DNS-Based Service Discovery (DNS-SD) Privacy and Security Requirements
RFC 8882

Document Type RFC - Informational (September 2020; No errata)
Authors Christian Huitema  , Daniel Kaiser 
Last updated 2020-09-10
Replaces draft-huitema-dnssd-prireq
Stream IETF
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Stream WG state Submitted to IESG for Publication
Document shepherd David Schinazi
Shepherd write-up Show (last changed 2020-01-16)
IESG IESG state RFC 8882 (Informational)
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Send notices to David Schinazi <dschinazi.ietf@gmail.com>


Internet Engineering Task Force (IETF)                        C. Huitema
Request for Comments: 8882                          Private Octopus Inc.
Category: Informational                                        D. Kaiser
ISSN: 2070-1721                                 University of Luxembourg
                                                          September 2020

 DNS-Based Service Discovery (DNS-SD) Privacy and Security Requirements

Abstract

   DNS-SD (DNS-based Service Discovery) normally discloses information
   about devices offering and requesting services.  This information
   includes hostnames, network parameters, and possibly a further
   description of the corresponding service instance.  Especially when
   mobile devices engage in DNS-based Service Discovery at a public
   hotspot, serious privacy problems arise.  We analyze the requirements
   of a privacy-respecting discovery service.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are candidates for any level of Internet
   Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8882.

Copyright Notice

   Copyright (c) 2020 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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   publication of this document.  Please review these documents
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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
   2.  Threat Model
   3.  Threat Analysis
     3.1.  Service Discovery Scenarios
       3.1.1.  Private Client and Public Server
       3.1.2.  Private Client and Private Server
       3.1.3.  Wearable Client and Server
     3.2.  DNS-SD Privacy Considerations
       3.2.1.  Information Made Available Via DNS-SD Resource Records
       3.2.2.  Privacy Implication of Publishing Service Instance
               Names
       3.2.3.  Privacy Implication of Publishing Node Names
       3.2.4.  Privacy Implication of Publishing Service Attributes
       3.2.5.  Device Fingerprinting
       3.2.6.  Privacy Implication of Discovering Services
     3.3.  Security Considerations
       3.3.1.  Authenticity, Integrity, and Freshness
       3.3.2.  Confidentiality
       3.3.3.  Resistance to Dictionary Attacks
       3.3.4.  Resistance to Denial-of-Service Attacks
       3.3.5.  Resistance to Sender Impersonation
       3.3.6.  Sender Deniability
     3.4.  Operational Considerations
       3.4.1.  Power Management
       3.4.2.  Protocol Efficiency
       3.4.3.  Secure Initialization and Trust Models
       3.4.4.  External Dependencies
   4.  Requirements for a DNS-SD Privacy Extension
     4.1.  Private Client Requirements
     4.2.  Private Server Requirements
     4.3.  Security and Operation
   5.  IANA Considerations
   6.  References
     6.1.  Normative References
     6.2.  Informative References
   Acknowledgments
   Authors' Addresses

1.  Introduction

   DNS-Based Service Discovery (DNS-SD) [RFC6763] over Multicast DNS
   (mDNS) [RFC6762] enables zero-configuration service discovery in
   local networks.  It is very convenient for users, but it requires the
   public exposure of the offering and requesting identities along with
   information about the offered and requested services.  Parts of the
   published information can seriously breach the user's privacy.  These
   privacy issues and potential solutions are discussed in [KW14a],
   [KW14b], and [K17].  While the multicast nature of mDNS makes these
   risks obvious, most risks derive from the observability of
   transactions.  These risks also need to be mitigated when using
   server-based variants of DNS-SD.

   There are cases when nodes connected to a network want to provide or
   consume services without exposing their identities to the other
   parties connected to the same network.  Consider, for example, a
   traveler wanting to upload pictures from a phone to a laptop when
   both are connected to the Wi-Fi network of an Internet cafe, or two
   travelers who want to share files between their laptops when waiting
   for their plane in an airport lounge.
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