Internet DRAFT - draft-appelbaum-dnsop-onion-tld
draft-appelbaum-dnsop-onion-tld
dnsop J. Appelbaum
Internet-Draft Tor Project Inc.
Intended status: Standards Track A. Muffett
Expires: October 16, 2015 Facebook
April 14, 2015
The .onion Special-Use Domain Name
draft-appelbaum-dnsop-onion-tld-01
Abstract
This document registers the ".onion" Special-Use Domain Name.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 2
2. The ".onion" Special-Use TLD . . . . . . . . . . . . . . . . 3
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . 3
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Normative References . . . . . . . . . . . . . . . . . . 5
5.2. Informative References . . . . . . . . . . . . . . . . . 5
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
The Tor network [Dingledine2004] has the ability to host network
services using the ".onion" Top-Level Domain. Such addresses 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.
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.
Like other TLDs, .onion addresses 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].
See [tor-address] and [tor-rendezvous] for the details of the
creation and use of .onion names.
Note that this draft was preceded by
[I-D.grothoff-iesg-special-use-p2p-names], which registered .onion
alongside other, similar TLDs. Because .onion is in wide use, it has
become urgent to expedite its registration. This does not indicate
that the other registrations should be abandoned.
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].
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2. The ".onion" Special-Use TLD
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, and also being only
available through software that is aware of onion addresses.
2. Application Software: Applications 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 that implement the
Tor protocol MUST either respond to requests for .onion names by
resolving them (see [tor-rendezvous]) or by responding with
NXDOMAIN. Other resolvers SHOULD respond with NXDOMAIN.
4. Caching DNS Servers: Caching servers SHOULD NOT attempt to look
up records for .onion names. They SHOULD generate NXDOMAIN for
all such queries.
5. Authoritative DNS Servers: Authoritative servers SHOULD respond
to queries for .onion with NXDOMAIN.
6. DNS Server Operators: Operators SHOULD 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.
3. IANA Considerations
This document registers the "onion" TLD in the registry of Special-
Use Domain Names [RFC6761]. See Section 2 for the registration
template.
4. Security Considerations
.onion names are often used 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
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not be disclosed through an optional cryptographic authentication
process.
These properties 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.
.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.
Users must take special precautions to ensure that the .onion name
they are communicating with is correct, as attackers may be able to
find keys which produce service names that are visually or apparently
semantically similar to the desired service.
Also, users need to understand the difference between a .onion name
used and accessed directly via Tor-capable software, versus .onion
subdomains of other TLDs 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
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.
If client software attempts to resolve a .onion name, it can leak the
identity of the service that the user is attempting to access to DNS
resolvers, authoritative DNS servers, and observers on the
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intervening network. This can be mitigated by following the
recommendations in Section 2.
5. References
5.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
RFC 6761, February 2013.
5.2. Informative References
[Dingledine2004]
Dingledine, R., Mathewson, N., and P. Syverson, "Tor: the
second-generation onion router", 2004, <https://www.onion-
router.net/Publications/tor-design.pdf>.
[I-D.grothoff-iesg-special-use-p2p-names]
Grothoff, C., Wachs, M., hellekin, h., Appelbaum, J., and
L. Ryge, "Special-Use Domain Names of Peer-to-Peer
Systems", draft-grothoff-iesg-special-use-p2p-names-04
(work in progress), January 2015.
[RFC1928] Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and
L. Jones, "SOCKS Protocol Version 5", RFC 1928, March
1996.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC
3986, January 2005.
[RFC7230] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Message Syntax and Routing", RFC 7230, June
2014.
[tor-address]
Mathewson, N. and R. Dingledine, "Special Hostnames in
Tor", September 2001,
<https://gitweb.torproject.org/torspec.git/plain/address-
spec.txt>.
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[tor-rendezvous]
Mathewson, N. and R. Dingledine, "Tor Rendezvous
Specification", April 2014,
<https://gitweb.torproject.org/torspec.git/plain/rend-
spec.txt>.
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 the .onion TLD in conjunction with other, similar TLDs.
Authors' Addresses
Jacob Appelbaum
Tor Project Inc.
Email: jacob@appelbaum.net
Alec Muffett
Facebook
Email: alecm@fb.com
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