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 distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. 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. Expires July 22, 2000 Martin [Page 1]
Internet Draft Managing Sieve Scripts January 17, 2000 TTaabbllee ooff CCoonntteennttss 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 Expires July 22, 2000 Martin [Page 2]
Internet Draft Managing Sieve Scripts January 17, 2000 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 Expires July 22, 2000 Martin [Page 3]
Internet Draft Managing Sieve Scripts January 17, 2000 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. Expires July 22, 2000 Martin [Page 4]
Internet Draft Managing Sieve Scripts January 17, 2000 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. Expires July 22, 2000 Martin [Page 5]
Internet Draft Managing Sieve Scripts January 17, 2000 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 Expires July 22, 2000 Martin [Page 6]
Internet Draft Managing Sieve Scripts January 17, 2000 [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 Expires July 22, 2000 Martin [Page 7]
Internet Draft Managing Sieve Scripts January 17, 2000 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" Expires July 22, 2000 Martin [Page 8]
Internet Draft Managing Sieve Scripts January 17, 2000 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. Expires July 22, 2000 Martin [Page 9]
Internet Draft Managing Sieve Scripts January 17, 2000 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 Expires July 22, 2000 Martin [Page 10]
Internet Draft Managing Sieve Scripts January 17, 2000 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 Expires July 22, 2000 Martin [Page 11]
Internet Draft Managing Sieve Scripts January 17, 2000 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 / Expires July 22, 2000 Martin [Page 12]
Internet Draft Managing Sieve Scripts January 17, 2000 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 Expires July 22, 2000 Martin [Page 13]
Internet Draft Managing Sieve Scripts January 17, 2000 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. Expires July 22, 2000 Martin [Page 14]
Internet Draft Managing Sieve Scripts January 17, 2000 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. Expires July 22, 2000 Martin [Page 15]
Internet Draft Managing Sieve Scripts January 17, 2000 [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 Expires July 22, 2000 Martin [Page 16]