TLS Encrypted Client Hello
draft-ietf-tls-esni-07

Document Type Active Internet-Draft (tls WG)
Last updated 2020-06-01
Replaces draft-rescorla-tls-esni
Stream IETF
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Stream WG state WG Document (wg milestone: Mar 2021 - Submit "Encrypted Se... )
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tls                                                          E. Rescorla
Internet-Draft                                                RTFM, Inc.
Intended status: Experimental                                     K. Oku
Expires: 3 December 2020                                          Fastly
                                                             N. Sullivan
                                                               C.A. Wood
                                                              Cloudflare
                                                             1 June 2020

                       TLS Encrypted Client Hello
                         draft-ietf-tls-esni-07

Abstract

   This document describes a mechanism in Transport Layer Security (TLS)
   for encrypting a ClientHello message under a server public key.

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   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 3 December 2020.

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
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Rescorla, et al.         Expires 3 December 2020                [Page 1]
Internet-Draft         TLS Encrypted Client Hello              June 2020

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   4
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Topologies  . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Encrypted ClientHello (ECH) . . . . . . . . . . . . . . .   5
   4.  Encrypted ClientHello Configuration . . . . . . . . . . . . .   6
   5.  The "encrypted_client_hello" extension  . . . . . . . . . . .   7
   6.  The "ech_nonce" extension . . . . . . . . . . . . . . . . . .   9
     6.1.  Incorporating Outer Extensions  . . . . . . . . . . . . .   9
   7.  Client Behavior . . . . . . . . . . . . . . . . . . . . . . .  10
     7.1.  Sending an encrypted ClientHello  . . . . . . . . . . . .  10
     7.2.  Recommended Padding Scheme  . . . . . . . . . . . . . . .  12
     7.3.  Handling the server response  . . . . . . . . . . . . . .  12
       7.3.1.  Accepted ECH  . . . . . . . . . . . . . . . . . . . .  13
       7.3.2.  Rejected ECH  . . . . . . . . . . . . . . . . . . . .  13
       7.3.3.  HelloRetryRequest . . . . . . . . . . . . . . . . . .  14
     7.4.  GREASE extensions . . . . . . . . . . . . . . . . . . . .  15
   8.  Client-Facing Server Behavior . . . . . . . . . . . . . . . .  16
   9.  Compatibility Issues  . . . . . . . . . . . . . . . . . . . .  18
     9.1.  Misconfiguration and Deployment Concerns  . . . . . . . .  18
     9.2.  Middleboxes . . . . . . . . . . . . . . . . . . . . . . .  19
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  19
     10.1.  Why is cleartext DNS OK? . . . . . . . . . . . . . . . .  19
     10.2.  Client Tracking  . . . . . . . . . . . . . . . . . . . .  20
     10.3.  Optional Record Digests and Trial Decryption . . . . . .  20
     10.4.  Related Privacy Leaks  . . . . . . . . . . . . . . . . .  20
     10.5.  Comparison Against Criteria  . . . . . . . . . . . . . .  21
       10.5.1.  Mitigate against replay attacks  . . . . . . . . . .  21
       10.5.2.  Avoid widely-deployed shared secrets . . . . . . . .  21
       10.5.3.  Prevent SNI-based DoS attacks  . . . . . . . . . . .  21
       10.5.4.  Do not stick out . . . . . . . . . . . . . . . . . .  21
       10.5.5.  Forward secrecy  . . . . . . . . . . . . . . . . . .  22
       10.5.6.  Proper security context  . . . . . . . . . . . . . .  22
       10.5.7.  Split server spoofing  . . . . . . . . . . . . . . .  22
       10.5.8.  Supporting multiple protocols  . . . . . . . . . . .  22
     10.6.  Padding Policy . . . . . . . . . . . . . . . . . . . . .  22
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