Weblog entry #60 for dkg

Avoiding erroneous OpenPGP certifications
Posted by dkg on Tue 23 Mar 2010 at 02:44

i'm aware that people don't always take proper measures during mass OpenPGP keysignings. Apparently, some keys even get signed with no one at the keysigning present speaking for that key (for example, if the key was submitted to the keysigning via online mechanisms beforehand, but the keyholder failed to show up).

Unverified certifications are potentially erroneous, and erroneous certifications are bad for the OpenPGP web of trust. Debian and other projects rely on the OpenPGP web of trust being reasonable and healthy. People should make a habit of doing proper verifications at keysignings. People who make unverified certifications should probably be made aware of better practices.

So for future keysignings, i may introduce a key to the set under consideration and see what sort of OpenPGP certifications that key receives. I won't pretend to hold that key in person, won't speak for it, and it won't have my name attached to it. But it may be on the list.

Depending on the certifications received on that key (and the feedback i get on this blog post), i'll either publish the list of wayward certifiers, or contact the certifiers privately. Wayward certifiers should review their keysigning practices and revoke any certifications they did not adequately verify.

Remember, at a keysigning party, for each key:

  • Check that the fingerprint on your copy exactly matches the one claimed by the person in question
  • Check that the person in question is actually who they say they are (e.g. gov't ID, with a photo that looks like them, with their name matching the name in the key's User ID)
  • If the fingerprints don't match, or you don't have confidence in the name or their identity, or no one stands up to claim the key, there's no harm done in simply choosing to not certify the user IDs associated with that key. You don't even need to tell the person you've decided to do so.
  • Take notes in hard copy. It will help you later.

After the keysigning, when you go to actually make your OpenPGP certifications:

  • Make sure you have the same physical document(s) that you had during the keysigning (no, downloading a file from the same URL is not the same thing)
  • Use your notes to decide which keys you actually want to make certifications over.
  • Explicitly check the fingerprints of the fetched key before you make any certification over any of its User IDs. If the fingerprint doesn't match, discard it and move on (you might want to also contact the person whose key it is to let them know).
  • If a key has several user IDs on it, and some of them do not match the person's name, simply don't certify the non-matching user IDs. You should certify only the user IDs you have verified.
  • If a key has a user ID with an e-mail address on it that you aren't absolutely sure belongs to the person in question, mail an encrypted copy of your certification for that User ID to the e-mail address in question. If they don't control that e-mail address, they won't get the certification, and it will never become public. caff (from the signing-party package) should help you to do that.

Feedback welcome!


Comments on this Entry

Posted by ajt (195.112.xx.xx) on Wed 24 Mar 2010 at 21:22
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We use the following policy in our LUG: www.hants.lug.org.uk/cgi-bin/wiki.pl?LinuxHints/KeySigning

"It's Not Magic, It's Work"

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Posted by dkg (216.254.xx.xx) on Tue 27 Apr 2010 at 17:46
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Adam, that page appears to be compromised right now.

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Posted by ajt (195.112.xx.xx) on Tue 27 Apr 2010 at 18:04
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Yup, we changed wiki and have not put back in place all the anti-spam provisions.

Thanks for the heads up.

"It's Not Magic, It's Work"

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