[Cryptography] QM giveth, QM taketh away

Jerry Leichter leichter at lrw.com
Fri Feb 12 21:39:31 EST 2021

>> 2. Quantum key distribution supposedly enables guaranteed
>> private distribution of OTP keys.
> I would think that if you can send a one-time-pad securely via QM, you
> might as well just send the message itself securely via QM, and not
> bother XORing it with a key.  You can only use the one-time-pad once anyway.

Quantum key distribution (theoretically) provides a way for Alice and Bob to share a random bitstream with strong randomness and privacy guarantees.  It doesn't give a way to transmit a message as such - but once they have that shared bitstream, then can use it as a one-time pad.

Note that the actual physical realization of QKD has proven to be much trickier than the neat theoretical examples.  Still, it seems to be getting there - if this is what you want.  Keep in mind that QKD (and encryption using XOR with a one-time pad) have theoretically perfect security properties, but provide no authentication (so as with raw DH, you can end up conducting a secure communication but with no way of knowing who you are actually communicating with).
                                                        -- Jerry

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