Internet Engineering Task Force (IETF) C. Grothoff IESG Approval document M. Wachs H. Wolf TU Munich Nov 13, 2013 Intended status: IESG Approved Expires: Special-Use Domain Names of Peer-to-Peer Name Systems Abstract 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 DNS names is desired, these overlay networks often define alternative pseudo Top-Level Domains (pTLDs) to integrate names from the P2P domain into the DNS hierarchy. This memo describes five Special-Use Domain Names [RFC 6761] Top Level Domains (TLDs) designed to help harden name resolution security (e.g., [RFC 6840][RFC 6975]), provide censorship resistance, and protect the users' privacy on the Internet. In this IESG Approval document we are asking for domain name reservations for those five Special-Use Domain Names [RFC 6761]. The TLDs are ".exit", ".gnu.", ".zkey.", ".onion.", and ".i2p.". Status of this Memo This is a WIP draft in preparation for submission to IESG at the end of this week. This draft is intended for feedback from the Tor community prior to submission to IESG. ------%<---------------------------------------------------------------- TODO: formatting, review text, review references. ------%<---------------------------------------------------------------- Copyright Notice 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 (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 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. 1. Introduction [RFC 6761] defines a mechanism for reserving DNS names for special use. This document is an IESG Approval document requesting the reservation of five pTLDs for special use: ".gnu.", ".i2p.", ".onion.", ".exit" and ".zkey.". These pTLDs are used in the GNU Name System (GNS), I2P and the Tor network to realize fully-decentralized and censorship-resistant secure alternatives for DNS or, in the case of ".exit", to control overlay routing. To facilitate integration with legacy applications, the overlay's namespaces can be accessed from applications that only speak DNS using these special TLDs, for example via specialized SOCKS proxies [RFC 1928]. We will describe the proposed special treatment for each of these pTLDs below following the questions from [RFC 6761]. 2. 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 "Key words for use in RFCs to Indicate Requirement Levels" [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 that is not yet registered with IANA. Specifically, it refers to one of the proposed Special-Use Domain Names already in use on the Internet and described in this document. 3. Description of Special-Use Domains in P2P Networks ------%<---------------------------------------------------------------- TODO Add .exit and .noconnect for Tor TODO Reorganize by app? ------%<---------------------------------------------------------------- 3.1. The Human-Memorable ".gnu" 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 [Schanzenbach 2012]. 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 names in the ".gnu" pTLD SHOULD follow the naming conventions of DNS. 3.2. The Cryptographic-Hash ".zkey" pTLD The ".zkey" TLD 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 the ".zkey" domain 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 [RFC 4648]. A GNS resolver uses the key to locate a record signed by the respective authority. 3.3. Circuit-Based Anonymizing pTLDs The Tor anonymization network makes use of three special domains to date [TorSpec]. 3.3.1. The Hidden Service ".onion" pTLD The widely deployed ".onion" pTLD designates an anonymous hidden service reachable via the Tor network [Dingledine 2004]. Such addresses are typically resolved via a local SOCKS proxy running on TCP port 9050. The purpose of using such a system is to make both the information provider and the person accessing the information more difficult to trace, whether by one another, by an intermediate network host, or by an outsider. Addresses in the ".onion" pTLD are opaque, non-mnemonic, alpha- semi-numeric hashes corresponding to the public key of the matching Tor hidden service. This "Onion key" is generated automatically when the hidden service is configured, following the Tor specifications [TorSpec]. It 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 [RFC 4648]. 3.3.2. The Exit Node ".exit" pTLD The ".exit" suffix marks a way to access a DNS host via a Tor relay nickname, in the form "host.nickname.exit". For example, "www.gnu.org.torservers.exit" will route the client to "www.gnu.org" via the Tor node named "torservers". In "[hostname].[name-or-digest].exit", "hostname" is a valid DNS hostname; "[name-or-digest]" is either the nickname of a Tor node or the hex-encoded digest of that node's public key. When Tor sees an address in this format, it uses the specified hostname as the exit node. If no "[hostname]" component is given, Tor defaults to the published IPv4 address of the exit node. 3.3.3. The Interrupting ".noconnect" pTLD The ".noconnect" suffix is used in Tor for testing purpose: 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 method and thus do not include ".noconnect" in the list of special-use domain names that should be reserved. 3.4. Packet-Switched-Based Anonymous ".i2p" pTLD I2P is an overlay network layer that allows applications to host websites within the I2P network. These so-called "eepsites" are addressed using names in the ".i2p" pTLD. They are resolved by the I2P proxy using either a local lookup table called the "addressbook", or by decoding Base32-encoded [RFC 4648] public keys and establishing a tunnel to the respective authority, similar to contacting hidden services in the ".onion" pTLD. I2P uses 52 characters (256 bits) of the SHA-256 hash of the public key. 4. IANA Considerations This document is requesting IANA to record the list of domains below as being Special-Use Domain Names [RFC 6761]: .gnu. .i2p. .onion. .zkey. .exit. 4.1. Domain Name Reservation Considerations The five domains listed above, and any names falling within those domains (e.g., "example.gnu.", "core.onion.", etc.) are special [RFC 6761] in the following ways: ------%<---------------------------------------------------------------- Are human users expected to recognize these names as special and use them differently? In what way? ------%<---------------------------------------------------------------- 1. Users MAY use these names as they would other DNS names, entering them anywhere that they would otherwise enter a conventional DNS 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 five proposed pTLDs is similar to the normal DNS resolution, and thus SHOULD not affect normal usage of most Internet applications. ------%<---------------------------------------------------------------- Are writers of application software expected to make their software recognize these names as special and treat them differently? In what way? (For example, if a human user enters such a name, should the application software reject it with an error message?) ------%<---------------------------------------------------------------- 2. Application Software MAY pass requests to any of the five 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 use this to access additional GNS-specific record types. As mentioned in sections 4.1.4 and 4.1.5 below, regular DNS resolution is expected to respond with NXDOMAIN for the five 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. ------%<---------------------------------------------------------------- Are writers of name resolution APIs and libraries expected to make their software recognize these names as special and treat them differently? If so, how? ------%<---------------------------------------------------------------- 3. Name Resolution APIs and Libraries MAY choose to support additional GNS record types over time and MAY choose to directly resolve those domains via a GNS-specific resolution protocol or API. However, for legacy applications and legacy name resolution APIs, no changes are required. The ".onion" pTLDs are typically accessed via SOCKS proxies and do not define additional record types. The ".i2p" pTLDs are typically accessed via HTTP or SOCKS proxies and do not define additional record types. ------%<---------------------------------------------------------------- Are developers of caching domain name servers expected to make their implementations recognize these names as special and treat them differently? If so, how? ------%<---------------------------------------------------------------- 4. If any request to one of the five considered pTLDs were to escape to the global operational DNS, the only valid answer from DNS is NXDOMAIN. Therefore, a caching DNS server MUST respond with NXDOMAIN. The caching DNS server MAY choose to cache that response. ------%<---------------------------------------------------------------- Are developers of authoritative domain name servers expected to make their implementations recognize these names as special and treat them differently? If so, how? ------%<---------------------------------------------------------------- 5. Authoritative DNS Servers are not expected to treat these TLDs specially. In practice, they SHOULD 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. ------%<---------------------------------------------------------------- Does this reserved Special-Use Domain Name have any potential impact on DNS server operators? If they try to configure their authoritative DNS server as authoritative for this reserved name, will compliant name server software reject it as invalid? Do DNS server operators need to know about that and understand why? Even if the name server software doesn't prevent them from using this reserved name, are there other ways that it may not work as expected, of which the DNS server operator should be aware? ------%<---------------------------------------------------------------- 6. DNS Server Operators SHOULD treat requests to the five considered pTLDs as typos, for correct installations MUST not allow 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. ------%<---------------------------------------------------------------- How should DNS Registries/Registrars treat requests to register this reserved domain name? Should such requests be denied? Should such requests be allowed, but only to a specially- designated entity? (For example, the name "www.example.org" is reserved for documentation examples and is not available for registration; however, the name is in fact registered; and there is even a web site at that name, which states circularly that the name is reserved for use in documentation and cannot be registered!) ------%<---------------------------------------------------------------- 7. DNS Registries/Registrars In order to avoid conflicts with the P2P namespaces, IANA should reserve all five considered pTLDs and forbid registrars from registering domains names within their respective scopes. 8. Security Considerations The five requested Special-Use Domain Names presented in this document are resolved by specific software 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 used 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 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 users. 9. Aknowledgements We thank the I2P developers for their constructive feedback. ------%<---------------------------------------------------------------- TODO ------%<---------------------------------------------------------------- 10. References ------%<---------------------------------------------------------------- TODO: validate ------%<---------------------------------------------------------------- 10.1. Normative References [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels," BCP 14, RFC 2119, March 1997. [RFC 6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names", RFC 6761, February 2013. 10.2. Informative References [Dingledine 2004] Dingledine, R., Mathewson, N., and Syverson, P., "Tor: the second-generation onion router", in SSYM'04 Proceedings of the 13th conference on USENIX Security Symposium - Volume 13, page 21, 2004. [RFC 1928] Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and L. Jones, "SOCKS Protocol Version 5", RFC 1928, March 1996. [RFC 4648] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, October 2006. [RFC 6840] Weiler, S., Ed., and D. Blacka, Ed., "Clarifications and Implementation Notes for DNS Security (DNSSEC)", RFC 6840, February 2013. [RFC 6975] Crocker, S. and S. Rose, "Signaling Cryptographic Algorithm Understanding in DNS Security Extensions (DNSSEC)", RFC 6975, July 2013. [Schanzenbach 2012] Schanzenbach, M., "Design and Implementation of a Censorship Resistant and Fully Decentralized Name System", September 2012. [TorSpec] Mathewson, N., Dingledine, R., "Special Hostnames in Tor", September 2011.