Special-Use Domain Name for Namecoin
draft-grothoff-iesg-special-use-p2p-bit-00

Abstract

This document registers a Special-Use Domain Name for use with the Namecoin system, 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 January 1, 2016.

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 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. Applicability
• 3. Terminology and Conventions Used in This Document
• 4. The "BIT" Timeline System pTLD
• 5. Security Considerations
• 6. IANA Considerations
• 7. Acknowledgements
• 8. References
• 8.1. Normative References
• 8.2. Informative References
• Authors' Addresses

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.

Namecoin offers a specific timeline-based mechanism to allocate, register, manage, and resolve names, independently from the DNS root and delegation tree.

As compatibility with applications using domain names is desired, Namecoin uses an exclusive alternative Top-Level Domain to avoid conflicts between the Namecoin 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 the Special-Use Domain Names "BIT" for use with Namecoin, as per [RFC6761].

Namecoin (also known as the Dot-Bit Project) uses this pTLD to realize censorship-resistant naming.

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 Special-Use Domain Name for Namecoin reserved by this document meets this requirement, as it has the following specificities:

• The "BIT" pTLD is not manageable by some designated administration. Instead, it is managed by a P2P protocol using a global public ledger.
• Namecoin does not depend on the DNS context for their resolution: Namecoin domains MAY use the DNS servers infrastructure, as they return DNS-compatible results; but it uses specific P2P protocols for regular name resolution, covered by the respective protocol specifications.
• When Namecoin is properly implemented, the implementation MUST intercept queries for the pTLD to ensure Namecoin names cannot leak into the DNS.
• The appropriate pTLD protocols can be implemented in existing software libraries and APIs to extend regular DNS operation and enable Namecoin name resolution. However, the default hierarchical DNS response to any request to any pTLD MUST be NXDOMAIN.
• Finally, in order for Namecoin to realize a censorship-resistant name system, 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 ".bit" peers in "BIT", but an .bit 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.

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 a proof-of-work calculation that uses 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 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:

• 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 has 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.
   
   
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 Namecoin 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 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 Namecoin 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 [SSAC-NXDOMAIN-Abuse]. 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 "BIT", 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.

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 Namecoin pTLD significantly increase the risk of ".bit" 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]:

• .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.

8. References

8.1. Normative References

8.2. Informative References

Authors' Addresses