[17595] in cryptography@c2.net mail archive
RSA gets a reprieve?
daemon@ATHENA.MIT.EDU (Heyman, Michael)
Thu Jun 30 16:08:36 2005
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Date: Thu, 30 Jun 2005 15:16:58 -0400
From: "Heyman, Michael" <Michael.Heyman@sparta.com>
To: <cryptography@metzdowd.com>
From:
<www.newscientist.com/channel/info-tech/mg18625054.000>
ATTEMPTS to build quantum computers could run up=20
against a fundamental limit on how long useful=20
information can persist inside them. Exceed the=20
limit and information could just leak away,=20
making computation impossible...Rather than=20
remaining in a superposition of two states, a=20
qubit will spontaneously collapse into one state=20
or another (Physical Review Letters, vol 94,=20
p 230401). "When we discovered this we were=20
stunned," says van den Brink...the time limit=20
for decoherence seems to grow shorter as systems=20
get smaller. Zaanen says that for some of the=20
most promising qubit technologies the limit=20
would be about 1 second. It's not a problem at=20
the moment, he says, because researchers are=20
fighting to get coherence times up to around a=20
microsecond. "But this fundamental limit is=20
getting within reach."
This plus the "no-cloning theorem" means that if a quantum computer
cannot factor an RSA modulus in under a second, RSA will remain
unbreakable. (I'm not a quantum physicist or quantum computer programmer
so I don't even know if the no-cloning theorem, which states qubits of
unknown states cannot be copied, applies.)
-Michael Heyman
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