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General dnsop Internet-Draft onion tld dns This document registers the “.onion” Special-Use Domain Name.

The Tor network has the ability to host network services using the “.onion” Special-Use Top-Level Domain. Such addresses can be used as other domain names would be (e.g., in URLs ), 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 Section 3; they require hardware and software implementations to change their handling, in order to achieve the desired properties of the name (see ). These differences are listed in . Like Top-Level Domain Names, .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 . See and for the details of the creation and use of .onion names.

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 .

These properties have the following effects upon parties using or processing .onion names (as per ): 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. 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 ) 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. Name Resolution APIs and Libraries: Resolvers MUST either either respond to requests for .onion names by resolving them according to or by responding with NXDOMAIN. Caching DNS Servers: Caching servers SHOULD NOT attempt to look up records for .onion names. They MUST generate NXDOMAIN for all such queries. Authoritative DNS Servers: Authoritative servers MUST respond to queries for .onion with NXDOMAIN. 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). DNS Registries/Registrars: Registrars MUST NOT register .onion names; all such requests MUST be denied.

This document registers “onion” in the registry of Special-Use Domain Names . See for the registration template.

.onion names are often 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. These properties can be compromised if, for example: The server “leaks” its identity in another way (e.g., in an application-level message), or The access protocol is implemented or deployed incorrectly, or 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 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 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 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 intervening network. This can be mitigated by following the recommendations in .

Harvard University

1350 Mass. Ave. Cambridge MA 02138 - +1 617 495 3864 sob@harvard.edu

General keyword In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. Authors who follow these guidelines should incorporate this phrase near the beginning of their 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 RFC 2119. Note that the force of these words is modified by the requirement level of the document in which they are used. This document describes what it means to say that a Domain Name (DNS name) is reserved for special use, when reserving such a name is appropriate, and the procedure for doing so. It establishes an IANA registry for such domain names, and seeds it with entries for some of the already established special domain names. Bell-Northern Research Ltd

P.O. Box 3511 Stn. C Ottawa Ontario K1Y 4H7 CA +1 613 763 9145 mleech@bnr.ca

International Business Machines NEC Systems Laboratory Unify Corporation Independent Consultant Hewlett-Packard Company World Wide Web Consortium

Massachusetts Institute of Technology 77 Massachusetts Avenue Cambridge MA 02139 USA +1-617-253-5702 +1-617-258-5999 timbl@w3.org http://www.w3.org/People/Berners-Lee/

Day Software

5251 California Ave., Suite 110 Irvine CA 92617 USA +1-949-679-2960 +1-949-679-2972 fielding@gbiv.com http://roy.gbiv.com/

Adobe Systems Incorporated

345 Park Ave San Jose CA 95110 USA +1-408-536-3024 LMM@acm.org http://larry.masinter.net/

Applications uniform resource identifier URI URL URN WWW resource A Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource. This specification defines the generic URI syntax and a process for resolving URI references that might be in relative form, along with guidelines and security considerations for the use of URIs on the Internet. The URI syntax defines a grammar that is a superset of all valid URIs, allowing an implementation to parse the common components of a URI reference without knowing the scheme-specific requirements of every possible identifier. This specification does not define a generative grammar for URIs; that task is performed by the individual specifications of each URI scheme. The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document provides an overview of HTTP architecture and its associated terminology, defines the "http" and "https" Uniform Resource Identifier (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements, and describes related security concerns for implementations.

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.