[linux-elitists] GPG luser rant

Joey Hess joey@kitenet.net
Fri Apr 13 01:25:58 PDT 2001


Karsten M. Self wrote:
>   - A cogent argument for why signing mail is a Good Thing®.

You may notice that I've not signed this mail. While I agree on most if
not all of the technical points and even with a great deal of the
background reasoning, I disagree on one central point: I don't believe
that signing every mail, or even most of your mail, serves any useful
purpose[1]. Instead, it dilutes the value of the occasional signed mail.


Let me digress and explain the security arrangements that one of my most
paranoid friends uses when he gpg signs something:

1. Check that noone except he and his wife are in the house, and that
   whatever outdoor security system he has is armed and doesn't detect
   anyone nearby.
2. Unlock his safe, and remove the CD containing his private key and
   a minimal linux system.
3. Disconnect all network cabling.
4. Hard reboot his computer onto this CD, mount the hard drive, and sign
   the document.
5. Remove the CD, replace it in the safe, boot back up into standard
   mode, get back on the network.

Well, while not perfect, that's pretty secure. It well illistrates the
maxim that security equates to inconvenience. My friend does this perhaps
once or twice a week, when he has need to send a document[2] at this level
of security. When I see a signed item from him, I *know* it's from him.

Compare with my reaction when I see a signed mail from another (slightly
hypothetical) friend, who I know keeps his private key on not just one, but
multiple networked machines, as well as an often physically insecure laptop 
that I've even had root on before. He also uses an environment variable to 
hold his key's passowrd, so he need not type it in every time. He can
easily sign *everything*, and well, that sig is probably from him, but if
things go south, I may need to resort to out of band communication and
shared secrets to be sure.


My next point has elements of FUD, but, I fear, elements of truth too.
Back in world war two, when crypto was fairly new, the worst way to
destroy the usefullness of a cryptographic code was to use it
incessantly, letting your enimy build up a large archive of data. They
could then brute force crack it, or failing that, pounce on your first
mistake and have a large body of data to work with. While current
cryptosystems have a much sounder theoretical grounding, I firmly believe
they will still be cracked one way or another, and it may well turn out
that the more data you have, the easier it is to crack a given key. (This
is certianly true for recently cracked systems, suce as WEP.)


And with the FUD out of the way, I have one more reason to prefer to use
signed and encrypted mail sparingly. When I do sign something, I want it
to stand out like a beacon:

	Joey Hess said this. He meant it, 100%. Take notice. 

Most of my email is much more at the level of a telephone conversation,
where sure, the guy on the other end of the line could be a clever
imitation, but if he is, you'll find out when you're out to lunch with
him next Wednesday.

-- 
see shy jo

[1] Except for raising public awareness.
[2] Or more likely, a signed peice of code.



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