It's two different things: - one, quantum computers can theoretically do factoring in polynomial time and therefore theoretically break schemes such as RSA (su

It's two different things: - one, quantum computers can theoretically do factoring in polynomial time and therefore theoretically break schemes such as RSA (such schemes are proven secure provided that some computational problem is intractable -- in the quantum world the problem becomes tractable) - two, you can theoretically use entanglement to achieve "perfect cryptography". The "perfectness" result is an absolute impossibility result in physics, and therefore no computer (classic or quantum) can break it. Details on wikipedia: http://en.wikipedia.org/wiki/Quantum_cryptography http://en.wikipedia.org/wiki/Quantum_cryptography The article refers to number two, although in a rather non-technical manner. Edit: clarifications.