Keysigning challenge policies/procedures

Todd Zullinger tmz at
Fri Jul 7 22:34:20 CEST 2006

Hash: SHA1

Ingo Klöcker wrote:
> On Friday 07 July 2006 16:56, Todd Zullinger wrote:
>> Could you elaborate a little on the procedure you use to generate the
>> challenges?  I'd love to have some examples of how other folks do
>> things to present to my fellow LUG members.
> My script does the following:
> For each key id that's given on the command line it first determines all 
> UIDs which are neither revoked nor expired nor have already been signed 
> by me. Then for each UID a random string is generated. I use the 
> command 
>   head -c 18 /dev/urandom | mimencode
> for this. (mimencode is part of metamail.) This challenge and the key id 
> and the UID are then inserted into a text explaining what the receiver 
> of the challenge has to do. This text is then encrypted with the key 
> corresponding to the key id. The encrypted text is then prepended with 
> another text explaining what the encrypted text is about. Finally the 
> resulting text is given to KMail together with the email address 
> (==UID). Now I only have to click on the Send button in KMail to send 
> the message.

Thank you much for this.

> (I could make KMail automatically send the messages, but I prefer to
> have a last look at them before I send them in order to check that
> everything worked correctly.)

Yeah, I understand that perfectly.  Too much automation can bite you
when you least expect it. :)

> I've attached the script.

And thank you very much for this!  It'll be very handy to have
something concrete to point others to for an example.  Between that
and the caff script in pgp-tools I've now got two nice perl examples
my fellow LUG members can check out and use or adapt.

>> Of course, but they can't sign it with the key I've been asked to
>> sign and which I verified from the key fingerprint and other owner
>> details, unless they are the proper owner of that key.
> Yes, they can if it was them who asked you to sign their key. For
> example, I could create a key with my name and your email address,
> go to a key signing party and make everybody sign the fake user id.
> And if I can intercept your mail then I can even reply to
> challenges.

But if you do this, then even encrypting the challenge wouldn't help,
as I'd be encrypting it to the key you presented to me.  It seems that
this is a problem outside the scope of what the challenge will solve.

Or am I missing something?  (I've been busy all morning fixing some
plumbing, so my mind isn't as sharp as usual -- not that I'm the
sharpest tool in the shed on a good day. ;)

Many thanks to you for indulging my questions and posting your
procedures and script!

- -- 
Todd        OpenPGP -> KeyID: 0xD654075A | URL:
Going to hell when I die would just be redundant.

Version: GnuPG v1.4.4 (GNU/Linux)
Comment: When crypto is outlawed bayl bhgynjf jvyy unir cevinpl.


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