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Network Working Group                                        E. Nordmark
Internet-Draft                                                    Zededa
Intended status: Standards Track                            July 2, 2018
Expires: January 3, 2019

            Privacy issues in ID/locator separation systems


   There exists several protocols and proposals for identifier/locator
   split which have some form of control plane by which participating
   nodes can use to share their current id to locator information with
   their peers.  This document explores some of the privacy
   considerations for such a system.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on January 3, 2019.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Keywords and Terminology  . . . . . . . . . . . . . . . . . .   3
   3.  Assumptions . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Threats against Privacy . . . . . . . . . . . . . . . . . . .   4
     4.1.  Location Privacy  . . . . . . . . . . . . . . . . . . . .   4
     4.2.  Movement Privacy  . . . . . . . . . . . . . . . . . . . .   4
   5.  Not everybody all the time  . . . . . . . . . . . . . . . . .   4
     5.1.  Optimized routing . . . . . . . . . . . . . . . . . . . .   4
     5.2.  Family and Friends  . . . . . . . . . . . . . . . . . . .   5
     5.3.  Business Assets . . . . . . . . . . . . . . . . . . . . .   5
   6.  Boundary between ID/locator part and rest of Internet . . . .   5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   When the IP address is separated, one way or another, into an
   identifier and a locator there is typically a need to be able to look
   up an identifier to find possible locators which can be used to reach
   the identified endpoint.  If such a system (think distributed
   database) was publicly available while identifiers are assigned to
   devices such as mobile phones which have a strong binding with an
   individual, then this would introduce additional privacy
   considerations which do not exist in the absence of the ID/locator

   Without an ID/locator split a device is already providing its IP
   address (in the form of a source address) to any network device along
   the path, and also to the remote endpoint.  That endpoint in
   particular might use IP geolocation databases to get a pretty good
   idea of where its peer is located, for instance to offer information
   and/or advertising relevant to that location.

   However, such such a device (e.g., a laptop or smartphone connected
   over WiFi) move e.g., from home to a coffee shop, the IP address
   changes.  This makes it harder for network devices along the paths to
   realize that the its is the same mobile device.  And if the mobile
   device is not retaining cookies or logged into websites, those remote
   peers would also have some difficulty determining it is the same
   mobile device.  Furthermore, a mobile device which is using typical
   cellular network technologies end up with an IP address, at least as
   seen by remote peers outside of the cellular network, which is
   associated with the cellular operator but does not necessarily
   indicate a particular location of the mobile device.

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   Note that even if the IP address isn't always useful to track a
   mobile device today, there are several mechanisms higher in the stack
   which can do this.  For instance cookies or SSL sessions,
   applications which share GPS location, or operators who offer
   additional location information (for instance based on which cellular
   base station a mobile device is using) to business partners.

   With that baseline in mind, let's look at what additional privacy
   considerations can be introduced by a system which provides ID to
   locator mappings.

2.  Keywords and Terminology

   SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
   document, are to be interpreted as described in [RFC2119].

3.  Assumptions

   We assume that there are benefits associated with sharing ID to
   locator mappings with some peers sometimes.  Those benefits can be

   o  Lower latency and higher bandwidth: If two peer devices have some
      locators which are topologically closer, then sharing all the
      locators means that the devices can find a short path (fewer hops
      and/or shorter round-trip time), or find a path which offer higher
      throughput, then if the devices only shared some form of default
   o  Higher availability and robustness: If two peer devices share all
      their locators, then if there is some network outage the devices
      can autonomously discover a working path using the different
      locator pairs.

   However, those benefits do not imply that it is a good idea to always
   share all of the locators with everybody.  That would make tracking
   by third parties trivial.

   A device can obfuscate itself by, instead of using a single long-
   lived identifier, using multiple short-lived identifiers.  In that
   case the value to the ID/locator binding for any particular
   identifier would be lower.  However, this assumes that the device can
   ensure unlinkablity between the different identifiers it is using
   either concurrently or over time.  Also, some of the benefits above
   implicitly assume that there can be some long-lived sessions or
   associations between pairs of identifiers.  For instance, if a device
   would need to go fetch the current identifier of its peer from some
   remove system, then it might not experience improved robustness since
   that fetch might depend on the failed external connectivity.  Thus we

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   believe that we can explore the core of the ID/locator privacy issue
   by looking at long-lived identifiers.

4.  Threats against Privacy

   This is the first version of this draft so this is very preliminary.
   But there seems to be at least two different privacy threats relating
   to ID/locator mapping systems.

4.1.  Location Privacy

   If a third party can at any time determine the IP location of some
   identifier, then the device can at one point be IP geolocated at
   home, and later a coffee shop.

4.2.  Movement Privacy

   If a third party can determine that an identifier has changed
   locator(s) at time T, then even without knowing the particular
   locators before and after, it can correlate this movement event with
   other information (e.g., security cameras) to create a binding
   between the identifier and a person.

5.  Not everybody all the time

   In order to see the benefits about but minimizing the privacy
   implication one can explore limiting to which peers and when the ID/
   locator binding are exposed.

   A few initial examples help illustrate this.

5.1.  Optimized routing

   If some operator of a network where there is a large amount of
   mobility wants to ensure efficient routing, then a ID/locator split
   approach might make sense.  Such a system can potentially be limited
   to the set of devices (routers etc) which are under the operators
   control.  If this is the case, then the ID/locator mapping system can
   provide access control so that only those trusted devices can access
   the mappings.

   Note that from a privacy perspective this isn't any different than
   the same operator using a link-state routing protocol to share host
   routes for all the mobile devices.  In that case all participants in
   the link-state protocol can determine the location (attached to which
   router) and notice any mobility events.  Of course, there are
   significant non-privacy differences between those two approaches.

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   Exposing the ID/locator mapping to attached devices (e.g., any mobile
   devices which wouldn't be trusted to participate in the link-state
   routing counterpart approach), will change the privacy implications.

5.2.  Family and Friends

   There are cases where it is quite reasonable to share location
   information with other family members or friends.  For instance,
   young children might run applications which enable their parents to
   track them on their way to/from school.  And I might share my
   location with friends so we can more easily find each other while out
   on town.

   Today such location sharing happens at an application layer using GPS
   coordinates.  But while such sharing is in effect, it wouldn't be
   unreasonable to also consider sharing IP locators to make it more
   efficient or more robust to e.g., route a video feed from one device
   to another.

5.3.  Business Assets

   In the area of Industrial IoT there are cases where an asset owner
   might want to ensure that their assets can communicate efficiently
   and robustly.  In many cases those assets might be decoupled from any
   persons, but there can still be strong reasons to not share the ID/
   locator binding with third parties, such as enabling competitors to
   determine the number of deployed devices in a particular IP prefix.

6.  Boundary between ID/locator part and rest of Internet

   If the access to the ID/locator mapping are restricted as suggested
   above, then most of the potential peer devices would not have access
   to the ID/locator mappings.  This means that there has to be a
   demarcation point between the part of the network which can access
   the ID/locator mappings for a particular identifier and the one which
   can not.  There might be several choices how to handle this such as
   still using an ID/locator system but pointing a locator for some
   fixed anchor point, or injecting routing prefixes for the ID prefixes
   into the normal routing system, or not providing any stable locators
   across this boundary; only allow ephemeral IP addresses per session
   or otherwise limited exposure.

7.  Security Considerations

   This document discusses privacy considerations, but does not explore
   any security considerations.

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8.  IANA Considerations

   There are no IANA actions needed for this document.

9.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997, <https://www.rfc-

Author's Address

   Erik Nordmark
   Santa Clara, CA

   Email: nordmark@sonic.net

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