biological systems and cryptography

[Eugen Leitl]

On Wed, 1 Jan 2003, Michael Cardenas wrote:

> People do break cyphers, by finding weaknesses in them. Are you saying
> that you think that current cyphers are unbreakable?

People break cyphers by

1) cryptoanalysis (mostly brain, a bit of muscle)
2) brute force (no brain at all, pure muscle)

So far we've been talking purely brute force here. It is easy to see that 
a current cypher requiring a 10^6..10^9 computer-years brute force can be 
broken in realtime if attacked by a massively parallel molecular 
electronics computer common several decades downstream. It is trivial to 
design cyphers running on today's hardware which would be safe from that 
attack. No one is doing that because you want speedy encryption on today's 
software. And secrets become stale quick.

The quantum computer is a dark horse, because no one really knows how much
quantum parallelism you can extract from a given pile of molecules. Plus,
not all algorithms can be mapped to a QM machine. It also seems that
entanglement is energy bound, but the field is still moving far too
quickly to say anything meaningful.
 
> Also, what about using biological systems to create strong cyphers,
> not to break them?

Molecules are molecules. Solvated linear biopolymers are lousy computers
in any case. So are 5-qubit QM machines which require an NMR machine, for
that matter. Whether classical, or QM, it has better be solid state, and
preferrably not require mK environment to run.
 
> It seems that all of these analyses assume that an instruction is a
> single mathematical operation in a turing machine. What if each
> operation was something else? I refuse to believe that the human mind
> is just a turing machine.

The human mind is not a Turing machine. But a Turing machine is an all
purpose computational device, so in principle it can simulate relevant
aspects of physical system evolution. Including the spiking, diffusion,
genomic activity networks in each cell and god knows what else in the
physical system residing between your ears.

Meaning, a suitably constructed machine could be intelligent. It can be 
even you if you keep your and its state synched.