Encrypted Server Name Indication for TLS 1.3
draft-ietf-tls-esni-04

Document Type Active Internet-Draft (tls WG)
Last updated 2019-07-08
Replaces draft-rescorla-tls-esni
Stream IETF
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tls                                                          E. Rescorla
Internet-Draft                                                RTFM, Inc.
Intended status: Experimental                                     K. Oku
Expires: January 9, 2020                                          Fastly
                                                             N. Sullivan
                                                              Cloudflare
                                                                 C. Wood
                                                             Apple, Inc.
                                                           July 08, 2019

              Encrypted Server Name Indication for TLS 1.3
                         draft-ietf-tls-esni-04

Abstract

   This document defines a simple mechanism for encrypting the Server
   Name Indication for TLS 1.3.

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 January 9, 2020.

Copyright Notice

   Copyright (c) 2019 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

Rescorla, et al.         Expires January 9, 2020                [Page 1]
Internet-Draft           TLS 1.3 SNI Encryption                July 2019

   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   4
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Topologies  . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  SNI Encryption  . . . . . . . . . . . . . . . . . . . . .   5
   4.  Publishing the SNI Encryption Key in the DNS  . . . . . . . .   5
     4.1.  Encrypted SNI Record  . . . . . . . . . . . . . . . . . .   6
     4.2.  Encrypted SNI DNS Resolution  . . . . . . . . . . . . . .   8
       4.2.1.  Address Set Extension . . . . . . . . . . . . . . . .   8
       4.2.2.  Resolution Algorithm  . . . . . . . . . . . . . . . .   9
   5.  The "encrypted_server_name" extension . . . . . . . . . . . .  10
     5.1.  Client Behavior . . . . . . . . . . . . . . . . . . . . .  11
       5.1.1.  Sending an encrypted SNI  . . . . . . . . . . . . . .  11
       5.1.2.  Handling the server response  . . . . . . . . . . . .  14
       5.1.3.  Authenticating for the public name  . . . . . . . . .  15
       5.1.4.  GREASE extensions . . . . . . . . . . . . . . . . . .  16
     5.2.  Client-Facing Server Behavior . . . . . . . . . . . . . .  17
     5.3.  Shared Mode Server Behavior . . . . . . . . . . . . . . .  19
     5.4.  Split Mode Server Behavior  . . . . . . . . . . . . . . .  19
   6.  Compatibility Issues  . . . . . . . . . . . . . . . . . . . .  20
     6.1.  Misconfiguration and Deployment Concerns  . . . . . . . .  20
     6.2.  Middleboxes . . . . . . . . . . . . . . . . . . . . . . .  20
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  21
     7.1.  Why is cleartext DNS OK?  . . . . . . . . . . . . . . . .  21
     7.2.  Optional Record Digests and Trial Decryption  . . . . . .  21
     7.3.  Encrypting other Extensions . . . . . . . . . . . . . . .  22
     7.4.  Related Privacy Leaks . . . . . . . . . . . . . . . . . .  22
     7.5.  Comparison Against Criteria . . . . . . . . . . . . . . .  22
       7.5.1.  Mitigate against replay attacks . . . . . . . . . . .  22
       7.5.2.  Avoid widely-deployed shared secrets  . . . . . . . .  23
       7.5.3.  Prevent SNI-based DoS attacks . . . . . . . . . . . .  23
       7.5.4.  Do not stick out  . . . . . . . . . . . . . . . . . .  23
       7.5.5.  Forward secrecy . . . . . . . . . . . . . . . . . . .  23
       7.5.6.  Proper security context . . . . . . . . . . . . . . .  23
       7.5.7.  Split server spoofing . . . . . . . . . . . . . . . .  24
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