Network Working Group J. Salowey Internet-Draft Cisco Systems Intended status: Standards Track S. Suehring Expires: May 14, 2011 November 10, 2010 Uniform Resource Identifier (URI) Scheme for Secure Shell (SSH) draft-salowey-secsh-uri-00.txt Abstract This document describes the Uniform Resource Identifiers used to locate resources for the Secure Shell (SSH) protocol. The document describes the generic syntax involved in URI definitions as well as specific definitions for the protocol. These specific definitions include user credentials such as username and other parameters such as host key fingerprint. 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 May 14, 2011. Copyright Notice Copyright (c) 2010 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 Salowey & Suehring Expires May 14, 2011 [Page 1] Internet-Draft URI Scheme for SSH November 2010 described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. General Syntax . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Secure Shell (SSH) URI . . . . . . . . . . . . . . . . . . . . 3 3.1. Scheme Name . . . . . . . . . . . . . . . . . . . . . . . . 3 3.2. Status . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.3. URI Scheme Syntax . . . . . . . . . . . . . . . . . . . . . 3 3.4. URI Semantics . . . . . . . . . . . . . . . . . . . . . . . 4 3.5. Encoding Considerations . . . . . . . . . . . . . . . . . . 5 3.6. Protocols using this URI scheme . . . . . . . . . . . . . . 5 3.7. Security Considerations . . . . . . . . . . . . . . . . . . 5 3.8. Contact . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. SSH connection parameters . . . . . . . . . . . . . . . . . 5 5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 7. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 9.1. Normative References . . . . . . . . . . . . . . . . . . . 7 9.2. Informative References . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 Salowey & Suehring Expires May 14, 2011 [Page 2] Internet-Draft URI Scheme for SSH November 2010 1. Introduction This document describes the Uniform Resource Identifiers (URIs) to be used with the Secure Shell (SSH) [RFC4251] protocos. 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]. 2. General Syntax A hierarchical URI shall consist of the scheme and the scheme specific portion separated by a colon ":" followed by the hierarchical part, as discussed in [RFC3986]. This specification uses the definitions "port", "host", "scheme", "userinfo", "path- empty", "path-abempty" and "authority" from [RFC3986]. This document follows the ABNF notation defined in [RFC5234]. 3. Secure Shell (SSH) URI This section describes the SSH URI and contains the information necessary to register the URI according to the template in [RFC4395]. 3.1. Scheme Name The Secure Shell scheme name is "ssh". 3.2. Status The requested status of the SSH URI is "permanent". 3.3. URI Scheme Syntax The Secure Shell (SSH) scheme shall consist of the scheme name "ssh" followed by a colon ":" followed by hier-part defined in [RFC3986]. The SSH URI ABNF definition follows. Salowey & Suehring Expires May 14, 2011 [Page 3] Internet-Draft URI Scheme for SSH November 2010 sshURI = "ssh:" hier-part hier-part = "//" authority path-abempty authority = [ [ ssh-info ] "@" ] host [ ":" port ] host = port = path-abempty = ssh-info = [ userinfo ] [";" c-param *("," c-param)] userinfo = c-param = paramname "=" paramvalue paramname = *( ALPHA / DIGIT / "-" ) paramvalue = *( ALPHA / DIGIT / "-" ) The following reserved characters from [RFC3986] are used as delimiters within the SSH URI: ";", ",", ":", and "=" . They must not be escaped when used as delimiters and must be escaped when the appear in other uses. 3.4. URI Semantics The intended usage of the SSH URI is to establish an interactive SSH terminal session with the host defined in the authority portion of the URI. The only operation defined for the URI is to establish an SSH terminal session with a remote host. If the userinfo or connection parameters are present the at-sign "@" shall precede the authority section of the URI. Optionally, the authority section MAY also include the port preceded by a colon ":". The host SHOULD be a non-empty string. If the port is not included, the default port is assumed. The ssh-info portion of the URI MAY include credentials consisting of a username followed by optional parameters. The convention of including the password separated from the username by a ":" in the URI is NOT RECOMMENDED and is deprecated in accordance with [RFC3986]. One or more optional connection parameters (c-param) may be specified within the userinfo section of the URI. These conn-parameters are separated from the userinfo by a semi-colon ";". The only connection parameter defined in this document is for the host-key fingerprint described in Section 4.1. It is possible that additional parameters be defined in the future. If a connection parameter is not understood it SHOULD be ignored. The SSH URI does not define a usage for a non-empty path element. If a non-empty path element is included in an SSH URI then it SHOULD be ignored. Salowey & Suehring Expires May 14, 2011 [Page 4] Internet-Draft URI Scheme for SSH November 2010 3.5. Encoding Considerations The encoding of the "host" portion of the URI is as defined in [RFC3986]. The encoding of the connection parameters is described in Section 4.1 3.6. Protocols using this URI scheme This URI scheme is used by the SSH protocol version 2 defined in [RFC4251]. 3.7. Security Considerations See Section 7. 3.8. Contact This document is discussed on the IETF SSH list: ietf-ssh@netbsd.org 4. Parameters 4.1. SSH connection parameters The following parameters are associated with an SSH connection and are applicable to SSH and SFTP. All parameters are optional and MUST NOT overwrite configured defaults. Individual parameters are separated by a comma (","). fingerprint The fingerprint parameter contains the fingerprint of the host key for the host specified in the URL. The fingerprint is encoded as host-key-alg-fingerprint. Host-key-alg is host public key algorithm defined in [RFC4253] and the fingerprint format is [RFC4716]. For use in a URI, the fingerprint shall use a single dash "-" as a separator instead of the colon ":" as described in [RFC4716]. This parameter MUST NOT overwrite a key that is already configured for the host. The fingerprint MAY be used to validate the authenticity of the host key if the URL was obtained from an authenticated source with its integrity protected. If this parameter is not included then the host key is validated using another method. See Security Considerations section for additional considerations. There MUST be only one fingerprint parameter present in a given URL. Salowey & Suehring Expires May 14, 2011 [Page 5] Internet-Draft URI Scheme for SSH November 2010 5. Examples The following section shows basic examples of URLs for each protocol. This section should not be considered to include all possible combinations of URLs for each protocol. An SSH connection to the host host.example.com on the standard port using username user. ssh://user@host.example.com An SSH connection to the host host.example.com on port 2222 using username user. ssh://user@host.example.com:2222 An SSH connection to the host having the specified host-key fingerprint at host.example.com on the standard port using username user. ssh://user;fingerprint=ssh-dss-c1-b1-30-29-d7-b8-de-6c-97- 77-10-d7-46-41-63-87@host.example.com 6. IANA Considerations Section 3 provides the information required in the URL registration template in accordance with [RFC4395]. 7. Security Considerations Passwords SHOULD NOT be included within the URI as doing so poses a security risk. URIs are usually sent in the clear with no encryption or other security, any password or other credentials included in the userinfo could be seen by a potential attacker. Although the host-key fingerprint is not confidential information, care must be taken in handling fingerprints associated with URIs because URIs transmitted or stored without protection may be modified by an attacker. In general an implementation cannot determine the source of a URI so a fingerprint received in a URI should have no more trust associated with it than a raw public key received in the SSH protocol itself. If a locally configured key exists for the server already it MUST NOT be automatically overwritten with information from the URI. If the host is unknown then the implementation should treat the fingerprint received with the same caution that it does with any unknown public key. The client MAY Salowey & Suehring Expires May 14, 2011 [Page 6] Internet-Draft URI Scheme for SSH November 2010 offer the fingerprint and URI for external validation before allowing a connection based on this information. If the client chooses to make a connection based on the URI information and it finds that the fingerprint in the URI and the public key offered by the server do not match then it SHOULD provide a warning and provide a means to abort the connection. Sections 4.1 and 9.2.4 of [RFC4251] provide a good discussion of handling public keys received in the SSH protocol. 8. Acknowledgements Ben Harris, Tom Petch and the members of the SSH working group have provided much useful feedback in the preparation of this document. 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. [RFC4251] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Protocol Architecture", RFC 4251, January 2006. [RFC4253] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Transport Layer Protocol", RFC 4253, January 2006. [RFC4716] Galbraith, J. and R. Thayer, "The Secure Shell (SSH) Public Key File Format", RFC 4716, November 2006. [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008. 9.2. Informative References [RFC4395] Hansen, T., Hardie, T., and L. Masinter, "Guidelines and Registration Procedures for New URI Schemes", BCP 35, RFC 4395, February 2006. Salowey & Suehring Expires May 14, 2011 [Page 7] Internet-Draft URI Scheme for SSH November 2010 Authors' Addresses Joseph Salowey Cisco Systems 2901 3rd Ave Seattle, WA 98121 US Email: jsalowey@cisco.com Steve Suehring PO BOX 1033 Stevens Point, WI 54481 US Email: suehring@braingia.com Salowey & Suehring Expires May 14, 2011 [Page 8]