TLS 1.3 Extension for Certificate-based Authentication with an External Pre-Shared Key
draft-housley-tls-tls13-cert-with-extern-psk-02

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Last updated 2018-09-26
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Network Working Group                                         R. Housley
Internet-Draft                                            Vigil Security
Intended status: Standards Track                      September 26, 2018
Expires: March 30, 2019

TLS 1.3 Extension for Certificate-based Authentication with an External
                             Pre-Shared Key
            draft-housley-tls-tls13-cert-with-extern-psk-02

Abstract

   This document specifies a TLS 1.3 extension that allows a server to
   authenticate with a certificate while also providing a pre-shared key
   (PSK) as an input to the key schedule.

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 March 30, 2019.

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1.  Introduction

   The TLS 1.3 [RFC8446] handshake protocol provides two mutually
   exclusive forms of server authentication.  First, the server can be
   authenticated by providing a signature certificate and creating a
   valid digital signature to demonstrate that it possesses the
   corresponding private key.  Second, the server can be authenticated
   by demonstrating that it possesses a pre-shared key (PSK) that was
   established by a previous handshake.  A PSK that is established in
   this fashion is called a resumption PSK.  A PSK that is established
   by any other means is called an external PSK.  This document
   specifies a TLS 1.3 extension permitting certificate-based server
   authentication to be combined with either of these two types of PSK
   as an input to the TLS 1.3 key schedule.

2.  Terminology

   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.

3.  Motivation and Design Rationale

   The motivation for using a certificate with an external PSK is
   different than the motivation for using a certificate with a
   resumption PSK.

3.1.  Certificate With External PSK

   The invention of a large-scale quantum computer would pose a serious
   challenge for the cryptographic algorithms that are widely deployed
   today, including the digital signature algorithms that are used to
   authenticate the server in the TLS 1.3 handshake protocol and key
   agreement algorithm used to establish a pairwise shared secret
   between the client and server.  It is an open question whether or not
   it is feasible to build a large-scale quantum computer, and if so,
   when that might happen.  However, if such a quantum computer is
   invented, many of the cryptographic algorithms and the security
   protocols that use them would become vulnerable.

   The TLS 1.3 handshake protocol employs key agreement algorithms that
   could be broken by the invention of a large-scale quantum computer
   [I-D.hoffman-c2pq].  These algorithms include Diffie-Hellman (DH)
   [DH] and Elliptic Curve Diffie-Hellman (ECDH) [IEEE1363].  As a
   result, an adversary that stores a TLS 1.3 handshake protocol

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   exchange today could decrypt the associated encrypted communications
   in the future when a large-scale quantum computer becomes available.

   When a certificate is used for authentication and a strong external
   PSK is used in conjunction with a key agreement algorithm, today's
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