WDIFF

draft-siemborski-rfc1734bis-03.txt --> draft-siemborski-rfc1734bis-04.txt

Network Working Group Robert Siemborski
INTERNET-DRAFT Carnegie Mellon University Google, Inc.
Intended Category: Proposed Standard April, 2004 February, 2005
Obsoletes: RFC 1734 Updates: RFC 2449

POP3 SASL Authentication Mechanism

<draft-siemborski-rfc1734bis-03.txt>

<draft-siemborski-rfc1734bis-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.

When published as an RFC this document will obsolete RFC 1734 and
update RFC 2449.

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POP3 SASL Authentication Mechanism February, 2005

Abstract

This document defines a profile of the Simple Authentication and
Security Layer (SASL) for the Post Office Protocol (POP3). This
extension allows a POP3 client to indicate an authentication
mechanism to the server, perform an authentication protocol
exchange, and optionally negotiate a security layer for subsequent
protocol interactions during this session.

In order

This document seeks to consolidate all of the authentication related information for related to POP3
AUTH into a single document, document. To this end, this document obsoletes
RFC 1734 and RFC 3206, 1734, replacing them it as a Proposed Standard. It
also Standard and updates
information contained in Section 6.3 and Section 8 of RFC 2449.

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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. . . . . . . . . . . . . . . . . . . . . 4
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. The [POP3] AUTH command [POP3-AUTH] in has suffered several problems
in its specification. The first is that it was very similar to a
[SASL] framework, but pre-dated the initial SASL specification. It
was therefore missing some key components, such as a way to list the
available authentication mechanisms.

Later, [POP3-EXT] attempted to remedy this situation by adding the
CAPA command and allowing an initial client response to the AUTH
command, however problems in the clarity of the specification of how
the initial client response was to be handled remained.

Additionally, there is yet another document, [POP3-CODES], that
provides additional response codes that are useful during
authentication. Together, this means creating a full POP3 AUTH
implementaiton requires an understanding of material in atleast six
different documents.

This document attempts to combine all of the POP3 SASL
authentication related details into a single document, in addition
to clarifying and updating the older specifications where
appropriate.

3. The SASL Capability

This section supercedes the definition of the SASL Capability in
section 6.3 of [POP3-EXT].

CAPA tag:
SASL

Arguments:
Supported SASL Mechanisms

Standard Commands Affected
None

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Announced states / possible differences:
both / no

Commands valid in states:
AUTHORIZATION

Specification Reference:
This Document, [SASL]

Discussion
The SASL capability permits the use of the AUTH command (as
defined in section . . . . . . . . . . . . . . . . . . . . . . . 4 of this document) to begin a [SASL]
negotiation.
4. The arguments to the SASL capability is a space-
separated list of SASL mechanisms which are supported.

If a server either does not support the CAPA command or does not
advertise the SASL capability, clients SHOULD NOT attempt the AUTH command. If a client does attempt the AUTH command in such
a situation, it MUST NOT supply the client initial response
parameter (for backwards compatibility with [POP3-AUTH]).

Note that the list of available mechanisms MAY change after a
successful STLS command [POP3-TLS]. Additionally,
implementations MAY choose to omit the SASL capability after a
successful AUTH command has been completed.

Example

S: +OK pop.example.com BlurdyBlurp POP3 server ready
C: CAPA
S: +OK List of capabilities follows
S: SASL KERBEROS_V4 GSSAPI ANONYMOUS
S: STLS
S: IMPLEMENTATION BlurdyBlurp POP3 server
S: .

4. The AUTH Command

AUTH mechanism [initial-response]

Arguments:
mechanism: A string identifying a [SASL] authentication
mechanism.

initial-response: An optional initial client response. If
present, this response MUST be encoded as specified in Section
3 of [BASE64].

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Restrictions:
After an AUTH command has been successfully completed, no more
AUTH commands may be issued in the same session. After a
successful AUTH command completes, a server MUST reject any
further AUTH commands with a -ERR reply.

The AUTH command may only be given during the AUTHORIZATION
state.

Discussion:
The AUTH command initiates a [SASL] authentication exchange
between the client and the server. The client identifies the
SASL mechanism to use with the first parameter of the AUTH
command. If the server supports the requested authentication
mechanism, it performs the SASL exchange to authenticate the
user. Optionally, it also negotiates a security layer for
subsequent protocol interactions during this session. If the
requested authentication mechanism is not supported, the
server rejects the AUTH command with a -ERR reply.

The authentication protocol exchange consists of a series of
server challenges and client responses that are specific to
the chosen [SASL] mechanism.

A server challenge is sent as a line consisting of a "+"
character followed by a single space and a string encoded as
specified in Section 3 of [BASE64]. This challenge MUST NOT
contain any text other than the BASE64 encoded challenge.

A client response consists of a line containing a string
encoded as defined in Section 3 of [BASE64]. If the client
wishes to cancel the authentication exchange, it issues a line
with a single "*". If the server receives such a response, it
MUST reject the AUTH command by sending a -ERR reply.

The optional initial response argument to the AUTH command is
used to save a round trip when using authentication mechanisms
that support an initial client response. If the initial
response argument is omitted and the chosen mechanism requires
an initial client response, the server MUST proceed as defined
in section 5.1 of [SASL]. In POP3, a server challenge with no
data is defined as line with only a "+" followed by a single
space. It MUST NOT contain any other data.

For the purposes of the initial client response, the line
length limitation defined in [POP3-EXT] still applies. If a
client initial send would cause the AUTH command to exceed
this length, the client MUST NOT use the initial response

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parameter (and instead proceed as defined in section 5.1 of
[SASL]).

If the client needs to send a zero-length initial response,
the client MUST transmit the response as a single equals sign
("="). This indicates that the response is present, but
contains no data.

If the client uses an initial-response argument to the AUTH
command with a SASL mechanism that does not support an initial
client send, the server MUST reject the AUTH command with a
-ERR reply.

If the server cannot [BASE64] decode any client response, it
MUST reject the AUTH command with a -ERR reply. If the client
cannot BASE64 decode any of the server's challenges, it MUST
cancel the authentication using the "*" response. In
particular, servers and clients MUST reject (and not ignore)
any character not explicitly allowed by the BASE64 alphabet,
and MUST reject 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 that these [BASE64] strings (excepting the initial client
response) may be of arbitrarily length. Clients and servers
MUST be able to handle the maximum encoded size of challenges
and responses generated by their supported authentication
mechanisms. This requirement is independent of any line
length limitations the client or server may have in other
parts of its protocol implementation.

If the server is unable to authenticate the client, it MUST
reject the AUTH command with a -ERR reply. Should the client
successfully complete the exchange, the server issues a +OK
reply. Additionally, upon success, the POP3 session enters
the TRANSACTION state.

The authorization identity generated by this [SASL] exchange
is a simple username, and MUST use the [SASLprep] profile of
the [StringPrep] algorithm to prepare these names for
matching. If preparation of the authorization identity fails
or results in an empty string (unless it was transmitted as
the empty string), the server MUST fail the authentication.

If a security layer is negotiated during the SASL exchange, it
takes effect for the client on the octet immediately following
the CRLF that concludes the last response generated by the
client. For the server, it takes effect immediately following

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the CRLF of its success reply.

When a security layer takes effect, the server MUST discard
any knowledge previously obtained from the client, which was
not obtained from the SASL negotiation itself. Likewise, the
client MUST discard any knowledge obtained from the server,
such as the list of available POP3 service extensions. After
a security layer is established, the server SHOULD NOT
advertise either the SASL or the STLS extension.

When both [TLS] and SASL security layers are in effect, the
TLS encoding MUST be applied after the SASL encoding,
regardless of the order in which the layers were negotiated.

The service name specified by this protocol's profile of SASL
is "pop".

If an AUTH command fails, the client may try another
authentication mechanism or present different credentials by
issuing another AUTH command (or by using one of the other
[POP3] authentication mechanisms). Likewise, the server MUST
behave as if the client had not issued the AUTH command.

To ensure interoperability, client and server implementations
of this extension MUST implement the [DIGEST-MD5] SASL
mechanism.

4.1. Formal Syntax

The following syntax specification uses the Augmented Backus-Naur
Form notation as specified in [ABNF].

Except as noted otherwise, all alphabetic characters are case-
insensitive. The use of upper or lower case characters to define
token strings is for editorial clarity only. Implementations MUST
accept these strings in a case-insensitive fashion.

UPALPHA = %x41-5A ;; Uppercase: A-Z

LOALPHA = %x61-7A ;; Lowercase: a-z

ALPHA = UPALPHA / LOALPHA ;; case insensitive

DIGIT = %x30-39 ;; Digits 0-9

AUTH_CHAR = ALPHA / DIGIT / "-" / "_"

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auth_type = 1*20AUTH_CHAR

auth_command = "AUTH" SPACE auth_type [SPACE (base64 / "=")]
*(CRLF [base64]) CRLF

base64 = base64_terminal /
( 1*(4base64_CHAR) [base64_terminal] )

base64_char = UPALPHA / LOALPHA / DIGIT / "+" / "/"
;; Case-sensitive

base64_terminal = (2base64_char "==") / (3base64_char "=")

continue_req = "+" SPACE [base64] CRLF

CR = %x0C ;; ASCII CR, carriage return

CRLF = CR LF

LF = %x0A ;; ASCII LF, line feed

SPACE = %x20 ;; ASCII SP, space Command . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.2. Examples

Here is an example of a client attempting AUTH PLAIN under TLS and
making use of the initial client response:

S: +OK pop.example.com BlurdyBlurp POP3 server ready
C: CAPA
S: +OK List of capabilities follows
S: SASL KERBEROS_V4 GSSAPI ANONYMOUS
S: STLS
S: IMPLEMENTATION BlurdyBlurp POP3 server
S: .
C: STLS
S: +OK Begin TLS negotiation now
... TLS negotiation proceeds, further commands protected by TLS layer ...
C: CAPA
S: +OK List of capabilities follows
S: SASL PLAIN KERBEROS_V4 GSSAPI ANONYMOUS
S: IMPLEMENTATION BlurdyBlurp POP3 server
S: .
C: AUTH PLAIN dGVzdAB0ZXN0AHRlc3Q=
S: +OK Maildrop locked and ready

Here is another client that is attempting AUTH PLAIN under a TLS

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layer, this time without the initial response. Parts of the
negotiation before the TLS layer was established have been omitted:

... TLS negotiation proceeds, further commands protected by TLS layer ...
C: CAPA
S: +OK List of capabilities follows
S: SASL PLAIN KERBEROS_V4 GSSAPI ANONYMOUS
S: IMPLEMENTATION BlurdyBlurp POP3 server
S: .
C: AUTH PLAIN
(note that there is a space following the '+' on the following line)
S: +
C: dGVzdAB0ZXN0AHRlc3Q=
S: +OK Maildrop locked and ready

Here is an example using a mechanism which does not support an
initial client send, and includes server challenges:

S: +OK pop.example.com BlurdyBlurp POP3 server ready
C: CAPA
S: +OK List of capabilities follows
S: SASL KERBEROS_V4 GSSAPI ANONYMOUS
S: STLS
S: IMPLEMENTATION BlurdyBlurp POP3 server
S: .
C: AUTH KERBEROS_V4
S: + ezLUFA==
(the following lines are broken for editorial clarity only)
C: BAYFQU5EUkVXLkNNVS5FRFUAOCCXeMiVyFe9K6Nwne7+sPLgIoF9YQ5ePfxUsMlJAf
C7aoNySU8nrqS9m8JAddsUeuyc5HFXXovaKLrZNo2bTLH0Lyolwy0W9ryJDojbKmHy
zSMqFsGD4EL0
S: + Z74fTwDw7KQ=
C: vSAF7ha6qotK2UHUgKlsEA==
S: +OK Maildrop locked and ready
... at this point a security layer has been established and additional
commands and responses proceed within it ...

5. Extended POP3 Response Codes

This section defines four POP3 response codes which can be used to
determine the reason for a failed login (provided that the server
advertises the RESP-CODES capability [POP3-EXT]). These definitions
supercede those in [POP3-EXT] and [POP3-CODES].

It is RECOMMENDED that server applications use these codes when
possible to allow clients a straightforward, interoperable way to
determine the cause of an authentication failure (as opposed to . . . . . . . . . . . . . . . . . . . . . . . 9
5. Protocol Actions . . . . . . . . . . . . . . . . . . . . . . . . 11
6. Intellectual Property Rights . . . . . . . . . . . . . . . . . . 11
7. Copyright . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
9. Changes From RFC 1734, RFC 2449. . . . . . . . . . . . . . . . . 14
10. Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 14
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 14

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parsing error text).

5.1. The LOGIN-DELAY Response Code

This occurs on an -ERR response February, 2005

1. How to an AUTH, USER (see note), PASS or
APOP command Read This Document

The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD
NOT", "RECOMMENDED", and indicates that the user has logged "MAY" in recently and
will not be allowed to login again until the login delay period has
expired.

Please see the Security Considerations section of this document for
an important note about returning this code in response to the USER
command.

5.2. The IN-USE Response Code

This occurs on an -ERR response are to an AUTH, APOP, or PASS command.
It indicates the authentication was successful, but the user's
maildrop is currently be
interpreted as defined in "Key words for use (probably in RFCs to Indicate
Requirement Levels" [KEYWORDS]

In examples, "C:" and "S:" indicate lines sent by another POP3 client).

5.3. the client and
server respectively.

2. Introduction

The [POP3] AUTH Response Code command [POP3-AUTH] has suffered several problems in
its specification. The AUTH response code informs the client that there first is that it was very similar to a problem
with
[SASL] framework, but pre-dated the user's credentials. This might be an incorrect password,
an unknown user name, an expired account, an attempt to authenticate
in violation of policy (such as from an invalid location or during
an unauthorized time), or initial SASL specification. It
was therefore missing some other problem.

The AUTH response code is valid with an -ERR response key components, such as a way to any
authentication command including AUTH, USER (see the note in the
Security Considerations section of this document), PASS, or APOP.

Servers which include list the AUTH response code with any
available authentication
failure SHOULD support mechanisms.

Later, [POP3-EXT] attempted to remedy this situation by adding the
CAPA command [POP3-EXT] and SHOULD
include allowing an initial client response to the AUTH-RESP-CODE capability (defined AUTH
command, however problems in the next section)
in clarity of the CAPA response. AUTH-RESP-CODE assures specification of how
the initial client response was to be handled remained.

Additionally, there is yet another document, [POP3-CODES], that
provides additional response codes that only
errors with the AUTH code are caused by credential problems.

5.3.1. useful during
authentication. Together, this means creating a full POP3 AUTH
implementaiton requires an understanding of material in at least
five (and probably six) different documents.

This document attempts to combine the information in [POP3-AUTH] and
[POP3-EXT] to simplify this situation. Additionally, it aims to
clarify and update the older specifications where appropriate.

3. The AUTH-RESP-CODE SASL Capability

This section supercedes the definition of the SASL Capability in
section 6.3 of [POP3-EXT].

CAPA tag:
AUTH-RESP-CODE
SASL

Arguments:
none
Supported SASL Mechanisms

Added commands:
none
AUTH

Standard Commands Affected

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Standard commands affected:
none February, 2005

None

Announced states / possible differences:
both / no

Commands valid in states:
n/a
AUTHORIZATION

Specification reference:
this document

Discussion: Reference:
This Document, [SASL]

Discussion
The AUTH-RESP-CODE SASL capability indicates that the server includes
the AUTH response code with any authentication error caused by a
problem with the user's credentials.

5.4. The SYS Response Code

The SYS response code announces that a failure is due to a system
error, as opposed to permits the user's credentials or an external
condition. It is hierarchical, with two possible second-level
codes: TEMP and PERM. (Case is not significant at any level use of the
hierarchy.)

SYS/TEMP indicates a problem which is likely to be temporary AUTH command (as
defined in
nature, and therefore there is no need section 4 of this document) to alarm the user, unless the
failure persists. Examples might include begin a central resource which
is currently locked or otherwise temporarily unavailable,
insufficient free disk or memory, etc.

SYS/PERM [SASL]
negotiation. The argument to the SASL capability is used for problems a space-
separated list of SASL mechanisms which are unlikely to be resolved
without intervention. It is appropriate to alert the user and
suggest that the organization's supported.

If a server either does not support the CAPA command or assistance personnel be
contacted. Examples include corrupted mailboxes, system
configuration errors, etc.

The SYS response code is valid with an -ERR response to any does not
advertise the SASL capability, clients SHOULD NOT attempt the
AUTH command.

6. Security Considerations

Security issues are discussed throughout this memo.

Before If a client does attempt the [SASL] negotiation has begun, any protocol interactions
are performed AUTH command in such
a situation, it MUST NOT supply the clear and may be modified client initial response
parameter (for backwards compatibility with [POP3-AUTH]).

Note that the list of available mechanisms MAY change after a
successful STLS command [POP3-TLS]. However, as required by an active
attacker. For this reason, clients and servers
[POP3-EXT] implementations MUST discard any
knowledge obtained prior continue to the start of include the SASL negotiation upon
the establishment
capability even after a successful AUTH command has been
completed (even though no further AUTH commands may be issued).

Example

S: +OK pop.example.com BlurdyBlurp POP3 server ready
C: CAPA
S: +OK List of capabilities follows
S: SASL KERBEROS_V4 GSSAPI ANONYMOUS
S: STLS
S: IMPLEMENTATION BlurdyBlurp POP3 server
S: .

4. The AUTH Command

AUTH mechanism [initial-response]

Arguments:
mechanism: A string identifying a security layer. [SASL] authentication
mechanism.

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Servers MAY implement February, 2005

initial-response: An optional initial client response. If
present, this response MUST be encoded as specified in Section
3 of [BASE64].

Restrictions:
After an AUTH command has been successfully completed, no more
AUTH commands may be issued in the same session. After a policy whereby
successful AUTH command completes, a server MUST reject any
further AUTH commands with an -ERR reply.

The AUTH command may only be given during the connection is dropped
after AUTHORIZATION
state.

Discussion:
The AUTH command initiates a number of failed [SASL] authentication attempts. If they do so,
they SHOULD NOT drop exchange
between the connection until atleast 3 attempts to
authenticate have failed.

Implementations MUST support a configuration where [SASL] mechanisms
that are vulnerable client and the server. The client identifies the
SASL mechanism to passive eavesdropping attacks (such as
[PLAIN]) are not advertised or used without use with the presence first parameter of an
external security layer such as [TLS].

Returning the LOGIN-DELAY or AUTH response codes to
command. If the USER command
avoids server supports the work of authenticating requested authentication
mechanism, it performs the user but is likely to reveal
information SASL exchange to authenticate the client about the existence of the account in
question. Unless
user. Optionally, it also negotiates a security layer for
subsequent protocol interactions during this session. If the server
requested authentication mechanism is operating in an environment where
user names are not secret (for example, many popular email clients
advertise supported, the POP server and user name in an outgoing mail header),
or where
server access is restricted, or rejects the AUTH command with an -ERR reply.

The authentication protocol exchange consists of a series of
server can verify challenges and client responses that
the connection is to the same user, the the server SHOULD NOT issue
this response code are specific to
the USER command. The chosen [SASL] mechanism.

A server still saves the
cost challenge is sent as a line consisting of opening the maildrop, which a "+"
character followed by a single space and a string encoded as
specified in some environments is the most
expensive step.

7. IANA Considerations

This document requests that the IANA update the entry for the "pop"
SASL protocol name to point at this document. Section 3 of [BASE64]. This document requests that the IANA update the entry for line MUST NOT
contain any text other than the SASL
POP3 capability to be BASE64 encoded challenge.

A client response consists of a line containing a string
encoded as defined in Section 3 of this document.

This document requests that [BASE64]. If the IANA update client
wishes to cancel the entry for authentication exchange, it issues a line
with a single "*". If the LOGIN-
DELAY, IN-USE, AUTH, SYS/TEMP, and SYS/PERM POP3 server receives such a response, it
MUST reject the AUTH command by sending an -ERR reply.

The optional initial response codes argument to
this document.

This document requests the AUTH command is
used to save a round trip when using authentication mechanisms
that support an initial client response. If the IANA update initial
response argument is omitted and the entry for chosen mechanism requires
an initial client response, the AUTH-
RESP-CODE capability to be server MUST proceed as defined
in Section 5.3.1 of this
document.

8. Protocol Actions

[RFC Editor: Remove this section before publication]

This document obsoletes RFC 1734 and replaces it as a Proposed
Standard. By moving RFC 1734 to Historic, RFC 1731 can also be
moved to Historic (as RFC 1734 was the last document to have 5.1 of [SASL]. In POP3, a
normative reference).

This document obsoletes RFC 3206 and replaces it server challenge with no
data is defined as line with only a Proposed "+" followed by a single
space. It MUST NOT contain any other data.

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POP3 SASL Authentication Mechanism April, 2004

Standard.

It also updates information contained in Section 6.3 and Section 8
of RFC 2449.

9. Intellectual Property Rights

The IETF takes no position regarding February, 2005

For the validity or scope purposes of any
intellectual property or other rights that might be claimed to
pertain the initial client response, the line
length limitation defined in [POP3-EXT] still applies. If a
client initial send would cause the AUTH command to exceed
this length, the implementation or client MUST NOT use of the technology described initial response
parameter (and instead proceed as defined in
this document or section 5.1 of
[SASL]).

If the extent client needs to which any license under such rights
might or might not be available; neither does it represent send a zero-length initial response,
the client MUST transmit the response as a single equals sign
("="). This indicates that it
has made any effort the response is present, but
contains no data.

If the client uses an initial-response argument to identify any such rights. Information on the
IETF's procedures AUTH
command 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 a SASL mechanism that does not support an initial
client send, the result of server MUST reject the AUTH command with an attempt made
to obtain
-ERR reply.

If the server cannot [BASE64] decode a general license or permission for client response, it
MUST reject the use of such
proprietary rights by implementors or users of this specification
can be obtained from AUTH command with an -ERR reply. If the IETF Secretariat.

The IETF invites
client cannot BASE64 decode a server challenge, it MUST cancel
the authentication using the "*" response. In particular,
servers and clients MUST reject (and not ignore) any interested party to bring to its attention character
not explicitly allowed by the BASE64 alphabet, and MUST reject
any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address sequence of BASE64 characters that contains the information to pad
character ('=') anywhere other than the IETF Executive
Director.

10. Copyright

This document and translations end of it may be copied and furnished to
others, the string
(e.g. "=AAA" and derivative works "AAA=BBB" are not allowed).

Note that comment on or otherwise explain it
or assist in its implementation these [BASE64] strings (excepting the initial client
response) may be prepared, copied, published of arbitrarily length. Clients and distributed, in whole or in part, without restriction servers
MUST be able to handle the maximum encoded size of challenges
and responses generated by their supported authentication
mechanisms. This requirement is independent of any
kind, provided that line
length limitations the above copyright notice and this paragraph
are included on all such copies and derivative works. However, this
document itself client or server may not be modified have in any way, such as by removing other
parts of its protocol implementation.

If the copyright notice or references server is unable to authenticate the Internet Society or other
Internet organizations, except as needed for client, it MUST
reject the AUTH command with an -ERR reply. Should the client
successfully complete the exchange, the server issues a +OK
reply. Additionally, upon success, the POP3 session enters
the TRANSACTION state.

The authorization identity generated by the [SASL] exchange is
a simple username, and MUST use the purpose [SASLprep] profile of
developing Internet standards in which case the procedures
[StringPrep] algorithm to prepare these names for
copyrights defined in matching.
If preparation of the Internet Standards process must be
followed, authorization identity fails or as required to translate results
in an empty string (unless it into languages other than
English.

This document and was transmitted as 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 empty
string), the server MUST fail the authentication.

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POP3 SASL Authentication Mechanism April, 2004

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.

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POP3 February, 2005

If a security layer is negotiated during the SASL Authentication Mechanism April, 2004

11. References

The exchange, it
takes effect for the client on the octet immediately following documents contain normative definitions or
specifications
the CRLF that are necessary for correct understanding concludes the last response generated by the
client. For the server, it takes effect immediately following
the CRLF of this
protocol:

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

[DIGEST-MD5]
Leach, P., Melnikov, A., and Newman C., "Using Digest
Authentication as its success reply.

When a security layer takes effect, the server MUST discard
any knowledge previously obtained from the client, which was
not obtained from the SASL Mechanism", draft-ietf-sasl-
rfc2831bis-*.txt, a work in progress.

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

[POP3] Myers, J. and Rose, M., "Post Office Protocol - Version 3",
STD 53, RFC 1939, May 1996.

[POP3-EXT] Gellens, R., Newman, C., and Lundblade, L., "POP3 Extension
Mechanism", RFC 2449, November 1998.

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

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

[SASLprep] Zeilega, K., "SASLprep: Stringprep profile for user names negotiation itself. Likewise, the
client MUST discard any knowledge obtained from the server,
such as the list of available POP3 service extensions.

When both [TLS] and passwords", draft-ietf-sasl-saslprep-*.txt, a work SASL security layers are in
progress

[StringPrep]
Hoffman, P. and Blanchet, M., "Preparation effect, the
TLS encoding MUST be applied after the SASL encoding,
regardless of
Internationalized Strings ("stringprep")", draft-hoffman-
rfc3454bis-*.txt, a work the order in progress which the layers were negotiated.

The following references are for informational purposes only:

[PLAIN] Zeilenga, K., "The Plain SASL Mechanism", draft-ietf-sasl-
plain-*.txt, a work in progress.

[POP3-AUTH] Myers, J., "POP3 AUTHentication Command", RFC 1734, January
1994.

[POP3-CODES]

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POP3 service name specified by this protocol's profile of SASL Authentication Mechanism April, 2004

Gellens, R., "The SYS and
is "pop".

If an AUTH POP Response Codes", RFC
3206, February 2002.

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

12. Changes From RFC 1734, RFC 2449, and RFC 3206

1. The SASL-based semantics defined in RFC 2449 are now
normative for command fails, the client may try another
authentication mechanism or present different credentials by
issuing another AUTH extension.

2. Clarifications and examples command (or by using one of the proper behavior of
initial other
[POP3] authentication mechanisms). Likewise, the server MUST
behave as if the client had not issued the AUTH command.

To ensure interoperability, client response handling.

3. Minimum requirement of support for DIGEST-MD5.

4. Clarify ordering of TLS and SASL security layers.

5. Update references to newer versions server implementations
of various
specifications.

6. Clarify that this extension MUST implement the mechanism list can change.

7. Add [DIGEST-MD5] SASL
mechanism.

4.1. Formal Syntax

The following syntax specification uses the Augmented Backus-Naur
Form notation as specified in [ABNF].

Except as noted otherwise, all alphabetic characters are case-
insensitive. The use of the SASLprep profile upper or lower case characters to define
token strings is for preparing
authorization identities.

8. General other editorial clarifications.

9. Consolidation of all applicable information into clarity only. Implementations MUST
accept these strings in a
single document.

13. 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

14. Acknowledgments:

The author would like to acknowledge the contributions of John
Myers, Randall Gellens, Chris Newman, Laurence Lundblade, and other
contributors to RFC 1734, RFC 2554, and RFC 3206, on which this
document draws heavily. case-insensitive fashion.

UPALPHA = %x41-5A ;; Uppercase: A-Z

LOALPHA = %x61-7A ;; Lowercase: a-z

ALPHA = UPALPHA / LOALPHA ;; case insensitive

DIGIT = %x30-39 ;; Digits 0-9

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The author would also like to thank Ken Murchison, Alexey Melnikov,
and Mark Crispin for February, 2005

AUTH_CHAR = ALPHA / DIGIT / "-" / "_"

auth_type = 1*20AUTH_CHAR

auth_command = "AUTH" SPACE auth_type [SPACE (base64 / "=")]
*(CRLF [base64]) CRLF

auth_resp = ("*" / base64) CRLF

base64 = base64_terminal /
( 1*(4base64_CHAR) [base64_terminal] )

base64_char = UPALPHA / LOALPHA / DIGIT / "+" / "/"
;; Case-sensitive

base64_terminal = (2base64_char "==") / (3base64_char "=")

continue_req = "+" SPACE [base64] CRLF

CR = %x0C ;; ASCII CR, carriage return

CRLF = CR LF

LF = %x0A ;; ASCII LF, line feed

SPACE = %x20 ;; ASCII SP, space

Additionally, the time they devoted to reviewing early drafts ABNF specified in [POP3-EXT] is updated as
follows:

response = greeting / single-line / capa-resp / multi-line /
continue_req

4.2. Examples

Here is an example of a client attempting AUTH PLAIN under TLS and
making use of this document. the initial client response:

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Table of Contents

1. How to Read This Document . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. The SASL Capability . . . . . . . . . . . . . . . . . . . . . . . 3
4. The AUTH Command . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5. Extended February, 2005

S: +OK pop.example.com BlurdyBlurp POP3 Response Codes . . . . . . . . . . . . . . . . . . 9
5.1. The LOGIN-DELAY Response Code . . . . . . . . . . . . . . . . . 10
5.2. The IN-USE Response Code . . . . . . . . . . . . . . . . . server ready
C: CAPA
S: +OK List of capabilities follows
S: SASL KERBEROS_V4 GSSAPI ANONYMOUS
S: STLS
S: IMPLEMENTATION BlurdyBlurp POP3 server
S: .
C: STLS
S: +OK Begin TLS negotiation now
... TLS negotiation proceeds, further commands protected by TLS layer ...
C: CAPA
S: +OK List of capabilities follows
S: SASL PLAIN KERBEROS_V4 GSSAPI ANONYMOUS
S: IMPLEMENTATION BlurdyBlurp POP3 server
S: . 10
5.3. The
C: AUTH Response Code . . . . . . . . . . . . . . . . . . . . 10
5.3.1. The AUTH-RESP-CODE Capability . . . . . . . . . . . . . . . . 10
5.4. The SYS Response Code . . . . . . . . . . . . . . . . . . . PLAIN dGVzdAB0ZXN0AHRlc3Q=
S: +OK Maildrop locked and ready

Here is another client that is attempting AUTH PLAIN under a TLS
layer, this time without the initial response. Parts of the
negotiation before the TLS layer was established have been omitted:

Here is an example using a mechanism which does not support an
initial client send, and includes server challenges:

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POP3 SASL Authentication Mechanism February, 2005

S: +OK pop.example.com BlurdyBlurp POP3 server ready
C: CAPA
S: +OK List of capabilities follows
S: SASL KERBEROS_V4 GSSAPI ANONYMOUS
S: STLS
S: IMPLEMENTATION BlurdyBlurp POP3 server
S: . 11
C: AUTH KERBEROS_V4
S: + ezLUFA==
(the following lines are broken for editorial clarity only)
C: BAYFQU5EUkVXLkNNVS5FRFUAOCCXeMiVyFe9K6Nwne7+sPLgIoF9YQ5ePfxUsMlJAf
C7aoNySU8nrqS9m8JAddsUeuyc5HFXXovaKLrZNo2bTLH0Lyolwy0W9ryJDojbKmHy
zSMqFsGD4EL0
S: + Z74fTwDw7KQ=
C: vSAF7ha6qotK2UHUgKlsEA==
S: +OK Maildrop locked and ready
... at this point a security layer has been established and additional
commands and responses proceed within it ...

5. Protocol Actions

[RFC Editor: Remove this section before publication]

It also updates information contained in Section 6.3 of RFC 2449.

6. Security Considerations . . . . . . . . . . . . . . . . . . . . . 11 Intellectual Property Rights

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

Siemborski Expires August, 2005 [Page 11]

POP3 SASL Authentication Mechanism February, 2005

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.

7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . . 12
8. Protocol Actions . . . . . . . . . . . . . . . . . . . . . . . . 12
9. Intellectual Property Rights . . . . . . . . . . . . . . . . . . 13
10. Copyright . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
11.

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 12]

POP3 SASL Authentication Mechanism February, 2005

8. References . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
12.

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

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

[DIGEST-MD5]
Leach, P., Melnikov, A., and Newman C., "Using Digest
Authentication as a SASL Mechanism", draft-ietf-sasl-
rfc2831bis-*.txt, a work in progress.

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

[POP3] Myers, J. and Rose, M., "Post Office Protocol - Version 3",
STD 53, RFC 1939, May 1996.

[POP3-EXT] Gellens, R., Newman, C., and Lundblade, L., "POP3 Extension
Mechanism", RFC 2449, November 1998.

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

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

[SASLprep] Zeilega, K., "SASLprep: Stringprep profile for user names
and passwords", draft-ietf-sasl-saslprep-*.txt, a work in
progress

[StringPrep]
Hoffman, P. and Blanchet, M., "Preparation of
Internationalized Strings ("stringprep")", draft-hoffman-
rfc3454bis-*.txt, a work in progress

The following references are for informational purposes only:

[PLAIN] Zeilenga, K., "The Plain SASL Mechanism", draft-ietf-sasl-
plain-*.txt, a work in progress.

[POP3-AUTH] Myers, J., "POP3 AUTHentication Command", RFC 1734, January
1994.

[POP3-CODES]

Siemborski Expires August, 2005 [Page 13]

POP3 SASL Authentication Mechanism February, 2005

Gellens, R., "The SYS and AUTH POP Response Codes", RFC
3206, February 2002.

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

9. Changes From RFC 1734, RFC 2449, and 2449.

1. The SASL-based semantics defined in RFC 3206 . . . . . . . . . 16
13. 2449 are now
normative for the AUTH extension.

2. Clarifications and examples of the proper behavior of
initial client response handling.

3. Minimum requirement of support for DIGEST-MD5.

4. Clarify ordering of TLS and SASL security layers.

5. Update references to newer versions of various
specifications.

6. Clarify that the mechanism list can change.

7. Add the use of the SASLprep profile for preparing
authorization identities.

8. General other editorial clarifications.

9. Consolidation of much applicable information into a
single document.

10. Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 16
14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 16 Address:

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

11. Acknowledgments:

The author would like to acknowledge the contributions of John
Myers, Randall Gellens, Chris Newman, Laurence Lundblade, and other
contributors to RFC 1734 and RFC 2554, on which this document draws
heavily.

The author would also like to thank Ken Murchison, Randall Gellens,

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POP3 SASL Authentication Mechanism February, 2005

Alexey Melnikov, and Mark Crispin for the time they devoted to
reviewing early drafts of this document.

Siemborski Expires August, 2005 [Page 15]

----