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   Network Working Group
   Internet Draft                                           S. Suehring
   Document: draft-ietf-secsh-scp-sftp-ssh-uri-        Sentry Insurance
   01.txt                                                    J. Salowey
                                                          Cisco Systems
   Expires: April 2004                                     October 2003


                          SCP/SFTP/SSH URI Format
                 draft-ietf-secsh-scp-sftp-ssh-uri-01.txt

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet Draft will expire on February 8, 2004.


Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.


Abstract

   This document describes the Uniform Resource Identifiers used to
   locate resources for the SCP, SFTP, and SSH protocols.  The document
   describes the generic syntax involved in URI definitions as well as
   specific definitions for each protocol.  These specific definitions
   may include user credentials such as username and password and also
   may include other parameters such as fingerprint.  In addition,
   security considerations and examples are also provided within this
   document.


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Table of Contents

   1. General Syntax.................................................2
      1.1 SSH URI....................................................2
      1.2 SCP and SFTP URI...........................................2
   2. Parameters.....................................................3
      2.1 SSH connection parameters..................................3
      2.2 SFTP Parameters............................................4
   3. Examples.......................................................4
   4. Security Considerations........................................4
   Normative References..............................................5
   Non-Normative References..........................................6
   Author Information................................................6

1.   General Syntax

   The URI for each protocol shall consist of the scheme and the scheme
   specific portion separated by a colon ":", as discussed in RFC 2396
   [1].  This specification shall adopt the definitions "port", "host",
   "scheme", "userinfo", and "authority" from RFC 2396.

1.1     SSH URI

   The SSH scheme shall consist of the protocol acronym followed by a
   colon ":" and a double slash "//" in accordance with RFC 2718.

   The first component of the scheme specific portion MAY include
   credentials (userinfo) consisting of a username and optionally also
   including a password.  Including the password in the URL is NOT
   RECOMMENDED.  The username and password components are separated by a
   single colon ":".

   Following the userinfo, if 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 ":". If the port is not
   included, the default port is assumed.  Following the port additional
   parameters may be specified.  These parameters are defined in the
   connection parameters section.

      ssh_URI = "ssh://" [ userinfo "@" ] host [ ":" port ]
         [;conn-parameter=value]

1.2     SCP and SFTP URI

   For SCP and SFTP, the scheme portion (scp: or sftp:) is followed by a
   double slash "//".




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   Both SCP and SFTP URLs are terminated by a single slash "/" followed
   by the path information to the requested resource.

   The first component of the scheme specific portion MAY include
   credentials (userinfo) consisting of a username and optionally also
   including a password.  Including the password in the URL is NOT
   RECOMMENDED.  The username and password components are separated by a
   single colon ":".

   Following the userinfo, if present, the at-sign "@" shall precede the
   authority section of the URL.  Optionally, the authority section MAY
   also include the port preceded by a colon ":".  If the port is not
   included, the default port is assumed.  Following the port additional
   parameters may be specified.  These parameters are defined in the
   connection parameters section.

      scp_URI = "scp://" [ userinfo "@" ] host [ ":" port ]
         [ ; parameter = value ] [ abs_path ]

   Following the port additional parameters may be specified.  These
   parameters are defined in the connection parameters section.
   Following the path additional sftp specific parameters may be
   specified.

      sftp_URI = "sftp://" [ userinfo "@" ] host [ ":" port ]
         [;conn-parameter=value] [ abs_path ] [;sftp-parameter=value]

   The URIs for SFTP and SCP are hierarcical URIs where each component
   of the abs_path consists of path elements separated by a '/'. This is
   the same format as used in the FTP URL described in section 2.2.2 of
   [5].


2.   Parameters

2.1     SSH connection parameters

   The following parameters are associated with an SSH connection and
   are applicable to SSH, SFTP and SCP.  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 [4] and the fingerprint format is defined in [2].



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   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 validity of the host key is validated using
   another method.  See Security Considerations section for additional
   considerations.  There MUST be only one fingerprint parameter per
   host-key-alg for a given URL.

2.2     SFTP Parameters

   The SFTP parameters determine how to handle the file transfer
   character translation.

   newline

   The newline parameter determines how the server translates new line
   indicators.  The possible choices are usually "\r" or "\n" or "\r\n".
   The default is "\r\n".

   typecode

   The typecode identifies the type of file which determines how it will
   be treated. Possible values are "i" for binary files, "a" for text
   files, and "d" for directory listings.

3.   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.

         ssh://user@host

         ssh://user@host:2222

         ssh://joeuser@example.com;fingerprint=ssh-dss:c1:b1:30:29:d7:b8
             :de:6c:97:77:10:d7:46:41:63:87

         scp://user:password@host/file.txt

         sftp://user@host/dir/path/file.txt

         sftp://joeuser@example.com:2222;fingerprint=ssh-dss:c1:b1:30
             :29:d7:b8:de:6c:97:77:10:d7:46:41:63:87,


4.   Security Considerations



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   In general, URIs themselves have no security considerations.
   However, since the password for each scheme can optionally be
   included within the URL it should be noted that doing so poses a
   security risk.  Since URLs are usually sent in the clear with no
   encryption or other security, any password or other credentials
   (userinfo) included could be seen by a potential attacker.

   Care must also be taken in handling fingerprints associated with URLs
   because URLs transmitted or stored without protection may be modified
   by an attacker.  In general an implementation cannot determine the
   source of a URL so a fingerprint received in a URL 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 URL. 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
   offer the fingerprint and URL for external validation before allowing
   a connection based on this information. If the client chooses to make
   a connection based on the URL information and it finds that the
   public key in the URL 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 3.1 and 8.2.4 of [3] provide a good
   discussion of handling public keys received in the SSH protocol.

Normative References

   [1] Berners-Lee, T., Fielding, R., Masinter, L., "Uniform Resource
      Identifiers (URI): Generic Syntax", RFC 2396, August 1998.

   [2] Markus Friedl, "SSH Fingerprint Format",
   http://www.ietf.org/internet-drafts/draft-ietf-secsh-fingerprint-
   01.txt, work in progress

   [3] Ylonen, T., "SSH Protocol Architecture",
   http://www.ietf.org/internet-drafts/draft-ietf-secsh-architecture-
   14.txt, work in progreess

   [4] Ylonen, T., "SSH Transport Layer Protocol",
   http://www.ietf.org/internet-drafts/draft-ietf-secsh-transport-
   16.txt, work in progress

   [5] Hoffman, P., Definitions of Early URI Schemes",
   http://www.ietf.org/internet-drafts/draft-hoffman-rfc1738bis-00.txt,
    work in progress






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Non-Normative References

   Masinter, L., et. al., "Guidelines for new URL Schemes", RFC 2718,
   November 1999.

   Mealling, M., Denenberg, R., "Report from the Joint W3C/IETF URI
   Planning Interest Group: Uniform Resource Identifiers (URIs), URLs,
   and Uniform Resource Names (URNs): Clarifications and
   Recommendations", RFC 3305, August 2002.


Author Information

   Steve Suehring
   Sentry Insurance
   1800 North Point Dr, G2/61-17
   Stevens Point, WI 54481
   suehring@braingia.com

   Joseph Salowey
   Cisco Systems
   2901 Third Avenue
   Seattle, WA 98121
   E-mail: jsalowey@cisco.com

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