Network Working Group S. Josefsson Internet-Draft RSA Security Expires: March 29, 2002 September 28, 2001 DNS URI scheme draft-josefsson-dns-url Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on March 29, 2002. Distribution of this document is unlimited. Comments and suggestions on this document are encouraged. 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 [3]. Copyright Notice Copyright (C) The Internet Society (2001). All Rights Reserved. Abstract This draft describes a URI scheme to locate DNS resources. Josefsson Expires March 29, 2002 [Page 1] Internet-Draft DNS URI scheme September 2001 Table of Contents 1. Introduction and Background . . . . . . . . . . . . . . . . . 3 2. URI Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. URI Scheme Syntax . . . . . . . . . . . . . . . . . . . . . . 3 4. Character Encoding Considerations . . . . . . . . . . . . . . 4 5. Intended Usage . . . . . . . . . . . . . . . . . . . . . . . . 4 6. Applications and/or Protocols Using This Scheme . . . . . . . 4 7. Interoperability Considerations . . . . . . . . . . . . . . . 4 8. Security Considerations . . . . . . . . . . . . . . . . . . . 4 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Author's Address . . . . . . . . . . . . . . . . . . . . . . . 6 References . . . . . . . . . . . . . . . . . . . . . . . . . . 5 A. IANA URI Registration Template . . . . . . . . . . . . . . . . 6 Full Copyright Statement . . . . . . . . . . . . . . . . . . . 8 Josefsson Expires March 29, 2002 [Page 2] Internet-Draft DNS URI scheme September 2001 1. Introduction and Background DNS [1][2] is a widely deployed protocol used to, among other things, translate domain names into IP addresses. More recent work has added support for storing cryptographic keys and certificates in DNS [6][7]. To be able to locate, for example, certificates via a network resource, URIs are often used. This document describes a URI scheme to locate DNS information. The DNS URI scheme described here can be used to reference any DNS data, not only certificates. The following sections are modelled after the Registration Template in [8]. The template can be found in Appendix A. 2. URI Scheme The name of the URI scheme defined in this document is "dns". A DNS URI designates a DNS resource record: By domain name, type and class and optionally server. The DNS URI follows the generic syntax from RFC 2396 [5], and is described using ABNF [4] in section 3. A DNS URI is of the following general form. This is intended to illustrate, not define, the scheme. dns:[//server/]domain[?type=TYPE;class=CLASS] 3. URI Scheme Syntax Strings are not case sensitive and free insertion of linear-white-space is not permitted. dnsurl = "dns:" [ "//" hostport "/" ] dnsname ["?" query] ; See RFC 2396 for "hostport" definition domainname = uric ; See RFC 2396 for "uric" definition query = queryelement [";" query] queryelement = ( "CLASS=" classval ) | ( "TYPE=" typeval ) | ( 1*alphanum "=" 1*alphanum ) classval = 1*digit / "IN" / "CH" / ... ; Any standard DNS class expressed as ; mnemonic or as decimal integer typeval = 1*digit / "A" / "NS" / "MD" / ... ; Any standard DNS type expressed as ; mnemonic or as decimal integer Josefsson Expires March 29, 2002 [Page 3] Internet-Draft DNS URI scheme September 2001 The digit representation of types and classes SHOULD NOT be used when a defined mnemonic for the corresponding value is known. Of the "reserved" characters in the "dnsname" element, the "?" character MUST be escaped, the rest MAY be escaped. Otherwise, it would be impossible to separate a domain name containing "?" from the "query" delimiter. Unless specified, the "server" is assumed to be locally (pre-)configured, and "class" to be the Internet class ("IN"), and "type" to be the Address (A) type. To resolve a DNS URI using the DNS protocol [2] a query is formed by using the domainname, classval and typeval from the URI string (or the previously mentioned default values if either classval or typeval is missing from the string). If hostport is given in the URI string, this server should receive the DNS query, otherwise the default DNS server should receive it. 4. Character Encoding Considerations The characters in the URI, in particular the "dnsname", MUST be encoded as per the "URI Generic Syntax" RFC [5]. This URI specification allows all possible DNS names to be encoded (of course following the encoding rules of [5]), however certain applications may restrict the set of valid characters and care should be taken so that invalid characters in these contexts does not cause harm. In particular, hostnames in DNS often have certain restrictions. It is up to these application to limit this subset, this URI scheme places no restrictions. 5. Intended Usage Broad usage. 6. Applications and/or Protocols Using This Scheme E.g. CNRP. 7. Interoperability Considerations The data referenced by this URI scheme might be transferred by protocols that aren't URI aware (such as the DNS protocol). This is not anticipated to have any serious interoperability impact though. 8. Security Considerations A DNS URI does not embed confidential information. If it references Josefsson Expires March 29, 2002 [Page 4] Internet-Draft DNS URI scheme September 2001 domains in the Internet DNS environment, even the information referenced by the URI is public information. If a DNS URI is used within an "internal" DNS environment, the same security considerations of the DNS environment apply to the use and handling of DNS URIs themselves as well as the data returned by looking up these URIs. If security related information is referenced by DNS URIs (such as certificates stored in DNS), care must be taken to prevent for man-in-the-middle attacks that maliciously replace the certificate. Techniques such as Secure DNS may be used. This draft does not affect the security considerations related to DNS itself. 9. IANA Considerations The IANA is asked to register the DNS URI scheme using this document as the template in accordance with RFC 2717 [8]. 10. Examples The following illustrate a DNS query for "www.example.org" for the Internet (IN) class and the Address (A) type: dns:www.example.org?class=IN;type=A The following illustrate a DNS query for "simon.example.org" for the CERT type in the Internet (IN) class: dns:simon.example.org?type=CERT The following illustrate a DNS query for "ftp.example.org" from the DNS server "internal-dns.example.org" server, in the Internet (IN) class and the address (A) type: dns://internal-dns.example.org/ftp.example.org?type=A The following illustrate a strange, albeit valid, DNS query: dns://internal-dns.example.org/*.%3f%20 %00%25+?type=TXT Acknowledgement Thanks to Michael Mealling, Steve Mattson and Stuart Cheshire for comments. References Josefsson Expires March 29, 2002 [Page 5] Internet-Draft DNS URI scheme September 2001 [1] Mockapetris, P., "Domain Names - Concepts and Facilities", RFC 1034, November 1987. [2] Mockapetris, P., "Domain Names - Implementation and Specification", RFC 1035, November 1987. [3] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. [4] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. [5] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifiers (URI): Generic Syntax", RFC 2396, August 1998. [6] Eastlake, D., "Domain Name System Security Extensions", RFC 2535, March 1999. [7] Eastlake, D. and O. Gudmundsson, "Storing Certificates in the Domain Name System (DNS)", RFC 2538, March 1999. [8] Petke, R. and I. King, "Registration Procedures for URL Scheme Names", RFC 2717, November 1999. Author's Address Simon Josefsson RSA Security Arenav„gen 29 Stockholm 121 29 Sweden Phone: +46 8 7250914 EMail: sjosefsson@rsasecurity.com Appendix A. IANA URI Registration Template URL scheme name: dns URL scheme syntax: Section 3 Character encoding considerations: Section 4 Intended usage: Section 5 Applications and/or protocols which use this scheme: Section 5. Josefsson Expires March 29, 2002 [Page 6] Internet-Draft DNS URI scheme September 2001 Interoperability considerations: Section 7. Security considerations: Section 8 Contact: sjosefsson@rsasecurity.com Author/Change Controller: IESG Josefsson Expires March 29, 2002 [Page 7] Internet-Draft DNS URI scheme September 2001 Full Copyright Statement Copyright (C) The Internet Society (2001). All Rights Reserved. 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