pgpverify - cryptographically verify Usenet control messages

pgpverify

The pgpverify program reads (on standard input) a Usenet control message that has been cryptographically signed using the signcontrol program. pgpverify then uses the pgp program to determine who signed the control message. If the control message was validly signed, pgpverify outputs (to stdout) the User ID of the key ID that signed the message.

The pgpverify program takes no options.

pgpverify returns the follow exit statuses for the following cases:

0

The control message had a good PGP signature.

1

The control message had no PGP signature.

2

The control message had an unknown PGP signature.

3

The control message had a bad PGP signature.

255

A problem occurred not directly related to PGP analysis of signature.

David C Lawrence <tale@isc.org>

pgpverify does not modify or otherwise alter the environment before invoking the pgp program. It is the responsibility of the person who installs pgpverify to ensure that when pgp runs, it has the ability to locate and read a PGP key file that contains the PGP public keys for the appropriate Usenet hierarchy administrators.

pgp(1)

Historically, Usenet news server administrators have configured their news servers to automatically honor Usenet control messages based on the originator of the control messages and the hierarchies for which the control messages applied. For example, in the past, David C Lawrence <tale@uunet.uu.net> always issued control messages for the "Big 8" hierarchies (comp, humanities, misc, news, rec, sci, soc, talk). Usenet news administrators would configure their news server software to automatically honor newgroup and rmgroup control messages that originated from David Lawrence and applied to any of the Big 8 hierarchies.

Unfortunately, Usenet news articles (including control messages) are notoriously easy to forge. Soon, malicious users realized they could create or remove (at least temporarily) any Big 8 newsgroup they wanted by simply forging an appropriate control message in David Lawrence's name. As Usenet became more widely used, forgeries became more common.

The pgpverify program was designed to allow Usenet news administrators to configure their servers to cryptographically verify control messages before automatically acting on them. Under the pgpverify system, a Usenet hierarchy maintainer creates a PGP public/private key pair and disseminates the public key. Whenever the hierarchy maintainer issues a control message, he uses the signcontrol program to sign the control message with the PGP private key. Usenet news administrators configure their news servers to run the pgpverify program on the appropriate control messages, and take action based on the PGP key User ID that signed the control message, not the name and address that appear in the control message's From or Sender headers.

Thus, using the signcontrol and pgpverify programs appropriately essentially eliminates the possibility of malicious users forging Usenet control messages that sites will act upon, as such users would have to obtain the PGP private key in order to forge a control message that would pass the cryptographic verification step. If the hierarchy administrators properly protect their PGP private keys, the only way a malicious user could forge a validly-signed control message would be by breaking the RSA encryption algorithm, which (at least at this time) is believed to be an NP-complete problem. If this is indeed the case, discovering the PGP private key based on the PGP public key is computationally impossible for PGP keys of a sufficient bit length.

<URL:ftp://ftp.isc.org/pub/pgpcontrol/> is where the most recent versions of signcontrol and pgpverify live, along with PGP public keys used for hierarchy administration.