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PGP Moose ========= by Greg Rose The aim of this software is to monitor the news postings of moderators of USENET newsgroups, and to automatically cancel forged messages purporting to be approved. This can be extended to the approvals of individual users to automatically cancel messages that appear without having been authorised by the user. This has (obviously) been prompted by the recent spammings and other events. This software and protocol is designed around cryptographic signatures. The protocol is designed to allow the use of different signature techniques. This implemention assumes the use of PGP signatures, but can be easily modified to use others, such as the Digital Signature Standard. PGP was chosen for its widespread availability around the world. PGP, the crux of the cryptographic software, was written by Phil Zimmermann , who otherwise has nothing to do with this. The cryptographic framework was written by Greg Rose , as were the INN news system hooks. Contents: -------- How Does It Work? The Bits: How Do You Register For The Service? Handling Multiple Moderated Groups: Possible Problems We've Forseen: Status: Obtaining, installing, configuring: The mailing list. It Really Wasn't That Hard. License Terms: Version: How Does It Work? ----------------- This document is written from the point of view of a newsgroup moderator, but individual users could also use the facility in analagous ways. When a moderator wants to protect their group from forged/unapproved postings, they should register their interest with one or more of the sites running PGP Moose by sending mail to the mailing list (see below), and pick up the submission script. As part of this process, the moderator would specify one or more PGP public keys that are allowed to approve postings. When a post comes in, and the moderator wishes to approve it, they do whatever they would normally do before actually using inews (or whatever) to post the message. As their last action, they run the PGP Moose Approval program "pmapp". This inserts a special header which looks like this: X-Auth: PGPMoose V1.0 PGP sci.crypt.research iQBVAgUBL1/Kg2zWcw3p062JAQEYIgH/Xyrz6LaGG+fHaSxoexMECovzkIoADrQx l73IXlUQEIoFl5jnDBBdHVvqTMEPS0118ytYVQZoQrdStuXB9Oc9gQ== =azqs If there are multiple moderated newsgroups, there might be multiple X-Auth: headers, one for each group that has requested assistance from the PGP Moose daemon. In this example you can see that the authentication carries the name of the authenticating program, a protocol version number, an identifier of the type of digital signature (currently only PGP) and the name of the newsgroup in question. These, as well as the From:, Subject: and Message-Id: lines, the list of newsgroups, and the non-blank lines of the message itself, are used as input to the PGP program to generate a signature. The lines of the message body are preprocessed in a way that is meant to render harmless any mangling that a typical news system might do to the article. The article itself is not changed, only the input to the signature generation. If a news system subsequently mangles the article in a "normal" way, for instance by inserting a ">" in front of a line starting with "From", it will still pass the signature check. The list of newsgroups must be handled specially, so that an article posted to multiple moderated controlled newsgroups can be appropriately handled. See below for a more detailed treatment of the issues of posting to multiple moderated newsgroups. The PGP signature is then inserted into the X-Auth: header, mostly so that it won't interfere with, or be confused with, any signature in the body of the message. Anybody can check whether the message has been modified in any significant way, simply by running the PGP Moose Approval Checking program "pmcheck". More importantly, though, the sites running the PGP Moose Checking Daemon will be doing this automatically for every posting to the registered newsgroups, or from the registered users. And, if a posting fails the checks, it may be automatically cancelled, and a notification sent to the moderator. (Initially, the automatic cancellation will be disabled, since it is a pretty powerful sledgehammer, but that is the intention anyway.) This software is made freely available for just about any purpose, but I've retained copyright so as to keep some semblance of involvement. See the last section of this file. The Bits: --------- The approval and checking part of the PGP Moose consists of a number of Bourne Shell scripts calling standard Unix utilities and PGP. I could have used perl more elegantly, but this stuff is marginally more widely available. If there are Unix version dependencies, they should be considered to be bugs and I'll happily attempt to remove them. pmapp usage: pmapp [newsgroup|user] [file] This script takes the not-yet-posted article, specified either by filename or from standard input, and creates a signature for it, which is then inserted in the X-Auth: header. The article, ready for posting, appears on the standard output. In the configuration section at the top of the script, the moderator may build in the default name of the newsgroup or user, PGP User Id to be used for the signature, and the corresponding password. This is simply for convenience, since spammers are not so likely to go cracking the computer to get the password, and it is a relatively simple matter to generate a new user if it is, indeed, compromised. For the paranoid, like myself, if the password is not configured into the script it is read from the terminal instead. pmcheck usage: pmcheck [newsgroup|user] [article] This script takes the article, specified either by filename or from standard input, and checks that the X-Auth: line is something it considers to be correct and that the article has not been tampered with. Pmcheck returns successfully if everything checks out. Otherwise it will return failure and issue one of a number of error messages, for example: Posting for $NEWSGROUP not approved with PGP Moose. Invalid designated signature from $GROUP No public key for signature $GROUP Signature doesn't match $FILE for $GROUP '$SIG' not accepted for $GROUP. Anybody can run pmcheck. It behaves slightly differently depending on the existence of a file called (by default) PGP_Moose_accept, and the presence or absence of a newsgroup or user argument. This file, if it exists, should contain lines with a newsgroup name or email address, some whitespace, and the PGP User Id approved by the moderator or user (usually made up specifically for this purpose). Multiple lines for the same newsgroup/user are allowed. For example: sci.crypt.research moderator sci.crypt.research moderator ggr@sydney.sterling.com Greg's News If such a file exists, and a specific newsgroup or user is specified, pmcheck is silent if all is well, and issues the last of the error messages above if everything else was all right but the signature was from the wrong person. There must, in this case, be a signature applying to the designated newsgroup or user. Without such a file, or if no specific newsgroup or user is given, all the signatures in the article are checked. In this case it is not considered an error if the signature cannot be checked due to a missing public key. If each signature is otherwise valid you will get a message like: Valid signature from '$SIG'. In any case, if there is a problem with a signature mentioned in the PGP_Moose_accept file, it will be reported and an error status will be returned. pmcanon pmnewsgroups These two scripts are used by pmapp and pmcheck to recreate the exact input for the signature, and to extract the list of newsgroups in the header, respectively. More documentation is in their manual pages. The PGP Moose checking daemon is packaged separately, as there would not seem to be a lot of value in having too many people running it. Accordingly, I was less precise in making it run absolutely everywhere. It requires the Korn shell or equivalent, and perl, and currently only interfaces to INN. I expect it would be easy to interface it to CNews, but I don't have one. pmdaemon Runs pmcheck to check the X-Auth: header for each controlled newsgroup for each article that arrives in an appropriate newsgroup. Mail is sent about any errant articles, and automatic cancellation may be enabled. pmcancel prepares a cancellation message based on the headers of another message. When (if) I get a chance, I will create mail server scripts that allow moderators who are not using Unix to use these facilities. The first allows a moderator to mail a PGP signed copy of the article to be posted. The server will then verify that the moderator sent it, and post it with a (different but corresponding) approval. The second will accept an article and return something that you can check the signature on. Either way, any moderator will still need PGP. How Do You Register For The Service? ------------------------------------ Ahhh, this is the hard part. After all, it would be pretty undesirable if someone, meaning well, took any old body's word for it that some important moderated group should start working this way, before the moderator was able to start approving postings. A great way to hijack a newsgroup. Similarly for hijacking some other user's postings (tempting though it might be :-). Another possibility is that someone, having seen what the valid signature looks like, simply creates a whole new PGP key that happens to have the same PGP User ID. Then they can sign and post stuff too. The solution to both of these problems is the classical one for public key systems. You need either a certifying authority or the PGP Web of Trust. We're using the Web of Trust. If you don't understand about PGP and the Web of Trust, go away now and come back after you really do understand it. For each newsgroup that wants to utilise this program, the moderator will have to create a special PGP key pair (preferably 512 bits to keep the X-Auth: down to two full lines), and sign it. They must then establish a path of trust to someone who is running the PGP Moose server. It will be up to the administrator of that server to make sure that only trusted moderators' keys ever get into the server's keyring. THERE CAN BE NO SHORTCUTS TO THIS PROCEDURE. Otherwise we are all back where we started. In the case of an individual user, again you should establish this verification path to one of the administrators of the PGP Moose service. Contact me for the time being to mutually figure out how to do this. Handling Multiple Moderated Groups: ---------------------------------- When I first proposed this tool, I was under the impression that postings to multiple moderated groups was an abberation that should be stamped out. This turns out not to be the case, and revisions to support this have been the cause of some delay in the deployment of this tool. When the news system sees that an article has been posted to one or more moderated groups, it checks for an Approved: header. If the header exists, the article is accepted and processed normally, otherwise it is mailed to the moderator of the first moderated newsgroup mentioned in the Newsgroups: header. There seem to be three cases of interest. The trivial case, and the most normal one, is that there is only one moderated newsgroup mentioned. The moderator approves the posting, and it is done. The next, and probably most important, case, is when a moderator wants to cross-post a FAQ to their own group, as well as news.answers (for example). In this case their approval counts for both groups, so they can insert the Approved: header and post away. Presumably the other groups are not under the control of the PGP Moose Daemon. In this case the moderator can just go ahead and put in the Approved: header, and save themself and pmapp a lot of time. It will be passed right through. The other case is harder to get right. This is when the article really is meant to be posted to two (or more) unrelated moderated newsgroups. Now, if the first moderated group's moderator approves the posting, the other ones never hear about the article, at all. If this second group is controlled by the PGP Moose an automatic cancel will be generated. So it becomes very important for the moderators to do what they should have been doing already, namely forward the article to the next moderator. This tool can't help people who don't use it, but it provides some support for those who do. The approval script checks whether there are any moderated newsgroups left that don't have X-Auth: headers for them. If there are none left, an Approved: header is inserted and the article gets posted. Otherwise, it issues a warning, and re-orders the newsgroups header with a newsgroup which is moderated but has no X-Auth: line at the start. When the article is posted, the news system will forward it to the moderator of the (new) first moderated group. If all moderators are sensible, and check for moderated newsgroups in this fashion, the mess should sort itself out and the last moderator will go ahead and post it. A warning nessage to the subsequent moderator NOT to change the article is also inserted, since such a modification would invalidate the previous signatures.. To ease this process, a second type of X-Auth: header is supported. this has the form: X-Auth: None ... Newsgroup The important fact about this is that the newsgroup appears last on the line, allowing a sort of partial approval, from moderators who don't use the PGP Moose. The Newsgroups: line is split into a sorted list of newsgroups for the purpose of generating the digital signature. Note that this means that once an article has been approved and authenticated by one moderator, it cannot be altered in any way by a moderator of a subsequent group, including altering the set of newsgroups mentioned in the Newsgroups: header, the body of the posting, or the other headers mentioned above. Possible Problems We've Forseen: -------------------------------- If an article is truly mangled e.g. by truncation, it will fail the authentication and be cancelled. Until it is demonstrated otherwise, this is assumed to be a rare and minor problem. When a cancel is issued, mail is sent to the moderator of the group telling them, and they can tell us if it becomes a problem. (In the initial deployment we expect that no automatic cancels will actually be generated, only the notification mail will be sent.) Currently the signature produced is assumed to be a PGP version 2.6 compatible one. Obtaining, installing, configuring: ----------------------------------- I regret that I don't have a public ftp site, but I do have a web page where you can get a compressed tar archive of the approval code. It is off my home page. It is hard to talk in detail about installation and configuration, since many users are not in charge of their own news server configuration. In my case, I run all of the things out of a subdirectory of my home directory. The only thing outside this area which must be changed is the INN newsfeeds file, if you are running the checking daemon. So, get the distribution file as above and unpack it whereever you want it to live. There are configuration sections at the top of pmcheck, pmapp and pmdaemon. I like to think that they are relatively self-explanatory. One of the harder decisions is whether to use a separate keyring for PGP Moose applications or not. It is very strongly recommended that you do, if you are going to run the PGP Moose checking daemon, as the keyring files will need to be readable by the userid which INN runs under (usually "news"). Most of these options can also be overridden by environment variables or command arguments, so it is possible to leave the scripts unmodified and simply put a wrapper around them (which is what I do). In the case of pmapp, the newsgroup or user that the authentication applies to can be specified on the command itself; The PGP user id and password, and the Approved: header's contents, can be specified by environment variables PMUSER, PMPASSWORD and APP, respectively. For pmcheck, the important one is the name of the configuration file specifying which signatures are valid for which newsgroups or users. Pmdaemon runs from INN, and needs some special care to set it up. "news" needs access permission to the directory and files for PGP Moose, and also read permission on the public keyring. Note that PGP creates keyrings with only owner permissions. The search path is rarely correct, and should be set at the top of the pmdaemon script. There are also a number of file names and mail addresses, but the comments should be clear enough. Lastly, you want to incorporate pmapp in your moderation script and possibly your posting script. In my case, the last line of my posting script basically said /usr/local/news/inews -S -h regarding how to donate. You can do it over the net using PGP! I probably also should thank the many people who have worked hard to bring encryption back out of the black chambers. Some names which directly come to mind are Diffie, Hellman, Merkle, Rivest, Shamir, Adelman, Lai, Massey, and probably many others. Share and Enjoy! License Terms: ------------- This software is copyrighted by Greg Rose, RoSecure Software, and other parties. The following terms apply to all files associated with the software unless explicitly disclaimed in individual files. The authors hereby grant permission to use, copy, modify, distribute, and license this software and its documentation for any purpose, provided that existing copyright notices are retained in all copies and that this notice is included verbatim in any distributions. No written agreement, license, or royalty fee is required for any of the authorized uses. Modifications to this software may be copyrighted by their authors and need not follow the licensing terms described here, provided that the new terms are clearly indicated on the first page of each file where they apply. IN NO EVENT SHALL THE AUTHORS OR DISTRIBUTORS BE LIABLE TO ANY PARTY FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OF THIS SOFTWARE, ITS DOCUMENTATION, OR ANY DERIVATIVES THEREOF, EVEN IF THE AUTHORS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. THE AUTHORS AND DISTRIBUTORS SPECIFICALLY DISCLAIM ANY WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT. THIS SOFTWARE IS PROVIDED ON AN "AS IS" BASIS, AND THE AUTHORS AND DISTRIBUTORS HAVE NO OBLIGATION TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS. Version: ------- @(#)README 1.7 (PGPMoose) 98/11/26