Opportunistic Security: Some Protection Most of the Time
draft-dukhovni-opportunistic-security-04

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Network Working Group                                        V. Dukhovni
Internet-Draft                                                 Two Sigma
Intended status: Informational                           August 25, 2014
Expires: February 26, 2015

        Opportunistic Security: Some Protection Most of the Time
                draft-dukhovni-opportunistic-security-04

Abstract

   This document defines the concept "Opportunistic Security" in the
   context of communications protocols.  Protocol designs based on
   Opportunistic Security remove barriers to the widespread use of
   encryption on the Internet by using encryption even when
   authentication is not available, and using authentication when
   possible.

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 February 26, 2015.

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   Copyright (c) 2014 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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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Background  . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  A New Perspective . . . . . . . . . . . . . . . . . . . .   5
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Opportunistic Security Design Principles  . . . . . . . . . .   6
   4.  Example: Opportunistic TLS in SMTP  . . . . . . . . . . . . .   8
   5.  Operational Considerations  . . . . . . . . . . . . . . . . .   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Broadly speaking, Opportunistic Security (OS) is a pragmatic risk
   management approach.  With Opportunistic Security, one applies the
   tools at hand to mitigate the risks that can reasonably be addressed,
   and accepts the rest.

   Definition:  In the context of communications protocols,
      "Opportunistic Security" is defined as the use of encryption when
      possible, with authentication when possible.  In the above, the
      phrase "when possible" means when support for the corresponding
      capability is advertised by the peer, ideally in a downgrade-
      resistant manner.

   Encryption is used to mitigate the risk of passive monitoring
   attacks, while authentication is used to mitigate the risk of active
   man-in-the-middle (MiTM) attacks.  When encryption capability is
   advertised over an insecure channel, MiTM downgrade attacks to
   cleartext may be possible.  Since encryption alone mitigates only
   passive attacks, this risk is consistent with the expected level of
   protection.  For authentication based on peer capabilities to protect
   against MiTM attacks, capability advertisements need to be over an
   out-of-band authenticated channel that is itself resistant to MiTM
   attack.

   To achieve widespread adoption, OS must support incremental
   deployment.  Incremental deployment implies that security
   capabilities will vary from peer to peer, perhaps for a very long
   time.  OS protocols will attempt to establish encrypted communication
   whenever both parties are capable of such, and authenticated
   communication if that is also possible.  Thus, use of an OS protocol
   may yield communication that is authenticated and encrypted,

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   unauthenticated but encrypted, or cleartext.  This last outcome will
   occur if not all parties to a communication support encryption (or if
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