Control message
Encyclopedia
Control messages are a special kind of Usenet
post that are used to control news server
s. They differ from ordinary posts by a header field named
There are two historical alternatives to header field
of the article to delete.
According to RFC 1036 only the author of the target message or the local news administrator is allowed to send a cancel. To verify authorization the From: line (or Sender: line, if it exists) of the cancel message must match the target article. This verification does not work well in modern day Usenet and is rarely used.
Anyway, additional hierarchy specific rules (see Breidbart Index
) allow cancelbot
s to send third-party cancels to remove spam
.
Example
Control: cancel <899qh19zehlhsdfa@example.com>
Subject: cmsg cancel <899qh19zehlhsdfa@example.com>
If the group already exists, only the status of the group is changed, i.e. whether it is moderated or nor not.
Typically newgroup messages having a correct digital signature are executed automatically. In some hierarchies (alt.*, free.*, de.alt.*) unsigned newgroup messages just serve as formalized proposal to create a new group. Objections to the proposal are then expressed with a rmgroup.
In many cases newgroup messages are archived by the Internet Systems Consortium
.
Example
Control: newgroup comp.object.moderated moderated
Subject: cmsg newgroup comp.object.moderated moderated
Typically rmgroup messages having a correct digital signature are executed automatically. In some hierarchies unsigned rmgroup messages are used to veto a preceding newgroup.
In the hierarchy de.alt.* removal and creation of groups is handled symmetrically, i.e. an unsigned rmgroup message is used as formalized proposal. Objections to the proposal are then expressed with a newgroup.
Example
Control: rmgroup comp.object.moderated
Subject: cmsg rmgroup comp.object.moderated
Example
Control: checkgroups
Subject: cmsg checkgroups
Example conforming to RFC 5537
Control: checkgroups de !de.alt #2009021301
The ihave/sendme protocol was obsoleted by NNTP.
Answering control messages with large emails can be exploited for a Denial of service attack. Thus news server
s stopped implementing sendsys long before it was declared obsolete by RFC 5537.
and E-mail
. The format provides no means of authentication
. Various extensions adding a digital signature
were developed to prevent forgeries.
For control message a special format is required since the essential information is in the header fields. Pgpcontrol was originally designed for PGP
but also works with OpenPGP.
and regional hierarchies) is done through signed control messages. Each hierarchy has unique key that is guarded by the hierarchy founders (or their successors). Most newsservers are configured to both automatically execute controls signed with the right key and ignore anything else.
Theoretically this system is also applicable to cancel messages. However, it would not only require a key pair for every Usenet user but also that the respective public key is known to every news server. Cancel-lock is much simpler, but neither commonly accepted, nor implemented in popular news servers and newsreaders.
. Instead many servers put them into pseudo newsgroups like
Google Groups
provides no means to read or write control messages. It does not even execute cancels.
The Internet Systems Consortium
archives newgroup and rmgroup together as a single file per group and checkgroups as one file per year.
Usenet
Usenet is a worldwide distributed Internet discussion system. It developed from the general purpose UUCP architecture of the same name.Duke University graduate students Tom Truscott and Jim Ellis conceived the idea in 1979 and it was established in 1980...
post that are used to control news server
News server
A news server is a set of computer software used to handle Usenet articles. It may also refer to a computer itself which is primarily or solely used for handling Usenet. A reader server provides an interface to read and post articles, generally with the assistance of a news client. A transit...
s. They differ from ordinary posts by a header field named
Control. The body of the field contains control name and arguments.There are two historical alternatives to header field
Control. They are not supported by contemporary software and forbidden according to RFC 5537. However, the traditional format of the subject line is widely used in addition to the Control header: the subject line consists of the word "cmsg" followed by control name and arguments.cancel
A cancel message requests the deletion of a specific article. The body of the Control field contains one argument, the Message-IDMessage-ID
Message-ID is a unique identifier for a digital message, most commonly a globally unique identifier used in email and Usenet newsgroups.Message-IDs are required to have a specific format which is a subset of an email address and to be globally unique...
of the article to delete.
According to RFC 1036 only the author of the target message or the local news administrator is allowed to send a cancel. To verify authorization the From: line (or Sender: line, if it exists) of the cancel message must match the target article. This verification does not work well in modern day Usenet and is rarely used.
Anyway, additional hierarchy specific rules (see Breidbart Index
Breidbart Index
The Breidbart Index, developed by Seth Breidbart, is the most significant cancel index in Usenet.A cancel index measures the dissemination intensity of substantively identical articles. If the index exceeds a threshold the articles are called newsgroup spam...
) allow cancelbot
Cancelbot
A cancelbot is an automated or semi-automated process for sending out third-party cancel messages over Usenet, commonly as a stopgap measure to combat spam.-History:...
s to send third-party cancels to remove spam
Spam (electronic)
Spam is the use of electronic messaging systems to send unsolicited bulk messages indiscriminately...
.
Example
Control: cancel <899qh19zehlhsdfa@example.com>
Subject: cmsg cancel <899qh19zehlhsdfa@example.com>
newgroup
A newgroup message is issued to create a new Usenet newsgroup. The body of the Control field contains one mandatory argument, the name of the new group. The second argument is optional. If present it consists of the keyword moderated. The body of the message typically contains tagline, charter and rationale.If the group already exists, only the status of the group is changed, i.e. whether it is moderated or nor not.
Typically newgroup messages having a correct digital signature are executed automatically. In some hierarchies (alt.*, free.*, de.alt.*) unsigned newgroup messages just serve as formalized proposal to create a new group. Objections to the proposal are then expressed with a rmgroup.
In many cases newgroup messages are archived by the Internet Systems Consortium
Internet Systems Consortium
Internet Systems Consortium, Inc., also known as ISC, is a Delaware-registered, 501 public benefit non-profit corporation dedicated to supporting the infrastructure of the universal connected self-organizing Internet by developing and maintaining core production quality software, protocols, and...
.
Example
Control: newgroup comp.object.moderated moderated
Subject: cmsg newgroup comp.object.moderated moderated
rmgroup
A rmgroup message is issued to remove a newsgroup. The body of the Control field contains one mandatory argument, the name of the group to remove.Typically rmgroup messages having a correct digital signature are executed automatically. In some hierarchies unsigned rmgroup messages are used to veto a preceding newgroup.
In the hierarchy de.alt.* removal and creation of groups is handled symmetrically, i.e. an unsigned rmgroup message is used as formalized proposal. Objections to the proposal are then expressed with a newgroup.
Example
Control: rmgroup comp.object.moderated
Subject: cmsg rmgroup comp.object.moderated
checkgroups
A checkgroups message lists all groups of a hierarchy.Example
Control: checkgroups
Subject: cmsg checkgroups
Example conforming to RFC 5537
Control: checkgroups de !de.alt #2009021301
Obsolete message types
| Name | Definition | Description |
|---|---|---|
| Ihave | RFC 850, RFC 1036, RFC 5537 | Announce arrival of particular message |
| Sendme | RFC 850, RFC 1036, RFC 5537 | Request transmission of particular message |
| Sendsys | RFC 850, RFC 1036, RFC 5537 | Request email with list of newsgroups sent to each neighbor |
| Senduuname | RFC 850, RFC 5537 | Request email with list of all uucp UUCP UUCP is an abbreviation for Unix-to-Unix Copy. The term generally refers to a suite of computer programs and protocols allowing remote execution of commands and transfer of files, email and netnews between computers. Specifically, a command named uucp is one of the programs in the suite; it... neighbors |
| Version | RFC 850, RFC 1036, RFC 5537 | Request email with name and version of Usenet software |
| Whogets | RFC 5537 | No description, just declared obsolete |
The ihave/sendme protocol was obsoleted by NNTP.
Answering control messages with large emails can be exploited for a Denial of service attack. Thus news server
News server
A news server is a set of computer software used to handle Usenet articles. It may also refer to a computer itself which is primarily or solely used for handling Usenet. A reader server provides an interface to read and post articles, generally with the assistance of a news client. A transit...
s stopped implementing sendsys long before it was declared obsolete by RFC 5537.
Header field "Approved:"
Messages of type newgroup and rmgroup are ignored unless there is an "Approved" line in the same message header. Newsservers traditionally allow only selected users to send articles with these lines. As long as there were only a handful of Usenet sites this provided sufficient protection against abuse.Digital signature
The format of "Arpa Internet Text Messages" is the common base for UsenetUsenet
Usenet is a worldwide distributed Internet discussion system. It developed from the general purpose UUCP architecture of the same name.Duke University graduate students Tom Truscott and Jim Ellis conceived the idea in 1979 and it was established in 1980...
and E-mail
E-mail
Electronic mail, commonly known as email or e-mail, is a method of exchanging digital messages from an author to one or more recipients. Modern email operates across the Internet or other computer networks. Some early email systems required that the author and the recipient both be online at the...
. The format provides no means of authentication
Authentication
Authentication is the act of confirming the truth of an attribute of a datum or entity...
. Various extensions adding a digital signature
Digital signature
A digital signature or digital signature scheme is a mathematical scheme for demonstrating the authenticity of a digital message or document. A valid digital signature gives a recipient reason to believe that the message was created by a known sender, and that it was not altered in transit...
were developed to prevent forgeries.
| Signature format | Covered data | Usage |
|---|---|---|
| PGP/INLINE | arbitrary text | NoCeM |
| PGP/MIME | MIME body parts | |
| S/MIME S/MIME S/MIME is a standard for public key encryption and signing of MIME data. S/MIME is on an IETF standards track and defined in a number of documents, most importantly RFCs. S/MIME was originally developed by RSA Data Security Inc... |
MIME body parts | |
| pgpcontrol | body and selected header fields | newgroup, rmgroup, checkgroups |
For control message a special format is required since the essential information is in the header fields. Pgpcontrol was originally designed for PGP
Pretty Good Privacy
Pretty Good Privacy is a data encryption and decryption computer program that provides cryptographic privacy and authentication for data communication. PGP is often used for signing, encrypting and decrypting texts, E-mails, files, directories and whole disk partitions to increase the security...
but also works with OpenPGP.
Hierarchy keys
Newsgroup maintenance of the main Usenet hierarchies (Big 8Big 8 (Usenet)
The Big 8 are a group of newsgroup hierarchies established after the Great Renaming, a restructuring of Usenet that took place in 1987. These hierarchies are managed by the Big 8 Management Board...
and regional hierarchies) is done through signed control messages. Each hierarchy has unique key that is guarded by the hierarchy founders (or their successors). Most newsservers are configured to both automatically execute controls signed with the right key and ignore anything else.
Theoretically this system is also applicable to cancel messages. However, it would not only require a key pair for every Usenet user but also that the respective public key is known to every news server. Cancel-lock is much simpler, but neither commonly accepted, nor implemented in popular news servers and newsreaders.
Archiving
Control messages are typically not shown in the target NewsgroupNewsgroup
A usenet newsgroup is a repository usually within the Usenet system, for messages posted from many users in different locations. The term may be confusing to some, because it is usually a discussion group. Newsgroups are technically distinct from, but functionally similar to, discussion forums on...
. Instead many servers put them into pseudo newsgroups like
control.Google Groups
Google Groups
Google Groups is a service from Google Inc. that supports discussion groups, including many Usenet newsgroups, based on common interests. The service was started in 1995 as Deja News, and was transitioned to Google Groups after a February 2001 buyout....
provides no means to read or write control messages. It does not even execute cancels.
The Internet Systems Consortium
Internet Systems Consortium
Internet Systems Consortium, Inc., also known as ISC, is a Delaware-registered, 501 public benefit non-profit corporation dedicated to supporting the infrastructure of the universal connected self-organizing Internet by developing and maintaining core production quality software, protocols, and...
archives newgroup and rmgroup together as a single file per group and checkgroups as one file per year.