Channel Bindings for SCRAM over TLS 1.3
draft-whited-tls-channel-bindings-for-tls13-01

Transport Layer Security                                       S. Whited
Internet-Draft                                                2 May 2020
Intended status: Experimental                                           
Expires: 3 November 2020

                Channel Bindings for SCRAM over TLS 1.3
             draft-whited-tls-channel-bindings-for-tls13-01

Abstract

   This document defines a channel binding type, tls-scram-exporter,
   that is compatible with SCRAM [RFC5802] and TLS 1.3 [RFC8446] in
   accordance with On Channel Binding [RFC5056].

Status of This Memo

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

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   This Internet-Draft will expire on 3 November 2020.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions and Terminology . . . . . . . . . . . . . . .   2
   2.  The 'tls-scram-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  . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   After problems were found with the channel binding types defined in
   [RFC5929] they were not defined for TLS 1.3 [RFC8446].  To facilitate
   channel binding with TLS 1.3, a new channel binding type using keying
   material obtained from [RFC5705] 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-scram-exporter' Channel Binding Type

   IANA will register the 'tls-scram-exporter' channel binding type to
   match the description below.

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

   The EKM is obtained using the keying material exporters for TLS as
   defined in [RFC5705] by supplying the following inputs.  The
   definition of "client-first-message-bare" and "server-first-message"
   can be found in [RFC5802].

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

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   Context value:  client-first-message-bare + "," + server-first-
      message

   Length:  32 bytes.

   When TLS renegotiation is enabled channel binding using the "tls-
   scram-exporter" type is not define and MUST NOT be supported.

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],
   [RFC5802], 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-scram-exporter

   Channel binding unique prefix:  tls-scram-exporter

   Channel binding type:  unique

   Channel type:  TLS [RFC8446]

   Published specification:
      draft-whited-tls-channel-bindings-for-tls13-00

   Channel binding is secret:  no

   Description:  <See specification>

   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.

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

   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-SCRAM-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>.

   [RFC5802]  Newman, C., Menon-Sen, A., Melnikov, A., and N. Williams,
              "Salted Challenge Response Authentication Mechanism
              (SCRAM) SASL and GSS-API Mechanisms", RFC 5802,
              DOI 10.17487/RFC5802, July 2010,
              <https://www.rfc-editor.org/info/rfc5802>.

   [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>.

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   [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>.

Author's Address

   Sam Whited
   Atlanta,  GA
   United States of America

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

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