One document matched: draft-martin-managesieve-00.txt
Network Working Group Tim Martin
Document: draft-martin-managesieve-00.txt Carnegie Mellon University
Expires July 22, 2000 17 January 2000
A Protocol for Remotely Managing Sieve Scripts
<draft-martin-managesieve-00.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. Internet-Drafts are
working documents of the Internet Engineering Task Force (IETF), its
areas, and its working groups. Note that other groups may also
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Internet-Drafts are draft documents valid for a maximum of six
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Distribution of this memo is unlimited.
Abstract
Sieve scripts allow users to filter incoming email. Message stores
are commonly sealed servers so users cannot log into them , yet
users must be able to update their scripts on them. This document
describes a protocol for securely managing Sieve scripts on a remote
server. This protocol allows a user to have multiple scripts, and
also alerts a user to syntactically flawed scripts.
This an interim measure as it is hoped that eventually Sieve scripts
will be stored on ACAP. This document is intended to proceed on the
experimental track.
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Status of this Memo . . . . . . . . . . . . . . . . . . . . . . . . 1
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Conventions Used in the Document . . . . . . . . . . . . . . 3
1.3. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.4. Active Script . . . . . . . . . . . . . . . . . . . . . . . . 4
1.5. Quotas . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.6. Script Names . . . . . . . . . . . . . . . . . . . . . . . . 4
1.7. Capabilities . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Commands . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. AUTHENTICATE Command . . . . . . . . . . . . . . . . . . . . 6
2.2. STARTTLS Command . . . . . . . . . . . . . . . . . . . . . . 7
2.3. LOGOUT Command . . . . . . . . . . . . . . . . . . . . . . . 8
2.4. CAPABILITY Command . . . . . . . . . . . . . . . . . . . . . 8
2.5. HAVESPACE Command . . . . . . . . . . . . . . . . . . . . . . 9
2.6. PUTSCRIPT Command . . . . . . . . . . . . . . . . . . . . . . 9
2.7. LISTSCRIPTS command . . . . . . . . . . . . . . . . . . . . . 10
2.8. SETACTIVE command . . . . . . . . . . . . . . . . . . . . . . 11
2.9. GETSCRIPT command . . . . . . . . . . . . . . . . . . . . . . 11
2.10. DELETESCRIPT command . . . . . . . . . . . . . . . . . . . . 12
3. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 12
4. Security Considerations . . . . . . . . . . . . . . . . . . . 14
5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
6. Copyright . . . . . . . . . . . . . . . . . . . . . . . . . . 15
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
8. Author's Address . . . . . . . . . . . . . . . . . . . . . . 16
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1. Introduction
1.1. Changes
Changes since 00
-dropped syncronized literals. added HAVESPACE command
-changed capability response syntax. added CAPABILITY command
-allowed pipelining
- "sieve" -> "Sieve". Other minor fixes
-made script names more flexible
-added starttls support
1.2. 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].
In examples, "C:" and "S:" indicate lines sent by the client and
server respectively. Line breaks that do not start a new "C:" or
"S:" exist for editorial reasons.
1.3. Syntax
This a line oriented protocol much like [IMAP] or [ACAP]. There are
three types: ATOMS, numbers and strings. Strings may be quoted or
literal. See [ACAP] for detailed descriptions of these types.
Each command consists of an atom followed by zero or more strings
and numbers terminated by a newline.
All client queries are replied to with either an OK or NO response.
Under extraordinary conditions the server may drop the connection.
Each OK or NO response may be followed by a string consisting of
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human readable text in the local language. The contents of the
string SHOULD be shown to the user and implementations MUST NOT
attempt to parse the message for meaning.
IANA registration is pending. Current implementations generally use
port number 2000.
1.4. Active Script
A user may have multiple Sieve scripts on the server, yet only one
script may be used for filtering of incoming messages. This is the
active script. Users may have zero or one active scripts and MUST
use the SETACTIVE command described below for changing the active
script or disabling Sieve processing. For example, a user may have
an everyday script they normally use and a special script they use
when they go on vacation. Users can change which script is being
used without having to download and upload a script stored somewhere
else.
1.5. Quotas
Servers SHOULD impose quotas to prevent malicious users from
overflowing available storage. If a command would place a user over
a quota setting, servers MUST reply with a NO response. Client
implementations MUST be able to handle commands failing because of
quota restrictions.
1.6. Script Names
Sieve script names may contain any valid UTF8 characters, but names
must be at least one character long. Servers MUST allow names of up
to 128 UTF8 octets in length, and may allow longer names.
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1.7. Capabilities
Server capabilities are sent by the server upon a client connection.
Clients may request the capabilites at a later time by issuing the
CAPABILITY command described later. The capabilities consist of a
series lines each with one or two strings. The first string is the
name of the capability. The second optional string is the value
associated with that capability.
The following capabilities are defined here:
IMPLEMENTATION - Name of implementation and version
SASL - List of SASL mechanisms supported by the server, each
separated by a space
SIEVE - List of space separated Sieve extensions supported
STARTTLS - If TLS[TLS] is supported by this implementation
A client implementation MUST ignore any other capabilities given
that it does not understand.
Example:
S: "IMPLEMENTATION" "CMU Cyrus Sieved v001"
S: "SASL" "KERBEROS_V4 GSSAPI"
S: "SIEVE" "FILEINTO VACATION"
S: "STARTTLS"
S: OK
2. Commands
The following commands are valid. Prior to successful authentication
only the AUTHENTICATE, CAPABILITY, STARTTLS, and LOOGOUT commands
are valid. Servers MUST reject all other commands with a NO
response. Clients may pipeline commands (send more than one command
at a time without waiting for completion of the first command ).
However, a group of commands sent together MUST NOT have a HAVESPACE
command anywhere but the last command in the list.
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2.1. AUTHENTICATE Command
Arguments:
String - mechanism
String - initial data (optional)
The AUTHENTICATE command indicates a SASL [SASL] authentication
mechanism to the server. If the server supports the requested
authentication mechanism, it performs an authentication protocol
exchange to authenticate and identify the user. Optionally, it also
negotiates a security layer for subsequent protocol interactions.
If the requested authentication mechanism is not supported, the
server rejects the AUTHENTICATE command by sending a NO response.
The authentication protocol exchange consists of a series of server
challenges and client answers that are specific to the
authentication mechanism. A server challenge consists of a string
followed by an endline. The contents of the string is a base-64
encoding of the SASL data. The client answer consists of a string
with the base-64 encoding of the SASL data followed by an endline.
If the mechanism dictates that the final response be sent by the
server this data MAY be placed within the OK response to save a
round trip. In this case the OK response MUST have two strings
following it. If there
is nothing pertinent for the user to see the second string is the
empty string.
The optional initial-response argument to the AUTHENTICATE command
is used to save a round trip when using authentication mechanisms
that are defined to send no data in the initial challenge. When the
initial-response argument is used with such a mechanism, the initial
empty challenge is not sent to the client and the server uses the
data in the initial-response argument as if it were sent in response
to the empty challenge. If the initial-response argument to the
AUTHENTICATE command is used with a mechanism that sends data in the
initial challenge, the server rejects the AUTHENTICATE command by
sending a tagged NO response.
The service name specified by this protocol's profile of SASL is
"imap" since implementations are generally tied to an IMAP
installation.
If a security layer is negotiated through the SASL authentication
exchange, it takes effect immediately following the CRLF that
concludes the authentication exchange for the client, and the CRLF
of the OK response for the server.
Implementations MUST NOT advertise the ANONYMOUS SASL mechanism
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[SASL-ANON]. SASL mechanisms which use plaintext passwords
(including the PLAIN mechanism [PLAIN]) MUST NOT be used unless a
security layer is active or backwards compatibility dictates other
wise.
Server implementations SHOULD support proxying so that an
administrator can administer a user's scripts. Proxying is when a
user authenticates as himself but logs in as another user.
If an AUTHENTICATE command fails with a NO response, the client may
try another authentication mechanism by issuing another AUTHENTICATE
command. In other words, the client may request authentication
types in decreasing order of preference.
Example:
S: "IMPLEMENTATION" "CMU Cyrus Sieved v001"
S: "SASL" "KERBEROS_V4 GSSAPI"
S: "SIEVE" "FILEINTO VACATION"
S: "STARTTLS"
S: OK
C: Authenticate "KERBEROS_V4"
S: "6UM4Ig=="
C: "BAYBQU5EUkVXLkNNVS5FRFUAOCjDCH77GOzSSOF1Df2Kb0zzPe
QJIrweAPyo6Q1T9xuYtCGylDqRYlbUFa77esDOtBJdDE5qRXcwHXQE5Dg
amqj0LqecZtKUCc8g2xpcqxn1fc/CH6QdZLOAGVpHTN1AX2Y="
S: "cmnEYo1x6wc="
C: "kjuaMkUeg2okQh+we2uiJw=="
S: OK
2.2. STARTTLS Command
The STARTTLS command requests to commencement of a TLS negotiation.
The negotiation begins immediately after the CRLF in the OK
response. After a client issues a STARTTLS command, it MUST NOT
issue further commands until a server response is seen and the TLS
negotiation is complete.
The STARTTLS command is only valid in non-authenticated state. The
server remains in non-authenticated state, even if client
credentials are supplied during the TLS negotiation. The SASL [SASL]
EXTERNAL mechanism MAY be used to authenticate once TLS clie nt
credentials are successfully exchanged, but servers supporting the
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STARTTLS command are not required to support the EXTERNAL mechanism.
After the TLS layer is established, the server MUST re-issue the
capability results. This is necessary to protect against man-in-the-
middle attacks which alter the capabilities list prior to STARTTLS.
The client MUST discard cached capability information and replace it
with the new information. The server MAY advertise different
capabilities after STARTTLS.
Example:
C: STARTTLS
S: OK
<TLS negotiation, further commands are under TLS layer>
S: "IMPLEMENTATION" "CMU Cyrus Sieved v001"
S: "SASL" "EXTERNAL PLAIN KERBEROS_V4 GSSAPI"
S: "SIEVE" "FILEINTO VACATION"
S: OK
2.3. LOGOUT Command
The client sends the LOGOUT command when it is finished with a
connection and wishes to terminate it. The server MUST reply with an
OK response and terminate the connection. The server MUST ignore
commands issued by the client after the LOGOUT command.
Example:
C: Logout
S: OK
<connection terminated>
2.4. CAPABILITY Command
The CAPABILITY command requests the server capabilities as described
earlier in this document. While the capabilities are sent upon
connection, they may change during authentication. Client SHOULD
issue a CAPABILITY command after sucessful authentication.
Example:
S: "IMPLEMENTATION" "CMU Cyrus Sieved v001"
S: "SASL" "PLAIN KERBEROS_V4 GSSAPI"
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S: "SIEVE" "FILEINTO VACATION"
S: "STARTTLS"
S: OK
2.5. HAVESPACE Command
Arguments:
String - name
Number - size
The HAVESPACE command is used to query the server for available
space. Clients specifiy the name wished to save the script as and
it's size in octets. Servers respond with an NO if storing a script
with that name and size would fail or OK otherwise. Clien ts should
issue this command before attempting to place a script on the
server.
Example:
C: HAVESPACE "myscript" 999999
S: NO "Quota exceeded"
C: HAVESPACE "foobar" 435
S: OK
2.6. PUTSCRIPT Command
Arguments:
String - Script name
String - Script content
The PUTSCRIPT command is used by the client to submit a Sieve script
to the server.
If the script already exists upon success the old script will be
overwritten. The old script MUST NOT be overwritten if PUTSCRIPT
fails in any way.
This command places the script on the server. It does not affect
whether the script is processed on incoming mail. The SETACRIVE
command is used to mark a script as active.
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When submitting large scripts clients SHOULD use the HAVESPACE
command beforehand to query if the server is willing to accept a
script of that size.
The server MUST check the submitted script for syntactic validity.
If the script fails this test the server MUST reply with a NO
response. Any script that fails the validity test MUST NOT be stored
on the server. The message given with a NO response MUST be human
readable and SHOULD contain a specific error message giving line
number of the first error. Implementors should strive to produce
helpful error messages similar to those given by programming
language compilers. Client implementations should note that this may
be a multiline literal string with more than one error message
separated by newlines.
Example:
C: Putscript "foo" {31+}
C: #comment
C: InvalidSieveCommand
C:
S: NO "line 2: Syntax error"
C: Putscript "mysievescript" {110+}
C: require ["fileinto"];
C:
C: if envelope :contains "to" "tmartin+sent" {
C: fileinto "INBOX.sent";
C: }
S: OK
2.7. LISTSCRIPTS command
This command lists the scripts the user has on the server. Upon
success a list of linebreak separated script names is returned
followed by an OK response. If there exists an active script the
atom ACTIVE is appended to the line of that script.
Example:
C: Listscripts
S: "summer_script"
S: "vacation_script"
S: "main_script" ACTIVE
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S: OK
2.8. SETACTIVE command
Arguments:
String - script name
This command sets a script active. If the script name is the empty
string (i.e. "") then any active script is disabled. If the script
does not exist on the server then the server MUST reply with a NO
response.
Examples:
C: Setactive "vacationscript"
S: Ok
C: Setactive ""
S: Ok
C: Setactive "baz"
S: No "There is no script by that name"
2.9. GETSCRIPT command
Arguments:
String - Script name
This command gets the contents of the specified script. If the
script does not exist the server MUST reply with a NO response. Upon
success a string with the contents of the script is returned
followed by a OK response.
Example:
C: Getscript "myscript"
S: {48+}
S: #this is my wonderful script
S: reject "I reject all";
S:
S: OK
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2.10. DELETESCRIPT command
Parameters:
sieve-name - Script name
This command is used to delete a user's Sieve script. Servers MUST
reply with a NO response if the script does not exist. The server
MUST NOT allow the client to delete an active script and reply with
a NO response if attempted. If a client wishes to delete an active
script it should use the SETACTIVE command to disable the script
first.
Example:
C: Deletescript "foo"
S: Ok
C: Deletescript "baz"
S: No "You may not delete an active script"
3. Formal Syntax
The following syntax specification uses the augmented Backus-Naur
Form (BNF) notation as specified in [ABNF]. This uses the ABNF core
rules as specified in Appendix A of the ABNF specification [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.
QUOTED-CHAR = SAFE-UTF8-CHAR / "
QUOTED-SPECIALS = <"> / "
SAFE-UTF8-CHAR = SAFE-CHAR / UTF8-2 / UTF8-3 / UTF8-4 /
UTF8-5 / UTF8-6
auth-type = <"> auth-type-name <">
auth-type-name = iana-token
;; as defined in SASL [SASL]
command = command-authenticate / command-logout / command-getscript /
command-setactive / command-listscripts / command-deletescript /
command-putscript / command-capability / command-havespace /
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command-starttls
command-authenticate = "AUTHENTICATE" SP auth-type [SP string] *(CRLF string)
command-capability = "CAPABILITY" CRLF
command-deletescript = "DELETESCRIPT" SP sieve-name CRLF
command-getscript = "GETSCRIPT" SP sieve-name CRLF
command-havespace = "HAVESPACE" SP sieve-name SP number CRLF
command-listscripts = "LISTSCRIPTS" CRLF
command-logout = "LOGOUT" CRLF
command-putscript = "PUTSCRIPT" SP sieve-name SP string CRLF
command-setactive = "SETACTIVE" SP sieve-name CRLF
command-starttls = "STARTTLS" CRLF
literal = "{" number [ "+" ] "}" CRLF *OCTET
;; The number represents the number of octets
;; MUST be literal-utf8 except for values
number = *DIGIT
;; A 32-bit unsigned number.
;; (0 <= n < 4,294,967,296)
quoted = <"> *QUOTED-CHAR <">
;; limited to 1024 octets between the <">s
response = response-authenticate / response-logout / response-getscript /
response-setactive / response-listscripts / response-deletescript /
response-putscript / response-capability / response-havespace /
response-starttls
response-authenticate = *(string CRLF / response-okno / response-special-ok)
response-capability = *(string [SP string] CRLF) response-okno
response-deletescript = response-okno
response-getscript = [string CRLF] response-okno
response-havespace = response-okno
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response-listscripts = *(sieve-name [SP "ACTIVE"] CRLF) response-okno
response-logout = response-okno
response-okno = ("OK" / "NO") [SP string] CRLF
response-putscript = response-okno
response-setactive = response-okno
response-special-ok = "OK" SP string SP string CRLF
response-starttls = response-okno
sieve-name = string
string = quoted / literal
4. Security Considerations
The AUTHENTICATE command uses SASL [SASL] and TLS [TLS] to provide
basic authentication, authorization, integrity and privacy services.
When a SASL mechanism is used the security considerations for that
mechanism apply.
This protocol transactions are susceptible to passive observers or
man in the middle attacks which alter the data, unless the optional
encryption and integrity services of the AUTHENTICATE command are
enabled, or an external security mechanism is used for protection.
It may be useful to allow configuration of both clients and servers
to refuse to transfer sensitive information in the absence of strong
encryption.
5. Acknowledgments
Thanks to Larry Greenfield, Allen Johnson, Chris Newman, Lyndon
Nerenberg, Tim Showalter, Sarah Robeson, and Walter Wong for help
with this document.
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6. Copyright
Copyright (C) The Internet Society 1999. All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph
are included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
7. References
[KEYWORDS] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997
<ftp://ftp.isi.edu/in-notes/rfc2119.txt>
[ABNF] Crocker, Overell, "Augmented BNF for Syntax Specifications:
ABNF", RFC 2234, Internet Mail Consortium, Demon Internet Ltd, November
1997.
[ACAP] Newman, Myers, "ACAP -- Application Configuration Access Proto-
col", RFC 2244, Innosoft, Netscape, November 1997.
[PLAIN] Newman, C. "Using TLS with IMAP, POP3 and ACAP", RFC 2595,
Innosoft, June 1999.
[SASL] Myers, J., "Simple Authentication and Security Layer (SASL)", RFC
2222, Netscape Communications, October 1997.
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[SASL-ANON] Newman, C., "Anonymous SASL Mechanism", RFC 2245, November
1997.
[SIEVE] Showalter, T, "Sieve -- a Mail Filtering Language", draft-
showalter-sieve-09.txt, Mirapoint, September 1999.
[TLS] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC 2246,
January 1999.
8. Author's Address
Tim Martin
Computing Services
Carnegie Mellon University
5000 Forbes Ave
Pittsburgh, Pa 15213
Phone: (412) 268-4646
EMail: tmartin@andrew.cmu.edu
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