rotor replacement

Paul Rubin http
Thu Jan 20 04:54:55 EST 2005

Robin Becker <robin at> writes:
> Apparently factorization based crypto is on the way out anyhow (as an
> article in Scientific American is reported to claim).

I haven't seen that SA article but I saw the Slashdot blurb.  They
have confused "quantum cryptography" with quantum computation, when
they are entirely different things.  Quantum cryptography (basically
communicating a message over an optical fiber in such a way that any
attempt to eavesdrop is supposed destroy the readability of the
message) has been done over quite long distances, 10's of km or even
more.  Quantum computation is mostly a theoretical speculation.  The
largest quantum computer ever built held seven bits, and factored the
number 15 into its factors 3 and 5.  Building larger ones seems to
have complexity exponential in the number of bits, which is not too
much better than using an exponential-time algorithm on a conventional
computer.  It's not even known in theory whether quantum computing is
possible on a significant scale.  There are just some theorems about
what properties such a computer would have, if it can exist.  One of
them, however, is being able to factor in P-time, and that caused
lots of excitement.

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