Authentication of Usenet Group Changes

This document addresses a method for the authentication of the special types of Usenet articles that are used to maintain the namespace of Usenet groups. A basic familiarity with what the Usenet control message types "newgroup", "rmgroup" and "checkgroups" do is assumed; this is not a tutorial in namespace administration.

Usenet articles are notoriously easy to forge, and control messages are no exception. Since administrators often want to have their news systems automatically honor requests from some particular people to add or remove newsgroups, it is risky to trust the From: and Sender: headers to identify the real sender of a message, as has historically been done. Thus a system using Philip Zimmerman's Pretty Good Privacy® (PGP® ) was developed to provide a more secure means of authenticating the sender of a control message.

Unlike traditional PGP authentication of messages, which just verifies that the contents of the body of a message are unchanged from when it was digitally "signed", this system also needed to sign a few headers of the control message to verify the action to be taken and to guard against certain other pitfalls. Another goal was to make the signature as unobtrusive as possible and require minimal changes to existing software in order to work.

How to Verify Control Messages

Listed below are the steps you need to take to enable PGP authentication of control messages on your system.

Here is the short and simple version for someone who feels confident hacking around the news system and doesn't like to read a lot:

Get and configure the software:
- ftp://ftp.uu.net/networking/news/misc/pgpcontrol/pgpverify
- ftp://ftp.uu.net/networking/news/misc/pgpcontrol/server-patches/
Add maintainers' PGP public keys to the news system key ring.
Enable verification through the news system authorization system.

INN:
Use the action verify-pgp_userid (possibly appended =logfile) in control.ctl.
Other systems:
Sorry, not implemented yet.
Test pgpverify. If you have the news.announce.newgroups key in your key ring, run ftp://ftp.uu.net/networking/news/misc/pgpcontrol/sample.control through pgpverify on stdin. It should spit out the string "news.announce.newgroups" on stdout.

Here is a more verbose version of the instructions:

Get the software.
There are two pieces of code that will need to be added to a news server to make use of this authentication system: a stand-alone script that verifies an article is what it says it is, and a patch to hook it into the news server's processing of control messages.
The stand-alone program, ftp://ftp.uu.net/networking/news/misc/pgpcontrol/pgpverify, is a Perl script that should work with Perl version 4 and up. (I have not tested it with earlier versions.) It does not contain any code making it dependent on any particular news server software.
ftp://ftp.uu.net/networking/news/misc/pgpcontrol/server-patches/ has patches (currently "a patch" is more correct) for hooking the system into existing news server software. Choose the one for your system from the list below.
- INN version 1.4sec
- INN version 1.4unoff4
I regret that I do not have the time to develop more patches, but I will gladly add patches for other systems to this page as they are made available to me. I am particularly interested in getting patches for C News version CR.E. The INN version 1.4sec patch will apply to all INN "unoff" versions, albeit with a little bit of fuzz.
Install it in your news system.
First you must ensure that the absolute paths to perl and to pgp are correct in the first few lines of the pgpverify program. No other configuration of options or pathnames should be needed.
Next, the following steps assume, solely for the sake of making it easy for me to write a simple recipe, that you have copied pgpverify and the patch for your system to your news server as /tmp/pgpverify and /tmp/pgpcontrol.pch respectively. I have tried to format this so that you should be able to cut and paste any of the lines in italics directly to your shell.
- If you are running INN:
```
cd to the executable program directory that has ctlinnd
mv /tmp/pgpverify pgpverify

cd to the root of your INN source tree 
cd site
patch < /tmp/pgpcontrol.pch
make install
```
  It has been reported to me that at least one AIX system has problems with patch not applying the last section of parsecontrol.pch. If you run AIX, double check it and apply by manually editing, if necessary.
- If you are running some other system:
  You're out of luck until someone writes a patch and instructions for your system and makes it available to me for redistribution.
Enable verification for the hierarchies that interest you.
To verify messages, you must have a PGP public key for each signer that you wish to trust. It should be entered in a key ring that is accessible to the user-id that runs the news system by running pgp -ka on a file containing the key to add. For example, at a site that runs the news server software as news, the following command run by the news user-id should add the key bounded by BEGIN and END "PGP PUBLIC KEY BLOCK" lines in the file /tmp/key to the default key ring that would be used for authentication:
```
pgp -ka /tmp/key
```
As a general policy rule, control message signers will not use their control message keys to introduce other keys, so when PGP asks you a question similar to, "Would you trust this user to act as an introducer and certify other people's public keys to you?" answer that you would not.
After you have added the appropriate key to your key ring, you need to tell the news software to validate the control messages received. As implemented, the system will perform the requested action if the message can be authenticated and it will mail the message to the news system administrator if it cannot. Clearly there are other possible actions that could be implemented, but I wanted to keep the patches minimal. Future releases of the server software will probably have increased flexibility.
- If you are running INN:
  Automatic processing of control messages is handled by control.ctl, which you edit in the same site subdirectory where you patched parsecontrol. control.ctl has several lines at the beginning of it that describe the format of the file, and there is an even longer control.ctl(5) manual page. To enable PGP verification in addition to the normal authorization done by control.ctl, use the action verify-pgp_userid in the fourth field.
  For example, if you trust tale@uunet.uu.net to manage groups in the "Big 8" hierarchies, you could have lines like these (but don't use the backslash continuation, which I have used here for readability; keep it all on one line):
```
newgroup:tale@uunet.uu.net:\
comp.*|humanities.*|misc.*|news.*|rec.*|sci.*|soc.*|talk.*:\
verify-news.announce.newgroups
rmgroup:tale@uunet.uu.net:\
comp.*|humanities.*|misc.*|news.*|rec.*|sci.*|soc.*|talk.*:\
verify-news.announce.newgroups
checkgroups:tale@uunet.uu.net:\
comp.*|humanities.*|misc.*|news.*|rec.*|sci.*|soc.*|talk.*:\
verify-news.announce.newgroups
```
  Additionally, if you like the logging feature available with the action doit=logfile, you can get the same logging by using verify-pgp_userid=logfile.
- If you are running some other system:
  You're out of luck until someone writes a patch and instructions for your system and makes it available to me for redistribution.
Test the system.
Get ftp://ftp.uu.net/networking/news/misc/pgpcontrol/sample.control and save it to a file on your system; /tmp/sample.control will be used for this example. You'll use it to make sure things will work as expected.
To verify the control message, you will need the key for news.announce.newgroups and authorization in your news system for tale@uunet.uu.net to automatically perform "newgroup". Go ahead and enable it for the test even if you don't want to really allow this, because it is easy enough to rescind after the test by editing the control message authorization file and removing the key with pgp -kr news.announce.newgroups.
You can check that the pgpverify part of the system will work properly simply by feeding it the sample control message on stdin:
```
pgpverify < /tmp/sample.control
```
If if could run pgp and find the correct key in the default key ring, the string news.announce.newgroups should be printed. The exit status of the script, found in most shells with the command echo $? as the next command after pgpverify, should be 0 (zero).
If it doesn't work and you've tried and tried to figure out why, email me a complete description of the problem you are having and how you have tried to remedy it. At a bare minimum, your mail should include a copy of the message you are trying to verify, a typescript of the attempted execution, and the output of pgp -kc and pgp -kvc news.announce.newgroups.
When pgpverify passes its test, use the appropriate procedure below for you news server to verify the authorization system.
- If you are running INN:
  First, cd to the directory where parsecontrol is installed. Then execute the following four lines, in order, as the user who owns the news system:
```
/bin/sh
PROG=newgroup
set -- tale@uunet.uu.net "" /tmp/sample.control
(. ./parsecontrol "$@"; echo $ACTION)
```
  If the message verified correctly, the echo command should output doit; otherwise, verification failed and the output should be mail.
  Edit /tmp/sample.control and change all occurences of newusers to newgroups. Then repeat the parsecontrol and echo lines. This time verification should fail.
- If you are running some other system:
  You're out of luck until someone writes a patch and instructions for your system and makes it available to me for redistribution.

Frequently Asked Questions

How come this presumably valid messages doesn't check out with pgpverify?

You don't have the latest version of pgpverify, which fixed whatever bug is causing authentication of the message to fail.
You don't have your PGP configuration files and keyrings in the default path used by pgp and PGPPATH is not correctly set in your environment. Either move your PGP directory to the default location or set the $ENV{'PGPPATH'} line in pgpverify. (Warning: some INN versions set $HOME to _PATH_NEWSLIB, so this might be the source of your trouble.)
You don't have the correct key for the user that signed it in your key ring.
You are using a non-English version of pgp, set up with a "Language = " line in your PGP config.txt file. This means pgpverify can't find the string it is looking for in the pgp output. pgpverify tries to overcome a non-English language specification by setting LANGUAGE in the environment before calling pgp, but pgp overrides the runtime environment with the config.txt variables.
You cut-and-pasted the message in your window system, which converted the tab characters in the original message into spaces in the message you are trying to decode. Having this handled completely correctly by the signing/verifying code is harder than you might first think.
You are running pgpverify on a saved copy of the article that includes an extraneous trailing newline, such as might be inserted by saving the message from a mail handler or news reader, that was not present in the original message.
You cut-and-pasted the sample INN control.ctl lines above and left the continuation lines in, instead of joining each group of three physical lines comprising one logical line to just one physical line.

List of PGP Public Keys for Newsgroup Administration

This is a list of keys known to be used for maintaining various parts of the newsgroup namespace. They are listed alphabetically by the hierarchies they are used for, along with the email address they are sent by and the pgp key userid of the signature (both for use in control.ctl). The group that people should follow if they are interested in tracking announcements about the hierarchy is also listed. The "Check also" references point to locations that should have identical public key blocks; it is best if you confirm the block listed here by checking against the others.

The existence of key here only means that I, David Lawrence, trust the person who uses it to be a responsible maintainer of that particular hierarchy of groups. You are solely responsible for deciding whether you will use the keys here at your own site.

clari

Control message sender: cl*@clarinet.com
(But see http://www.clari.net/tech/inn.html#signing )
Key User ID: ClariNet.Group
Administrative group: clari.net.admin
Check also:

http://www.clari.net/tech/clarikey.txt

comp, humanities, misc, news, rec, sci, soc, talk

Control message sender: tale@uunet.uu.net
Key User ID: news.announce.newgroups
Administrative group: news.announce.newgroups
Check also:

ftp://ftp.uu.net/usenet/news.announce.newgroups/PGP.PUBLICKEY
pgp-public-keys-beta@pgp.ai.mit.edu ("Subject: GET 0xB88DA9C1", empty body)

de

Control message sender: moderator@dana.de
Key User ID: de.admin.news.announce
Administrative group: de.admin.news.announce
Check also:

ftp://ftp.thur.de/pub/people/lutz/pgpnews/German/PGPKEYS
pgp-public-keys@pgp.ai.mit.edu ("Subject: GET 0xD3033C99", empty body)

fr

Control message sender: control@usenet.fr.net
Key User ID: fr.announce.newgroups
Administrative group: fr.announce.newgroups
Check also:

pgp-public-keys-beta@pgp.ai.mit.edu ("Subject: GET 0x382B64FD", empty body)

humanities

See the comp hierarchy entry.

misc

See the comp hierarchy entry.

news

See the comp hierarchy entry.

rec

See the comp hierarchy entry.

sat

Control message sender: satgroup@endicor.com
Key User ID: satgroup@endicor.com
Administrative group: sat.usenet.config
Check also:

send-satgroup-pubkey@endicor.com (Subject: and body don't matter)
pgp-public-keys@pgp.ai.mit.edu ("Subject: GET 0x98690EE9", empty body)

sci

See the comp hierarchy entry.

soc

See the comp hierarchy entry.

talk

See the comp hierarchy entry.

uk

Control message sender: control@usenet.org.uk
Key User ID: uk.net.news.announce
Administrative group: uk.net.news.announce.config
Check also:

pgp-public-keys@pgp.ai.mit.edu ("Subject: GET 0x21F2F1D9", empty body)

Signing Control Messages

If you are responsible for sending control messages about authorized changes to a newsgroup hierarchy, then ftp://ftp.uu.net/networking/news/misc/pgpcontrol/signcontrol will sign your control messages so that pgpverify can authenticate them. It is a Perl script that requires Perl version 5 or higher to work. It has several configuration parameters that should be reviewed before use.

When establishing a PGP key and control message sender, please use tokens that are not tied to a particular individual. This makes it easier to transfer the administrative responsibility when it finally comes time. (The all-too-common "tale@uunet.uu.net" sender is still used for control messages because of its legacy in the installed server base; I would prefer to use newgroups-request@uunet.uu.net.) Please also do not sign other keys with the key that is used for control messages.

If you will be using this script to sign control messages, please let me know the hierarchy that you are responsible for maintaining and the information that you would like to appear in the List of PGP Public Keys for Newsgroup Administration.

How to Get PGP

Information about obtaining PGP can be found in the Where to get the latest PGP FAQ article, posted regularly in the alt.security.pgp newsgroup.

How to Get Perl

Information about obtaining Perl can be found in the comp.lang.perl.* FAQ 1/5 - Availability article, posted regularly in the comp.lang.perl.misc newsgroup.

Last modified: 30 October 1996

David C Lawrence
tale@uunet.uu.net