Control message

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A control message is a special form of posting on Usenet . Control messages differ from normal messages by a line in the header (which also includes the sender, subject, newsgroups, date, etc.) with the keyword Control:. The rest of this line consists of the control command followed by parameters.

There are two historical alternatives to the header Control. They are not supported by contemporary software and are prohibited by RFC 5537 . The traditional form of the subject line is often used in addition to Control: the subject line consists of the word "cmsg" followed by the control command and the parameters.

Types of control messages

cancel

A cancel message is a request that can be automatically evaluated by software to delete a specific item locally. This is called canceling . The message has one parameter, the message ID of the posting to be deleted.

example 

Control: cancel <899qh19zehlhsdfa@foo.bar.com>
Subject: cmsg cancel <899qh19zehlhsdfa@foo.bar.com>

newgroup

A newgroup control is used to create a new group. The first parameter is the name of the new group. The second parameter is the optional specification of the keyword moderated. This creates moderated groups. The text of the post usually contains a short description ( tagline ), charter and a reason for setting up the group.

If the group already exists, the newgroup control only changes the status of the group (i.e. moderated or unmoderated).

In established hierarchies, newgroup messages with the correct digital signature are automatically executed. In some hierarchies ( alt.*, free.*, de.alt.*) are unsigned newgroup messages only as a formal proposal. Objections to the proposal are then expressed through an rmgroup message.

In any case, newgroup messages are archived by the Internet Systems Consortium .

example 

Control: newgroup de.soc.usenet
Subject: cmsg newgroup de.soc.usenet

rmgroup

An rmgroup control ( rm is an abbreviation for "remove") is used to delete a group.

example 

Control: rmgroup de.comp.sys.next
Subject: cmsg rmgroup de.comp.sys.next

checkgroups

A checkgroups control contains a list of all groups in a hierarchy.

example 

Control: checkgroups
Subject: cmsg checkgroups

Example according to RFC 5537 

Control: checkgroups de!de.alt #2009021301

Obsolete message types

Surname definition description
I have RFC 850 , RFC 1036 , RFC 5537 Report the arrival of a specific message
Sendme RFC 850 , RFC 1036 , RFC 5537 Request transmission of a specific message
Sendsys RFC 850 , RFC 1036 , RFC 5537 Request an email that contains a list of the groups sent to neighboring servers
Senduuname RFC 850 , RFC 5537 Request an email containing a list of all UUCP neighbors
version RFC 850 , RFC 1036 , RFC 5537 Request an email containing the name and version number of the Usenet software
Whogets RFC 5537 Declared out of date without description

The ihave / sendme protocol was made obsolete by NNTP .

Answering control messages with large e-mails can be exploited for a denial of service attack. Therefore, sendsysit was no longer supported long before it was deprecated by RFC 5537 .

Security aspects

Header "Approved:"

Control messages of the type newgroupand rmgroupare ignored if they are not provided with a header Approved:. Traditionally, news servers are configured so that only selected users are allowed to send messages with these lines. As long as there were only a handful of servers worldwide, this measure provided sufficient protection against misuse.

Digital signature

The format for "Arpa Internet Text Messages" is the common basis for Usenet and e-mail . There is no possibility of authentication . As a result, various extensions to the format to include a digital signature were developed.

Signature format Subject of the signature operation area
PGP / INLINE any text NoCeM
PGP / MIME MIME bodyparts e-mail
S / MIME MIME bodyparts e-mail
pgpcontrol Body and selected headers newgroup, rmgroup, checkgroups

Since the most important information is in the header of a control message, a special format is required. pgpcontrol was originally developed for PGP , but also works with OpenPGP .

Hierarchy key

Changes to the group inventory are carried out in the large hierarchies ( Big Eight and regional hierarchies ) with signed control messages. Each hierarchy has its own key, which is managed by the hierarchy founders or their successors. Most news servers are configured to automatically execute control messages signed with the correct key. All other control messages are ignored.

Theoretically, this procedure is also suitable for cancel messages . To do this, not only would a pair of keys exist for each Usenet user, but each news server would also have to know the respective public key. Cancel-Lock is much easier.

Archiving

Control messages usually appear illegible in the relevant newsgroup. Many news servers instead sort them into pseudo-groups like controla.

Google Groups does not provide the ability to read or write tax messages, and does not even execute Cancel Messages .

The Internet Systems Consortium archives newgroupand rmgroupcollectively in one file per group and checkgroupsin one file per year.

Individual evidence

  1. ↑ Internet News has all.all.ctlnever supported. Version 1.0 was released in 1990.
  2. ↑ "Subject: cmsg" is only described in RFC 1036 (published in December 1987), but not in RFC 850 (published in June 1983). In INN this functionality was removed in version 2.3. See INN Changes and Upgrade Information ( Memento of 21 February 2007 at the Internet Archive ).
  3. ↑ RFC 5537 , 5. Control Messages: […] The presence of a Subject header field starting with the string "cmsg" MUST NOT cause an article to be interpreted as a control message. […] Likewise, the presence of a <newsgroup-name> ending in ".ctl" in the Newsgroups header field or the presence of an Also-Control header field MUST NOT cause the article to be interpreted as a control message.
  4. ↑ RFC 1036 , Section 3.3
  5. ↑ Section 5.2.1. of RFC 5537 describes it as follows: The newgroup control message requests that the specified group be created or, if already existing, that its moderation status or description be changed. But the functionality is much older. For example, the description of the program ctlinnd (part of INN) contains the following: If the newsgroup already exists, this is equivalent to the changegroup command.
  6. ↑ * How To Write a Good Newgroup Message ( Memento of the original from April 15, 2008 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.gweep.ca
  7. ↑ Rules for setting up, changing and removing Usenet groups
  8. ↑ ftp://ftp.isc.org/pub/usenet/control/
  9. ↑ RFC 1036 , Section 3.4
  10. ↑ RFC 1036 , Section 3.7
  11. ↑ Section 3.5. of RFC 1036 contains the following clause: “This information is considered public information, and it is a requirement of membership in USENET that this information be provided on request, either automatically in response to this control message, or manually, by mailing the requested information to the author of the message. "
  12. ↑ RFC 1036 , Section “3.3. Newgroup "and" 3.4. Rmgroup ". Interestingly, this clause is missing in section “3.7. Checkgroups ".
  13. ↑ RFC 822 , published August 1982
  14. ↑ RFC 1036 , Section “2. Message Format "
  15. ↑ RFC 2822 , replaced RFC 822 in April 2001
  16. ↑ ftp://ftp.isc.org/pub/pgpcontrol/
  17. ↑ INN normally stores control messages in the pseudo group control. However, if there is a subgroup of controlthat matches the control command, the message is placed in this group.
  18. ↑ ftp://ftp.isc.org/pub/usenet/control/
  19. ↑ ftp://ftp.isc.org/pub/usenet/control/other.ctl/