Cointelegraph: Experts Split on Practical Implications of Quantum Cryptography

Bill Stewart billstewart at
Mon Jun 29 22:37:55 PDT 2020

On 6/29/2020 6:57 PM, Punk-Stasi 2.0 wrote:
> On Sun, 28 Jun 2020 23:54:43 +0000 (UTC)
> jim bell <jdb10987 at> wrote:
>> Cointelegraph: Experts Split on Practical Implications of Quantum Cryptography.
> 	bullshit as usual.
> 	As far as I know so called 'quantum key distribution' needs an authenticated 'classical channel' to work, so it's completely pointless.

There seem to be two kinds of Quantum Crypto out there
- the kind that needs a piece of fiber
- the kind that lets you send your photons in free space between ground 
and satellite.

The former's a very niche application, and doesn't protect you about 
things like pseudonymity vs contact tracing (because you follow the 
piece of fiber and see who's at the other end, or follow the money and 
see who's renting the fiber :-).
It's more useful if your threat model is "Auditors" than "Spies"; 
otherwise you can send an extra diverse dude with a briefcase handcuffed 
to their arm for an initial authentication key exchange and then use 
another layer of Diffie-Hellman for authentication, maybe with an 
annoyingly long ECC key, while also printing the authentication public 
key in a classified ad in the NY Times or Pravda or Federal Register.

The latter's "interesting"; I'm skeptical about its usefulness, but 
haven't looked into it deeply, beyond a quick read of
There seem to be three approaches
- one end-to-end quantum-protected hop (ground to bird to ground)
- two (ground to bird-in-the-middle, bird-in-the-middle to ground)
- two (trusted-bird sends entangled pair, one to Alice, one to Bob)
Approach 1 doesn't appear to exist, approach 2 lets you use two 
prepare-and-measure channels (meh), approach three could be useful-ish

> 	Also, my current guess/understanding is that there isn't any 'entanglement' at all.The "trusted-bird sends entangled pair, one to Alice, one to Bob" method 
uses entanglement, but needs a bigger satellite than the 
bird-in-the-middle approach.  (According to the paper, it needs more 
than a 100kg satellite, as opposed to a single-end thing which can fit 
on an under-10kg cubesat.)

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