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Network Working Group                                            P. Sood
Internet-Draft                                                    Google
Intended status: Standards Track                              P. Hoffman
Expires: January 1, 2021                                           ICANN
                                                           June 30, 2020


       Upgrading Communication from Stub Resolvers to DoT or DoH
                      draft-pp-add-stub-upgrade-02

Abstract

   This document describes methods for a DNS stub resolver to upgrade
   its communications with a known recursive resolver to include
   encrytion using DoT or DoH.  This protocol is designed for the
   scenario where the stub resolver already has the IP address of the
   recursive resolver.

   Other protocols under develpment address scenarios where the stub
   resolver wants to discover recursive resolvers that use DoT or DoH.
   This document does not cover such discovery.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 1, 2021.

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
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
   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
     1.1.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Using RESINFO Responses for Upgrade . . . . . . . . . . . . .   3
     2.1.  Contacting This Resolver Using DoH  . . . . . . . . . . .   3
     2.2.  Contacting This Resolver Using DoT  . . . . . . . . . . .   3
     2.3.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Method Overview . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Order of Desired Protocols  . . . . . . . . . . . . . . .   6
   4.  Method Details  . . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  Inputs to the Process . . . . . . . . . . . . . . . . . .   6
     4.2.  TLS Authentication  . . . . . . . . . . . . . . . . . . .   7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  Registration for doh-templates in the IANA DNS Resolver
           Information Registry  . . . . . . . . . . . . . . . . . .   7
     5.2.  Registration for dot-ports in the IANA DNS Resolver
           Information Registry  . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   A stub resolver (hereafter called "a stub") using traditional DNS
   over port 53 may wish to use encrypted communication with the
   recursive resolver (hereafter called "a resolver").  In such a
   scenario, the stub needs to know how to probe the resolver to find
   out if it can use encrypted communication.  This document describes a
   mechanism for a stub that knows the IP address of the resolver to do
   so.  It is assumed that the IP address was received insecurely, such
   as through DHCP.

   The method in this document assumes that a stub wants to attempt to
   upgrade its communication with the resolver to either DNS-over-TLS
   (DoT, [RFC7858]) or DNS-over-HTTPS (DoH, [RFC8484]).  The method is
   basically to use a DNS request as defined in [I-D.pp-add-resinfo] to
   get information about whether the resolver supports DoT or DoH.  The
   method can later be extended to other secure transports for stub-to-
   resolver communication transports.



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1.1.  Definitions

   In the rest of this document, the term "resolver" without
   qualification means "recursive resolver" as defined in [RFC8499].
   Also, the term "stub" is used to mean "stub resolver".

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Using RESINFO Responses for Upgrade

   This document defines two entries for the IANA DNS Resolver
   Information Registry that is defined in [I-D.pp-add-resinfo].

2.1.  Contacting This Resolver Using DoH

   The "doh-templates" name is used to specify the URI template or
   templates that can be used by the stub resolver for DoH queries.  The
   value MUST be an array of URI templates.  Each element of the array
   in the value is a JSON string.  The host part of the URI template
   MUST be an IP address.

   [[ For future: maybe drop the "MUST be an IP address" restriction and
   say that it can be either an IP address or host name.  ]]

   The array in the value can be empty, which indicates that the
   resolver does not offer DoH service.  An empty array and the absence
   of a name/value pair for "doh-templates" have identical meanings.

   The value of "doh-templates" is an array of strings instead of just
   one string because a resolver might have more than one IP address or
   URL paths.  The order of the elements in the array has no meaning;
   that is, the array could instead be considered a set.

   [[ This section needs to be updated to handle DoH over HTTP/3.  These
   updates then need to be reflected in Section 3.  ]]

2.2.  Contacting This Resolver Using DoT

   The "dot-ports" name is used to specify the port(s) that can be used
   by the stub resolver for DoT queries.  The value MUST be an array of
   port numbers.  Each element of the array in the value is a JSON
   number.





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   The value of "dot-ports" is an array of numbers instead of just one
   number because a resolver might support DoT on more than one port.
   The order of the elements in the array has no meaning; that is, the
   array could instead be considered a set.

   The array in the value can be empty, which indicates that the
   resolver does not offer DoT service.  An empty array and the absence
   of a name/value pair for "dot-ports" have identical meanings.

   [[ For future: maybe add "dot-hostnames" to enable authentication.
   ]]

2.3.  Examples

   A resolver has two IP addresses, 192.0.2.222 and 203.0.113.77.  It
   offers DoH service, and offers DoT service on the default port.  It's
   response to the RESINFO query might be either one of:

   { "dot-ports": [ 853 ], "doh-templates":
      [ "https://203.0.113.77//dns-query{?dns}",
      "https://192.0.2.222//dns-query{?dns}" ] }

   A resolver does not offer DoH service, but does offer DoT service on
   the default port.  It's response to the RESINFO query might be either
   one of:

   { "dot-ports": [ 853 ], "doh-templates": [] }

   or

   { "dot-ports": [ 853 ] }

3.  Method Overview

   The pseudocode for the method is:

   # Things the stub resolver knows
   # dohCapable    Does the stub know how to do DoH
   # dotCapable    Does the stub know how to do DoT
   # resIP         IP address of resolver
   # upgradeNoAuth Does the stub want to upgrade even if it can't
                   authenticate the TLS session
   # insecureOK    Does the stub want to use unauthenticated classic
                   DNS if DoH/DoT upgrades fail

   [[ Need to fix dohCapable to deal with DoH templates that point to
   resolvers other than the one queried.  ]]




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   if dohCapable:
       send a DNS query of resolver-info.arpa/IN/RESINFO
       if there is a non-empty "doh-templates" name in the response:
           for each template in the name/value pair:
               start TLS session on resIP, port from DoH template
               if it succeeds
                   if it authenticates correctly
                       resolve the URI template
                       if 200-level response
                           use result to do DoH; finished
                       else if 300-level response
                               follow redirect, act appropriately
                       else if 400-level response
                               continue
                   else if upgradeNoAuth:
                       resolve the URI template
                       if 200-level response
                           use result to do DoH; finished
                       else if 300-level response
                           follow redirect, act appropriately
                       else if 400-level response
                           continue
                   else
                       continue
               else
                   continue
           # no DoH template worked

   if dotCapable:
       send a DNS query of resolver-info.arpa/IN/RESINFO
       if there is a non-empty "dot-ports" name in the response:
           for each port in the name/value pair:
               start TLS session on resIP and the port number
               if it succeeds
                   if it authenticates correctly
                       start doing DoT; finished
                   else if upgradeNoAuth:
                       start doing DoT; finished
                   else
                       continue
               else
                   continue
           # no DoT port worked

   if insecureOK:
       Use unencrypted DNS on port 53
   else
       DNS transport setup failed



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3.1.  Order of Desired Protocols

   The pseudocode in the previous section attempts to use DoH, DoT, and
   unencrypted DNS, in that order.  This is done to keep the pseudocode
   simple while demonstrating one possible order of transport selection.
   A stub implementation could attempt some or all of the available DNS
   transports in an implementation-specific or user-defined order.  For
   example, possible lists of transports to attempt might be:

   o  DoH, DoT, classic DNS

   o  DoT, DoH

   o  DoT, classic DNS

   o  Classic DNS

4.  Method Details

4.1.  Inputs to the Process

   The method described here requires the following information.  It is
   listed with variable names from the pseudocode in Section 3.

   resIP  The IP address of resolver.  This can be either an IPv4 or
      IPv6 address.

   dohCapable  Set to true if the stub knows how to be a DoH client

   dotCapable  Set to true if the stub knows how to be a DoT client

   upgradeNoAuth  Set to true the stub wants to use unauthenticated DoT
      or DoH if it is available.  Note that using unauthenticated DoT or
      DoH is inherently insecure because an on-path attacker can
      impersonate the resolver.

   insecureOK  Set to true if the stub wants to keep using classic
      (unencrypted) DNS on port 53 if the attempt to upgrade fails.
      Note that setting this to false will cause further DNS queries to
      fail if upgrade fails.

   [[ Add some possible implementation examples.  Here's one.  ]]

   For example, if an OS implementation's design is "just try TLS on
   port 853 of the current resolver", resIP is the resolver address,
   dohCapable is false, dotCapable is true, and upgradeNoAuth is set to
   true.




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4.2.  TLS Authentication

   In this mechanism, the stub has an IP address of the resolver.  It
   does not necessarily have a domain name associated with that IP
   address.

   In order to authenticate TLS sessions, the stub resolver must have a
   set of TLS trust anchors, such as those maintained by some operating
   systems.

   If the stub has a domain name associated with the resolver's IP
   address, and if the resolver uses that domain name in one of the
   subject identifiers in its certificate during the TLS exchange, the
   stub can use the domain name for authentication of the TLS session.

   The stub always has an IP address for the resolver.  If the resolver
   uses the same IP address used by the stub in one of the subject
   identifiers in its certificate during the TLS exchange, the stub can
   use the IP address for authentication of the TLS session.

   A resolver that uses this method to publish its information SHOULD,
   if possible, have a TLS certificate whose subject identifiers contain
   any of the IP addresses that stubs might be using for the resolver.
   At the time that this document is published, getting IP addresses in
   TLS certificates is possible, but there are only a few widely-trusted
   CAs that issue such certificates.  [RFC8738] describes a protocol
   that may cause IP address certificates to become more common.

5.  IANA Considerations

   This document defines two entries for the IANA DNS Resolver
   Information Registry that is defined in [I-D.pp-add-resinfo].

5.1.  Registration for doh-templates in the IANA DNS Resolver
      Information Registry

   Name: doh-templates

   Value type: Array of strings

   Specification: This document, Section 2.1

5.2.  Registration for dot-ports in the IANA DNS Resolver Information
      Registry

   Name: dot-ports

   Value type: Array of numbers



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   Specification: This document, Section 2.2

6.  Security Considerations

   The method described in this document explicitly allows a stub to
   perform DNS communications over traditional unencrypted,
   unauthenticated DNS on port 53.

   The method described in this document explicitly allows a stub to
   choose to allow unauthenticated TLS.  In this case, the resulting
   communication will be susceptible to obvious and well-understood
   attacks from an attacker in the path of the communications.

7.  References

7.1.  Normative References

   [I-D.pp-add-resinfo]
              Sood, P. and P. Hoffman, "DNS Resolver Information Self-
              publication", draft-pp-add-resinfo-01 (work in progress),
              May 2020.

   [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-editor.org/info/rfc2119>.

   [RFC7858]  Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
              and P. Hoffman, "Specification for DNS over Transport
              Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
              2016, <https://www.rfc-editor.org/info/rfc7858>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8484]  Hoffman, P. and P. McManus, "DNS Queries over HTTPS
              (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
              <https://www.rfc-editor.org/info/rfc8484>.

   [RFC8499]  Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
              Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
              January 2019, <https://www.rfc-editor.org/info/rfc8499>.








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7.2.  Informative References

   [RFC8738]  Shoemaker, R., "Automated Certificate Management
              Environment (ACME) IP Identifier Validation Extension",
              RFC 8738, DOI 10.17487/RFC8738, February 2020,
              <https://www.rfc-editor.org/info/rfc8738>.

Authors' Addresses

   Puneet Sood
   Google

   Email: puneets@google.com


   Paul Hoffman
   ICANN

   Email: paul.hoffman@icann.org
































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