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I am having difficulty understanding quantum cryptography concepts. I've searched the internet and watched some videos on youtube explaining the topic, but it is still hard to understand how it works.

What makes it more secure comparing to the traditional cryptography algorithms? How does it work? What is wrong with traditional cryptography?

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Nothing is wrong with traditional symmetric crypto. The popular asymmetric schemes (RSA, DH, Elliptic curves) will be broken by large quantum computers, but we have alternatives (McElise, NTRU,...) which are believed to resist quantum computers. => IMO quantum crypto is useless –  CodesInChaos Dec 13 '13 at 9:15
    
@CodesInChaos it's not useless. It's more secure, but it's impossible to actually implement as of now. –  Jan Dvorak Dec 13 '13 at 9:18
    
@JanDvorak It's perfectly secure if you have the physical quantum connection. AFAIK the best record so far was ~20km - hardly useful for anything. Might as well drive tanks with OTP tapes then - a lot less easy to mess with. –  nightcracker Dec 13 '13 at 9:39
    
@nightcracker that's why I said "as of now". Also, 20km is pretty impressive IMO –  Jan Dvorak Dec 13 '13 at 9:42
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QKD is what is meant when speaking about quantum cryptography. If you mean cryptography that is still secure in the presence of quantum computers you mean post quantum cryptography. –  DrLecter Dec 13 '13 at 10:02
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