Internet Engineering Task Force                              C. Grothoff
Internet-Draft                                                  M. Wachs
Intended status: Informational                                 TU Munich
Expires: June 8, 2014                                       H. Wolf, Ed.
                                                           GNU consensus
                                                            J. Appelbaum
                                                        Tor Project Inc.
                                                       December 05, 2013

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


   This document describes common Special-Use Domain Names pseudo Top-
   Level Domain names designed to help harden name resolution security,
   provide censorship resistance, and protect the users' privacy on the

   This is an IESG Approval document requesting the reservation of six
   Top-Level Domains for special use, in conformance with the
   registration procedure defined in RFC 6761, section 4.

   The six domains relate to peer-to-peer systems that, given their
   decentralized design, do not require a central authority to register
   names.  They are: ".gnu", ".zkey", ".onion", ".exit", ".i2p", and

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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 8, 2014.

Copyright Notice

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   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
   ( in effect on the date of
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology and Conventions Used in This Document . . . . . .   3
   3.  Description of Special-Use Domains in P2P Networks  . . . . .   4
     3.1.  The ".gnu" Relative pTLD  . . . . . . . . . . . . . . . .   4
     3.2.  The ".zkey" Compressed Public Key pTLD  . . . . . . . . .   4
     3.3.  Geographically Anonymous pTLDs  . . . . . . . . . . . . .   4
       3.3.1.  The ".onion" Hidden Service pTLD  . . . . . . . . . .   4
       3.3.2.  The ".exit" Client Source Routing pTLD  . . . . . . .   5
       3.3.3.  The ".noconnect" Client Interruption pTLD . . . . . .   6
     3.4.  The ".i2p" Addressbook pTLD . . . . . . . . . . . . . . .   6
     3.5.  The ".bit" Timeline System pTLD . . . . . . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  Domain Name Reservation Considerations  . . . . . . . . .   7
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   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 domain names is desired, these
   overlay networks often define exclusive alternative pseudo Top-Level
   Domains (pTLDs) to avoid conflict between the P2P namespace and the
   DNS hierarchy.

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   The purpose of this document is to inform the Internet community
   about current practice of such pseudo-TLDs within peer-to-peer
   systems, and to normalize their usage according to the rules of RFC
   6761.  Given their decentralized design, such P2P systems do not
   require a central authority to register names nor do they belong to
   the DNS resolution tree.

   RFC 6761 defines a mechanism for reserving domain names for special
   use.  This document is an IESG Approval document requesting the
   reservation of six pTLDs for special use: ".gnu", ".zkey", ".onion",
   ".exit", ".i2p", and ".bit".

   The GNU Name System (GNS) (".gnu", ".zkey"), the Tor network
   (".onion", ".exit"), the Invisible Internet Project (".i2p"), and the
   .Bit Project (".bit") use these pseudo-Top-Level Domains (pTLDs) to
   realize fully-decentralized and censorship-resistant secure
   alternatives for DNS or, in the case of the ".exit" pTLD, to control
   overlay routing and to securely specify path selection choices

   To facilitate integration with legacy applications, the overlay's
   namespaces can be accessed from applications to resolve these special
   TLDs, for example via specialized SOCKS proxies [RFC1928],
   specialized DNS servers, or transparent name resolution and ephemeral
   address mapping.

2.  Terminology and Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in 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 not present in
   operational DNS, and not registered with IANA for use within the
   scope of operational DNS.  Specifically, it refers to one of the
   Special-Use Domain Names already in use on the Internet and described
   in this document.

   In this document, ".tld" (with quotes) means: any domain or hostname
   within the scope of a given pTLD, while .tld (without quotes), or
   dot-tld, both refer to an adjective form.  For example, a collection
   of ".gnu" peers, but an .onion URL.  The pTLD itself is mentioned
   with dot, and within double quotes, and usually followed by the word

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   The Tor-related names such as 'circuit', 'exit', 'node', 'relay',
   'stream', and related Tor terms are described in [Dingledine2004] and
   the Tor protocol specification [TOR-PROTOCOL].

3.  Description of Special-Use Domains in P2P Networks

3.1.  The ".gnu" Relative 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 [Schanzenbach2012].  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 ".gnu"
   names SHOULD follow the naming conventions of DNS.

   ".gnu" names are personal, relative, and transitive: each user of the
   GNS controls their own zone that is authoritative for all ".gnu"
   domains; zones can be delegated between authorities, so that any user
   can share names, and chain labels to resolve names out of the
   requesting user's zone of control, including across several zones.

   For example, if Alice wants to access the Web service of Bob's friend
   Dave, she might be able to lookup: "www.dave.bob.gnu", whereas Bob
   will simply ask for "www.dave.gnu" to obtain the same result.

3.2.  The ".zkey" Compressed Public Key pTLD

   The ".zkey" pTLD 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 ".zkey" 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 [RFC4648].  A GNS resolver uses the key to locate a
   record signed by the respective authority.

   The ".zkey" pTLD provides a (reverse) mapping from globally unique
   hashes to public key, therefore names in ".zkey" are non-memorable,
   and are expected to be hidden from the user [Schanzenbach2012].

3.3.  Geographically Anonymous pTLDs

   The Tor anonymization network makes use of several special pTLD
   labels, three of which have seen widespread usage to date

3.3.1.  The ".onion" Hidden Service pTLD

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   The widely deployed ".onion" pTLD designates an anonymous Tor Hidden
   Service reachable via the Tor network [Dingledine2004].  These .onion
   URLs are self-authenticating addresses for use with any TCP service.
   Such addresses are typically resolved, reached and authenticated
   through transparent proxying or through a local SOCKS proxy running
   on TCP port 9050, TCP port 9150 or another user selected TCP port.
   The purpose of the Tor Hidden Services system is to provide
   geographic anonymity for the .onion host and for all clients visiting
   the hidden service as well as other purposes such as NAT traversal,
   strong authentication, anonymity and censorship resistance.

   Addresses in ".onion" are opaque, non-mnemonic, alpha-semi-numeric
   hashes corresponding to an 80-bit truncated SHA1 hash over a given
   Tor hidden service's public key.  This hash 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 [RFC4648].  Tor
   generates this "Onion key" automatically when the hidden service is
   configured.  Tor clients use it following the Tor Rendezvous
   specifications [TOR-RENDEZVOUS].

3.3.2.  The ".exit" Client Source Routing pTLD

   The dot-exit suffix is used as an in-band source routing control
   channel, usually for selection of a specific Tor relay during path
   creation as the last node in the Tor circuit.

   It may be used to access a DNS host via specific Torservers, in the
   form "hostname.nickname-or-fingerprint.exit", where the "hostname" is
   a valid hostname, and the "nickname-or-fingerprint" is either the
   nickname of a Tor relay in the Tor network consensus, or the hex-
   encoded SHA1 digest of the given node's public key (fingerprint).

   For example, "" will route the client to
   "" via the Tor node nicknamed "noisetor".  Using the
   fingerprint instead of the nickname ensures that the path selection
   uses a specific Tor exit node, and is harder to remember: e.g.,

   When Tor sees an address in this format, it uses the specified
   "nickname-or-fingerprint" as the exit node.  If no "hostname"
   component is given, Tor defaults to the published IPv4 address of the
   Tor exit node [TOR-EXTSOCKS].

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3.3.3.  The ".noconnect" Client Interruption pTLD

   The dot-noconnect suffix is used in Tor for testing purposes: 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 pTLD and thus we do not include the ".noconnect"
   pTLD in the list of Special-Use Domain Names that should be reserved.

3.4.  The ".i2p" Addressbook pTLD

   The ".i2p" pTLD provides accessibility to anonymous services
   ("eepsites") within the I2P network.  I2P is a scalable, self-
   organizing, resilient packet switched anonymous network layer, upon
   which any number of different anonymity or security-conscious
   applications can operate.

   The local I2P proxy resolves such names either by looking up a local
   table called the addressbook, or by decoding Base32-encoded [RFC4648]
   public keys and establishing a tunnel to the respective authority,
   similar to contacting .onion hidden services.

   I2P uses 52 characters (256 bits) of the SHA-256 hash of the public
   key to identify eepsites [I2P-NAMING].  These identifiers can be used
   to address a peer as, e.g.:

   Apart from the ".b32.i2p" domain that is reserved for SHA-256 hashes,
   other hostnames within the ".i2p." pTLD are non-hierarchical and can
   be assigned locally: example.i2p and other.example.i2p do not
   necessarily belong to the same authority.

   As the system is decentralized, example.i2p may also resolve
   differently for different peers, depending on the state of their
   respective addressbooks.

3.5.  The ".bit" Timeline System pTLD

   The ".bit" pTLD provides a name space where names are registered via
   transactions in the Namecoin currency [Namecoin].  Like Bitcoins,
   Namecoins are created using a proof-of-work calculation, which is
   also used to establish a decentralized, multi-party consensus on the
   valid transaction history, and thus the set of registered names and
   their values [SquareZooko].

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   The Namecoin used in a transaction to register a name in ".bit" is
   lost.  This is not a fundamental problem as more coins can be
   generated via mining (proof-of-work calculations).  The registration
   cost is set to decrease over time, to prevent early adopters from
   registering too many names.

   The owner of a name can update the associated value by issuing an
   update, which is a transaction that uses a special coin which is
   generated as change during the registration operation.  If a name is
   not updated for a long time, the registration expires.

4.  Security Considerations

   Specific software performs the resolution of the six requested
   Special-Use Domain Names presented in this document; this resolution
   process happens 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 misused 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 [SAC45] 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

5.  IANA Considerations

   The P2P Name Systems domains listed below, and any domains falling
   within those domains are Special-Use Domain Names [RFC6761]:







5.1.  Domain Name Reservation Considerations

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   The six domains listed above, and any names falling within those
   domains (e.g., "example.gnu.", "j6im4v42ur6dpic3.onion.", etc.) are
   special according to RFC 6761, section 5 [RFC6761], in the following

   1.  Users MAY use these names as they would other domain names,
       entering them anywhere that they would otherwise enter a
       conventional DNS domain 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 six proposed pTLDs is similar to
       the normal DNS resolution, and thus SHOULD NOT affect normal
       usage of most Internet applications.

   2.  Application Software MAY pass requests to any of the six 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 and ".bit", use
       this to access additional record types that are not defined in

       As mentioned in points 4. and 5. below, regular DNS resolution is
       expected to respond with NXDOMAIN for five of the six 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.

   3.  For legacy applications and legacy name resolution APIs expecting
       DNS resolution, no changes are required.

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

       However, Name Resolution APIs and Libraries MAY choose to support
       additional record types over time for the GNS and ".bit" names.

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       They MAY choose to directly resolve those domains via appropriate
       APIs or mechanisms such as GNS-specific resolution protocol, or
       blockchain-based resolution for dot-bit names.

   4.  If any request to one of the considered pTLDs, with the exception
       of ".bit" names, is sent to the global operational DNS, the only
       valid answer from DNS is NXDOMAIN.  Therefore, a caching DNS
       server MUST respond with NXDOMAIN in that case, and MAY choose to
       cache that response.

       But given that ".bit" users have no special privacy requirements,
       and those names are globally unique, caching DNS servers MAY
       choose to treat them as regular DNS names, and cache the
       responses obtained from the Namecoin block chain as if they were
       resolved from the regular DNS tree.

   5.  Authoritative DNS Servers are not expected to treat these TLDs
       specially.  In practice, they MUST 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.

   6.  DNS Server Operators MAY choose to resolve ".bit" names using the
       Namecoin block chain, and if they do so SHOULD treat such domains
       like they would regular DNS names.

       DNS Server Operators SHOULD treat requests to the other five
       considered pTLDs as typos, for correct installations MUST NOT
       allow such 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 user.

   7.  DNS Registries/Registrars

       In order to avoid conflicts with the P2P namespaces [SAC45], IANA
       should reserve all six considered pTLDs, and thereby ensure that
       those labels cannot be registered within the DNS tree, nor their
       management delegated to any particular organization.

6.  Acknowledgements

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   The authors thank the I2P developers for their constructive feedback,
   and Leif Ryge for his proof-reading and valuable feedback.

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC6761]  Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
              RFC 6761, February 2013.

7.2.  Informative References

              Bernstein, D., "Curve25519: new Diffie-Hellman speed
              record", February 2006,

              Dingledine, R., Mathewson, N., and P. Syverson, "Tor: the
              second-generation onion router", 2004, <https://www.onion-

   [EdDSA]    Bernstein, D., Duif, N., Lange, T., Schwabe, P., and Y.
              Yang, "High-speed, high-security signatures", September
              2011, <>.

              Random, J., "Naming in I2P and Addressbook", 2003,

              The .bit Project, "Namecoin DNS - DotBIT Project", 2013,

   [RFC1928]  Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and
              L. Jones, "SOCKS Protocol Version 5", RFC 1928, March

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, October 2006.

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   [SAC45]    ICANN Security and Stability Advisory Committee, "Invalid
              Top Level Domain Queries at the Root Level of the Domain
              Name System", November 2010, <

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

              Swartz, A., "Squaring the Triangle: Secure, Decentralized,
              Human-Readable Names", 2011,

              Mathewson, N. and R. Dingledine, "Special Hostnames in
              Tor", September 2011, <

              Mathewson, N. and R. Dingledine, "Tor's extensions to the
              SOCKS protocol", September 2011, <https://

              Mathewson, N. and R. Dingledine, "Tor Path Specification",
              April 2013, <

              Dingledine, R. and N. Mathewson, "Tor Protocol
              Specification", November 2013, <https://

              Mathewson, N. and R. Dingledine, "Tor Rendezvous
              Specification", September 2013, <https://

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Authors' Addresses

   Christian Grothoff
   TU Munich
   Free Secure Network Systems Group
   Lehrstuhl fuer Netzarchitekturen und Netzdienste
   Boltzmannstrasse 3
   Technische Universitaet Muenchen
   Garching bei Muenchen, Bayern  D-85748


   Matthias Wachs
   TU Munich
   Free Secure Network Systems Group
   Lehrstuhl fuer Netzarchitekturen und Netzdienste
   Boltzmannstrasse 3
   Technische Universitaet Muenchen
   Garching bei Muenchen, Bayern  D-85748


   Hellekin O. Wolf (editor)
   GNU consensus


   Jacob Appelbaum
   Tor Project Inc.


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