INTERNET DRAFT Joel N. Weber II June 20, 2003 Expires December 20, 2003 Secure Shell ``none'' Public Key Algorithm draft-weber-secsh-pkalg-none-00.txt This document is an Internet-Draft and is subject to all the 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/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html The distribution of this memo is unlimited. It is filed as draft- weber-secsh-pkalg-none-00.txt, and expires 20 December 2003. Please send comments to the author or to ietf-ssh@netbsd.org ABSTRACT This document describes the ``none'' public key encryption algorithm for the Secure Shell protocol, which is useful for rekeying when the server has no keys to support for non-GSSAPI key exchange and when GSSAPI credentials are expired, or for use in embedded systems where there is a desire to minimize the overhead of rekeying to prevent sequence number rollover. INTRODUCTION The mechanisms currently defined for key exchange in the Secure Shell protocol all have the property of requiring host key verification. This is valuable at the begining of an ssh session, but key exchange is also used to rekey in the middle of a session to prevent problems with sequence number rollover. Given that [SECSH] recommends Weber Secure Shell ``none'' Public Key Algorithm [Page 1] draft-weber-secsh-pkalg-none-00.txt June 20 2003 rekeying based upon the need to prevent sequence number rollover, and does not describe any other expected threats, it may be reasonable to assume that PFS within a session is of limited importance. [SECSHGSS] defines a family of key exchange methods which can be used to do key exchange in the Secure Shell protocol using GSSAPI. Some GSSAPI mechanisms, such as Kerberos 5, use credentials which expire, and will fail if the credentials expire. The convention used is often to allow connections to remain active indefinitely as long as the credentials were valid at the time the connection was initiated. It is possible for a host which uses a GSSAPI mechanism to not have a host key which is usable with the diffie-hellman-group1-sha1 key exchange method. In such a case, one may want to be able to rekey the session without having any host key available. There is also some concern about rekeying potentially being computationally intensive for some embedded devices, and removing the need to make a public key signature may be worthwhile. This document defines the use of the ``none'' host key algorithm with the diffie-hellman-group1-sha1 and similar key exchange algorithms that support the same set of host key algorithms. GENERATING AND VERIFYING SIGNATURES When using the ``none'' algorithm, the server public key data and signature data sent from the server to the client is zero length, and the client verifies these things by ensuring that they are zero length. APPLICABILITY The ``none'' algorithm MUST NOT be used for initial key exchange. It MAY be used when rekeying. SECURITY CONSIDERATIONS When using ``none'' for rekeying, an attacker who has compromised the symetric encryption keys can perform a man in the middle attack against the key exchange, in which the attacker does key exchange with the client, and does key exchange with the server, rather than allowing the client to do key exchange with the server. If an algorithm other than ``none'' is used, the client will notice that such an attack has happened. However, such an attack is believed to be essentially impossible to carry out, due to the use of strong symmetric encryption algorithms. AUTHOR'S ADDRESS Weber Secure Shell ``none'' Public Key Algorithm [Page 2] draft-weber-secsh-pkalg-none-00.txt June 20 2003 Joel N. Weber II 185 Lowell St #2 Somerville MA 02144-2629 Email: weber@joelweber.com NORMATIVE REFERENCES [SECSH] RFC-Editor: To be replaced by RFC number for draft-ietf- secsh-architecture [RFC2026] S. Bradner, RFC2026, BCP 9: "The Internet Standard Process - Revision 3," October 1996, Obsoletes - RFC 1602, Status: Best Current Practice. [RFC2119] S. Bradner, RFC 2119, BCP 14: "Key words for use in RFCs to Indicate Requirement Levels", March 1997. INFORMATIVE REFERENCES [SECSHGSS] RFC-Editor: To be replaced by RFC number for draft-ietf- secsh-gsskeyex IPR NOTICES 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. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. COPYRIGHT NOTICE Copyright (C) The Internet Society 2003. All Rights Reserved. Weber Secure Shell ``none'' Public Key Algorithm [Page 3] draft-weber-secsh-pkalg-none-00.txt June 20 2003 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 implmentation 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. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Weber Secure Shell ``none'' Public Key Algorithm [Page 4]