What is the benefit of signing an encrypted email
Robert J. Hansen
rjh at sixdemonbag.org
Wed Jan 12 22:09:13 CET 2011
On 1/12/2011 11:24 AM, Daniel Kahn Gillmor wrote:
> "look -- here is Mr. X claiming that he is going to poison the
> reservoir. Please take this seriously, and note that it could only have
> come from Mr. X because it is signed with his key."
Mr. X has a conspirator, Ms. Y. Mr. X deliberately avoids installing an
OS patch so that Ms. Y can pwn the box. Now that you've made this
accusation against Mr. X, Mr. X reveals "hey, my box was cracked! I've
been rooted and I've been sending out signed emails without my
knowledge! How /dare/ you impugn me without having all the facts!"
Or, a less contrived example: imagine that Mr. X is a stockbroker. He
conspires with Ms. Y to pwn the box. You receive a signed message from
Mr. X saying, "I want to buy 1000 shares of Yoyodyne from you at
$10/share." On the basis of this, you send him 1000 shares. Yoyodyne
immediately tanks. A week later Mr. X returns. "Hi, I was off in Bali
on a beach sipping mai tais. Anything interesting happen while I was
gone? What the heck? My box got pwn3d! I didn't place that order!
Ack! I'm so sorry about this. Here, take your 1000 shares back, and
I'll take my $10,000 back." (Of course, if Yoyodyne had gone up in
value, Mr. X would not have repudiated the signature.)
OpenPGP's nonrepudiability is largely a myth. I have never seen it
tested in court. Given the fragility of our computer systems and how
easily they're compromised, I think it's worthwhile to be very skeptical
of any analysis that's predicated on nonrepudiability.
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