Channel Bindings for TLS 1.3
draft-ietf-kitten-tls-channel-bindings-for-tls13-01

Document Type Active Internet-Draft (kitten WG)
Author Sam Whited 
Last updated 2020-11-18
Replaces draft-whited-tls-channel-bindings-for-tls13
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Transport Layer Security                                       S. Whited
Internet-Draft                                          18 November 2020
Updates: 5802, 8446 (if approved)                                       
Intended status: Standards Track                                        
Expires: 22 May 2021

                      Channel Bindings for TLS 1.3
          draft-ietf-kitten-tls-channel-bindings-for-tls13-01

Abstract

   This document defines a channel binding type, tls-exporter, that is
   compatible with TLS 1.3 in accordance with RFC 5056, On Channel
   Binding.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   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 22 May 2021.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 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
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   provided without warranty as described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions and Terminology . . . . . . . . . . . . . . .   2
   2.  The 'tls-exporter' Channel Binding Type . . . . . . . . . . .   2
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
     4.1.  Registration of Channel Binding Type  . . . . . . . . . .   3
     4.2.  Registration of Channel Binding TLS Exporter Label  . . .   4
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   The channel binding types defined in [RFC5929] were found to be
   vulnerable to the "triple handshake vulnerability" [TRIPLE-HANDSHAKE]
   without the extended master secret extension defined in [RFC7627].
   Because of this they were not defined for TLS 1.3 (see [RFC8446]
   section C.5).  To facilitate channel binding with TLS 1.3, a new
   channel binding type is needed.

1.1.  Conventions and Terminology

   Throughout this document the acronym "EKM" is used to refer to
   Exported Keying Material as defined in [RFC5705].

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "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.  The 'tls-exporter' Channel Binding Type

   Channel binding mechanisms are not useful until TLS implementations
   expose the required data.  To facilitate this, "tls-exporter" uses
   exported keying material (EKM) which is already widely exposed by TLS
   implementations.  The EKM is obtained using the keying material
   exporters for TLS as defined in [RFC5705] and [RFC8446] section 7.5
   by supplying the following inputs:

   Label:  The ASCII string "EXPORTER-Channel-Binding" with no
      terminating NUL.

   Context value:  Empty context value.

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   Length:  32 bytes.

   When TLS renegotiation is enabled the "tls-exporter" channel binding
   type is not defined and implementations MUST NOT support it.

3.  Security Considerations

   While it is possible to use this channel binding mechanism with TLS
   versions below 1.3, extra precaution must be taken to ensure that the
   chosen cipher suites always result in unique master secrets.  For
   more information see the Security Considerations section of
   [RFC5705].

   The Security Considerations sections of [RFC5056], [RFC5705], and
   [RFC8446] apply to this document.

4.  IANA Considerations

4.1.  Registration of Channel Binding Type

   This document adds the following registration in the "Channel-Binding
   Types" registry:

   Subject:  Registration of channel binding tls-exporter

   Channel binding unique prefix:  tls-exporter

   Channel binding type:  unique

   Channel type:  TLS [RFC8446]

   Published specification:  draft-ietf-kitten-tls-channel-bindings-for-
      tls13-01

   Channel binding is secret:  no

   Description:  The EKM value obtained from the current TLS connection.

   Intended usage:  COMMON

   Person and email address to contact for further information:  Sam
      Whited <sam@samwhited.com>.

   Owner/Change controller name and email address:  IESG.

   Expert reviewer name and contact information:  IETF KITTEN or TLS WG
      (kitten@ietf.org or tls@ietf.org, failing that, ietf@ietf.org).

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   Note:  See the published specification for advice on the
      applicability of this channel binding type.

4.2.  Registration of Channel Binding TLS Exporter Label

   This document adds the following registration in the "TLS Exporter
   Labels" registry:

   Value:  EXPORTER-Channel-Binding

   DTLS-OK:  Y

   Recommended:  N

   Reference:  This document

5.  References

5.1.  Normative References

   [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>.

   [RFC5056]  Williams, N., "On the Use of Channel Bindings to Secure
              Channels", RFC 5056, DOI 10.17487/RFC5056, November 2007,
              <https://www.rfc-editor.org/info/rfc5056>.

   [RFC5705]  Rescorla, E., "Keying Material Exporters for Transport
              Layer Security (TLS)", RFC 5705, DOI 10.17487/RFC5705,
              March 2010, <https://www.rfc-editor.org/info/rfc5705>.

   [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>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

5.2.  Informative References

   [RFC5929]  Altman, J., Williams, N., and L. Zhu, "Channel Bindings
              for TLS", RFC 5929, DOI 10.17487/RFC5929, July 2010,
              <https://www.rfc-editor.org/info/rfc5929>.

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   [RFC7627]  Bhargavan, K., Ed., Delignat-Lavaud, A., Pironti, A.,
              Langley, A., and M. Ray, "Transport Layer Security (TLS)
              Session Hash and Extended Master Secret Extension",
              RFC 7627, DOI 10.17487/RFC7627, September 2015,
              <https://www.rfc-editor.org/info/rfc7627>.

   [TRIPLE-HANDSHAKE]
              Bhargavan, K., Delignat-Lavaud, A., Fournet, C., Pironti,
              A., and P. Strub, "Password Storage", March 2014,
              <https://www.mitls.org/pages/attacks/3SHAKE>.

Author's Address

   Sam Whited
   Atlanta,  GA
   United States of America

   Email: sam@samwhited.com
   URI:   https://blog.samwhited.com/

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