Key by Quasimondo
While planning a Keysigning Party, the organizer suggested that among the things to bring:
Some ID would also be a good idea, for those who do not already know you.
No no no.
If people don’t know you, then they shouldn’t be signing your key. If you don’t know someone, then you shouldn’t be signing their key.
Using ID of any sort is assigning trust by proxy to an “authority”. You’re no longer vouching for a person based on your own knowledge, but relying on the “authority” to provide that trust. If you’re going to rely on third-party authorities you might as well revert to a hierarchical PKI and pay lots of money to a certificate authority to assign levels of trust for you.
The point of the keysigning is to associate a key value with a real person, with no opportunity for a Man in the Middle attack [1]. It is not to verify name, address and permission to drive in Ontario.
When I sign your key it is not because the government says that you’re allowed to drive under your name, but I sign your key because I believe that you’re the same guy who drinks Jagermeister and hacks on Blackberries and hangs out at the Syrup Festival. It is based on my personal knowledge of you, and my trust in your claim that you own the GPG key with fingerprint D2CCE5EA [2].
The Web of Trust extends this, so that since I trust your identity and judgment, I’m also likely to grant some level of trust to the people you trust. After a successful keysigning party then I’m going to trust many more people because they’re all trusted by people I trust. And I’ll be trusted by more people, because they trust the people who have signed my key.
So, how do you hold a keysigning party? Here’s an excerpt from the PGP FAQ:
I’ve written complete instructions for holding a Formal Keysigning.
The comp.security.pgp FAQ
Wouter Slegers
Copyright © 1996, 1997, 1998, 1999, 2000,
2001 by Arnoud Engelfriet
Copyright © 2002 by Wouter Slegers
This FAQ is copyright © 2001 by Wouter Slegers.
It may be distributed freely in online electronic form, provided the copyright notice is left intact. Since this FAQ is always available from USENET and the PGP network, there should be no problems getting access to it. However mirrors with outdated versions can confuse the users, so I request you not to mirror this FAQ elsewhere.
[…]
Q: What’s a key signing party?
A: A key signing party is a get-together with various other users of PGP for the purpose of meeting and signing keys. This helps to extend the web of trust to a great degree, making it easier for you to find one or more trusted paths to someone whose public key you didn’t have.
Kevin Herron has an example of a keysigning party announcement page [3].
Q: How do I organize a key signing party?
A: Though the idea is simple, actually doing it is a bit complex, because you don’t want to compromise other people’s private keys or spread viruses (which is a risk whenever floppies are swapped willy-nilly). Usually, these parties involve meeting everyone at the party, verifying their identity and getting key fingerprints from them, and signing their key at home.
Derek Atkins has recommended this method:
There are many ways to hold a key-signing session. Many viable suggestions have been given. And, just to add more signal to this newsgroup, I will suggest another one which seems to work very well and also solves the N-squared problem of distributing and signing keys. Here is the process:
-
You announce the keysigning session, and ask everyone who plans to come to send you (or some single person who will be there) their public key. The RSVP also allows for a count of the number of people for step 3.
-
You compile the public keys into a single keyring, run pgp -kvc on that keyring, and save the output to a file.
-
Print out N copies of the pgp -kvc file onto hardcopy, and bring this and the keyring on media to the meeting.
-
At the meeting, distribute the printouts, and provide a site to retrieve the keyring (an ftp site works, or you can make floppy copies, or whatever — it doesn’t matter).
-
When you are all in the room, each person stands up, and people vouch for this person (e.g., “Yes, this really is Derek Atkins — I went to school with him for 6 years, and lived with him for 2”).
-
Each person securely obtains their own fingerprint, and after being vouched for, they then read out their fingerprint out loud so everyone can verify it on the printout they have.
-
After everyone finishes this protocol, they can go home, obtain the keyring, run pgp -kvc on it themselves, and re-verify the bits, and sign the keys at their own leisure.
-
To save load on the keyservers, you can optionally send all signatures to the original person, who can collate them again into a single keyring and propagate that single keyring to the keyservers and to each individual.
I’m going to have to put my key signature where my mouth is. Hopefully there will be another key signing party soon, for which I will be more prepared.
–Bob.
Yes, it is still possible to have a meatspace MitM attack if you’re signing keys for people you don’t know and relying on ID. If you’ve never met me before then it is possible that someone mugs me in the parking lot, takes my ID and wears my goofy hat. If you don’t know me you would never be able to tell the difference, and you’d be signing a key for the wrong person.
Although that’s really my PGP key, so as not to divulge the identity of innocent and unsuspecting Key Signing Party Organizers.
Sadly, Kevin Herron makes the same mistake of requiring "Positive picture ID". Please ignore that part.
Key by Quasimondo is used under a Creative Commons by-nc license.
Tags: certificate authority, Crypto, gpg, key, keysigning, keysigning party, man in the middle, party, pgp, PKI, public key infrastructure, signature, signing, trust, web of trust
Posted in PGP/GPG, privacy | 1 Comment »
PoliBlog
WatCamp
Creative Commons — Attribution — CC BY