Internet DRAFT - draft-ietf-dnsop-onion-tld
draft-ietf-dnsop-onion-tld
dnsop J. Appelbaum
Internet-Draft The Tor Project, Inc
Intended status: Standards Track A. Muffett
Expires: March 12, 2016 Facebook
September 9, 2015
The .onion Special-Use Domain Name
draft-ietf-dnsop-onion-tld-01
Abstract
This document registers the ".onion" Special-Use Domain Name.
Status of This Memo
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Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. The ".onion" Special-Use Domain Name . . . . . . . . . . . . 3
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Normative References . . . . . . . . . . . . . . . . . . 5
5.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
The Tor network [Dingledine2004] has the ability to host network
services using the ".onion" Special-Use Top-Level Domain. Such names
can be used as other domain names would be (e.g., in URLs [RFC3986]),
but instead of using the DNS infrastructure, .onion names
functionally correspond to the identity of a given service, thereby
combining location and authentication.
.onion names are used to provide access to end to end encrypted,
secure, anonymized services; that is, the identity and location of
the server is obscured from the client. The location of the client
is obscured from the server. The identity of the client may or may
not be disclosed through an optional cryptographic authentication
process.
.onion names are self-authenticating, in that they are derived from
the cryptographic keys used by the server in a client-verifiable
manner during connection establishment. As a result, the
cryptographic label component of a .onion name is not intended to be
human-meaningful.
The Tor network is designed to not be subject to any central
controlling authorities with regards to routing and service
publication, so .onion names cannot be registered, assigned,
transferred or revoked. "Ownership" of a .onion name is derived
solely from control of a public/private key pair which corresponds to
the algorithmic derivation of the name.
In this way, .onion names are "special" in the sense defined by
[RFC6761] Section 3; they require hardware and software
implementations to change their handling in order to achieve the
desired properties of the name (see Section 4). These differences
are listed in Section 2.
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Like Top-Level Domain Names, .onion names can have an arbitrary
number of subdomain components. This information is not meaningful
to the Tor protocol, but can be used in application protocols like
HTTP [RFC7230].
Note that .onion names are required conform to DNS name syntax (as
defined in Section 3.5 of [RFC1034] and Section 2.1 of [RFC1123]), as
they will still be exposed to DNS implementations.
See [tor-address] and [tor-rendezvous] for the details of the
creation and use of .onion names.
1.1. Notational Conventions
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].
2. The ".onion" Special-Use Domain Name
These properties have the following effects upon parties using or
processing .onion names (as per [RFC6761]):
1. Users: Human users are expected to recognize .onion names as
having different security properties (see Section 1), and also as
being only available through software that is aware of onion
names.
2. Application Software: Applications (including proxies) that
implement the Tor protocol MUST recognize .onion names as special
by either accessing them directly, or using a proxy (e.g., SOCKS
[RFC1928]) to do so. Applications that do not implement the Tor
protocol SHOULD generate an error upon the use of .onion, and
SHOULD NOT perform a DNS lookup.
3. Name Resolution APIs and Libraries: Resolvers MUST either respond
to requests for .onion names by resolving them according to
[tor-rendezvous] or by responding with NXDOMAIN.
4. Caching DNS Servers: Caching servers, where not explicitly
adapted to interoperate with Tor, SHOULD NOT attempt to look up
records for .onion names. They MUST generate NXDOMAIN for all
such queries.
5. Authoritative DNS Servers: Authoritative servers MUST respond to
queries for .onion with NXDOMAIN.
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6. DNS Server Operators: Operators MUST NOT configure an
authoritative DNS server to answer queries for .onion. If they
do so, client software is likely to ignore any results (see
above).
7. DNS Registries/Registrars: Registrars MUST NOT register .onion
names; all such requests MUST be denied.
Note that the restriction upon the registration of .onion names does
not prohibit IANA from inserting a record into the root zone database
to reserve the name.
Likewise, it does not prevent non-DNS service providers (such as
trust providers) from supporting .onion names in their applications.
3. IANA Considerations
This document registers "onion" in the registry of Special-Use Domain
Names [RFC6761]. See Section 2 for the registration template.
4. Security Considerations
The security properties of .onion names can be compromised if, for
example:
o The server "leaks" its identity in another way (e.g., in an
application-level message), or
o The access protocol is implemented or deployed incorrectly, or
o The access protocol itself is found to have a flaw.
Users must take special precautions to ensure that the .onion name
they are communicating with is the intended one, as attackers may be
able to find keys which produce service names that are visually or
semantically similar to the desired service. This risk is magnified
because .onion names are typically not human-meaningful. It can be
mitigated by generating human meaningful .onion names (at
considerable computing expense), or through users using bookmarks and
other trusted stores when following links.
Also, users need to understand the difference between a .onion name
used and accessed directly via Tor-capable software, versus .onion
subdomains of other top-level domain names and providers (e.g., the
difference between example.onion and example.onion.tld).
The cryptographic label for a .onion name is constructed by applying
a function to the public key of the server, the output of which is
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rendered as a string and concatenated with the string ".onion".
Dependent upon the specifics of the function used, an attacker may be
able to find a key that produces a collision with the same .onion
name with substantially less work than a cryptographic attack on the
full strength key. If this is possible the attacker may be able to
impersonate the service on the network.
A legacy client may inadvertently attempt to resolve a ".onion" name
through the DNS. This causes a disclosure that the client is
attempting to use Tor to reach a specific service. Malicious
resolvers could be engineered to capture and record such leaks, which
might have very adverse consequences for the well-being of the Tor
user. This issue is mitigated if the client's Tor software is
updated to not leak such queries, or if the client's DNS software is
updated to drop any request to the ".onion" TLD.
5. References
5.1. Normative References
[Dingledine2004]
Dingledine, R., Mathewson, N., and P. Syverson, "Tor: the
second-generation onion router", 2004,
<https://spec.torproject.org/tor-spec>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
RFC 6761, DOI 10.17487/RFC6761, February 2013,
<http://www.rfc-editor.org/info/rfc6761>.
[tor-address]
Mathewson, N. and R. Dingledine, "Special Hostnames in
Tor", September 2001, <https://spec.torproject.org/
address-spec>.
[tor-rendezvous]
Mathewson, N. and R. Dingledine, "Tor Rendezvous
Specification", April 2014, <https://spec.torproject.org/
rend-spec>.
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5.2. Informative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<http://www.rfc-editor.org/info/rfc1034>.
[RFC1123] Braden, R., Ed., "Requirements for Internet Hosts -
Application and Support", STD 3, RFC 1123, DOI 10.17487/
RFC1123, October 1989,
<http://www.rfc-editor.org/info/rfc1123>.
[RFC1928] Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and
L. Jones, "SOCKS Protocol Version 5", RFC 1928, DOI
10.17487/RFC1928, March 1996,
<http://www.rfc-editor.org/info/rfc1928>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC
3986, DOI 10.17487/RFC3986, January 2005,
<http://www.rfc-editor.org/info/rfc3986>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing", RFC
7230, DOI 10.17487/RFC7230, June 2014,
<http://www.rfc-editor.org/info/rfc7230>.
Appendix A. Acknowledgements
Thanks to Roger Dingledine, Linus Nordberg, and Seth David Schoen for
their input and review.
This specification builds upon previous work by Christian Grothoff,
Matthias Wachs, Hellekin O. Wolf, Jacob Appelbaum, and Leif Ryge to
register .onion in conjunction with other, similar Special-Use Top-
Level Domain Names.
Authors' Addresses
Jacob Appelbaum
The Tor Project, Inc
Email: jacob@appelbaum.net
Alec Muffett
Facebook
Email: alecm@fb.com
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