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When it comes to exchanging secure information over an insecure channel, this approach is considered. It all depends on the nature of photons in which the third polarization is focused. It can easily be trusted when it comes to exchanging the Secret keys without facing any issue.

  • What is Quantum Cryptography?
  • What are the differences between modern cryptography and quantum cryptography?
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    $\begingroup$ Possible duplicate of What makes Quantum Cryptography secure? $\endgroup$ Commented Jun 17, 2019 at 18:40
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    $\begingroup$ Other possible duplicate: crypto.stackexchange.com/q/59066 $\endgroup$ Commented Jun 17, 2019 at 18:43
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    $\begingroup$ Can you identify what you are substantively asking about that is not already addressed in the other questions? $\endgroup$ Commented Jun 17, 2019 at 19:27
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    $\begingroup$ @SqueamishOssifrage It seems different to me because this is asking about terminology. The former isn't an answer because, if OP doesn't know what quantum cryptography is, an answer explaining why it's secure isn't helpful. The latter also requires you to know what quantum cryptography is to ask about QKD. While they are extremely related, I think this question is just different enough to be on-topic. $\endgroup$
    – forest
    Commented Jun 18, 2019 at 3:38
  • $\begingroup$ @forest What makes a question a duplicate is not whether the text of the question is the same, but whether the answers are already subsumed by the answers to existing questions—that is, whether there is anything in this question that is not addressed by the other questions. So, after you read the answers to the other questions, what is left that you are still wondering about in this question? $\endgroup$ Commented Jun 18, 2019 at 20:35

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What is Quantum Cryptography?

Today's "normal" cryptography relies mostly on mathematical principles. For example RSA is based on the practical difficulty of the factorization of the product of two large prime numbers, the so-called "factoring problem".

Quantum cryptography (quote from Wikipedia):

Quantum cryptography is the science of exploiting quantum mechanical properties to perform cryptographic tasks.

So instead of relying only on mathematical principles, quantum cryptography relies more on quantum mechanical properties (physics). Some of these properties include:

How secure are data that encrypted with Quantum Cryptography methods?

Quantum cryptographic tasks (often incorrectly called quantum cryptography) are theoretically 100% secure, even against quantum-computers.

The method described in your question is Quantum key distribution (QKD). QKD has provable security based on information theory, and forward secrecy. This is based on the No-cloning theorem, which states that it is impossible to create an identical copy of an arbitrary unknown quantum state.

If Quantum Computing becomes practical and is mass-produced, will we be facing with next-generation of cybersecurity?

Not necessarily. I personally think that quantum computers won't fully replace classical computers, because quantum computers only outperform classical computers in certain areas (i.e. large-scale simulations).

But if quantum computers were available they would break some of today's cryptography used on classical computers, i.e. RSA or Diffie-Hellman. We would then have to switch to post-quantum cryptographic algorithms like Supersingular isogeny key exchange. So ultimately, I think, we would just switch to quantum-resistant algrorithms and go on with our lives.

EDIT: This answer provides some additional information.

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    $\begingroup$ Actually QKD only offers theoretically 100% security as attackers can hide in the natural noise, see also fgrieu's canonical quantum answer. "No Cloning" should probably also be named here. $\endgroup$
    – SEJPM
    Commented Sep 3, 2018 at 13:52

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