From: Ray Arachelian <sunder@brainlink.com>
Date: Wed, 11 Jun 1997 03:34:23 +0800
To: Kent Crispin <kent@songbird.com>
Subject: BAD ADVICE WARNING from Kent: Access to Storage and Communication Keys
In-Reply-To: <19970610112926.04400@bywater.songbird.com>
Message-ID: <Pine.SUN.3.96.970610145359.9093F-100000@beast.brainlink.com>
MIME-Version: 1.0
Content-Type: text/plain



On Tue, 10 Jun 1997, the spooks made the tentacle named Kent Crispin
write the following bad advice:

> If you have data you wish to guard from disclosure I think that in
> most circumstances you want to back up ciphertext.  It is a *lot*
> cheaper to secure a piece of paper with a passphrase on it (in a safe
> deposit box, for example) than it is guard a gigabyte of backup tapes. 

BBBBZZZZZZZZZT!  Wrong!

Passphrases can be memorized.  4mm DAT tapes hold several gigs and are
tiny.  Ever see one?  Fits in your pocket.  It's smaller that an audio
cassette. Fairly easy to guard, but, if your data is backed up in
encrypted form (cyphertext), and not clear text, you don't even need to
bother protecting the tape. (That is unless your backup software uses a
weak cypher as most tend to do.)  [FYI: Your knowledge of tape
technologies is severly lacking. 4mm tapes hold 2-4Gb.  Exabytes 5Gb-10Gb. 
Mamouth Exabytes (same size as 8mm camcorder video tapes, smaller than
audio cassettes) hold as much as 40Gb in a very small form factor.]

Or if you are afraid of loss to EMI and such, backup to MO media, or to
CDR media.  You can get 4Gb MO's these days fairly cheap, and since
they're just like hard drives you don't need to use backup software.
They're impervious to accidental wiping by magnetic waves, and they're
rewriteable, which means you don't have to pay much money to do new
backups.  OTOH, they are rewriteable, you might want to burn CD's, which
only store 650M, but two of them will easily store 1.2Gb, and prevent
loss by erasure.  At less than $6 in bulk this is very cheap.  You sti.l
have to protect the media from heat, direct sunlight, dust, scratches,
liquids, etc...

The best way to go is to have an encrypted volume, unmount the volume
before backing it up, and backup the sectors on the volume instead of
individual files.  To be safe, I'd run several backups since if the tape
goes bad on a spot that holds inodes, you've lost several directories...

But you can leave the tapes unprotected in clear view of the world. 
They're useless to those that don't have the passphrase.  Hence it costs
you $0.0 to secure tapes that hold strongly encrypted information.  It
costs a lot more to protect that said piece of paper.  (I would still
advocate keeping a set of tapes offsite in case of fire or other local
physical disaster - but the security risk of keeping them unsecured is
still zero if you are using a good hard drive encryptor that uses strong
crypto.)  If you are paranoid, you could encrypt your backup with a
different cypher.  (i.e. use IDEA on the hard drive, then backup and
encrypt the encrypted drive with 3DES and Blowfish, all using different
passphrases.)

Yes, you can write your passphrase on paper, but if someone finds it you
are screwed.  Giving such advice is dangerous.  It is as if you told
someone to put a PostIt(tm) note with their account and password on their
monitor, or to use their birthday as their password, or their dog's name.
Paper is very easily compromised.  Weak passwords and passphrases are also
easily compromised.

If you want to protect your passphrase agaist memory failures (human
memory that is), break it up with a secure split function, and save it to
disk (or print it out in hex), then give a piece to each of several
trusted parties - who do not know each other. Something along the lines of
a K of N system where you'd need 5 pieces out of 8 to restore the
passphrase.  

Oh, and those trusted parties should not be government agencies for the
simple reason of how beurocracies work. One could be a safety deposit box,
another could be a family lawyer (but make sure it's not a big agency),
another a cousin in a differnet city, another a neighbor, etc...  

(I.E. I wouldn't leave anything with the CIA - see the news headlines for
all the reports of double agents bought off by the Russians, etc... though
it is more likely that the NSA would be safer place to store, either
because it has better controls on the data, or more likely because reports
of double agents there never reached the media...)  Still I wouldn't go
that route, though you personally might.  In general, you don't want to
leave them in the hands of corporations/agencies where folks getting paid
$5.50/hour can be easily bribed, or leaned on, or rubberhose persuaded, or
sold to the "If you knew what I knew" and "I'm from your government and
here to help you" lines.

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