[nzlug] OT: computer read/write access to paper?

[Michael Field]

Hi Phillip,

If you are so worried about latent images on you storage medium, why 
not use two storage devices? One holding a random string equaling your
keyfile length, the other being your key XORed with the random string.
Neither has the entire actual key on it. Keep one on you key ring, and 
one in you wallet - what is the chances of loosing both at the same 
time?  The downside is that if you loose one device, then you have lost 
all you data.

If you wanted to make it really hard nut to crack, you could have a 
really big glob of random data on both, and then have a secret 
pass-phrase you know that hashes down two different 'unrelated' ways 
to two offsets. 

You start XORing the data from Memory Device 1 at offest1, and then 
memory device2 from offset2 revealing you secret data. (Of course 
you will have to seed the data on one device to give you the answer 
you want... just XOR you plain text with the data in Memory Device1 
at offset 1 and write it to Memory Device2 at offset 2).

If you use two 128MB USB keys with 100,000,000 byte files, even if 
the 'nasty guy' gets both keys, but does not know the pass phrase
they will need to try about 50,000,000 different relative offsets, 
scanning all 100,000,000 bytes for a possible key string = around 
5,000TB of data to analyze.

Of course this assumes that you have a good source for 200MB of 
truly random data. If not, somebody might be able to see where you 
have 'seeded' the message, dramatically reducing the searching 
required.

Mike

-----Original Message-----
From: nzlug-bounces at linux.net.nz [mailto:nzlug-bounces at linux.net.nz] On
Behalf Of Phillip Hutchings
Sent: Friday, 22 June 2007 10:28 a.m.
To: NZLUG Mailing List
Subject: Re: [nzlug] computer read/write access to paper?

On 6/22/07, Karl. <kmw1 at free.net.nz> wrote:
> Every now and then there are small files (encryption keyfiles) that
I'd
> like to store in some robust offline fashion.  I have a vague
> recollection of software to print out a file as a 2D barcode, and then
> something to read it back from a scan of the page.  Anyone here got
any
> pointers on how to do this?

Actually, that's a very good idea. I've been trying to think of a
secure method of keeping an encryption key off disk for a while now.
I'd been thinking of a removable USB drive, but even that can be read
from after erasure. Now I'm thinking of a 2D barcode and a webcam,
that could work...

-- 
Phillip Hutchings
http://www.sitharus.com/

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