[117097] in Cypherpunks
Re: Project: Hardening Crypto Against Big Brother's "BlackBag"
daemon@ATHENA.MIT.EDU (Sunder)
Thu Aug 26 12:54:20 1999
Message-ID: <37C56CD3.80617638@brainlink.com>
Date: Thu, 26 Aug 1999 12:35:31 -0400
From: Sunder <sunder@brainlink.com>
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To: kurtbuff@lightmail.com
CC: cypherpunks@cyberpass.net
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Reply-To: Sunder <sunder@brainlink.com>
I've spent a few hours shooting the shit with an old pro-crypto friend, and
bouncing ideas off (and drinking.) :)
It's losing proposition IMHO as far as I can figure (unless someone can figure
out some other thing.)
So far the system seems to be a big box with encrypted disks that uses a small
box with enough CPU to decrypt the disks and let you access it. Small box can
be a PDA or a PC Card... You play good guy, I play bad guy:
Here are the flaws/fixes:
If I backdoor the big box, you login with your little box and start doing
work. I can now cache the plaintext somewhere where I can get to it.
If you use the big box for disk access only (say as a file server) and use the
small box to do work, (the protocol doesn't allow any programs to run on your
small box from the big box) then you must keep it with you at all times to
prevent it from being backdoored.
So now I'd have to somehow get my hands on your small box to bug it.
There are several ways to do this.
Most importantly at some point you will sleep. When you do (and your sleep
may be chemically enhanced) I could get to your small box and add the back
doors. So you'd have to add some C4 to the small box to blow my fingers off
if I touch it. Barring sleep, you could be mugged, pick pocketed, etc...
If I have tempest equipment I could get at your display and even figure out
what your small box's CPU is doing. So you'll also have to tempest proof your
machine somehow. It's no longer such a small box. :)
If you do have some sort of trap that will blow my fingers off, then I could
attempt several things: freeze it to near zero to disarm the trap, wait until
the batteries run out, X-Ray it to find out where the trap is, etc. You'll
have to put sensors in to watch for temperature extremes, XRays and blow the
C4 before the circuits that do that die, etc... if the battery gets too low,
fry all data on it, etc...
This is the type of equipment you will need. The small box is looking more
and more like a low end portable computer. I'd say Palm, but their CPUs
aren't going to have enough horse power to do real time disk decryption. I'm
not quite pushing a mickeysoft product so don't get your panties in a bunch,
but wince boxes are based on RISC cpu's, and may have flashable ROM's... If
they do, you flash'em with your own OS, etc... Better yet one of the Libretto
or small mini Sony Vaio's...
You'll also have to keep this box off the net incase I do manage to install
back doors.
Keep the keys on a PC card encrypted with a passphrase, but typing it in
shouldn't be the only thing. Do all your work from this small machine. (Of
course CPU power will limit you a lot.)
You'll also need some sort of dead man's switch that's easily accessible. A
few mercury switches well positioned could arm it, and if you don't type in
the right passphrase in the right amount of time, it wipes the card, maybe
beeps at you in a pattern (or better yet plays Yankee Doodle Dandy :^), to let
you know it's too late, and then blows itself to bits.
When you do use your key, it should wipe the card incase you don't get a
chance to do so, or they manage to eject it. When you tell it to shut down,
it should write the key back, but with a new random salt.
(There are also issues of key recovery if the hardware does go bad, or if your
pet cat/dog/lizard/ferret/rodent lands on it and sets off the deadman switch,
but presumably, you wouldn't leave the machine lying around at all. If you do
you open yourself up for a hardware bug being planted. If you do put an XRay
detector in it, be sure to disable it when you go through airports incase they
don't do hand inspections - but then C4 becomes an issue, etc...)
It's not perfect, it's not easy, but it's a thought... Any more?
Kurt Buff wrote:
>
> -----BEGIN PGP SIGNED MESSAGE-----
>
> Agree with your comments, but the site does mention a 12MHz processor
> and 128bytes(?!) of RAM, and a physical fuse to prevent file readout.
> All sounds like a good start, but needs good verification to be sure.
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