Linkable Identifiers
draft-wood-linkable-identifiers-00

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Last updated 2018-10-22
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Network Working Group                                            C. Wood
Internet-Draft                                                Apple Inc.
Intended status: Informational                          October 22, 2018
Expires: April 25, 2019

                          Linkable Identifiers
                 draft-wood-linkable-identifiers-00

Abstract

   Rotating public identifiers is encouraged as best practice as a means
   of protecting endpoint privacy.  For example, regular MAC address
   randomization helps mitigate device tracking across time and space.
   Other protocols beyond those in the link layer also have public
   identifiers or parameters that should rotate over time, in unison
   with coupled protocol identifiers, and perhaps with application level
   identifiers.  This document surveys such privacy-related identifiers
   exposed by common Internet protocols at various layers in a network
   stack.  It provides advice for rotating linked identifiers such that
   privacy violations do not occur from rotating one identifier while
   neglecting to rotate coupled identifiers.

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 April 25, 2019.

Copyright Notice

   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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of

Wood                     Expires April 25, 2019                 [Page 1]
Internet-Draft            linkable-identifiers              October 2018

   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Sticky Protocol Identifiers . . . . . . . . . . . . . . . . .   3
     2.1.  Internet and Link Layer . . . . . . . . . . . . . . . . .   3
     2.2.  Transport and Session Layer . . . . . . . . . . . . . . .   4
     2.3.  Application Layer:  . . . . . . . . . . . . . . . . . . .   5
   3.  Identifier Scope and Threat Model . . . . . . . . . . . . . .   6
   4.  Limiting Linkable Identifiers . . . . . . . . . . . . . . . .   6
     4.1.  Time and Path Linkability . . . . . . . . . . . . . . . .   7
   5.  Timing Considerations . . . . . . . . . . . . . . . . . . . .   8
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   8.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   8
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   10. Normative References  . . . . . . . . . . . . . . . . . . . .   9
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   [RFC6973] defines the correlation of information relevant to or
   associated with a specific user as a significant attack on privacy.
   Different layers of the network stack use identifiers to uniquely
   address hosts or information flows.  To mitigate the privacy concern,
   many standards suggest randomizing or otherwise rotating such
   identifiers on a regular basis.  For example, a MAC address may be
   used to link otherwise unrelated network packets to a single device.
   Rotating the MAC address prevents this association at the link layer.
   However, when multiple identifiers are simultaneously present on
   different layers of the stack, breaking the association at any
   individual layer might be insufficient to disassociate a host from
   their network traffic.  Linkability can also occur across protocols
   and/or across layers.  For example, TLS connections are commonly
   preceded by DNS queries for a particular endpoint (host name), e.g.
   example.com.  Moreover, in the TLS handshake, this same host name is
   sent in cleartext in the Server Name Indication extension.  Thus,
   observing either the DNS query or TLS SNI reveals information about
   the other.  Similarly, while an IP address of a device may rotate, if
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