SNI Encryption in TLS Through Tunneling
draft-ietf-tls-sni-encryption-00

Document Type Active Internet-Draft (tls WG)
Last updated 2017-08-29
Replaces draft-huitema-tls-sni-encryption
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Network Working Group                                         C. Huitema
Internet-Draft                                      Private Octopus Inc.
Intended status: Standards Track                             E. Rescorla
Expires: March 2, 2018                                        RTFM, Inc.
                                                         August 29, 2017

                SNI Encryption in TLS Through Tunneling
                  draft-ietf-tls-sni-encryption-00.txt

Abstract

   This draft describes the general problem of encryption of the Server
   Name Identification (SNI) parameter.  The proposed solutions hide a
   Hidden Service behind a Fronting Service, only disclosing the SNI of
   the Fronting Service to external observers.  The draft starts by
   listing known attacks against SNI encryption, discusses the current
   "co-tenancy fronting" solution, and then presents two potential TLS
   layer solutions that might mitigate these attacks.
   The first solution is based on TLS in TLS "quasi tunneling", and the
   second solution is based on "combined tickets".  These solutions only
   require minimal extensions to the TLS protocol.

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 2, 2018.

Copyright Notice

   Copyright (c) 2017 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
   (http://trustee.ietf.org/license-info) in effect on the date of

Huitema & Rescorla        Expires March 2, 2018                 [Page 1]
Internet-Draft            SNI Encryption in TLS              August 2017

   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Key Words . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Security and Privacy Requirements for SNI Encryption  . . . .   4
     2.1.  Mitigate Replay Attacks . . . . . . . . . . . . . . . . .   4
     2.2.  Avoid Widely Shared Secrets . . . . . . . . . . . . . . .   4
     2.3.  Prevent SNI-based Denial of Service Attacks . . . . . . .   4
     2.4.  Do not stick out  . . . . . . . . . . . . . . . . . . . .   5
     2.5.  Forward Secrecy . . . . . . . . . . . . . . . . . . . . .   5
     2.6.  Proper Security Context . . . . . . . . . . . . . . . . .   5
     2.7.  Fronting Server Spoofing  . . . . . . . . . . . . . . . .   6
   3.  HTTP Co-Tenancy Fronting  . . . . . . . . . . . . . . . . . .   6
     3.1.  HTTPS Tunnels . . . . . . . . . . . . . . . . . . . . . .   7
     3.2.  Delegation Token  . . . . . . . . . . . . . . . . . . . .   7
   4.  SNI Encapsulation Specification . . . . . . . . . . . . . . .   8
     4.1.  Tunneling TLS in TLS  . . . . . . . . . . . . . . . . . .   9
     4.2.  Tunneling design issues . . . . . . . . . . . . . . . . .  11
       4.2.1.  Fronting Server logic . . . . . . . . . . . . . . . .  12
       4.2.2.  Early data  . . . . . . . . . . . . . . . . . . . . .  13
       4.2.3.  Client requirements . . . . . . . . . . . . . . . . .  13
   5.  SNI encryption with combined tickets  . . . . . . . . . . . .  13
     5.1.  Session resumption with combined tickets  . . . . . . . .  14
     5.2.  New Combined Session Ticket . . . . . . . . . . . . . . .  16
     5.3.  First session . . . . . . . . . . . . . . . . . . . . . .  18
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
     6.1.  Replay attacks and side channels  . . . . . . . . . . . .  19
     6.2.  Sticking out  . . . . . . . . . . . . . . . . . . . . . .  20
     6.3.  Forward Secrecy . . . . . . . . . . . . . . . . . . . . .  20
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  21
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