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What makes Quantum Cryptography secure?

TL;DR     The answer is classical cryptography. Besides a quantum link, secure data communication with Quantum Cryptography (more precisely, Quantum Key Distribution) uses classical links, ...
fgrieu's user avatar
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24 votes
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Why Quantum Key Distribution (QKD) is impractical

When we say a solution is impractical, we don't mean that it can't work at all; instead, we mean that it has serious deficiencies compared to other ways to solve the same problem. For example, one ...
Geoffroy Couteau's user avatar
11 votes
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How does quantum encryption work?

There are a few key distinctions to make Quantum cryptanalysis This is what you hear all the buzzing about. Specifically, there is something called Shor's algorithm, that when used to break modern ...
J.A.K.'s user avatar
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10 votes

In quantum cryptography, why can a qubit can be both 0 and 1 at the same?

“Both 0 and 1 simultaneously” is a lie-to-children: it's a simplification intended to be comprehensible and not fully accurate. It's not a very good one. A better way to present it is that a qubit is ...
Gilles 'SO- stop being evil''s user avatar
10 votes

What makes Quantum Cryptography secure?

@fgrieu already wrote a little book, so I'll restrict my answer to a minimum to avoid repetitions. Think of this as an extended comment (which indeed wouldn't have fit the comment size limits). What ...
e-sushi's user avatar
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8 votes

How does quantum encryption work?

Quantum key distribution takes advantage of physics to create a communication channel that can't be cleanly intercepted without corrupting part of the message. This can be used to create a shared ...
Macil's user avatar
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8 votes
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Is quantum cryptography unbreakable?

You have to distinguish between "theoretically" and "practically" breakable. Pretty much any cryptosystem can be broken in practice by violating the assumptions that the ...
Ella Rose's user avatar
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7 votes

Why Quantum Key Distribution (QKD) is impractical

Impracticability of Quantum Key Distribution (QKD), starting with the two showstoppers QKD is network-adverse, because it requires setting up a QDK-compatible link between the two crypto endpoints. ...
fgrieu's user avatar
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7 votes

What makes Quantum Cryptography secure?

My turn! In classical cryptography between two peers over a channel such as the internet, an eavesdropper on the channel learns a transcript of information from which secrets could theoretically be ...
Squeamish Ossifrage's user avatar
7 votes

what is the motivation behind quantum key distribution with Continuous variable?

It's easier to work with a lot of photons in a stream than to work with a single photon at once. This is explained in the paper introducing continuous-variable quantum key distribution. (With ...
Squeamish Ossifrage's user avatar
6 votes

How does quantum encryption work?

In addition to the other answers, I want to add that D-Wave makes a type of machine called an Adiabatic Quantum Computer, which is fundamentally different from the general-purpose quantum computers ...
Mike Ounsworth's user avatar
6 votes
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Can quantum computers break quantum cryptography?

I happened to learn that encryption by quantum cryptography would be impossible to break as it's state changes the instant an eavesdropping event (by non-quantum systems) occurs. Actually, the QKD ...
poncho's user avatar
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6 votes

Is E91 safer than BBM92?

The answer is both yes and no, as I explain below. 1. No, BBM92 is better (or at least, we initially thought so) E91 was the initial idea which led to the more rigorous BBM92. In the E91 paper, there ...
Frédéric Grosshans's user avatar
5 votes
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challenges in quantum key distribution

The article cited in the question (Eleni Diamanti, Hoi-Kwong Lo, Bing Qi, and Zhiliang Yuan: Practical challenges in quantum key distribution, in npj Quantum Information 2016, a Nature Partner Journal)...
fgrieu's user avatar
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5 votes

Two untrusting people want to come up with a random number

The random number required is an integer between 0 and $\ell$. Each person picks a random number $x_i$ between 0 and $\ell$, and each person picks an $n$-bit random blinding factor $b_i$ where $n\geq ...
knaccc's user avatar
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5 votes

What makes Quantum Cryptography secure?

There is some confusion regarding QKD. The confusion revolves around the underlying principle and it's nuts & bolts implementation in the physical world. The two are conflated, which I believe ...
Paul Uszak's user avatar
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5 votes

Understanding Quantum Key Distribution

How Alice and Bob agree on which of the two beam splitters bases (Horizontal-Vertical and Right-Left) correspond to which of the classical bits (1 and 0) ? How do Alice and Bob agree on when actual ...
fgrieu's user avatar
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5 votes
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what is the motivation behind quantum key distribution with Continuous variable?

Since the question was labelled unclear, I’ll first clarify my understanding of the question, and then give various motivations (academics, then practical). This answer turned out to be quite long ...
Frédéric Grosshans's user avatar
5 votes

Does Quantum Key Distribution (aka: QKD) qualify as "Cryptography"?

The whole point of most Cryptographic devices, protocols, algorithms, etc. was to transform information in a way that no matter how it is carried, where it is stored, etc. remains incomprehensible to ...
poncho's user avatar
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3 votes

Is quantum cryptography unbreakable?

The difference between cryptographic algorithms and quantum key distribution (QKD) is that the algorithms operate purely in the mathematical realm of information theory. QKD is a physical process. ...
Cort Ammon's user avatar
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2 votes

How do quantum key distribution systems tolerate noise?

That question is essentially A.1 of this lengthy post, with some elements of answer in B.1 For your convenience, here’s quoting those specific sections of his linked answer: A. Issues prevent ...
e-sushi's user avatar
  • 17.9k
2 votes

Density operator

The density operator of a pure quantum state $|\psi\rangle$ is simply its outer product with itself: $|\psi\rangle\langle\psi|$. For each of the four BB84 states $|0\rangle$, $|1\rangle$, $|+\rangle$, ...
Daniel S's user avatar
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2 votes

Which QKD schemes don’t utilize an authenticated classical channel?

Which QKD schemes don’t utilize an authenticated classical channel? None that can be trusted. All secure Key Distribution systems, quantum or not, require an authenticated channel at setup, before ...
fgrieu's user avatar
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2 votes
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Has anyone implemented the BB84 protocol?

Has anyone implemented the BB84 protocol and put it in production? There are a number of commercial QKD devices on the market, including ones by IDQuantique, QuintessenceLabs, MagicQ and SeQureNet. ...
poncho's user avatar
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1 vote

Two untrusting people want to come up with a random number

I think this paper solves at least partially your problem.
Ievgeni's user avatar
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1 vote

Why Quantum Key Distribution (QKD) is impractical

Just to interject a voice of sanity, can I tell you about Keith? I have a Mini(Keith). He's little and a grand piano won't fit into the trunk. Neither will a small flock of sheep. He also has a wading ...
Paul Uszak's user avatar
  • 15.5k
1 vote

Does the bit generated password using QKD protocols need to be converted to another base?

Do the bits generated password using QKD protocols need to be converted to another base before being used as a key for the one time pad? No, if the OTP encrypts symbols that are bits, as does the ...
fgrieu's user avatar
  • 142k
1 vote

Does the bit generated password using QKD protocols need to be converted to another base?

As you know, most computers talk in binary " (with only 1s and 0s)". So $E_K(P) = C$ in any base as long as encryption function $E$ is a bijection. Therefore $E'_{K}(C) = P$ reveals the ...
Paul Uszak's user avatar
  • 15.5k
1 vote

Determination of the key rate of BBM92 Quantum Key Distribution (numerically)

The BBM92 paper discusses that it is, in fact, exactly equivalent to the BB84 protocol. It is not discussed in the paper, but that would naturally imply that the key-rate equation is the same for ...
Qubed's user avatar
  • 56
1 vote

How is QKD (Quantum Key Distribution) advantageous over McEliece/AES?

QKD is "popular" as it doesn't rely on an algorithm that can possibly be broken. McEliece doesn't have a security proof. So although it is thought to be secure after many years of analysis, ...
Maarten Bodewes's user avatar
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