Secure Shell Working Group J. Galbraith Internet-Draft J. Van Dyke Expires: April 18, 2003 B. McClure VanDyke Software October 18, 2002 Secure Shell Public-Key Subsystem draft-galb-secsh-publickey-subsystem-00.txt Status of this Memo This document is an Internet-Draft and is in full conformance with 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 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/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 18, 2003. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract SECSH defines an authentication mechanism that is based on public keys, but does not define any mechanism for key distribution. No common key management solution exists in current implementations. This document describes a protocol that can be used to configure public keys in an implementation-independent fashion, allowing client software to take on the burden of this configuration. This protocol is intended to be used from the Secure Shell Connection Protocol [4] as a subsystem, as described in Section ``Starting a Shell or a Command''. The subsystem name used with this protocol is Galbraith, et al. Expires April 18, 2003 [Page 1] Internet-Draft Secure Shell Public-Key Subsystem October 2002 "publickey@vandyke.com". The public-key subsystem provides a server-independent mechanism for clients to add public keys, remove public keys, and list the current public keys known by the server. Rights to manage public keys are specific and limited to the authenticated user. A public key may also be associated with a mandatory command. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Public-Key Subsystem Overview . . . . . . . . . . . . . . . 4 2.1 Opening the Public-Key Subsystem . . . . . . . . . . . . . . 4 2.2 Requests . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.3 Responses . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.3.1 The Status Response . . . . . . . . . . . . . . . . . . . . 5 3. Public-Key Subsystem Operations . . . . . . . . . . . . . . 7 3.1 Version Packet . . . . . . . . . . . . . . . . . . . . . . . 7 3.2 Adding a public key . . . . . . . . . . . . . . . . . . . . 7 3.3 Removing a public key . . . . . . . . . . . . . . . . . . . 7 3.4 Listing public keys . . . . . . . . . . . . . . . . . . . . 8 3.5 Associate public key with a mandatory command . . . . . . . 8 References . . . . . . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 9 Full Copyright Statement . . . . . . . . . . . . . . . . . . 11 Galbraith, et al. Expires April 18, 2003 [Page 2] Internet-Draft Secure Shell Public-Key Subsystem October 2002 1. Introduction SECSH is a protocol for secure remote login and other secure network services over an insecure network. SECSH defines an authentication mechanism that is based on public keys, but does not define any mechanism for key distribution. Common practice is to authenticate once with password authentication and transfer the public key to the server. However, to date no two implementations use the same mechanism to configure a public key for use. This document describes a subsystem that can be used to configure public keys in an implementation-independent fashion. This approach allows client software to take on the burden of this configuration. The public-key subsystem protocol is designed for extreme simplicity in implementation. It is not intended as a PKIX replacement. The Secure Shell Public-Key subsystem has been designed to run on top of the SECSH transport layer [2] and user authentication protocols [3]. It provides a simple mechanism for the client to manage public keys on the server. This document should be read only after reading the SECSH architecture [1] and SECSH connection [4] documents. This protocol requires that the user be able to authenticate in some fashion before it can be used. If password authentication is used, servers SHOULD provide a configuration option to disable the use of password authentication after the first public key is added. Galbraith, et al. Expires April 18, 2003 [Page 3] Internet-Draft Secure Shell Public-Key Subsystem October 2002 2. Public-Key Subsystem Overview The public-key subsystem provides a server-independent mechanism for clients to add public keys, remove public keys, and list the current public keys known by the server. The subsystem name is "publickey@vandyke.com". The public keys added, removed, and listed using this protocol are specific and limited to those of the authenticated user. The operations to add, remove and list the authenticated user's public keys are performed as request packets sent to the server. The server sends response packets that indicate success or failure as well as provide specific response data. The format of public-key blobs are detailed in the SSH Transport Protocol document [2]. 2.1 Opening the Public-Key Subsystem The public-key subsystem is opened when the clients sends a SSH_MSG_CHANNEL_REQUEST over an existing session. The details of how a session is opened are described in the SSH Connection Protocol document [4] in the section "Opening a Session". To open the public-key subsystem, the client sends: byte SSH_MSG_CHANNEL_REQUEST uint32 recipient channel string "subsystem" boolean want reply string "publickey@vandyke.com" Client implementations SHOULD reject this request; it is normally only sent by the client. If want reply is TRUE, the server will respond with SSH_MSG_CHANNEL_SUCCESS if the public-key subsystem was successfully started or SSH_MSG_CHANNEL_FAILURE if the server failed to start or does not support the public-key subsystem. The server SHOULD respond with SSH_MSG_CHANNEL_FAILURE if the user authenticated with a restricted public key that does not allow access to the publickey subsystem. It is RECOMMENDED that clients request and check the reply for this request. Galbraith, et al. Expires April 18, 2003 [Page 4] Internet-Draft Secure Shell Public-Key Subsystem October 2002 2.2 Requests All public-key subsystem requests are sent request in the following form: string request-name ... request specific data follows The client MUST receive acknowledgement of each request prior to sending a new request. All requests described in Section 3 are a description of the 'data' portion of the packet. 2.3 Responses All public-key subsystem requests are sent request in the following form: string response-name ... response specific data follows 2.3.1 The Status Response A request is acknowledged by sending a status packet. If there is data in response to the request, the status packet is sent after all data has been sent. string "status" uint32 status code string description [RFC-2279] string language tag [RFC-1766] A status message MUST be sent for any unrecognized packets and the request SHOULD NOT close the subsystem. 2.3.1.1 Status Codes The status code gives the status in a more machine-readable format (suitable for localization), and can have the following values: Galbraith, et al. Expires April 18, 2003 [Page 5] Internet-Draft Secure Shell Public-Key Subsystem October 2002 SUCCESS 0 ACCESS_DENIED 1 STORAGE_EXCEEDED 2 REQUEST_NOT_SUPPORTED 3 KEY_NOT_FOUND 4 KEY_NOT_SUPPORTED 5 GENERAL_FAILURE 6 Galbraith, et al. Expires April 18, 2003 [Page 6] Internet-Draft Secure Shell Public-Key Subsystem October 2002 3. Public-Key Subsystem Operations The public-key subsystem currently defines four operations: add, remove, list, and command. 3.1 Version Packet Both sides MUST start by sending a version packet that indicates the version of the protocol they are using. string "version" uint32 protocol-version-number The version of the protocol described by this document is version 1. Both sides send the highest version that they implement. The lower of the version numbers is the version of the protocol to use. If either side can't support the lower version, it should close the subsystem. Both sides MUST wait to receive this version before continuing. 3.2 Adding a public key If the client wishes to add a public key, the client sends: string "add" string comment string public-key algorithm name string public-key blob The server MUST attempt to store the public key for the user in the appropriate location so the public key can be used for subsequent public-key authentications. The comment field contains user-specified text about the public key and MAY be empty. 3.3 Removing a public key If the client wishes to remove a public key, the client sends: string "remove" string public-key algorithm name string public-key blob The server MUST attempt to remove the public key for the user from the appropriate location, so that the public key cannot be used for Galbraith, et al. Expires April 18, 2003 [Page 7] Internet-Draft Secure Shell Public-Key Subsystem October 2002 subsequent authentications. 3.4 Listing public keys If the client wishes to list the known public keys, the client sends: string "list" The server will respond with zero or more of the following responses: string "publickey" string comment string public-key algorithm name string public-key blob The comment field contains user-specified text about the public key and MAY be empty. Following the last "publickey" response, a status packet MUST be sent. An implementation MAY choose not to support this request. 3.5 Associate public key with a mandatory command If the client wishes to associate a command with a specific public key, the client sends: string "command" string public-key algorithm name string public-key blob string command The request MUST fail if the public key does not already exist on the server. An implementation MAY choose not to support this request. Galbraith, et al. Expires April 18, 2003 [Page 8] Internet-Draft Secure Shell Public-Key Subsystem October 2002 References [1] Ylonen, T., Kivinen, T., Saarinen, M., Rinne, T. and S. Lehtinen, "SSH Protocol Architecture", draft-ietf-secsh- architecture-13 (work in progress), January 2002. [2] Ylonen, T., Kivinen, T., Saarinen, M., Rinne, T. and S. Lehtinen, "SSH Transport Layer Protocol", draft-ietf-secsh- transport-15 (work in progress), March 2002. [3] Ylonen, T., Kivinen, T., Saarinen, M., Rinne, T. and S. Lehtinen, "SSH Authentication Protocol", draft-ietf-secsh- userauth-16 (work in progress), February 2002. [4] Ylonen, T., Kivinen, T., Saarinen, M., Rinne, T. and S. Lehtinen, "SSH Connection Protocol", draft-ietf-secsh-connect-16 (work in progress), January 2002. [5] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC 2279, January 1998. Authors' Addresses Joseph Galbraith VanDyke Software 4848 Tramway Ridge Blvd Suite 101 Albuquerque, NM 87111 US Phone: +1 505 332 5700 EMail: galb-list@vandyke.com Jeff P. Van Dyke VanDyke Software 4848 Tramway Ridge Blvd Suite 101 Albuquerque, NM 87111 US Phone: +1 505 332 5700 EMail: jpv@vandyke.com Galbraith, et al. Expires April 18, 2003 [Page 9] Internet-Draft Secure Shell Public-Key Subsystem October 2002 Brent McClure VanDyke Software 4848 Tramway Ridge Blvd Suite 101 Albuquerque, NM 87111 US Phone: +1 505 332 5700 EMail: bdm@vandyke.com Galbraith, et al. Expires April 18, 2003 [Page 10] Internet-Draft Secure Shell Public-Key Subsystem October 2002 Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. 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