🚀 go-pugleaf

lwloen@rchland.vnet.ibm.com (Larry Loen) writes:

>The problem is, of course, random number generators designed to satisfy
>statistical randomness may well not satisfy at all the need for being
>unpredictable in a cryptographic situation; most are very poor at this, in
>fact, not having been designed with the problem in mind.  Most novices do
>not understand the distinction between "randomness" as in passing Chi Square
>and "unpredictable" as in frustrating analysis.  So, they grab any old
>random number generator out of Knuth or something and usually grab wrong.

Well, one possibility is to point out that *by definition* there is *no*
pattern to to digit stream that constitutes an irrational number, but
the digit stream is *totally* predictable! So *statistically* the 
digits from an irrational (like pi or sqrt(2)) are random. But crypto
folks would find them pretty useless. 


As a trivial example, I could send a message using PI as the key. But
if you have any info about the message (say knowing that many messages
from me start out in a certain way) you can try *assuming* that plaintext.
Then when you see that the key comes out 314159 for the first part of the
message, you may go "gee, that looks like Pi.." So you try plugging in
the next few digits. If reasonable plaintext results, I'd be willing to
bet you'd be looking for a table with Pi to a few hundred digits *fast*.

I've *seen* a key get compromised this way (In a friendly environment).
Someone saw that the plaintext messages between certain users allways
had the same heading. So it was a reasonable assumption for the "enemy"
to see what happened if he plugged in the heading and solved for the key.

He never *did* figure out our key change schedule, but since this was only
a battle of wits, we were only using a 20 digit key. So he could solve
fotr the header and have a chunk of the message. Then he'd try to fill
in the blanks per normal practice when you have a partial key. 

Now I know why lazy code clerks and standard message forms are so 
beloved of folks like the NSA!
-- 
Leonard Erickson		      leonard@qiclab.scn.rain.com
CIS: [70465,203]			 70465.203@compuserve.com
FIDO:   1:105/51	 Leonard.Erickson@f51.n105.z1.fidonet.org
(The CIS & Fido addresses are preferred)