Summary: Windows GUI recommendation for USB disk

Robert J. Hansen rjh at
Fri Nov 3 17:39:54 CET 2006

David SMITH wrote:
> the moment.

Welcome to the Second Law of Thermodynamics!  Enjoy your stay.

By the Second Law, every time a bit of information is erased you have to
pay the entropy tax of (kT * ln 2) J.  Let's assume that for each key
you try, you have to erase 1000 bits of information--this is wildly
optimistic, given how complex key schedules usually are, but it'll make
for nice numbers.

On average you'll have to brute-force 2**127 keys before you find the
proper 128-bit AES key.

1000 = 10**3
2**127 approx. eq. 10**38

10**41 * (3 * 10**-21) = 3 * 10**20 J

A one-megaton nuclear weapon liberates approximately 10**15 J of energy.

3 * 10**20 J divided by 10**15 J = 300,000 megatons

By comparison, the 1863 Krakatoa explosion liberated about 21,000 megatons.

If you're interested, we can also do a quantum-mechanical analysis of
the minimum time required to do this computation.  It gets equally silly.

... It's true that quantum computers and reversible computing will both
reduce this number considerably.  However, if you're going to talk about
science fiction--which is what large-scale quantum and reversible
computing is nowadays--then why not go whole-hog and posit the existence
of a psychic who's 100% effective in predicting keys?

More information about the Gnupg-users mailing list