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Network Working Group                                        S. Suehring
Internet-Draft
Expires: December 16, 2005                                    J. Salowey
                                                           Cisco Systems
                                                           June 14, 2005


                        SCP/SFTP/SSH URI Format
                draft-ietf-secsh-scp-sftp-ssh-uri-02.txt

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   This Internet-Draft will expire on December 16, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2005).

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



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   document.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  General Syntax . . . . . . . . . . . . . . . . . . . . . . . .  3
     2.1   SSH URI  . . . . . . . . . . . . . . . . . . . . . . . . .  3
     2.2   SCP and SFTP URI . . . . . . . . . . . . . . . . . . . . .  3
   3.  Parameters . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.1   SSH connection parameters  . . . . . . . . . . . . . . . .  4
     3.2   SFTP Parameters  . . . . . . . . . . . . . . . . . . . . .  5
   4.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  6
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     6.1   Normative References . . . . . . . . . . . . . . . . . . .  6
     6.2   Informative References . . . . . . . . . . . . . . . . . .  7
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . .  7
       Intellectual Property and Copyright Statements . . . . . . . .  8

































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1.  Introduction

   This document describes the Uniform Resource Identifiers (URIs) to be
   used with the SSH, SCP, and SFTP protocols.

2.  General Syntax

   The URI for each protocol shall consist of the scheme and the scheme
   specific portion separated by a colon ":", as discussed in [RFC3986]
   This specification shall adopt the definitions "port", "host",
   "scheme", "userinfo", and "authority" from [RFC3986].

2.1  SSH URI

   The SSH scheme shall consist of the protocol acronym followed by a
   colon ":" and a double slash "//" in accordance with [RFC2718].

   The first component of the scheme specific portion MAY include
   credentials (userinfo) consisting of a username and optionally also
   including a password, separated by a colon ":".  Including the
   password in the URI is NOT RECOMMENDED and is deprecated in
   accordance with [RFC3986]

   One or more optional connection parameters (conn-parameters) may be
   specified within the userinfo section of the URI.  These conn-
   parameters are separated from the credentials by a semi-colon ";" and
   from each other by a comma ",".

   Following the userinfo, if present, and the conn-parameters, 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.

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

2.2  SCP and SFTP URI

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

   Both SCP and SFTP URIs 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, separated by a colon ":".  Including the



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   password in the URI is NOT RECOMMENDED and is deprecated in
   accordance with [RFC3986]

   One or more optional connection parameters (conn-parameters) may be
   specified within the userinfo section of the URI.  These conn-
   parameters are separated from the credentials by a semi-colon ";" and
   from each other by a comma ",".

   Following the userinfo, if present, and the conn-parameters, 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.

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

   The URIs for SFTP and SCP are hierarchical URIs where each component
   of the abs_path consists of path elements separated by a '/'.  This
   formatting is meant to represent the path information as in Section 5
   of [I-D.ietf-secsh-filexfer].

3.  Parameters


3.1   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 (",").  Additional parameters MAY be used.

   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 [I-D.ietf-secsh-transport] and the
      fingerprint format is [I-D.ietf-secsh-publickeyfile].  For use in
      a URI, the fingerprint shall use a single dash "-" as a separator



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      instead of the colon ":" as described in [I-D.ietf-secsh-
      publickeyfile].  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.

3.2  SFTP Parameters

   The SFTP parameters determine how to handle the file transfer
   character translation.  Additional parameters MAY be used.

   newline

      The newline parameter determines how the server translates new
      line indicators.  The default is CRLF and implemented in
      accordance with Section 4.3 of [I-D.ietf-secsh-filexfer].

   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.

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

   scp://user@host.example.com/file.txt

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

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





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5.  Security Considerations

   In general, URIs themselves have no security considerations.
   However, since the password for each scheme can optionally be
   included within the URI it should be noted that doing so poses a
   security risk.  Since URIs 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 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
   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
   public key 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 [I-D.ietf-secsh-
   architecture] provide a good discussion of handling public keys
   received in the SSH protocol.


6.  References

6.1  Normative References

   [I-D.ietf-secsh-architecture]
              Ylonen, T. and C. Lonvick, "SSH Protocol Architecture",
              draft-ietf-secsh-architecture-22 (work in progress),
              March 2005.

   [I-D.ietf-secsh-filexfer]
              Galbraith, J., "SSH File Transfer Protocol",
              draft-ietf-secsh-filexfer-09 (work in progress),
              June 2005.

   [I-D.ietf-secsh-publickeyfile]
              Galbraith, J. and R. Thayer, "SSH Public Key File Format",
              draft-ietf-secsh-publickeyfile-08 (work in progress),
              April 2005.




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   [I-D.ietf-secsh-transport]
              Lonvick, C., "SSH Transport Layer Protocol",
              draft-ietf-secsh-transport-24 (work in progress),
              March 2005.

   [RFC2718]  Masinter, L., Alvestrand, H., Zigmond, D., and R. Petke,
              "Guidelines for new URL Schemes", RFC 2718, November 1999.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

6.2  Informative References

   [RFC3305]  Mealling, M. and R. Denenberg, "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.


Authors' Addresses

   Steve Suehring
   PO BOX 1033
   Stevens Point, WI  54481
   US

   Email: suehring@braingia.com


   Joseph Salowey
   Cisco Systems
   2901 3rd Ave
   Seattle, WA  98121
   US

   Email: jsalowey@cisco.com













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   Copyright (C) The Internet Society (2005).  This document is subject
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Acknowledgment

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   Internet Society.




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