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Internet Engineering Task Force                              C. Grothoff
Internet-Draft                                                     INRIA
Intended status: Informational                                  M. Wachs
Expires: July 28, 2015                  Technische Universitaet Muenchen
                                                            H. Wolf, Ed.
                                                           GNU consensus
                                                            J. Appelbaum
                                                                 L. Ryge
                                                        Tor Project Inc.
                                                        January 24, 2015


            Special-Use Domain Names of Peer-to-Peer Systems
              draft-grothoff-iesg-special-use-p2p-names-04

Abstract

   This document registers a set of Special-Use Domain Names for use
   with Peer-to-Peer (P2P) systems, as per RFC6761.

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 http://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 July 28, 2015.

Copyright Notice

   Copyright (c) 2015 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



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   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
   2.  Applicability . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Terminology and Conventions Used in This Document . . . . . .   4
   4.  Description of Special-Use Domains in P2P Networks  . . . . .   5
     4.1.  The "GNU" Relative pTLD . . . . . . . . . . . . . . . . .   5
     4.2.  The "ZKEY" Compressed Public Key pTLD . . . . . . . . . .   6
     4.3.  Geographically Anonymous pTLDs  . . . . . . . . . . . . .   8
       4.3.1.  The "ONION" Hidden Service pTLD . . . . . . . . . . .   8
       4.3.2.  The "EXIT" Client Source Routing pTLD . . . . . . . .  10
       4.3.3.  The "I2P" Addressbook pTLD  . . . . . . . . . . . . .  12
     4.4.  The "BIT" Timeline System pTLD  . . . . . . . . . . . . .  14
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  18
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  19
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

1.  Introduction

   The Domain Name System (DNS) is primarily used to map human-memorable
   names to IP addresses, which are used for routing but generally not
   meaningful for humans.

   Peer-to-Peer (P2P) systems use specific decentralized mechanisms to
   allocate, register, manage, and resolve names.  However, the
   hierarchical nature of DNS makes it unsuitable for various P2P Name
   Systems.  Such P2P Name Systems operate entirely outside of DNS,
   independently from the DNS root and delegation tree.

   As compatibility with applications using domain names is desired,
   these P2P overlay networks often define exclusive alternative Top-
   Level Domains to avoid conflict between the P2P namespace and the DNS
   hierarchy.

   In order to avoid interoperability issues with DNS as well as to
   address security and privacy concerns, this document registers a set
   of Special-Use Domain Names for use with P2P systems (pTLDs), as per
   [RFC6761],: "GNU", "ZKEY", "ONION", "EXIT", "I2P", and "BIT".





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   The GNU Name System (GNS) ("GNU", "ZKEY"), the Tor network ("ONION",
   "EXIT"), the Invisible Internet Project ("I2P"), and the Dot-Bit
   Project ("BIT") use these pTLDs to realize fully-decentralized and
   censorship-resistant naming.  The "EXIT" pTLD is used to control
   overlay routing and to securely specify path selection choices
   [TOR-PATH].

2.  Applicability

   [RFC6761] Section 3 states:

      "[I]f a domain name has special properties that affect the way
      hardware and software implementations handle the name, that apply
      universally regardless of what network the implementation may be
      connected to, then that domain name may be a candidate for having
      the IETF declare it to be a Special-Use Domain Name and specify
      what special treatment implementations should give to that name.
      On the other hand, if declaring a given name to be special would
      result in no change to any implementations, then that suggests
      that the name may not be special in any material way, and it may
      be more appropriate to use the existing DNS mechanisms [RFC1034]
      to provide the desired delegation, data, or lack-of-data, for the
      name in question.  Where the desired behaviour can be achieved via
      the existing domain name registration processes, that process
      should be used.  Reservation of a Special-Use Domain Name is not a
      mechanism for circumventing normal domain name registration
      processes."

   The set of Special-Use Domain Names for Peer-to-Peer Systems (pTLDs)
   reserved by this document meet this requirement, as they share the
   following specificities:

   o  pTLDs are not manageable by some designated administration.
      Instead, they are managed according to various alternate
      strategies or combinations thereof, introduced in this document,
      and their respective protocol specifications: automated
      cryptographic assignment (".onion", ".zkey"), user-controled
      assignment in a private scope (".gnu", ".i2p"), or in a global
      public ledger (".bit"), or used as a source-routing mechanism to
      delegate DNS resolution to a remote peer (".exit").

   o  pTLDs do not depend on the DNS context for their resolution: GNS
      and Namecoin domains MAY use the DNS servers infrastructure, as
      they return DNS-compatible results; and all pTLDs use specific P2P
      protocols for regular name resolution, covered by their respective
      protocol specifications.





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   o  When a pTLD protocol has been implemented, the implementation MUST
      intercept queries for the pTLD to ensure P2P names cannot leak
      into the DNS.

   o  The appropriate pTLD protocols can be implemented in existing
      software libraries and APIs to extend regular DNS operation and
      enable P2P name resolution.  However, the default hierarchical DNS
      response to any request to any pTLD MUST be NXDOMAIN.

   o  Finally, in order for pTLDs to realize a censorship-resistant,
      fully-decentralized name system, and provide security and privacy
      features matching user expectations, this document specifies
      changes required in existing DNS software and DNS operations.

3.  Terminology and Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   The word "peer" is used in the meaning of a individual system on the
   network.

   The abbreviation "pTLD" is used in this document to mean a pseudo
   Top-Level Domain, i.e., a Special-Use Domain Name per [RFC6761]
   reserved to P2P Systems in this document.  A pTLD is mentioned in
   capitals, and within double quotes to mark the difference with a
   regular DNS gTLD.

   In this document, ".tld" (lowercase, with quotes) means: any domain
   or hostname within the scope of a given pTLD, while .tld (lowercase,
   without quotes) refers to an adjective form.  For example, a
   collection of ".gnu" peers in "GNU", but an .onion URL.  [TO REMOVE:
   in the IANA Considerations section, we use the simple .tld format to
   request TLD reservation for consistency with previous RFCs].

   The word "NXDOMAIN" refers to an alternate expression for the "Name
   Error" RCODE as described in section 4.1.1 of [RFC1035].  When
   referring to "NXDOMAIN" and negative caching [RFC2308] response, this
   document means an authoritative (AA=1) name error (RCODE=3) response
   exclusively.

   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].

   The I2P-related names such as 'Destination' are described in
   [zzz2009].



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4.  Description of Special-Use Domains in P2P Networks

4.1.  The "GNU" Relative pTLD

   "GNU" is used to specify that a domain name should be resolved using
   GNS.  The GNS resolution process is documented in [Wachs2014].

   The "GNU" domain is special in the following ways:

   1.  Users can use these names as they would other domain names,
       entering them anywhere that they would otherwise enter a
       conventional DNS domain name.

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

       Legacy applications MAY expect the DNS-to-GNS proxy to return DNS
       compatible results for the resolution of .gnu domains.



   2.  Legacy application software does not need to recognize .gnu
       domains as special, and may continue to use these names as they
       would other domain names.

       GNS-aware applications MAY also use GNS resolvers directly to
       resolve .gnu domains (in particular, if they want access to GNS-
       specific record types).



   3.  Name resolution APIs and libraries SHOULD either respond to
       requests for .gnu names by resolving them via the GNS protocol,
       or respond with NXDOMAIN.



   4.  Caching DNS servers SHOULD recognize .gnu names as special and
       SHOULD NOT attempt to look up NS records for them, or otherwise
       query authoritative DNS servers in an attempt to resolve .gnu
       names.  Instead, caching DNS servers SHOULD generate immediate
       negative responses for all such queries.



   5.  Authoritative DNS servers are not expected to treat .gnu domain
       requests specially.  In practice, they MUST answer with NXDOMAIN,



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       as "GNU" is not available via global DNS resolution, and not
       doing so can put users' privacy at risk (see item 6).



   6.  DNS server operators SHOULD be aware that .gnu names are reserved
       for use with GNS, and MUST NOT override their resolution (e.g.,
       to redirect users to another service or error information).



   7.  DNS registries/registrars MUST NOT grant any request to register
       .gnu names.  This helps avoid conflicts [SAC45].  These names are
       defined by the GNS protocol specification, and they fall outside
       the set of names available for allocation by registries/
       registrars.



4.2.  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
   Crockford's variant of base32hex [RFC4648] (with additionally 'U'
   being considered equal to 'V') for easier optical character
   recognition.  A GNS resolver uses the key to locate a record signed
   by the respective authority.

   "ZKEY" provides a (reverse) mapping from globally unique hashes to
   public key, therefore .zkey names are non-memorable, and are expected
   to be hidden from the user [Wachs2014].

   The "ZKEY" domain is special in the following ways:

   1.  Users can use these names as they would other domain names,
       entering them anywhere that they would otherwise enter a
       conventional DNS domain name.

       Since there is no central authority necessary or possible for
       assigning .zkey names, and those names match cryptographic keys,
       users need to be aware that they do not belong to regular DNS,
       but are still global in their scope.

       Legacy applications MAY expect the DNS-to-GNS proxy to return
       DNS-compatible results for the resolution of .zkey domains.



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   2.  Application software does not need to recognize .zkey domains as
       special, and may continue to use these names as they would other
       domain names.

       GNS-aware applications MAY also use GNS resolvers directly to
       resolve .zkey domains



   3.  Name resolution APIs and libraries SHOULD either respond to
       requests for .zkey names by resolving them via the GNS protocol,
       or respond with NXDOMAIN.



   4.  Caching DNS servers SHOULD recognize .zkey names as special and
       SHOULD NOT attempt to look up NS records for them, or otherwise
       query authoritative DNS servers in an attempt to resolve .zkey
       names.  Instead, caching DNS servers SHOULD generate immediate
       negative responses for all such queries.



   5.  Authoritative DNS Servers are not expected to treat .zkey domain
       requests specially.  In practice, they MUST answer with NXDOMAIN,
       as "ZKEY" is not available via global DNS resolution, and not
       doing so MAY put users' privacy at risk (see item 6).



   6.  DNS server operators SHOULD be aware that .zkey names are
       reserved for use with GNS, and MUST NOT override their resolution
       (e.g., to redirect users to another service or error
       information).



   7.  DNS registries/registrars MUST NOT grant any request to register
       .zkey names.  This helps avoid conflicts [SAC45].  These names
       are defined as described above, and they fall outside the set of
       names available for allocation by registries/registrars.










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4.3.  Geographically Anonymous pTLDs

   Both the Tor "Onionspace" and the I2P network are designed to provide
   geographic anonymity to services and all clients visiting them.  They
   provide additional properties such as NAT traversal, strong
   authentication, anonymity, and censorship resistance.

   The Tor anonymization network makes use of several special pTLD
   labels, three of which have seen widespread usage to date.  This
   document introduces two of them, "ONION" and "EXIT".  The interested
   reader is invited to refer to [TOR-ADDRESS] for further information
   on the "NOCONNECT" pTLD, whose limited testing scope does not warrant
   the attention of the larger Internet community.

   The I2P network uses a single pTLD, "I2P", but the specific subdomain
   "B32.I2P" offers properties similar to Tor's "ONION" and GNS's "ZKEY"

   The public literature often uses the term "Hidden Service" to refer
   to both Tor's Hidden Service protocol and services, and I2P's
   Destinations.  This term suggests that such services are hidden from
   view, whereas only their geographic location is unknown: given their
   name and the appropriate name resolver, such services are as much
   accessible as any other regular Web site or Internet service.

4.3.1.  The "ONION" Hidden Service pTLD

   The widely deployed "ONION" designates the "Onionspace", an anonymous
   Tor Hidden Service reachable via the Tor network [Dingledine2004].
   These .onion hostnames are self-authenticating addresses for use with
   any TCP service.

   Addresses in "ONION" are opaque, non-mnemonic, alpha-semi-numeric
   digest hashes corresponding to the unique identity key of a given Tor
   hidden service.  Therefore such .onion addresses are self-
   authenticating.  The algorithm to obtain the .onion hash from the Tor
   hidden service's public key is out of scope of this document, and
   described in the Tor Address specification [TOR-ADDRESS].  Tor
   generates this "Onion key" automatically when the hidden service is
   configured.  Tor clients use it following the Tor Rendezvous
   specifications [TOR-RENDEZVOUS].

   The "ONION" domain is special in the following ways:

   1.  Users can use these names as they would other domain names,
       entering them anywhere that they would otherwise enter a
       conventional DNS domain name.





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       Since there is no central authority necessary or possible for
       assigning .onion names, and those names correspond to
       cryptographic keys, users need to be aware that they do not
       belong to regular DNS, but are still global in their scope.



   2.  Application software MAY recognize .onion domains as special, and
       SHOULD use these names as they would other domain names.

       Application software MAY implement mechanisms helping the user to
       ensure their privacy expectations are met, such as warning the
       user if they do not detect an active local Tor resolver,
       displaying a warning on first-use of an .onion domain to explain
       the necessity of a Tor resolver to reach such domains, etc.

       If an application knows how to differenciate between DNS and P2P
       name resolution, it:

       *  SHOULD NOT pass requests for .onion domains to DNS resolvers
          or libraries,

       *  MUST expect NXDOMAIN as the only valid DNS response, and

       *  SHOULD treat other answers from DNS as errors.

       Tor-aware applications MAY also use Tor resolvers directly.



   3.  Name resolution APIs and libraries SHOULD either respond to
       requests for .onion names by resolving them via the Tor protocol,
       or respond with NXDOMAIN.



   4.  Caching DNS servers SHOULD recognize .onion names as special and
       SHOULD NOT attempt to look up NS records for them, or otherwise
       query authoritative DNS servers in an attempt to resolve .onion
       names.  Instead, caching DNS servers SHOULD generate immediate
       negative responses for all such queries.



   5.  Authoritative DNS servers are not expected to treat .onion domain
       requests specially.  In practice, they MUST answer with NXDOMAIN,
       as "ONION" is not available via global DNS resolution, and not
       doing so MAY put users' privacy at risk (see item 6).



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   6.  DNS server operators SHOULD be aware that .onion names are
       reserved for use with Tor, and MUST NOT override their resolution
       (e.g., to redirect users to another service or error
       information).



   7.  DNS registries/registrars MUST NOT grant any request to register
       .onion names.  This helps avoid conflicts [SAC45].  These names
       are defined the Tor protocol specification [TOR-PROTOCOL], and
       they fall outside the set of names available for allocation by
       registries/registrars.



4.3.2.  The "EXIT" Client Source Routing pTLD

   The .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, "gnu.org.noisetor.exit" will route the client to
   "gnu.org" 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.,
   "gnu.org.f97f3b153fed6604230cd497a3d1e9815b007637.exit".

   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].

   Because "hostname" is allegedly valid, the total length of a .exit
   construct may exceed the maximum length allowed for domain names.
   Moreover, the resolution of "hostname" happens at the exit node.
   Trying to resolve such invalid domain names, including chaining .exit
   names will likely return a DNS lookup failure at the first exit node.

   The "EXIT" domain is special in the following ways:






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   1.  Users can use these names as they would other domain names,
       entering them anywhere that they would otherwise enter a
       conventional DNS domain name.

       Since .exit names correspond to a Tor-specific routing construct
       to reach target hosts via chosen Tor exit nodes, users need to be
       aware that they do not belong to regular DNS and that the actual
       target precedes the second-level domain name.



   2.  Application software MAY recognize that .exit domains are special
       and when they do SHOULD NOT pass requests for these domains to
       DNS resolvers and libraries.

       As mentioned in items 4 and 5 below, regular DNS resolution is
       expected to respond with NXDOMAIN.  Therefore, if it can
       differentiate between DNS and P2P name resolution, application
       software:

       *  MUST expect NXDOMAIN as the only valid DNS response, and

       *  SHOULD treat other answers from DNS as errors.

       Tor-aware applications MAY also use Tor resolvers directly.

   3.  Name resolution APIs and libraries SHOULD either respond to
       requests for .exit names by resolving them via the Tor protocol,
       or respond with NXDOMAIN.



   4.  Caching DNS servers SHOULD recognize .exit names as special and
       SHOULD NOT, by default, attempt to look up NS records for them,
       or otherwise query authoritative DNS servers in an attempt to
       resolve .exit names.  Instead, caching DNS servers SHOULD, by
       default, generate immediate negative responses for all such
       queries.



   5.  Authoritative DNS servers are not expected to treat .exit domain
       requests specially.  In practice, they MUST answer with NXDOMAIN,
       as "EXIT" is not available via global DNS resolution, and not
       doing so MAY put users' privacy at risk (see item 6).






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   6.  DNS server operators SHOULD be aware that .exit names are
       reserved for use with Tor, and MUST NOT override their resolution
       (e.g., to redirect users to another service or error
       information).



   7.  DNS registries/registrars MUST NOT grant any request to register
       .exit names.  This helps avoid conflicts [SAC45].  These names
       are defined by the Tor address specification, and they fall
       outside the set of names available for allocation by registries/
       registrars.



4.3.3.  The "I2P" Addressbook pTLD

   "I2P" provides accessibility to hidden services within the I2P
   network [zzz2009].  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,
   using any protocol.

   I2P hidden services and clients are identified by Destinations,
   anonymous analogues of IP addresses.  The "I2P" pTLD, chosen in 2003
   [I2P-CHOICE], houses two methods for looking up Destinations:

      A local table called the addressbook stores a map of .i2p
      addresses to Destinations.  Each user maintains their own mappings
      that can be shared with others, allowing them to "discover" new
      names by importing published addressbooks of peers, and they can
      emulate traditional DNS by choosing to treat these peers as name
      servers.  The comparison however stops here, as only local
      uniqueness is mandated.  As the system is decentralized,
      "example.i2p" may resolve differently for different peers
      depending on the state of their respective addressbooks.

      To address globally unique names, the I2P developers dedicated the
      "B32.I2P" subdomain to hold Base32-encoded [RFC4648] references to
      Destinations.  Like .onion addresses, .b32.i2p addresses are self-
      authenticating.  The details of the encoding are out of scope for
      this document, and documented in [I2P-NAMING].  The purpose of
      .b32.i2p addresses is similar to ".zkey", that is to enable
      (reverse) mapping for a globally unique hidden service that may
      not have a defined entry in the local addressbook.

   The "I2P" domain is special in the following ways:




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   1.  Users can use these names as they would other domain names,
       entering them anywhere that they would otherwise enter a
       conventional DNS domain name.

       Since there is no central authority responsible for assigning
       .i2p names, and that the ultimate mapping is decided by the local
       peer, users need to be aware of that specificity.



   2.  Application software SHOULD recognize .i2p domains as special and
       SHOULD NOT use them as they would other domains.

       Applications SHOULD NOT pass requests for .i2p domains to DNS
       resolvers and libraries.

       As mentioned in points 4 and 5 below, regular DNS resolution is
       expected to respond with NXDOMAIN.  Therefore, if it can
       differentiate between DNS and P2P name resolution, application
       software can expect such a response, and can choose to treat
       other responses from resolvers and libraries as errors.



   3.  Name resolution APIs and libraries SHOULD either respond to
       requests for .i2p names by resolving them via the I2P protocol,
       or respond with NXDOMAIN.



   4.  Caching DNS servers SHOULD recognize .i2p names as special and
       SHOULD NOT attempt to look up NS records for them, or otherwise
       query authoritative DNS servers in an attempt to resolve .i2p
       names.  Instead, caching DNS servers SHOULD generate immediate
       negative responses for all such queries.



   5.  Authoritative DNS servers are not expected to treat .i2p domain
       requests specially.  In practice, they MUST answer with NXDOMAIN,
       as "I2P" is not available via global DNS resolution, and not
       doing so MAY put users' privacy at risk (see item 6).



   6.  DNS server operators SHOULD be aware that .i2p names are reserved
       for use with I2P, and MUST NOT override their resolution (e.g.,
       to redirect users to another service or error information).



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   7.  DNS registries/registrars MUST NOT grant any request to register
       .i2p names.  This helps avoid conflicts [SAC45].  These names are
       defined by the I2P protocol specification, and they fall outside
       the set of names available for allocation by registries/
       registrars.



4.4.  The "BIT" Timeline System pTLD

   Namecoin is a timeline-based system in the style of Bitcoin to create
   a global, secure, and memorable name system.  It creates a single,
   globally accessible, append-only timeline of name registrations.
   Timeline-based systems rely on a peer-to-peer network to manage
   updates and store the timeline.  In the Namecoin system,
   modifications to key-value mapping are attached to transactions which
   are committed to the timeline by "mining".  Mining is the use of
   brute-force methods to find (partial) hash collisions with a state
   summary (fingerprint) representing the complete global state --
   including the full history -- of the timeline .

   "BIT" 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].

   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.  This coin
   is generated as change during the registration operation.  If a name
   is not updated for a long time, the registration expires.

   Performing a lookup for a name with Namecoin consists in checking the
   timeline for correctness to ensure the validity of the blockchain,
   and traversing it to see if it contains an entry for the desired
   name.  Namecoin supports resolution for other peer-to-peer systems
   such as ".onion" and ".i2p" via specific resource records.

   Like DNS registry, the Dot-Bit registry is public.  But unlike DNS,
   the public registry is maintained by network consensus on the
   blockchain.  It departs from DNS in three ways:



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      first, domain names are not delegated to an authority that can
      assign them, but acquired by the operating party (the "domain
      owner"), in the form of a historical claim made directly by
      appending to the Namecoin blockchain.  The domain is thus bound
      not to a legal contract with an administrative authority, but to a
      cryptographic coin, and the network consensus on the timeline.

      second, the timeline contains the entire registry for all .bit
      domains: the Namecoin blockchain itself is the complete domain
      database.  As participant peers maintain the consensus on the
      timeline, they store a local copy of the Namecoin blockchain.
      Therefore, to those peers, name resolution and registry traversal
      are both local and private.  Each participant theoretically owns
      the whole domain's database.  In practice, some users can trust a
      name server to access the Namecoin blockchain on their behalf.

      third, the Namecoin system is not limited to domain names and can
      store arbitrary data types.  Each record must follow the same
      rules (expiry time, data size limits, etc.).  The Namecoin's
      Domain Name Specification [Namecoin-DNS] defines the "d namespace"
      for use with "BIT" and other unrelated namespaces co-exist on the
      Namecoin blockchain.

   The "BIT" domain is special in the following ways:

   1.  Users can use these names as they would other domain names,
       entering them anywhere that they would otherwise enter a
       conventional DNS domain name.

       From the user's perspective, the resolution of .bit names is
       similar to the normal DNS resolution, and thus should not affect
       normal usage of most Internet applications.



   2.  Application software SHOULD NOT recognize .bit domains as special
       and SHOULD treat them as they would other domains.

       Applications MAY pass requests to the "BIT" pTLD to DNS resolvers
       and libraries if A/AAAA records are desired.  If available, the
       local resolver can intercept such requests within the respective
       operating system hooks and return DNS-compatible results.

       Namecoin-aware applications MAY choose to talk directly to the
       respective P2P resolver, and use this to access additional record
       types that are not defined in DNS.





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   3.  Name resolution APIs and libraries SHOULD either respond to
       requests for .bit names by resolving them via the Namecoin
       protocol, or respond with NXDOMAIN.



   4.  Caching DNS servers SHOULD recognize .bit names as special and
       SHOULD NOT attempt to resolve them.  Instead, caching DNS servers
       SHOULD generate immediate negative responses for all such
       queries.

       Given that .bit users typically have no special privacy
       expectations, and those names are globally unique, local caching
       DNS servers MAY choose to treat them as regular domain names, and
       cache the responses obtained from the Namecoin blockchain.  In
       that case however, NXDOMAIN results SHOULD NOT be cached, as new
       .bit domains may become active at any time.



   5.  Authoritative DNS servers are not expected to treat .bit domain
       requests specially.  In practice, they MUST answer with NXDOMAIN,
       as "BIT" is not available via global DNS resolution.



   6.  DNS server operators SHOULD be aware that .bit names are reserved
       for use with Namecoin, and MUST NOT override their resolution
       (e.g., to redirect users to another service or error
       information).



   7.  DNS registries/registrars MUST NOT grant any request to register
       .bit names.  This helps avoid conflicts [SAC45].  These names are
       defined by the Namecoin protocol specification, and they fall
       outside the set of names available for allocation by registries/
       registrars.



5.  Security Considerations

   Specific software performs the resolution of the six 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



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   trust, and lead to privacy issues with potentially tragic
   consequences for the user.

   This document reserves these Top-Level Domain names to minimize the
   possibility of confusion, conflict, and especially privacy risks for
   users.

   In the introduction of this document, there's a requirement that DNS
   operators do not override resolution of the P2P Names.  This is a
   regulatory measure and cannot prevent such malicious abuse in
   practice.  Its purpose is to limit any information leak that would
   result from incorrectly configured systems, and to avoid that
   resolvers make unnecessary contact to the DNS Root Zone for such
   domains.  Verisign, Inc., as well as several Internet service
   providers (ISPs) have notoriously abused their position to override
   NXDOMAIN responses to their customers in the past.  For example, if a
   DNS operator would decide to override NXDOMAIN and send advertising
   to leaked .onion sites, the information leak to the DNS would extend
   to the advertising server, with unpredictable consequences.  Thus,
   implementors should be aware that any positive response coming from
   DNS must be considered with extra care, as it suggests a leak to DNS
   has been made, contrary to user's privacy expectations.

   The reality of X.509 Certificate Authorities (CAs) creating
   misleading certificates for these pTLDs due to ignorance stresses the
   need to document their special use.  X.509 Certificate Authorities
   MAY create certificates for "ONION", "BIT", and "ZKEY" given CSRs
   signed with the respective private keys corresponding to the
   respective names.  For "BIT", the Certificate Authority SHOULD limit
   the expiration time of the certificate to match the registration.
   Certificate Authorities MUST NOT create certificates for the "EXIT",
   "GNU", and "I2P" Top-Level domains.  Nevertheless, clients SHOULD
   accept certificates for these Top-Level domains as they may be
   created legitimately by local proxies on the fly.

   [SAC57] reports, page 11, that the CA/Browser forum stated: "Also as
   of the Effective Date [1 July 2012], the CA SHALL NOT issue a
   certificate with an Expiry Date later than 1 November 2015 with a
   subjectAlternativeName extension or Subject commonName field
   containing a Reserved IP Address or Internal Server Name."

   It is not clear whether e.g., .onion sites are considered "Internal
   Server Names", however, we can expect that services doubling their
   public Web site with an onion site would use a single SSL certificate
   for both, as did Facebook with "facebookcorewwwi.onion".  Given this
   forum also declared the CAs would revoke such SSL certificates in
   October 2016, that opens a three (now two) years period of
   vulnerability for new gTLDs to suffer MiTM attacks over HTTPS.  Such



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   practice by CAs to validate certificates to invalid TLDs without
   verification may lead, e.g., to mailicious third parties without any
   relation to an existing .onion site to register a fake certificate
   for that site in order to facilitate attacks, especially when
   combined with name collision risk as explained in [SAC62].

   Because the Namecoin system uses a timeline-based blockchain for name
   assignment and resolution, it grants query privacy to the users who
   maintain their own copy of the blockchain (Section 4.4), but the
   entire zone of a .bit domains is publicly available in the Namecoin
   blockchain, making enumeration of names within a .bit zone ("zone
   walking") a trivial attack to conduct.  This might be a concern to
   some domain operators as it exposes their infrastructure to potential
   adversaries.  That concern may be addressed in future versions of
   Namecoin, but the records already in the blockchain will remain there
   unprotected.

   Finally, legacy applications that do not explicitly support the pTLDs
   significantly increase the risk of pTLD queries escaping to DNS, as
   they are entirely dependent on the correct configuration on the
   operating system.

6.  IANA Considerations

   The Internet Assigned Numbers Authority (IANA) reserved the following
   entries in the Special-Use Domain Names registry [RFC6761]:

      .gnu

      .zkey

      .onion

      .exit

      .i2p

      .bit

   [TO REMOVE: the assignement URL is https://www.iana.org/assignments/
   special-use-domain-names/ ]

7.  Acknowledgements

   The authors thank the I2P and Namecoin developers for their
   constructive feedback, as well as Mark Nottingham for his proof-
   reading and valuable feedback.  The authors also thank the members of
   DNSOP WG for their critiques and suggestions.



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8.  References

8.1.  Normative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

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

   [RFC2308]  Andrews, M., "Negative Caching of DNS Queries (DNS
              NCACHE)", RFC 2308, March 1998.

   [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.

8.2.  Informative References

   [Curve25519]
              Bernstein, D., "Curve25519: new Diffie-Hellman speed
              record", February 2006,
              <http://cr.yp.to/ecdh/curve25519-20060209.pdf>.

   [Dingledine2004]
              Dingledine, R., Mathewson, N., and P. Syverson, "Tor: the
              second-generation onion router", 2004, <https://www.onion-
              router.net/Publications/tor-design.pdf>.

   [EdDSA]    Bernstein, D., Duif, N., Lange, T., Schwabe, P., and Y.
              Yang, "High-speed, high-security signatures", September
              2011, <http://ed25519.cr.yp.to/ed25519-20110926.pdf>.

   [I2P-CHOICE]
              Hacker, J. and The I2P Community, "I2P Dev Meeting 059",
              September 2003, <https://geti2p.net/en/meetings/059>.

   [I2P-NAMING]
              Hacker, J. and The I2P Community, "Naming in I2P and
              Addressbook", April 2014, <https://geti2p.net/en/docs/
              naming>.




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   [Namecoin]
              The .bit Project, "Namecoin", 2013,
              <https://namecoin.org/>.

   [Namecoin-DNS]
              The .bit Project, "Namecoin Domain Name Specification",
              2015, <https://bit.namecoin.org/spec>.

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

   [SAC45]    ICANN Security and Stability Advisory Committee, "Invalid
              Top Level Domain Queries at the Root Level of the Domain
              Name System", November 2010, <http://www.icann.org/en/
              groups/ssac/documents/sac-045-en.pdf>.

   [SAC57]    ICANN Security and Stability Advisory Committee, "SSAC
              Advisory on Internal Name Certificates", March 2013,
              <http://www.icann.org/en/groups/ssac/documents/
              sac-057-en.pdf>.

   [SAC62]    ICANN Security and Stability Advisory Committee, "SSAC
              Advisory Concerning the Mitigation of Name Collision
              Risk", November 2013, <http://www.icann.org/en/groups/
              ssac/documents/sac-062-en.pdf>.

   [SquareZooko]
              Swartz, A., "Squaring the Triangle: Secure, Decentralized,
              Human-Readable Names", 2011,
              <http://www.aaronsw.com/weblog/squarezooko>.

   [TOR-ADDRESS]
              Mathewson, N. and R. Dingledine, "Special Hostnames in
              Tor", September 2011, <https://gitweb.torproject.org/
              torspec.git/plain/address-spec.txt>.

   [TOR-EXTSOCKS]
              Mathewson, N. and R. Dingledine, "Tor's extensions to the
              SOCKS protocol", February 2014, <https://gitweb.torproject
              .org/torspec.git/plain/socks-extensions.txt>.

   [TOR-PATH]
              Mathewson, N. and R. Dingledine, "Tor Path Specification",
              November 2014, <https://gitweb.torproject.org/torspec.git/
              plain/path-spec.txt>.






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   [TOR-PROTOCOL]
              Dingledine, R. and N. Mathewson, "Tor Protocol
              Specification", August 2014, <https://gitweb.torproject
              .org/torspec.git/plain/tor-spec.txt>.

   [TOR-RENDEZVOUS]
              Mathewson, N. and R. Dingledine, "Tor Rendezvous
              Specification", April 2014, <https://gitweb.torproject
              .org/torspec.git/plain/rend-spec.txt>.

   [Wachs2014]
              Wachs, M., Schanzenbach, M., and C. Grothoff, "A
              Censorship-Resistant, Privacy-Enhancing and Fully
              Decentralized Name System", October 2014, <https://gnunet
              .org/gns-paper>.

   [zzz2009]  The I2P Project and L. Schimmer, "Peer Profiling and
              Selection in the I2P Anonymous Network", January 2009,
              <https://geti2p.net/_static/pdf/I2P-PET-CON-2009.1.pdf>.

Authors' Addresses

   Christian Grothoff
   INRIA
   Equipe Decentralisee
   INRIA Rennes Bretagne Atlantique
   263 avenue du General Leclerc
   Campus Universitaire de Beaulieu
   Rennes, Bretagne  F-35042
   FR

   Email: christian@grothoff.org


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

   Email: wachs@net.in.tum.de







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   Hellekin O. Wolf (editor)
   GNU consensus

   Email: hellekin@gnu.org


   Jacob Appelbaum
   Tor Project Inc.

   Email: jacob@appelbaum.net


   Leif Ryge
   Tor Project Inc.

   Email: leif@synthesize.us



































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