Internet Draft K. Murchison
Category: Informational M. Crispin
Expires: March 2, 2004 28 August 2003
The LOGIN SASL Mechanism
<draft-murchison-sasl-login-00.txt>
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society 2003. All Rights Reserved.
Abstract
This document documents the obsolete clear-text user/password Simple
Authentication and Security Layer (SASL) mechanism called the LOGIN
mechanism. The LOGIN mechanism was intended to be used, in
combination with data confidentiality services provided by a lower
layer, in protocols which lack a simple password authentication
command.
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Conventions Used in the Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [KEYWORDS].
1. Background and Intended Usage
This document documents the obsolete LOGIN Simple Authentication and
Security Layer ([SASL]) mechanism which was in use in protocols with
no clear-text login command (e.g., [SMTP-AUTH]).
Note: The LOGIN SASL mechanism is obsoleted in favor of the PLAIN
SASL mechanism ([PLAIN]). The LOGIN mechanism is documented here
only for the purpose of backwards compatibility with legacy software.
Clients SHOULD implement the PLAIN SASL mechanism and use it whenever
offered by a server. The LOGIN SASL mechanism SHOULD NOT be used by
a client when other plaintext mechanisms are offered by a server.
The name associated with this mechanism is "LOGIN".
The LOGIN SASL mechanism does not provide a security layer. This
mechanism MUST NOT be used without adequate security protection as
the mechanism affords no integrity nor confidentiality protection
itself. The LOGIN SASL mechanism MUST NOT be advertised or used in
any configuration that prohibits the PLAIN mechanism or plaintext
LOGIN (or USER/PASS) command that sends passwords in the clear.
2. LOGIN SASL Mechanism
The authorization identity is the same string as the "username" in
the traditional (non-SASL) LOGIN or USER commands; the authorization
authenticator is the same string as the traditional "password". The
authentication identity is the same as the authorization identity in
this mechanism.
Only US-ASCII printable characters SHOULD be used in the username and
password to permit maximal interoperability. If non-US-ASCII
characters are used in a username, they MUST use UTF-8. Passwords
MAY contain arbitrary binary data excluding NUL, CR and LF
characters. However, if a password is supplied to the client as a
sequence of characters (e.g., a password dialog box), those
characters MUST be encoded as UTF-8.
The username MUST be less than 64 characters in length.
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2.1. Client side of authentication protocol exchange
The client expects the server to issue a challenge. The client then
responds with the authorization identity. The client then expects
the server to issue a second challenge. The client then responds
with the authorization authenticator. The contents of both
challenges SHOULD be ignored.
2.2. Server side of authentication protocol exchange
The server issues the string "User Name" in challenge, and receives a
client response. This response is recorded as the authorization
identity. The server then issues the string "Password" in challenge,
and receives a client response. This response is recorded as the
authorization authenticator. The server must verify that the
authorization authenticator permits login as the authorization
identity.
Note: There is at least one widely deployed client which requires
that the challenge strings transmitted by the server be "Username:"
and "Password:" respectively. For this reason, server
implementations MAY send these challenge strings instead of those
listed above.
2.3. Example
This example shows the use of the LOGIN mechanism with the SMTP AUTH
command [SMTP-AUTH] under the protection of SMTP STARTTLS [SMTP-TLS].
The user name is "tim" and the password is "tanstaaftanstaaf". The
base64 encoding of the challenges and responses is part of the SMTP
AUTH command, not part of the LOGIN specification itself. "C:" and
"S:" indicate lines sent by the client and server respectively.
S: 220 smtp.example.com ESMTP server ready
C: EHLO test.example.com
S: 250-smtp.example.com
S: 250-STARTTLS
S: 250 AUTH CRAM-MD5
C: STARTTLS
S: 220 Ready to start TLS
<TLS negotiation, further commands are under TLS layer>
C: EHLO test.example.com
S: 250-smtp.example.com
S: 250 AUTH LOGIN CRAM-MD5
C: AUTH LOGIN
S: 334 VXNlciBOYW1lAA==
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C: dGlt
S: 334 UGFzc3dvcmQA
C: dGFuc3RhYWZ0YW5zdGFhZg==
S: 235 Authentication successful.
3.
Security Considerations
The LOGIN mechanism relies upon an underlying encryption layer or
other secure channel for security. When used without an encryption
layer or secure channel, it is vulnerable to a common network
eavesdropping attack. Therefore the LOGIN mechanism MUST NOT be
advertised or used in any configuration that prohibits the PLAIN
mechanism or a plaintext LOGIN (or USER/PASS) command that sends
passwords in the clear.
4.
IANA Considerations
The registration for the LOGIN SASL mechanism follows:
SASL mechanism name: LOGIN
Security Considerations: See section 3 of this memo
Published specification: this memo
Person & email address to contact for futher information:
See section 7 of this memo
Intended usage: OBSOLETE
Owner/Change controller: See section 7 of this memo
5.
References
5.1.
Normative References
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", Harvard University, RFC 2119, March 1997.
[SASL] Melnikov, A., Ed., "Simple Authentication and Security Layer
(SASL)", Isode, draft-ietf-sasl-rfc2222bis-xx.txt, Work In
Progress.
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5.2. Informative References
[PLAIN] Zeilenga, Kurt D., Ed., "The Plain SASL Mechanism",
OpenLDAP Foundation, draft-ietf-sasl-plain-xx.txt, Work In
Progress.
[SMTP-AUTH] Myers, J., "SMTP Service Extension for Authentication",
Netscape Communications, RFC 2554, March 1999.
[SMTP-TLS] Hoffman, P., "SMTP Service Extension for Secure SMTP
over Transport Layer Security", Internet Mail Consortium, RFC
3207, February 2002.
6. Acknowledgments
Thanks to Rob Siemborski for his input and feedback on this document.
7.
Author's Address
Kenneth Murchison
Oceana Matrix Ltd.
21 Princeton Place
Orchard Park, NY 14127
Phone: (716) 662-8973
EMail: ken@oceana.com
Mark R. Crispin
Networks and Distributed Computing
University of Washington
4545 15th Avenue NE
Seattle, WA 98105-4527
Phone: (206) 543-5762
EMail: MRC@CAC.Washington.EDU
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8.
Intellectual Property Considerations
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.
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9.
Full Copyright Statement
Copyright (C) The Internet Society 2003. All Rights Reserved.
This document and translations of it may be copied and furnished to
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or assist in its implmentation may be prepared, copied, published and
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The limited permissions granted above are perpetual and will not be
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