[tor-dev] Registering special-use domain names of peer-to-peer name systems with IETF

Christian Grothoff christian at grothoff.org
Wed Nov 6 07:32:45 UTC 2013

Dear all,

Together with Matthias Wachs and Hellekin Wolf, I'm preparing an IESG
approval request
for the reservation of special-use domain names for P2P networks
according to RFC 6761.
The goal is to reserve .onion, .exit, .i2p, .gnu and .zkey (so that they
don't become
ordinary commercial TLDs at some point) and to at the same time document
their use and
how they should be processed for the broader community.

I've attached the current draft which we plan to submit shortly (unless,
of course, we
receive insightful comments that require major revisions).  As two of
the five pTLDs
involve Tor, we would be happy for feedback from the Tor developer

Happy hacking!

-------------- next part --------------
Internet Engineering Task Force (IETF)                       C. Grothoff
IESG Approval document                                          M. Wachs
                                                                 H. Wolf
                                                               TU Munich
                                                            Nov 13, 2013
Intended status: IESG Approved

          Special-Use Domain Names of Peer-to-Peer Name Systems


   Today, the Domain Name System (DNS) is a key service for the
   Internet.  DNS is primarily used to map human-memorable names to IP
   addresses, which are used for routing but generally not meaningful
   for humans.  However, the hierarchical nature of DNS makes it
   unsuitable for various Peer-to-Peer (P2P) Name Systems.  As
   compatibility with applications using DNS names is desired, these
   overlay networks often define alternative pseudo Top-Level Domains
   (pTLDs) to integrate names from the P2P domain into the DNS

   This memo describes five Special-Use Domain Names [RFC 6761] Top
   Level Domains (TLDs) designed to help harden name resolution
   security (e.g., [RFC 6840][RFC 6975]), provide censorship
   resistance, and protect the users' privacy on the Internet.

   In this IESG Approval document we are asking for domain name
   reservations for those five Special-Use Domain Names [RFC 6761].
   The TLDs are ".exit", ".gnu.", ".zkey.", ".onion.", and ".i2p.".

Status of this Memo

   This is a WIP draft in preparation for submission to IESG at the
   end of this week.  This draft is intended for feedback from the
   Tor community prior to submission to IESG.

   TODO: formatting, review text, review references.

Copyright Notice

   Copyright (c) 2013 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
   publication of this document. Please review these documents
   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.

1.  Introduction

   [RFC 6761] defines a mechanism for reserving DNS names for special

   This document is an IESG Approval document requesting the
   reservation of five pTLDs for special use: ".gnu.", ".i2p.",
   ".onion.", ".exit" and ".zkey.".

   These pTLDs are used in the GNU Name System (GNS), I2P and the Tor
   network to realize fully-decentralized and censorship-resistant
   secure alternatives for DNS or, in the case of ".exit", to control
   overlay routing.  To facilitate integration with legacy
   applications, the overlay's namespaces can be accessed from
   applications that only speak DNS using these special TLDs, for
   example via specialized SOCKS proxies [RFC 1928].

   We will describe the proposed special treatment for each of these
   pTLDs below following the questions from [RFC 6761].

2.  Terminology and Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   this document are to be interpreted as described in "Key words for
   use in RFCs to Indicate Requirement Levels" [RFC 2119].

   The word "peer" is used in the meaning of a individual system on
   the network.  Thus, "local peer" means the localhost.

   The acronym "pTLD" is used as a shortcut to mean a
   pseudo-top-level-domain, i.e., a name or label for a network that
   is not yet registered with IANA.  Specifically, it refers to one of
   the proposed Special-Use Domain Names already in use on the
   Internet and described in this document.

3.  Description of Special-Use Domains in P2P Networks

    TODO Add .exit and .noconnect for Tor
    TODO Reorganize by app?

3.1. The Human-Memorable ".gnu" pTLD

   The ".gnu" pTLD is used to specify that a domain name should be
   resolved using GNS instead of DNS.  The GNS resolution process is
   documented in [Schanzenbach 2012].  As GNS users need to install a
   GNS resolver on their individual system and as GNS resolution does
   not depend on DNS, there are no considerations for DNS with respect
   to the internals of the GNS resolution process itself.  Note that
   names in the ".gnu" pTLD SHOULD follow the naming conventions of

3.2. The Cryptographic-Hash ".zkey" pTLD

   The ".zkey" TLD is used to signify that resolution of the given
   name MUST be performed using a record signed by an authority that
   is in possession of a particular public key.  Names in the ".zkey"
   domain MUST end with a domain which is the compressed point
   representation from EdDSA on Curve25519 of the public key of the
   authority, encoded using base32hex [RFC 4648].  A GNS resolver uses
   the key to locate a record signed by the respective authority.

3.3. Circuit-Based Anonymizing pTLDs

   The Tor anonymization network makes use of three special domains to
   date [TorSpec].

3.3.1. The Hidden Service ".onion" pTLD

   The widely deployed ".onion" pTLD designates an anonymous hidden
   service reachable via the Tor network [Dingledine 2004].  Such
   addresses are typically resolved via a local SOCKS proxy running on
   TCP port 9050.  The purpose of using such a system is to make both
   the information provider and the person accessing the information
   more difficult to trace, whether by one another, by an intermediate
   network host, or by an outsider.

   Addresses in the ".onion" pTLD are opaque, non-mnemonic, alpha-
   semi-numeric hashes corresponding to the public key of the
   matching Tor hidden service.  This "Onion key" is generated
   automatically when the hidden service is configured, following the
   Tor specifications [TorSpec].  It can be made up of any letter of
   the alphabet and decimal digits beginning with 2 and ending with 7,
   thus representing a number in base32 [RFC 4648].

3.3.2. The Exit Node ".exit" pTLD

   The ".exit" suffix marks a way to access a DNS host via a Tor relay
   nickname, in the form "host.nickname.exit".  For example,
   "www.gnu.org.torservers.exit" will route the client to "www.gnu.org"
   via the Tor node named "torservers".  In
   "[hostname].[name-or-digest].exit", "hostname" is a valid DNS hostname;
   "[name-or-digest]" is either the nickname of a Tor node or the
   hex-encoded digest of that node's public key.  When Tor sees an
   address in this format, it uses the specified hostname as the exit
   node.  If no "[hostname]" component is given, Tor defaults to the
   published IPv4 address of the exit node.

3.3.3. The Interrupting ".noconnect" pTLD

   The ".noconnect" suffix is used in Tor for testing purpose: when
   Tor sees an address in this format, it immediately closes the
   connection without attaching it to any circuits.  It is useful for
   controllers that want to test whether a given application is indeed
   using the same instance of Tor that they're controlling.  This is
   a deprecated method and thus do not include ".noconnect" in the
   list of special-use domain names that should be reserved.

3.4. Packet-Switched-Based Anonymous ".i2p" pTLD

   I2P is an overlay network layer that allows applications to host
   websites within the I2P network.  These so-called "eepsites" are
   addressed using names in the ".i2p" pTLD.  They are resolved by the
   I2P proxy using either a local lookup table called the
   "addressbook", or by decoding Base32-encoded [RFC 4648] public keys
   and establishing a tunnel to the respective authority, similar to
   contacting hidden services in the ".onion" pTLD.  I2P uses 52
   characters (256 bits) of the SHA-256 hash of the public key.

4. IANA Considerations

   This document is requesting IANA to record the list of domains
   below as being Special-Use Domain Names [RFC 6761]:


4.1. Domain Name Reservation Considerations

   The five domains listed above, and any names falling within those
   domains (e.g., "example.gnu.", "core.onion.", etc.) are special
   [RFC 6761] in the following ways:

       Are human users expected to recognize these names as special and
       use them differently?  In what way?

      1. Users MAY use these names as they would other DNS names,
      entering them anywhere that they would otherwise enter a
      conventional DNS name, or a dotted decimal IPv4 address, or a
      literal IPv6 address.

      Since there is no central authority responsible for assigning
      dot-gnu and dot-i2p names, and that specific domain is local to
      the local peer, users SHOULD be aware of that specificity.

      Since there is no central authority responsible for assigning
      dot-b32-dot-i2p, dot-onion, and dot-zkey names, and those names
      match cryptographic keys, users SHOULD be aware that they don't
      belong to regular DNS, but are still global in their scope.

      In any case, resolution of the five proposed pTLDs is similar to
      the normal DNS resolution, and thus SHOULD not affect normal
      usage of most Internet applications.

       Are writers of application software expected to make their
       software recognize these names as special and treat them
       differently?  In what way?  (For example, if a human user enters
       such a name, should the application software reject it with an
       error message?)

      2. Application Software MAY pass requests to any of the five
      proposed pTLDs for normal DNS resolution if A/AAAA records are
      desired.  If available, the local DNS resolver MUST intercept
      such requests within the respective operating system hooks and
      behave like DNS.  However, P2P-aware application MAY choose to
      talk directly to the respective P2P resolver, and in the case of
      GNS use this to access additional GNS-specific record types.

      As mentioned in sections 4.1.4 and 4.1.5 below, regular DNS
      resolution is expected to respond with NXDOMAIN for the five
      proposed pTLDs.  Therefore, if it can differentiate between DNS
      and P2P name resolution, application software MAY expect such a
      response, and MAY choose to treat other responses from the DNS
      as errors.

       Are writers of name resolution APIs and libraries expected to
       make their software recognize these names as special and treat
       them differently?  If so, how?

      3. Name Resolution APIs and Libraries MAY choose to support
      additional GNS record types over time and MAY choose to directly
      resolve those domains via a GNS-specific resolution protocol or
      API.  However, for legacy applications and legacy name
      resolution APIs, no changes are required.

      The ".onion" pTLDs are typically accessed via SOCKS proxies and
      do not define additional record types.

      The ".i2p" pTLDs are typically accessed via HTTP or SOCKS
      proxies and do not define additional record types.

       Are developers of caching domain name servers expected to make
       their implementations recognize these names as special and treat
       them differently?  If so, how?

      4. If any request to one of the five considered pTLDs were to
      escape to the global operational DNS, the only valid answer from
      DNS is NXDOMAIN.  Therefore, a caching DNS server MUST respond
      with NXDOMAIN.  The caching DNS server MAY choose to cache that

       Are developers of authoritative domain name servers expected to
       make their implementations recognize these names as special and
       treat them differently?  If so, how?

      5. Authoritative DNS Servers are not expected to treat these
      TLDs specially. In practice, they SHOULD answer with NXDOMAIN,
      as none of the considered pTLDs are normally available via global
      DNS resolution, and not doing so MAY put users' privacy at risk,
      e.g., as suggested in the next point.

       Does this reserved Special-Use Domain Name have any potential
       impact on DNS server operators?  If they try to configure their
       authoritative DNS server as authoritative for this reserved name,
       will compliant name server software reject it as invalid?  Do DNS
       server operators need to know about that and understand why?
       Even if the name server software doesn't prevent them from using
       this reserved name, are there other ways that it may not work as
       expected, of which the DNS server operator should be aware?

      6. DNS Server Operators SHOULD treat requests to the five
      considered pTLDs as typos, for correct installations MUST not
      allow P2P requests to escape to DNS.  DNS operators SHOULD NOT
      choose to redirect such bogus requests to a site, not even to
      explain to the user that their P2P resolver is missing or
      mis-configured as this MAY violate privacy expectations of the

       How should DNS Registries/Registrars treat requests to register
       this reserved domain name?  Should such requests be denied?
       Should such requests be allowed, but only to a specially-
       designated entity?  (For example, the name "www.example.org" is
       reserved for documentation examples and is not available for
       registration; however, the name is in fact registered; and there
       is even a web site at that name, which states circularly that the
       name is reserved for use in documentation and cannot be

      7. DNS Registries/Registrars

      In order to avoid conflicts with the P2P namespaces, IANA should
      reserve all five considered pTLDs and forbid registrars from
      registering domains names within their respective scopes.

8. Security Considerations

   The five requested Special-Use Domain Names presented in this
   document are resolved by specific software outside of the scope of
   DNS.  Leakage of requests to such domains to the global operational
   DNS can cause interception of traffic that might be used to
   monitor, censor, or abuse the user's trust, and lead to privacy
   issues with potentially dramatic consequences for the user.

   Operation of said TLDs into the global DNS scope could as well
   produce conflicts due to later real use and the possible
   acquisition of intellectual property rights in such names.

   The reservation of several top level domain names for these
   purposes will minimize such confusion and conflict, and safety
   risks for users.

9. Aknowledgements

   We thank the I2P developers for their constructive feedback.


10. References

    TODO: validate

10.1. Normative References

   [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels," BCP 14, RFC 2119, March 1997.

   [RFC 6761] Cheshire, S. and M. Krochmal, "Special-Use Domain
              Names", RFC 6761, February 2013.

10.2. Informative References

   [Dingledine 2004] Dingledine, R., Mathewson, N., and Syverson, P.,
              "Tor: the second-generation onion router", in SSYM'04
              Proceedings of the 13th conference on USENIX Security
              Symposium - Volume 13, page 21, 2004.

   [RFC 1928] Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D.,
              and L. Jones, "SOCKS Protocol Version 5", RFC 1928,
              March 1996.

   [RFC 4648] Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, October 2006.

   [RFC 6840] Weiler, S., Ed., and D. Blacka, Ed., "Clarifications and
              Implementation Notes for DNS Security (DNSSEC)", RFC
              6840, February 2013.

   [RFC 6975] Crocker, S. and S. Rose, "Signaling Cryptographic
              Algorithm Understanding in DNS Security Extensions
              (DNSSEC)", RFC 6975, July 2013.

   [Schanzenbach 2012] Schanzenbach, M., "Design and Implementation of
              a Censorship Resistant and Fully Decentralized Name
              System", September 2012.

   [TorSpec]  Mathewson, N., Dingledine, R., "Special Hostnames in
              Tor", September 2011.

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