Channel Bindings for SCRAM over TLS 1.3
draft-whited-tls-channel-bindings-for-tls13-02

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Transport Layer Security                                       S. Whited
Internet-Draft                                                4 May 2020
Intended status: Experimental                                           
Expires: 5 November 2020

                Channel Bindings for SCRAM over TLS 1.3
             draft-whited-tls-channel-bindings-for-tls13-02

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.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on 5 November 2020.

Copyright Notice

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   document authors.  All rights reserved.

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   Please review these documents carefully, as they describe your rights
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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],
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