Channel type: TLS [RFC8446] 128 Published specification: draft-ietf-kitten-tls-channel-bindings-for- 129 tls13-02 131 Channel binding is secret: no 133 Description: The EKM value obtained from the current TLS connection. 135 Intended usage: COMMON 137 Person and email address to contact for further information: Sam 138 Whited . 140 Owner/Change controller name and email address: IESG. 142 Expert reviewer name and contact information: IETF KITTEN or TLS WG 143 (kitten@ietf.org or tls@ietf.org, failing that, ietf@ietf.org). 145 Note: See the published specification for advice on the 146 applicability of this channel binding type. 148 4.2. Registration of Channel Binding TLS Exporter Label 150 This document adds the following registration in the "TLS Exporter 151 Labels" registry: 153 Value: EXPORTER-Channel-Binding 155 DTLS-OK: Y 157 Recommended: N 159 Reference: This document 161 5. References 163 5.1. Normative References 165 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 166 Requirement Levels", BCP 14, RFC 2119, 167 DOI 10.17487/RFC2119, March 1997, 168 . 170 [RFC5056] Williams, N., "On the Use of Channel Bindings to Secure 171 Channels", RFC 5056, DOI 10.17487/RFC5056, November 2007, 172 . 174 [RFC5705] Rescorla, E., "Keying Material Exporters for Transport 175 Layer Security (TLS)", RFC 5705, DOI 10.17487/RFC5705, 176 March 2010, . 178 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 179 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 180 May 2017, . 182 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 183 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 184 . 186 5.2. Informative References 188 [RFC5929] Altman, J., Williams, N., and L. Zhu, "Channel Bindings 189 for TLS", RFC 5929, DOI 10.17487/RFC5929, July 2010, 190 . 192 [RFC7627] Bhargavan, K., Ed., Delignat-Lavaud, A., Pironti, A., 193 Langley, A., and M. Ray, "Transport Layer Security (TLS) 194 Session Hash and Extended Master Secret Extension", 195 RFC 7627, DOI 10.17487/RFC7627, September 2015, 196 . 198 [TRIPLE-HANDSHAKE] 199 Bhargavan, K., Delignat-Lavaud, A., Fournet, C., Pironti, 200 A., and P. Strub, "Password Storage", March 2014, 201 . 203 Author's Address 205 Sam Whited 206 Atlanta, GA 207 United States of America 209 Email: sam@samwhited.com 210 URI: https://blog.samwhited.com/