Security for under a buck fifty

The dilemma with the pass phrase issue seems to boil down to the
balance between entropy and memorability.

The "shocking nonsense" guidelines sound like about the best
suggestions I've heard for humans to generate pass phrases, but I
would suggest that even shocking nonsense can be broken by
somebody--or something--that thinks like Charles Dodgson. If it came
from a process that includes any logic at all, that logic will be
discovered if economical to an attacker.

But who can remember a 132-bit true random number? Take, for example:

0X997D6C32FC8F99104FDCC8BF4B24C7031

I got that number by grabbing handfuls of pennies out of a pile of
132--a true random number generator that cots less than
breakfast--though, I will admit that it's somewhat cumbersome.

But a number can be represented in many different ways. Create a
six-bit character set, filling from 000000 to 111111 with a-z, A-Z,
0-9, . [period], and - [hyphen]. Now, the key becomes:

Mx1SmVYpMrbp3mI-sYthaX

Not impressed yet? Try using the human brain's wonderful talent for
seeing patterns in randomness. If your mind just happened to work
exactly like mine, you would get:

Mx1 misSiles moVe Yp; Mr. bop of 3m I-s Yt haX. [Yt as in the
element.]

I would suggest that it would only take the average person a minute
or two to memorize such a phrase, especially if she were the one to
do the pattern-matching in the first place.

So, the end result is a ten-word pass phrase that isn't hard to
learn, is only vulnerable to a brute-force attack, and would take
about a sextillion years to brute-force at a trillion encrypts per
second--and the universe is "only" a hundred billion years old.

Can anybody suggest how to implement this? Can a computer program
suggest mnemonics that would mean anything to a person? Even if the
computer gives the user a screenful of such? Or, how about giving a
screenful of "words," and letting the user mix-n-match?

Obviously, you would need a real random number generator and a
secure terminal for all this.

Maybe it's time for me to write some code....

b&

--
Ben.Goren@asu.edu, Arizona State University School of Music
 net.proselytizing (write for info): Protect your privacy; oppose Clipper.
 Voice concern over proposed Internet pricing schemes. Stamp out spamming.
 Finger ben@tux.music.asu.edu for PGP 2.3a public key.

>... 
> I got that number by grabbing handfuls of pennies out of a pile of
> 132--a true random number generator that cots less than
> breakfast--though, I will admit that it's somewhat cumbersome.
> 
> But a number can be represented in many different ways. Create a
> six-bit character set, filling from 000000 to 111111 with a-z, A-Z,
> 0-9, . [period], and - [hyphen]. Now, the key becomes:
> 
> Mx1SmVYpMrbp3mI-sYthaX
> 
> Not impressed yet? Try using the human brain's wonderful talent for
> seeing patterns in randomness. If your mind just happened to work
> exactly like mine, you would get:
> 
> Mx1 misSiles moVe Yp; Mr. bop of 3m I-s Yt haX. [Yt as in the
> element.]
> 
> I would suggest that it would only take the average person a minute
> or two to memorize such a phrase, especially if she were the one to
> do the pattern-matching in the first place.
>... 
> Can anybody suggest how to implement this? Can a computer program
> suggest mnemonics that would mean anything to a person? Even if the
> computer gives the user a screenful of such? Or, how about giving a
> screenful of "words," and letting the user mix-n-match?

I already do this -- except that I use a keystroke- timing program for 
the true random source, and I do the mnomonic generation with my brain 
instead of the program.  My program just converts the random numbers to 
uniformly distributed printable ASCII (values between space and del), for 
a little more entropy than 6 bits per character.

A more automated way to generate a pass phrase might be to convert every 
16 bits of random numbers to one of 65536 words and names in your 
favorite languages.  That way, you would have real words to memorize, but 
in a strange order.  For example, a 128 bit key might be:
tree elephant action roof xymurgy eight top slash.

You could try to think of some story to link the 8 originally unrelated 
words together and help you to remember it.