WDIFF

draft-siemborski-imap-sasl-initial-response-03.txt --> draft-siemborski-imap-sasl-initial-response-04.txt

Network Working Group Robert Siemborski
INTERNET-DRAFT Carnegie Mellon University Google, Inc.
Intended Category: Standards Track April, 2004 February, 2005

IMAP Extension for SASL Initial Client Response
<draft-siemborski-imap-sasl-initial-response-03.txt>
<draft-siemborski-imap-sasl-initial-response-04.txt>

Status of this Memo
This document is an Internet-Draft

By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been disclosed,
and is any of which I become aware will be disclosed, in full conformance accordance
with
all provisions of Section 10 of RFC2026.

Internet-Drafts RFC 3668.

Internet Drafts are working documents of the Internet Engineering
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A revised version of this draft document will be submitted to the
RFC editor as a Standards Track RFC for the Internet Community.
Discussion and suggestions for improvement are requested.
Distribution of this memo draft is unlimited.

Siemborski Expires August, 2005 [Page 1]

IMAP Extension for SASL Initial Client Response February, 2005

Abstract

To date, the Internet Message Access Protocol (IMAP) has used a
Simple Authentication and Security Layer (SASL) profile which always
required at least one complete round trip for an authentication, as
it did not support an initial client response argument. This
additional round trip at the beginning of the session is
undesirable, especially when round trip costs are high.

This document defines an extension to IMAP which allows clients and
servers to avoid this round trip by allowing an initial client
response argument to the IMAP AUTHENTICATE command.

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IMAP Extension for SASL Initial Client Response April, 2004 February, 2005

Table of Contents

1. How to Read This Document

The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD
NOT", "RECOMMENDED", and "MAY" in this document are to be
interpreted as defined in "Key words for use in RFCs to Indicate
Requirement Levels" [KEYWORDS]

In examples, "C:" and "S:" indicate lines sent by the client and
server respectively.

Formal syntax is defined using [ABNF] as modified by [IMAP4]. . . . . . . . . . . . . . . . . . . . . 4
2. Introduction

The [SASL] initial client response extension is present in any
[IMAP4] server implementation which returns "SASL-IR" as one of the
supported capabilities in its CAPABILITY response.

Servers which support this extension will accept an optional initial
client response with the AUTHENTICATE command for any [SASL]
mechanisms which support it. . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. IMAP Changes to the IMAP AUTHENTICATE Command

This extension adds an optional second argument to the AUTHENTICATE
command that is defined in Section 6.2.2 of [IMAP4]. If this second
argument is present, it represents the contents of the "initial
client response" defined in section 5.1 of [SASL].

As with any other client response, this initial client response MUST
be encoded as defined in Section 3 of [BASE64]. It also MUST be
transmitted outside of a quoted string or literal. To send a zero-
length initial response, the client MUST send a single pad character
("="). This indicates that the response is present, but is a zero-
length string.

When decoding the [BASE64] data in the initial client response,
decoding errors MUST be treated as [IMAP4] would handle them in any
normal SASL client response. In particular, the server should check
for any characters not explicitly allowed by the BASE64 alphabet, as
well as any sequence of BASE64 characters that contains the pad
character ('=') anywhere other than the end of the string (e.g.
"=AAA" and "AAA=BBB" are not allowed).

Note: support and use of the initial client response is optional for
both clients and servers. Servers which implement this extension
MUST support clients which omit the initial client response, and
clients which implement this extension MUST NOT send an initial

Siemborski Expires October, 2004 [Page 3]

IMAP Extension for SASL Initial Client Response April, 2004

client response to servers which do not advertise the SASL-IR
capability. In such a situation, clients MUST fall back to an
[IMAP4] compatible mode.

If either the client or the server do not support the SASL-IR
capability, a mechanism which uses an initial client response is
negotiated using the challenge/response exchange described in
[IMAP4], with an initial zero-length server challenge.

4. Examples

The following is an example authentication using the [PLAIN] SASL
mechanism (under a [TLS] protection layer) and an initial client
response:

... client connects to server and negotiates a TLS protection layer ...
C: C01 CAPABILITY
S: * CAPABILITY IMAP4 IMAP4rev1 SASL-IR AUTH=PLAIN
S: C01 OK Completed
C: A01 AUTHENTICATE PLAIN dGVzdAB0ZXN0AHRlc3Q=
S: A01 OK Success (tls protection)

Note that even when a server supports this extension, the following
negotiation (which does not use the initial response) is still valid
and MUST be supported by the server:

... client connects to server and negotiates a TLS protection layer ...
C: C01 CAPABILITY
S: * CAPABILITY IMAP4 IMAP4rev1 SASL-IR AUTH=PLAIN
S: C01 OK Completed
C: A01 AUTHENTICATE PLAIN
(note that there is a space following the "+" in the following line)
S: +
C: dGVzdAB0ZXN0AHRlc3Q=
S: A01 OK Success (tls protection)

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The following is an example authentication using the EXTERNAL [SASL]
mechanism (under a [TLS] protection layer) and an empty initial
client response:

... client connects to server and negotiates a TLS protection layer ...
C: C01 CAPABILITY
S: * CAPABILITY IMAP4 IMAP4rev1 SASL-IR AUTH=PLAIN AUTH=EXTERNAL
S: C01 OK Completed
C: A01 AUTHENTICATE EXTERNAL =
S: A01 OK Success (tls protection)

This is in contrast with the handling of such a situation when an
initial response is omitted:

5. Formal Syntax

The following syntax specification uses the Augmented Bakus-Naur
Form [ABNF] notation. Non-terminals referenced but not defined
below are as defined by [IMAP4].

capability =/ "SASL-IR"

authenticate = "AUTHENTICATE" SP auth-type [SP (base64 / "=")]
*(CRLF base64)
;;redefine AUTHENTICATE command defined in [IMAP4] . . . . . . . . . . . . 4
4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations

The extension defined in this document is subject to many of the
Security Considerations defined in [IMAP4] and [SASL].

Server implementations MUST treat the omission of an initial client
response from the AUTHENTICATE command as defined by [IMAP4] (as if
this extension did not exist).

Although [IMAP4] has no express line length limitations, some . . . . . . . . . . . . . . . . . . . . . 6
7. Intellectual Property Rights . . . . . . . . . . . . . . . . . . 7
8. Copyright . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
10. Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 8
12. Changes since -01 . . . . . . . . . . . . . . . . . . . . . . . 9
13. Changes since -00 . . . . . . . . . . . . . . . . . . . . . . . 9

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IMAP Extension for SASL Initial Client Response April, 2004

implementations choose to enforce them anyway. Such implementations
MUST be aware that the addition of the initial response parameter to
AUTHENTICATE may increase the maximum line length that IMAP parsers
may expect to support. Server implementations MUST be able February, 2005

1. How to
receive the largest possible initial client response that their
supported mechanisms might receive.

7. Intellectual Property Rights Read This Document

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 key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD
NOT", "RECOMMENDED", and "MAY" 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 are to rights in standards-track and
standards-related documentation can be found
interpreted as defined 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 "Key words for the use of such
proprietary rights in RFCs to Indicate
Requirement Levels" [KEYWORDS]

In examples, "C:" and "S:" indicate lines sent by implementors or users of this specification
can be obtained from the IETF Secretariat. client and
server respectively.

Formal syntax is defined using [ABNF] as modified by [IMAP4].

2. Introduction

The IETF invites [SASL] initial client response extension is present in any interested party to bring to
[IMAP4] server implementation which returns "SASL-IR" as one of the
supported capabilities in its attention any
copyrights, patents or patent applications, or other proprietary
rights CAPABILITY response.

Servers which may cover technology that may be required to practice support this standard. Please address extension will accept an optional initial
client response with the information AUTHENTICATE command for any [SASL]
mechanisms which support it.

3. IMAP Changes to the IETF Executive
Director.

8. Copyright

This document and translations of it may be copied and furnished extension adds an optional second argument to
others, and derivative works the AUTHENTICATE
command that comment on or otherwise explain is defined in Section 6.2.2 of [IMAP4]. If this second
argument is present, it
or assist represents the contents of the "initial
client response" defined in its implementation may section 5.1 of [SASL].

As with any other client response, this initial client response MUST
be prepared, copied, published
and distributed, in whole or encoded as defined in part, without restriction Section 3 of any
kind, provided [BASE64]. It also MUST be
transmitted outside of a quoted string or literal. To send a zero-
length initial response, the client MUST send a single pad character
("="). This indicates that the above copyright notice and this paragraph
are included on all such copies and derivative works. However, this
document itself may not response is present, but is a zero-
length string.

When decoding the [BASE64] data in the initial client response,
decoding errors MUST be modified treated as [IMAP4] would handle them in any way, such as by removing
the copyright notice or references to
normal SASL client response. In particular, the Internet Society or other
Internet organizations, except as needed server should check
for any characters not explicitly allowed by the purpose BASE64 alphabet, as
well as any sequence of
developing Internet standards in which case the procedures for
copyrights defined in BASE64 characters that contains the Internet Standards process must be
followed, or as required to translate it into languages pad
character ('=') anywhere other than
English.

This document the end of the string (e.g.
"=AAA" and "AAA=BBB" are not allowed).

Note: support and use of the information contained herein initial client response is provided on optional for
both clients and servers. Servers which implement this extension
MUST support clients which omit the initial client response, and
clients which implement this extension MUST NOT send an initial

Siemborski Expires October, 2004 August, 2005 [Page 6] 4]

IMAP Extension for SASL Initial Client Response April, 2004

"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.

9. References

The following documents contain normative definitions or
specifications that are necessary for correct understanding of this
protocol:

[ABNF] Crocker, D., "Augmented BNF for Syntax Specifications:
ABNF", RFC 2234, November, 1997.

[BASE64] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 3548, July 2003.

[IMAP4] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.

[KEYWORDS] Bradner, S., "Key words for use in RFCs February, 2005

client response to servers which do not advertise the SASL-IR
capability. In such a situation, clients MUST fall back to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[SASL] Melnikov, A., "Simple Authentication and Security Layer
(SASL)", draft-ietf-sasl-rfc2222bis-*.txt, an
[IMAP4] compatible mode.

If either the client or the server do not support the SASL-IR
capability, a work mechanism which uses an initial client response is
negotiated using the challenge/response exchange described in
progress.
[IMAP4], with an initial zero-length server challenge.

4. Examples

The following references are for informational purposes only: is an example authentication using the [PLAIN] Newman, C. "Using SASL
mechanism (under a [TLS] protection layer) and an initial client
response:

... client connects to server and negotiates a TLS with IMAP, POP3, protection layer ...
C: C01 CAPABILITY
S: * CAPABILITY IMAP4 IMAP4rev1 SASL-IR AUTH=PLAIN
S: C01 OK Completed
C: A01 AUTHENTICATE PLAIN dGVzdAB0ZXN0AHRlc3Q=
S: A01 OK Success (tls protection)

Note that even when a server supports this extension, the following
negotiation (which does not use the initial response) is still valid
and ACAP", RFC 2595,
June 1999.

[TLS] Dierks, T. MUST be supported by the server:

... client connects to server and C. Allen, "The negotiates a TLS Protocol Version 1.0", RFC
2246, January 1999.

10. Author's Address:

Robert Siemborski
Carnegie Mellon, Andrew Systems Group
Cyert Hall 207
5000 Forbes Avenue
Pittsburgh, PA 15213
+1 412 268 7456
rjs3+@andrew.cmu.edu protection layer ...
C: C01 CAPABILITY
S: * CAPABILITY IMAP4 IMAP4rev1 SASL-IR AUTH=PLAIN
S: C01 OK Completed
C: A01 AUTHENTICATE PLAIN
(note that there is a space following the "+" in the following line)
S: +
C: dGVzdAB0ZXN0AHRlc3Q=
S: A01 OK Success (tls protection)

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IMAP Extension for SASL Initial Client Response April, 2004

11. Acknowledgments: February, 2005

The author would like following is an example authentication using the EXTERNAL [SASL]
mechanism (under a [TLS] protection layer) and an empty initial
client response:

... client connects to acknowledge the contributions of Ken
Murchison server and Mark Crispin, along negotiates a TLS protection layer ...
C: C01 CAPABILITY
S: * CAPABILITY IMAP4 IMAP4rev1 SASL-IR AUTH=PLAIN AUTH=EXTERNAL
S: C01 OK Completed
C: A01 AUTHENTICATE EXTERNAL =
S: A01 OK Success (tls protection)

This is in contrast with the rest handling of the IMAPEXT
Working Group for their assistance in reviewing this document.

Alexey Melnikov such a situation when an
initial response is omitted:

... client connects to server and Cyrus Daboo also had some early discussions
about this extension

12. Changes since -01

(RFC Editor: Remove this section before publication) - Remove
implicit SHOULD behavior for clients.

- Indicate that the Section 3 BASE64 encoding should be used.

13. Changes since -00

(RFC Editor: Remove this section before publication) - Add missing negotiates a TLS protection layer ...
C: C01 CAPABILITY
S: * CAPABILITY IMAP4 IMAP4rev1 SASL-IR AUTH=PLAIN AUTH=EXTERNAL
S: C01 OK responses Completed
C: A01 AUTHENTICATE EXTERNAL
(note that there is a space following the "+" in examples

- Change the following line)
S: +
C:
S: A01 OK Success (tls protection)

5. Formal Syntax

The following syntax specification uses the Augmented Bakus-Naur
Form [ABNF] notation. Non-terminals referenced but not defined
below are as defined by [IMAP4].

capability string to =/ "SASL-IR"

- Fix a nit regarding an "="

authenticate = "AUTHENTICATE" SP auth-type [SP (base64 / "=")]
*(CRLF base64)
;;redefine AUTHENTICATE command defined in the initial response ABNF

- Clean up wording of BASE64 decoding requirements [IMAP4]

6. Security Considerations

The extension defined in this document is subject to be more many of the
Security Considerations defined in
line with [IMAP4]

- Add examples and [SASL].

Server implementations MUST treat the omission of an empty initial client response, and move
examples into their own section

- Update SASL reference to rfc2222bis
response from the AUTHENTICATE command as defined by [IMAP4] (as if
this extension did not exist).

Although [IMAP4] has no express line length limitations, some

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IMAP Extension for SASL Initial Client Response April, 2004

Table of Contents

1. How to Read This Document . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Changes February, 2005

implementations choose to enforce them anyway. Such implementations
MUST be aware that the IMAP addition of the initial response parameter to
AUTHENTICATE Command . . . . . . . . . . . . 3
4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . . 5 may increase the maximum line length that IMAP parsers
may expect to support. Server implementations MUST be able to
receive the largest possible initial client response that their
supported mechanisms might receive.

7. Intellectual Property Rights . . . . . . . . . . . . . . . . . . 6
8. Copyright . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

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.

8. Copyright

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.

This document and the information contained herein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
INTERNET ENGINEERING TASK FORCE DISCLAIM 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.

Siemborski Expires August, 2005 [Page 7]

IMAP Extension for SASL Initial Client Response February, 2005

9. References . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

The following documents contain normative definitions or
specifications that are necessary for correct understanding of this
protocol:

[ABNF] Crocker, D., "Augmented BNF for Syntax Specifications:
ABNF", RFC 2234, November, 1997.

[BASE64] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 3548, July 2003.

[IMAP4] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.

[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[SASL] Melnikov, A., "Simple Authentication and Security Layer
(SASL)", draft-ietf-sasl-rfc2222bis-*.txt, a work in
progress.

The following references are for informational purposes only:

[PLAIN] Newman, C. "Using TLS with IMAP, POP3, and ACAP", RFC 2595,
June 1999.

[TLS] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC
2246, January 1999.

10. Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7 Address:

Robert Siemborski
Google, Inc.
1600 Ampitheatre Parkway
Mountain View, CA 94043
+1 650 623 6925
robsiemb@google.com

11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 8 Acknowledgments:

The author would like to acknowledge the contributions of Ken
Murchison and Mark Crispin, along with the rest of the IMAPEXT
Working Group for their assistance in reviewing this document.

Alexey Melnikov and Cyrus Daboo also had some early discussions
about this extension

Siemborski Expires August, 2005 [Page 8]

IMAP Extension for SASL Initial Client Response February, 2005

12. Changes since -01 . . . . . . . . . . . . . . . . . . . . . . . 8

(RFC Editor: Remove this section before publication) - Remove
implicit SHOULD behavior for clients.

- Indicate that the Section 3 BASE64 encoding should be used.

13. Changes since -00 . . . . . . . . . . . . . . . . . . . . . . . 8

(RFC Editor: Remove this section before publication) - Add missing
CAPABILITY OK responses in examples

- Change capability string to "SASL-IR"

- Fix a nit regarding an "=" in the initial response ABNF

- Clean up wording of BASE64 decoding requirements to be more in
line with [IMAP4]

- Add examples of an empty initial client response, and move
examples into their own section

- Update SASL reference to rfc2222bis

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