Network Working Group Internet Draft S. Suehring
Internet-DraftDocument: draft-ietf-secsh-scp-sftp-ssh-uri- Sentry Insurance Expires February 8, 200401.txt J. Salowey Cisco Systems August 8,Expires: April 2004 October 2003 SCP/SFTP/SSH URI Format draft-ietf-secsh-scp-sftp-ssh-uri-00.txtdraft-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 Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts.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/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html 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. SCP/SFTP/SSH URI Format October 2003 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 . 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 .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 22is 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 "//". SCP/SFTP/SSH URI Format October 2003 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 22is 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 . 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  and the fingerprint format is defined in .. SCP/SFTP/SSH URI Format October 2003 This parameter MUST NOT overwrite a key that is already configured for the host. TheyThe 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. cipher2.2 SFTP Parameters The cipher parameter indicates an acceptable encryption mechanismSFTP parameters determine how to use in makinghandle the connection.file transfer character translation. newline The value is the string specifying the SSH cipher type. This parameter MUST NOT add a mechanism to a configured list of default configured acceptable encryption types. If thisnewline parameter is not specified thendetermines how the server translates new line indicators. The possible choices are usually "\r" or "\n" or "\r\n". The default configured cipher listis used. There may be more than one cipher parameter. integrity"\r\n". typecode The integrity parameter indicates an acceptable data integrity mechanism to use in makingtypecode identifies the connection.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 value is the string specifying the SSH data integrity type. This parameter MUST NOT add a mechanism to a configured listfollowing section shows basic examples of default configured acceptable data integrity types. If this parameter isURLs for each protocol. This section should not specified then the default configured data integrity list is used. There maybe more than one integrity parameter. key-xchg The key-xchg parameter indicates an acceptable key exchange mechanism to use when making the connection. The value is the string specifying the SSH key exchange type. This parameter MUST NOT add a mechanism to a configured list of default configured acceptable key exchange types. If this parameter is not specified then the default configured key exchange list is used. There may be more than one key-xchg parameter. host-key-alg The host-key-alg parameter indicates an host key to use when making the connection. The value is the string specifying the SSH host key type. This parameter MUST NOT add a mechanism to a configured list of default configured acceptable host key types. If this parameter is not specified then the default configured host key type list is used. There may be more than one host-key-alg parameter. user-auth The user-auth parameter indicates a user authentication mechanism to use when making the connection. The value is the string specifying the SSH user authentication mechanism type. This parameter MUST NOT add a mechanism to a configured list of default configured acceptable user authentication mechanism types. If this parameter is not specified then the default configured user authentication mechanism type list is used. There may be more than one user-auth parameter. 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. Examples The following section shows basic examples of URLs for each protocol. This section should not be consideredconsidered to include all possible combinations of URLs for each protocol. ssh://user@host ssh://user@host:2222 ssh://firstname.lastname@example.org;fingerprint=c1:b1:30:29:d7:b8:de:6c :97:77:10:d7:46:41:63:87,cipher=aes-cbcssh://email@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://firstname.lastname@example.org:2222;fingerprint=c1:b1:30:29:d7:b8 :de:6c:97:77:10:d7:46:41:63:87,cipher= aes-cbc/pub/docs/test.txt;typecode=asftp://email@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 SCP/SFTP/SSH URI Format October 2003 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. The fingerprint should onlyCare must also be used to validatetaken 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 hostsource of a URL so a fingerprint received in a URL should have no more trust associated with it than a raw public key only ifreceived in the URL can be determined to be authentic fromSSH protocol itself. If a trusted entity. For example,locally configured key exists for the URL mayserver already it MUST NOT be received through secure email or HTTPSautomatically overwritten with information from a trusted and verifiable source. Itthe URL. If the host is possible thatunknown then the SSHimplementation may not be able to determine ifshould treat the URL is authentic in which casefingerprint received with the same caution that it SHOULD promptdoes with any unknown public key. The client MAY offer the user to either allow or disallowfingerprint 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 provided. The SSH implementation MUST NOT overwrite a currently configuredand it finds that the public key based onin the URL alone. The other connection parameters MUST NOT add any mechanismand the public key offered by the server do not match then it SHOULD provide a warning and provide a means to abort the listconnection. Sections 3.1 and 8.2.4 of configured acceptable mechanisms defined provide a good discussion of handling public keys received in the SSH client.protocol. Normative References  Berners-Lee, T., Fielding, R., Masinter, L., "Uniform Resource Identifiers (URI): Generic Syntax", RFC 2396, August 1998.  Markus Friedl, "SSH Fingerprint Format", http://www.ietf.org/internet-drafts/draft-ietf-secsh-fingerprint- 01.txt, work in progress  Ylonen, T., "SSH Protocol Architecture", http://www.ietf.org/internet-drafts/draft-ietf-secsh-architecture- 14.txt, work in progreess  Ylonen, T., "SSH Transport Layer Protocol", http://www.ietf.org/internet-drafts/draft-ietf-secsh-transport- 16.txt, work in progress  Hoffman, P., Definitions of Early URI Schemes", http://www.ietf.org/internet-drafts/draft-hoffman-rfc1738bis-00.txt, work in progress SCP/SFTP/SSH URI Format October 2003 Non-Normative References Masinter, L., et. al., "Guidelines for new URL Schemes", RFC 2718, November 1999.  Markus Friedl, "SSH Fingerprint Format", http://www.ietf.org/internet-drafts/ draft-ietf-secsh-fingerprint-01.txt, work in progress Non-Normative ReferencesMealling, 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 firstname.lastname@example.org Joseph Salowey Cisco Systems 2901 Third Avenue Seattle, WA 98121 E-mail: email@example.com Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. 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