Quantum Cryptography

Not heard of this until I read this article:


Any thoughts? :101:

“Unhackable” definitely deserves quotes. 5 years ago I had a lecture from guy who had successfully hacked one of these systems.


Eh, except quantum encryption like this really is considered mathematically, well, not necessarily unhackable, but ‘noticable’. Sure you can get a packet of data out of it, but in doing so the receiver never gets it or gets it altered, thus alerting them to the attempt. So you can get data out of it as a third party, but they will just stop after a single packet or so.

And I really really doubt that happened 5 years ago since we did not have the technology for it then. :wink:


Sure you can get a packet of data out of it, but in doing so the receiver never gets it or gets it altered, thus alerting them to the attempt.


This quantum stuff is always a fascinating read, but the idea is that the reality on the smallest scale is nothing logical, but pure weirdness :slight_smile:

In case of quantum cryptography it’s about the act of measurement (or observation) that changes the observed object, this way anyone who eavesdrops automatically “corrupts” the sent data. So the unhackability claim is not that unrealistic.

I also wonder how the programming of quantum computers will look like, something alongside the true, false and true and false booleans :smiley: There are lots of advancements in the field http://www.wired.co.uk/article/quantum-computing-explained

It’s an interesting time we live in :slight_smile:

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The idea here is not to be able or not to hack, it’s to know when you are getting hacked, so probably the system can identify it and act upon. :slight_smile:

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Nothing of the sort actually. Quantum computers are actually horribly inefficient for ‘classical’ computing work. They really come into usefulness when you get certain parts of ‘operations’ that can be done in massively parallel ways but where you can also ‘entangle’ the inputs in such a way that the outputs get entangled as well to get the result you want. It is very much a kind of dance in math, but if it works for you problem space than all the better for it.

As one example, current cryptography works by having 2 very large prime numbers multiplied together, and you have to reverse that, I.E. factoring. Well quantum computers are as bad at factoring as classical computers. However there is one tiny little operation in factoring that if you split it up juuuust right happens to be the ‘slow’ part, the loop with everything else that can be put outside of it or so. That operation has a quantum math operation, named the Shor’s Algorithm, that can be done that entangles the particles in just the right way that you can do ‘that’ operation quickly, which then makes prime number factoring from, say, O(log(N)^256) or so down to O(N*4) (basically constant) when you have a classical computer do the rest of the before and after operations.

Also a lot of that article is hogwashBuzzWords, sure it is accurate but does not really explain just how hard the math is. A quick youtube search with no sound (I’m at work, no sound) implies that these two video’s explain the real difficulty much more accurately:


For me one question I have is … how much does it actually matter if you can intercept communication if simply observing it will effect the message. So basically the receiving application will notify the user that this message has already been seen or destroy it. If it destroys the message, then basically anyone can effectively prevent communication by simply observing it.

So it’s kinda like a choice between denial of service or lack of privacy. Seems like a lot of tech involved just to let you know that it’s happening. But I guess that how everything is at first during transitions in technological shifts right?


Usually you don’t exchange the message, but the key only. The message itself is then transmitted on another way. This way the sender and receiver can see if a given key has been compromised before even using it to encrypt the message and try to negotiate another one.


Precisely this, this is why it is actually quite a secure setup.


Nothing of the sort actually. Quantum computers are actually horribly inefficient for ‘classical’ computing work.

Yep, I know (the theoretical part, not the math :)) The booleans statement was kinda joke based on the fact that the qbits have an extra superposition state. But honestly if these things spread we might need another programming paradigm change.

I’m not totally sold on them sucking at classical computing though, I remember the time when LSD vs CRT monitors was totally “a thing” and the fact that CRT will have it’s niche was just that: a fact :slight_smile: Same with VCR and what not, we’ll see where we get with these computers when we get there.

The vids barely touch the hardcore math (which I wouldn’t get anyway), but I enjoyed them -way past the working hours here, so thanks!

PS here’s a good one https://xkcd.com/1240/


In 2011, there was already a quantum network working in my city :slight_smile:



No. the only new bit is the scope of this implementation of quantum key distribution. which is impressive.
I was working on these systems with fibre optics for the connection medium in 2011- 2012.

By hacked I mean that the end users were unaware of an eves dropper, i.e. completely compromised. The theory proves the system is unhackable for a perfect implementation. Unfortunately a perfect implementation is impossible.
As with many hacks the trick is to change abstraction level. The hack I was show was able to trick the detectors into thinking they had received one photon in a window where they had in fact received many photons, thus upsetting the trigger voltages for the detectors.

An update on this story:

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Another related story:

And the world’s first intercontinental video call protected by a quantum key was successfully carried out about a week ago…


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