Issues and Requirements for SNI Encryption in TLS
draft-ietf-tls-sni-encryption-03

Document Type Active Internet-Draft (tls WG)
Last updated 2018-05-20
Replaces draft-huitema-tls-sni-encryption
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Network Working Group                                         C. Huitema
Internet-Draft                                      Private Octopus Inc.
Intended status: Informational                               E. Rescorla
Expires: November 21, 2018                                    RTFM, Inc.
                                                            May 20, 2018

           Issues and Requirements for SNI Encryption in TLS
                    draft-ietf-tls-sni-encryption-03

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 lists known
   attacks against SNI encryption, discusses the current "co-tenancy
   fronting" solution, and presents requirements for future TLS layer
   solutions.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on November 21, 2018.

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   Copyright (c) 2018 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
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Huitema & Rescorla      Expires November 21, 2018               [Page 1]
Internet-Draft       TLS-SNI Encryption Requirements            May 2018

   include Simplified BSD License text as described in Section 4.e of
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  History of the TLS SNI extension  . . . . . . . . . . . . . .   3
     2.1.  Unanticipated usage of SNI information  . . . . . . . . .   3
     2.2.  SNI encryption timeliness . . . . . . . . . . . . . . . .   4
     2.3.  End-to-end alternatives . . . . . . . . . . . . . . . . .   4
   3.  Security and Privacy Requirements for SNI Encryption  . . . .   5
     3.1.  Mitigate Replay Attacks . . . . . . . . . . . . . . . . .   5
     3.2.  Avoid Widely Shared Secrets . . . . . . . . . . . . . . .   5
     3.3.  Prevent SNI-based Denial of Service Attacks . . . . . . .   6
     3.4.  Do not stick out  . . . . . . . . . . . . . . . . . . . .   6
     3.5.  Forward Secrecy . . . . . . . . . . . . . . . . . . . . .   6
     3.6.  Proper Security Context . . . . . . . . . . . . . . . . .   6
     3.7.  Fronting Server Spoofing  . . . . . . . . . . . . . . . .   7
     3.8.  Supporting multiple protocols . . . . . . . . . . . . . .   7
       3.8.1.  Hiding the Application Layer Protocol Negotiation . .   8
       3.8.2.  Support other transports than HTTP  . . . . . . . . .   8
     3.9.  Fail to fronting  . . . . . . . . . . . . . . . . . . . .   8
   4.  HTTP Co-Tenancy Fronting  . . . . . . . . . . . . . . . . . .   9
     4.1.  HTTPS Tunnels . . . . . . . . . . . . . . . . . . . . . .  10
     4.2.  Delegation Control  . . . . . . . . . . . . . . . . . . .  10
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   Historically, adversaries have been able to monitor the use of web
   services through three channels: looking at DNS requests, looking at
   IP addresses in packet headers, and looking at the data stream
   between user and services.  These channels are getting progressively
   closed.  A growing fraction of Internet communication is encrypted,
   mostly using Transport Layer Security (TLS) [RFC5246].  Progressive
   deployment of solutions like DNS in TLS [RFC7858] mitigates the
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