GPG public key signing post-party automation with KMail

This past Ubucon’s key signing party was my first key signing party. One thing I noticed–signing keys after a key signing party is a boring repetitive task. Summarized from the Ubuntu wiki entry on typical key signing post-party protocol:

  1. Retrieve all public keys of key signing party participants, using gpg –-recv-key
  2. Compare the hardcopy fingerprint from the keysigning party to the fingerprint of the retrieved public keys, using gpg –-fingerprint
  3. Sign the key, using gpg –-sign Send the signed key back, either by
    • E-mail: export the key, then e-mail it to the key owner, using gpg –-export -a | mail -s “Your signed key”
    • Key server: send the key to a public keyserver, using gpg –send-keys

This is incredibly monotonous—and people have to wonder why Web of Trust-based encryption is not more popular?

The Debian signing-party package provides the utility caff to automate some of this. It’s not very friendly to “desktop” users, however:

  • it’s a CLI application
  • it requires a local MTA (/usr/sbin/sendmail in particular), or an “open” SMTP server, with no support for authenticated SMTP or SMTP/SSL
  • the configuration file syntax is Perl and confusing; there are also few examples on the Internet

You could add authenticated SMTP or SMTP/SSL support to the script, but having to know how to hack Perl definitely disqualifies caffe from being a desktop-friendly application.

So, I hacked together my own key signing party script in Python that would send signed keys back to people via KMail. To use it, create a text file listing all key IDs you wish to sign, one per line. Pipe the contents of this list into the script:

cat list-of-ids.txt |

The script will download each key, ask you to verify the fingerprint, and then sign it. It then will open a KMail composer window, pre-filled with the key owner’s e-mail address, a friendly template message (customizable in the script), and attached key. Review each e-mail to make sure it is kosher, and click send. Other than continuing to be a CLI program, I think this is much friendlier–the only manual work done is the creation of list of keys to sign, comparing fingerprints (this could be automated, but it seems in the spirit of the Web of Trust-based systems not to), and clicking send in a familiar desktop e-mail client.

Now for some notes…

It uses the DCOP automation features of KDE’s Kmail to send messages. You could similarly use Evolution and D-Bus, but I don’t use Evolution so I can’t contribute that bit of functionality. Mozilla’s Thunderbird unfortunately does not yet support any kind of automation features (as far as I know, anyway), so you’re completely out of luck if you use it.

DCOP with Python is a complete, utter, pain. The easy way to drag-and-drop boiler-plate code with kdcop did not work, as it appears the APIs have changed. A problem with KDE/Python dcopext’s module and multiple identically-named-functions sealed the deal for me and I gave up trying to use DCOP with Python, and instead settled for a hack of using the shell instead. I’m looking forward the one Linux desktop IPC protocol to rule them all, D-Bus, to debut in KDE4.

My script does not provide all the functionality of caffe. It, for example, does not encrypt the messages and their keys back to their owners. There doesn’t appear to be an easy way to do this with KMail and DCOP, so it’s a feature that will have to wait.

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