The Secure Shell (SSH) Authentication Protocol
The information below is for an old version of the document that is already published as an RFC.
This is an older version of an Internet-Draft that was ultimately published as RFC 4252.
|Authors||Chris M. Lonvick , Tatu Ylonen|
|Last updated||2015-10-14 (Latest revision 2005-03-16)|
|RFC stream||Internet Engineering Task Force (IETF)|
|Additional resources||Mailing list discussion|
|Stream||WG state||WG Document|
|IESG||IESG state||RFC 4252 (Proposed Standard)|
|Responsible AD||Russ Housley|
|Send notices to||(None)|
Network Working Group T. Ylonen Internet-Draft SSH Communications Security Corp Expires: September 15, 2005 C. Lonvick, Ed. Cisco Systems, Inc. March 14, 2005 SSH Authentication Protocol draft-ietf-secsh-userauth-27.txt Status of this Memo This document is an Internet-Draft and is subject to all provisions of Section 3 of RFC 3667. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she become aware will be disclosed, in accordance with RFC 3668. 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 September 15, 2005. Copyright Notice Copyright (C) The Internet Society (2005). Abstract SSH is a protocol for secure remote login and other secure network services over an insecure network. This document describes the SSH authentication protocol framework and public key, password, and host-based client authentication methods. Additional authentication methods are described in separate documents. The SSH authentication Ylonen & Lonvick Expires September 15, 2005 [Page 1] Internet-Draft SSH Authentication Protocol March 2005 protocol runs on top of the SSH transport layer protocol and provides a single authenticated tunnel for the SSH connection protocol. Table of Contents 1. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Conventions Used in This Document . . . . . . . . . . . . . 3 4. The Authentication Protocol Framework . . . . . . . . . . . 4 5. Authentication Requests . . . . . . . . . . . . . . . . . . 5 5.1 Responses to Authentication Requests . . . . . . . . . . . 6 5.2 The "none" Authentication Request . . . . . . . . . . . . 7 5.3 Completion of User Authentication . . . . . . . . . . . . 7 5.4 Banner Message . . . . . . . . . . . . . . . . . . . . . . 7 6. Authentication Protocol Message Numbers . . . . . . . . . . 8 7. Public Key Authentication Method: publickey . . . . . . . . 8 8. Password Authentication Method: password . . . . . . . . . . 10 9. Host-Based Authentication: hostbased . . . . . . . . . . . . 12 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . 13 11. Security Considerations . . . . . . . . . . . . . . . . . . 14 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 12.1 Normative . . . . . . . . . . . . . . . . . . . . . . . 14 12.2 Informative . . . . . . . . . . . . . . . . . . . . . . 15 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 15 A. Trademark Notice . . . . . . . . . . . . . . . . . . . . . . 15 Intellectual Property and Copyright Statements . . . . . . . 16 Ylonen & Lonvick Expires September 15, 2005 [Page 2] Internet-Draft SSH Authentication Protocol March 2005 1. Contributors The major original contributors of this set of documents have been: Tatu Ylonen, Tero Kivinen, Timo J. Rinne, Sami Lehtinen (all of SSH Communications Security Corp), and Markku-Juhani O. Saarinen (University of Jyvaskyla). Darren Moffit was the original editor of this set of documents and also made very substantial contributions. Many people contributed to the development of this document over the years. People who should be acknowledged include Mats Andersson, Ben Harris, Brent McClure, Niels Moller, Damien Miller, Derek Fawcus, Frank Cusack, Heikki Nousiainen, Jakob Schlyter, Jeff Van Dyke, Jeffrey Altman, Jeffrey Hutzelman, Jon Bright, Joseph Galbraith, Ken Hornstein, Markus Friedl, Martin Forssen, Nicolas Williams, Niels Provos, Perry Metzger, Peter Gutmann, Simon Josefsson, Simon Tatham, Wei Dai, Denis Bider, der Mouse, and Tadayoshi Kohno. Listing their names here does not mean that they endorse this document, but that they have contributed to it. 2. Introduction The SSH authentication protocol is a general-purpose user authentication protocol. It is intended to be run over the SSH transport layer protocol [SSH-TRANS]. This protocol assumes that the underlying protocols provide integrity and confidentiality protection. This document should be read only after reading the SSH architecture document [SSH-ARCH]. This document freely uses terminology and notation from the architecture document without reference or further explanation. The 'service name' for this protocol is "ssh-userauth". When this protocol starts, it receives the session identifier from the lower-level protocol (this is the exchange hash H from the first key exchange). The session identifier uniquely identifies this session and is suitable for signing in order to prove ownership of a private key. This protocol also needs to know whether the lower-level protocol provides confidentiality protection. 3. Conventions Used in This Document All documents related to the SSH protocols shall use the keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" to describe requirements. These keywords are to be interpreted as described in [RFC2119]. Ylonen & Lonvick Expires September 15, 2005 [Page 3] Internet-Draft SSH Authentication Protocol March 2005 The keywords "PRIVATE USE", "HIERARCHICAL ALLOCATION", "FIRST COME FIRST SERVED", "EXPERT REVIEW", "SPECIFICATION REQUIRED", "IESG APPROVAL", "IETF CONSENSUS", and "STANDARDS ACTION" that appear in this document when used to describe namespace allocation are to be interpreted as described in [RFC2434]. Protocol fields and possible values to fill them are defined in this set of documents. Protocol fields will be defined in the message definitions. As an example, SSH_MSG_CHANNEL_DATA is defined as follows. byte SSH_MSG_CHANNEL_DATA uint32 recipient channel string data Throughout these documents, when the fields are referenced, they will appear within single quotes. When values to fill those fields are referenced, they will appear within double quotes. Using the above example, possible values for 'data' are "foo" and "bar". 4. The Authentication Protocol Framework The server drives the authentication by telling the client which authentication methods can be used to continue the exchange at any given time. The client has the freedom to try the methods listed by the server in any order. This gives the server complete control over the authentication process if desired, but also gives enough flexibility for the client to use the methods it supports or that are most convenient for the user, when multiple methods are offered by the server. Authentication methods are identified by their name, as defined in [SSH-ARCH]. The "none" method is reserved, and MUST NOT be listed as supported. However, it MAY be sent by the client. The server MUST always reject this request, unless the client is to be allowed in without any authentication, in which case the server MUST accept this request. The main purpose of sending this request is to get the list of supported methods from the server. The server SHOULD have a timeout for authentication, and disconnect if the authentication has not been accepted within the timeout period. The RECOMMENDED timeout period is 10 minutes. Additionally, the implementation SHOULD limit the number of failed authentication attempts a client may perform in a single session (the RECOMMENDED limit is 20 attempts). If the threshold is exceeded, the server SHOULD disconnect. Additional thoughts about authentication timeouts and retries may be Ylonen & Lonvick Expires September 15, 2005 [Page 4] Internet-Draft SSH Authentication Protocol March 2005 found in [ssh-1.2.30]. 5. Authentication Requests All authentication requests MUST use the following message format. Only the first few fields are defined; the remaining fields depend on the authentication method. byte SSH_MSG_USERAUTH_REQUEST string user name in ISO-10646 UTF-8 encoding string service name in US-ASCII string method name in US-ASCII The rest of the packet is method-specific. The 'user name' and 'service name' are repeated in every new authentication attempt, and MAY change. The server implementation MUST carefully check them in every message, and MUST flush any accumulated authentication states if they change. If it is unable to flush some authentication state, it MUST disconnect if the 'user name' or 'service name' changes. The 'service name' specifies the service to start after authentication. There may be several different authenticated services provided. If the requested service is not available, the server MAY disconnect immediately or at any later time. Sending a proper disconnect message is RECOMMENDED. In any case, if the service does not exist, authentication MUST NOT be accepted. If the requested 'user name' does not exist, the server MAY disconnect, or MAY send a bogus list of acceptable authentication 'method name' values, but never accept any. This makes it possible for the server to avoid disclosing information on which accounts exist. In any case, if the 'user name' does not exist, the authentication request MUST NOT be accepted. While there is usually little point for clients to send requests that the server does not list as acceptable, sending such requests is not an error, and the server SHOULD simply reject requests that it does not recognize. An authentication request MAY result in a further exchange of messages. All such messages depend on the authentication 'method name' used, and the client MAY at any time continue with a new SSH_MSG_USERAUTH_REQUEST message, in which case the server MUST abandon the previous authentication attempt and continue with the new one. The following 'method name' values are defined. Ylonen & Lonvick Expires September 15, 2005 [Page 5] Internet-Draft SSH Authentication Protocol March 2005 public key REQUIRED password OPTIONAL hostbased OPTIONAL none NOT RECOMMENDED Additional 'method name' values may be defined as specified in [SSH-ARCH] and [SSH-NUMBERS]. 5.1 Responses to Authentication Requests If the server rejects the authentication request, it MUST respond with the following: byte SSH_MSG_USERAUTH_FAILURE name-list authentications that can continue boolean partial success The 'authentications that can continue' is a comma-separated name-list of authentication 'method name' values that may productively continue the authentication dialog. It is RECOMMENDED that servers only include those 'method name' values in the name-list that are actually useful. However, it is not illegal to include 'method name' values that cannot be used to authenticate the user. Already successfully completed authentications SHOULD NOT be included in the name-list, unless they really should be performed again for some reason. The value of 'partial success' MUST be TRUE if the authentication request to which this is a response was successful. It MUST be FALSE if the request was not successfully processed. When the server accepts authentication, it MUST respond with the following: byte SSH_MSG_USERAUTH_SUCCESS Note that this is not sent after each step in a multi-method authentication sequence, but only when the authentication is complete. The client MAY send several authentication requests without waiting for responses from previous requests. The server MUST process each request completely and acknowledge any failed requests with a SSH_MSG_USERAUTH_FAILURE message before processing the next request. Ylonen & Lonvick Expires September 15, 2005 [Page 6] Internet-Draft SSH Authentication Protocol March 2005 A request that results in further exchange of messages will be aborted by a second request. It is not possible to send a second request without waiting for a response from the server, if the first request will result in further exchange of messages. No SSH_MSG_USERAUTH_FAILURE message will be sent for the aborted method. SSH_MSG_USERAUTH_SUCCESS MUST be sent only once. When SSH_MSG_USERAUTH_SUCCESS has been sent, any further authentication requests received after that SHOULD be silently ignored. Any non-authentication messages sent by the client after the request that resulted in SSH_MSG_USERAUTH_SUCCESS being sent MUST be passed to the service being run on top of this protocol. Such messages can be identified by their message numbers (see Section 6). 5.2 The "none" Authentication Request A client may request a list of authentication 'method name' values that may continue by using the "none" authentication 'method name'. If no authentication at all is needed for the user, the server MUST return SSH_MSG_USERAUTH_SUCCESS. Otherwise, the server MUST return SSH_MSG_USERAUTH_FAILURE and MAY return with it a list of authentication 'method name' values that can continue. This 'method name' MUST NOT be listed as supported by the server. 5.3 Completion of User Authentication Authentication is complete when the server has responded with SSH_MSG_USERAUTH_SUCCESS. All authentication related messages received after sending this message SHOULD be silently ignored. After sending SSH_MSG_USERAUTH_SUCCESS, the server starts the requested service. 5.4 Banner Message In some jurisdictions, sending a warning message before authentication may be relevant for getting legal protection. Many UNIX machines, for example, normally display text from '/etc/issue', or use "tcp wrappers" or similar software to display a banner before issuing a login prompt. The SSH server may send a SSH_MSG_USERAUTH_BANNER message at any time after this authentication protocol starts and before authentication is successful. This message contains text to be displayed to the client user before authentication is attempted. The format is as Ylonen & Lonvick Expires September 15, 2005 [Page 7] Internet-Draft SSH Authentication Protocol March 2005 follows: byte SSH_MSG_USERAUTH_BANNER string message in ISO-10646 UTF-8 encoding string language tag as defined in [RFC3066] The client SHOULD by default display the 'message' on the screen. However, since the 'message' is likely to be sent for every login attempt, and since some client software will need to open a separate window for this warning, the client software may allow the user to explicitly disable the display of banners from the server. The 'message' may consist of multiple lines. If the 'message' string is displayed, control character filtering discussed in [SSH-ARCH] SHOULD be used to avoid attacks by sending terminal control characters. 6. Authentication Protocol Message Numbers All message numbers used by this authentication protocol are in the range from 50 to 79, which is part of the range reserved for protocols running on top of the SSH transport layer protocol. Message numbers of 80 and higher are reserved for protocols running after this authentication protocol, so receiving one of them before authentication is complete is an error, to which the server MUST respond by disconnecting, preferably with a proper disconnect message sent to ease troubleshooting. After successful authentication, such messages are passed to the higher-level service. These are the general authentication message codes: SSH_MSG_USERAUTH_REQUEST 50 SSH_MSG_USERAUTH_FAILURE 51 SSH_MSG_USERAUTH_SUCCESS 52 SSH_MSG_USERAUTH_BANNER 53 In addition to the above, there is a range of message numbers (60..79) reserved for method-specific messages. These messages are only sent by the server (client sends only SSH_MSG_USERAUTH_REQUEST messages). Different authentication methods reuse the same message numbers. 7. Public Key Authentication Method: publickey The only REQUIRED authentication 'method name' is public key authentication. All implementations MUST support this method; Ylonen & Lonvick Expires September 15, 2005 [Page 8] Internet-Draft SSH Authentication Protocol March 2005 however, not all users need to have public keys, and most local policies are not likely to require public key authentication for all users in the near future. With this method, the possession of a private key serves as authentication. This method works by sending a 'signature' created with a private key of the user. The server MUST check that the key is a valid authenticator for the user, and MUST check that the 'signature' is valid. If both hold, the authentication request MUST be accepted; otherwise it MUST be rejected. (Note that the server MAY require additional authentications after successful authentication.) Private keys are often stored in an encrypted form at the client host, and the user must supply a passphrase before the signature can be generated. Even if they are not, the signing operation involves some expensive computation. To avoid unnecessary processing and user interaction, the following message is provided for querying whether authentication using the key would be acceptable. byte SSH_MSG_USERAUTH_REQUEST string user name in ISO-10646 UTF-8 encoding string service name in US-ASCII string "publickey" boolean FALSE string public key algorithm name string public key blob Public key algorithms are defined in the transport layer specification [SSH-TRANS]. The 'public key blob' may contain certificates. Any public key algorithm may be offered for use in authentication. In particular, the list is not constrained by what was negotiated during key exchange. If the server does not support some algorithm, it MUST simply reject the request. The server MUST respond to this message with either SSH_MSG_USERAUTH_FAILURE or with the following: byte SSH_MSG_USERAUTH_PK_OK string public key algorithm name from the request string public key blob from the request To perform actual authentication, the client MAY then send a signature generated using the private key. The client MAY send the signature directly without first verifying whether the key is acceptable. The signature is sent using the following packet: Ylonen & Lonvick Expires September 15, 2005 [Page 9] Internet-Draft SSH Authentication Protocol March 2005 byte SSH_MSG_USERAUTH_REQUEST string user name string service string "publickey" boolean TRUE string public key algorithm name string public key to be used for authentication string signature The value of 'signature' is a signature by the corresponding private key over the following data, in the following order: string session identifier byte SSH_MSG_USERAUTH_REQUEST string user name string service string "publickey" boolean TRUE string public key algorithm name string public key to be used for authentication When the server receives this message, it MUST check whether the supplied key is acceptable for authentication, and if so, it MUST check whether the signature is correct. If both checks succeed, this method is successful. Note that the server may require additional authentications. The server MUST respond with SSH_MSG_USERAUTH_SUCCESS (if no more authentications are needed), or SSH_MSG_USERAUTH_FAILURE (if the request failed, or more authentications are needed). The following method-specific message numbers are used by the publickey authentication method. SSH_MSG_USERAUTH_PK_OK 60 8. Password Authentication Method: password Password authentication uses the following packets. Note that a server MAY request the user to change the password. All implementations SHOULD support password authentication. byte SSH_MSG_USERAUTH_REQUEST string user name string service string "password" boolean FALSE Ylonen & Lonvick Expires September 15, 2005 [Page 10] Internet-Draft SSH Authentication Protocol March 2005 string plaintext password in ISO-10646 UTF-8 encoding Note that the 'plaintext password' value is encoded in ISO-10646 UTF-8. It is up to the server how it interprets the password and validates it against the password database. However, if the client reads the password in some other encoding (e.g., ISO 8859-1 - ISO Latin1), it MUST convert the password to ISO-10646 UTF-8 before transmitting, and the server MUST convert the password to the encoding used on that system for passwords. From an internationalization standpoint, it is desired that if a user enters their password the authentication process will work regardless of what OS and client software they are using. Doing so requires normalization. Systems supporting non-ASCII passwords SHOULD always normalize passwords and usernames whenever they are added to the database, or compared (with or without hashing) to existing entries in the database. SSH implementations that both store the passwords and compare them SHOULD use [I-D.ietf-sasl-saslprep] for normalization. Note that even though the cleartext password is transmitted in the packet, the entire packet is encrypted by the transport layer. Both the server and the client should check whether the underlying transport layer provides confidentiality (i.e., if encryption is being used). If no confidentiality is provided ("none" cipher), password authentication SHOULD be disabled. If there is no confidentiality or no MAC, password change SHOULD be disabled. Normally, the server responds to this message with success or failure. However, if the password has expired the server SHOULD indicate this by responding with SSH_MSG_USERAUTH_PASSWD_CHANGEREQ. In any case the server MUST NOT allow an expired password to be used for authentication. byte SSH_MSG_USERAUTH_PASSWD_CHANGEREQ string prompt in ISO-10646 UTF-8 encoding string language tag as defined in [RFC3066] In this case, the client MAY continue with a different authentication method, or request a new password from the user and retry password authentication using the following message. The client MAY also send this message instead of the normal password authentication request without the server asking for it. byte SSH_MSG_USERAUTH_REQUEST string user name string service string "password" boolean TRUE Ylonen & Lonvick Expires September 15, 2005 [Page 11] Internet-Draft SSH Authentication Protocol March 2005 string plaintext old password in ISO-10646 UTF-8 encoding string plaintext new password in ISO-10646 UTF-8 encoding The server must reply to each request message with SSH_MSG_USERAUTH_SUCCESS, SSH_MSG_USERAUTH_FAILURE, or another SSH_MSG_USERAUTH_PASSWD_CHANGEREQ. The meaning of these is as follows: SSH_MSG_USERAUTH_SUCCESS - The password has been changed, and authentication has been successfully completed. SSH_MSG_USERAUTH_FAILURE with partial success - The password has been changed, but more authentications are needed. SSH_MSG_USERAUTH_FAILURE without partial success - The password has not been changed. Either password changing was not supported, or the old password was bad. Note that if the server has already sent SSH_MSG_USERAUTH_PASSWD_CHANGEREQ, we know that it supports changing the password. SSH_MSG_USERAUTH_CHANGEREQ - The password was not changed because the new password was not acceptable (e.g., too easy to guess). The following method-specific message numbers are used by the password authentication method. SSH_MSG_USERAUTH_PASSWD_CHANGEREQ 60 9. Host-Based Authentication: hostbased Some sites wish to allow authentication based on the host where the user is coming from, and the user name on the remote host. While this form of authentication is not suitable for high-security sites, it can be very convenient in many environments. This form of authentication is OPTIONAL. When used, special care SHOULD be taken to prevent a regular user from obtaining the private host key. The client requests this form of authentication by sending the following message. It is similar to the UNIX "rhosts" and "hosts.equiv" styles of authentication, except that the identity of the client host is checked more rigorously. This method works by having the client send a signature created with the private key of the client host, which the server checks with that host's public key. Once the client host's identity is established, authorization (but no further authentication) is performed based on the user names on the server and the client, and the client host Ylonen & Lonvick Expires September 15, 2005 [Page 12] Internet-Draft SSH Authentication Protocol March 2005 name. byte SSH_MSG_USERAUTH_REQUEST string user name string service string "hostbased" string public key algorithm for host key string public host key and certificates for client host string client host name expressed as the FQDN in US-ASCII string user name on the client host in ISO-10646 UTF-8 encoding string signature Public key algorithm names for use in 'public key algorithm for host key' are defined in the transport layer specification. The 'public host key and certificates for client host' may include certificates. The value of 'signature' is a signature with the private host key of the following data, in this order: string session identifier byte SSH_MSG_USERAUTH_REQUEST string user name string service string "hostbased" string public key algorithm for host key string public host key and certificates for client host string client host name expressed as the FQDN in US-ASCII string user name on the client host in ISO-10646 UTF-8 encoding The server MUST verify that the host key actually belongs to the client host named in the message, that the given user on that host is allowed to log in, and that the 'signature' value is a valid signature on the appropriate value by the given host key. The server MAY ignore the client 'user name', if it wants to authenticate only the client host. It is RECOMMENDED that whenever possible, the server perform additional checks to verify that the network address obtained from the (untrusted) network matches the given client host name. This makes exploiting compromised host keys more difficult. Note that this may require special handling for connections coming through a firewall. 10. IANA Considerations This document is part of a set. The IANA considerations for the SSH protocol as defined in [SSH-ARCH], [SSH-TRANS], [SSH-CONNECT], and this document, are detailed in [SSH-NUMBERS]. Ylonen & Lonvick Expires September 15, 2005 [Page 13] Internet-Draft SSH Authentication Protocol March 2005 11. Security Considerations The purpose of this protocol is to perform client user authentication. It assumed that this runs over a secure transport layer protocol, which has already authenticated the server machine, established an encrypted communications channel, and computed a unique session identifier for this session. The transport layer provides forward secrecy for password authentication and other methods that rely on secret data. Full security considerations for this protocol are provided in [SSH-ARCH]. 12. References 12.1 Normative [SSH-ARCH] Lonvick, C., "SSH Protocol Architecture", I-D draft-ietf-secsh-architecture-22.txt, March 2005. [SSH-CONNECT] Lonvick, C., "SSH Connection Protocol", I-D draft-ietf-secsh-connect-25.txt, March 2005. [SSH-TRANS] Lonvick, C., "SSH Transport Layer Protocol", I-D draft-ietf-secsh-transport-24.txt, March 2005. [SSH-NUMBERS] Lonvick, C., "SSH Protocol Assigned Numbers", I-D draft-ietf-secsh-assignednumbers-12.txt, March 2005. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. [RFC3066] Alvestrand, H., "Tags for the Identification of Languages", BCP 47, RFC 3066, January 2001. [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003. [I-D.ietf-sasl-saslprep] Zeilenga, K., "SASLprep: Stringprep profile for user names Ylonen & Lonvick Expires September 15, 2005 [Page 14] Internet-Draft SSH Authentication Protocol March 2005 and passwords", Internet-Draft draft-ietf-sasl-saslprep-10, July 2004. 12.2 Informative [ssh-1.2.30] Ylonen, T., "ssh-1.2.30/RFC", File within compressed tarball ftp://ftp.funet.fi/pub/unix/security/login/ssh/ ssh-1.2.30.tar.gz, November 1995. Authors' Addresses Tatu Ylonen SSH Communications Security Corp Fredrikinkatu 42 HELSINKI FIN-00100 Finland Email: firstname.lastname@example.org Chris Lonvick (editor) Cisco Systems, Inc. 12515 Research Blvd. Austin 78759 USA Email: email@example.com Appendix A. Trademark Notice "ssh" is a registered trademark in the United States and/or other countries. Note to the RFC Editor: This should be a separate section like the subsequent ones, and not an appendix. This paragraph to be removed before publication. Ylonen & Lonvick Expires September 15, 2005 [Page 15] Internet-Draft SSH Authentication Protocol March 2005 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights 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; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat 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 implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. 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Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Ylonen & Lonvick Expires September 15, 2005 [Page 16] Internet-Draft SSH Authentication Protocol March 2005 Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Ylonen & Lonvick Expires September 15, 2005 [Page 17]