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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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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