27 votes
Accepted

Is it possible for an encryption method to exist which is impossible to crack, even using quantum computers?

The title of your question asks for techniques that are impossible to break, to which the One Time Pad (OTP) is the correct answer, as pointed out in the other answers. The OTP is information-...
Ella Rose's user avatar
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19 votes

Is it possible for an encryption method to exist which is impossible to crack, even using quantum computers?

I suppose there is a type of encryption that is not crackable using quantum computers: a one-time pad such as the Vigenère cipher. This is a cipher with a keypad that has at least the length of the ...
luap42's user avatar
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18 votes
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Is quantum cryptography safer than classical cryptography?

If you are talking specifically about quantum key distribution (quantum cryptography being an umbrella term that could apply to lots of stuff), then once we have a quantum key distribution scheme, ...
DaftWullie's user avatar
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18 votes

Advantage of quantum key distribution over post-quantum cryptography

Quantum key distribution requires that you wholesale replace your entire communications infrastructure built out of 5 EUR ethernet cables and 0.50 EUR CPUs by multimillion-euro dedicated fiber links ...
Squeamish Ossifrage's user avatar
17 votes

Is it possible for an encryption method to exist which is impossible to crack, even using quantum computers?

Yes, there are a lot of proposals for Post-quantum cryptographical algorithms that provide the cryptographic primitives that we are used to (including asymmetric encryption with private and public ...
Sir Cornflakes's user avatar
16 votes
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Can a quantum computer break quantum cryptography?

This is a good question that highlights the unfortunately broad use of the term "quantum cryptography". Either way, the TL/DR of it is that, although quantum computers break many currently ...
Mark Spinelli's user avatar
15 votes
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Advantage of quantum key distribution over post-quantum cryptography

If it is proven that a given asymmetric encryption protocol relies on a problem which cannot be solved efficiently even by a quantum computer, then quantum cryptography becomes largely irrelevant. ...
glS's user avatar
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15 votes
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Rigorous security proof for Wiesner's quantum money

Abel Molina, Thomas Vidick, and I proved that the correct answer is $c=3/4$ in this paper: A. Molina, T. Vidick, and J. Watrous. Optimal counterfeiting attacks and generalizations for Wiesner's ...
John Watrous's user avatar
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14 votes
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Density matrix after measurement on density matrix

So, Bob is given the following state (also called the maximally-mixed state): $\rho = \frac{1}{2}|0\rangle\langle 0| + \frac{1}{2}|1\rangle\langle 1| = \begin{bmatrix} \frac{1}{2} & 0 \\ 0 & \...
ahelwer's user avatar
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13 votes
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Are there any encryption suites which can be cracked by classical computers but not quantum computers?

This is not a very enlightening concept, because most interesting quantum algorithms, such as Shor's algorithm, involve some classical computations as well. While you can always shoehorn a classical ...
Squeamish Ossifrage's user avatar
12 votes
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How is quantum cryptography different from cryptography used nowadays?

Quantum cryptography relies on elaborate physical machinery to execute cryptographic protocols whose security rests upon axioms of quantum mechanics (theoretically, anyways). To quote the wikipedia ...
Ella Rose's user avatar
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11 votes

Is quantum cryptography safer than classical cryptography?

Most attacks now on classical computers don't actually break the encryption, they trick the systems / communication protocols into using it in a weak way, or into exposing information via side ...
Peter Cordes's user avatar
9 votes

Blind quantum computing — generic structure variable selection

As one of the authors of the paper, and of the original theory papers on which that experimental realisation is based, perhaps I can attempt to answer. The BQC protocol used in that paper is based on ...
Joe Fitzsimons's user avatar
8 votes
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How many bits do Alice and Bob needs to compare to make sure the channel is secure in BB84?

Your analysis of Eve's cheating doesn't seem quite right (although the final answer is correct). What you need to say is: Assume Alice prepares a particular state in one of the bases. You could assume ...
DaftWullie's user avatar
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8 votes
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Can we speed up the Grover's Algorithm by running parallel processes?

Certainly! Imagine you have $K=2^k$ copies of the search oracle $U_S$ that you can use. Normally, you'd search by iterating the action $$ H^{\otimes n}(\mathbb{I}_n-2|0\rangle\langle 0|^{\otimes n})H^{...
DaftWullie's user avatar
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7 votes
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How can we reliably know if a key size is still safe to use as new quantum computers are created?

We (i.e. the current state of research) just don't know, but we can guess. We guess that there may be a problem if Post Quantum Crypto (PQC) lags behind, as Shor's algorithm can solve the factoring ...
Discrete lizard's user avatar
7 votes

Rigorous security proof for Wiesner's quantum money

"I'm looking for an explicit upper bound on the probability of successful counterfeiting ...". In "An adaptive attack on Wiesner's quantum money", by Aharon Brodutch, Daniel Nagaj, Or Sattath, and ...
Rob's user avatar
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7 votes

How would Blockchain technologies change to survive a post-quantum world?

Bitcoin uses elliptic-curve cryptography to sign transactions, which can easily be broken by Shor's algorithm. I didn't actually read the article because it looked kind of dumb, but I gathered that ...
tparker's user avatar
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7 votes
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Blind quantum computing — generic structure variable selection

It looks like you're asking about this part of the paper: Therefore, a quantum computation is hidden as long as these measurements are successfully hidden. In order to achieve this, the BQC protocol ...
Nat's user avatar
  • 1,497
7 votes

Does quantum computing threaten blockchain?

Are the current implementations of blockchain resistant to attacks using quantum computation? Quick answers: Resistant against near-term technology? Sure. Reliably secure in the long term? ...
Nat's user avatar
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7 votes
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Has the possibility of there being a classical cryptography algorithm able to withstand quantum computing been proven?

[0001] Regarding the OP's first paragraph and the comments therein, there is no protocol, call it $X$, that can be executed efficiently on classical computers, that has been proven to be secure ...
Mark Spinelli's user avatar
6 votes

'Rectilinear' and 'Diagonal' Basis in BB84 Protocol

Talking about bases such as $\left|0\rangle\langle0\right|$ and $\left|1\rangle\langle1\right|$ (or the equivalent vector notation $\left|0\right>$ and $\left|1\right>$, which I'll use in this ...
Mithrandir24601's user avatar
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6 votes

Is it possible for an encryption method to exist which is impossible to crack, even using quantum computers?

To follow up on Ella Rose's answer: most practical encryption schemes used today (e.g. Diffie-Hellman, RSA, elliptic curve, lattice-based) are centered around the difficulty of solving the hidden ...
tparker's user avatar
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6 votes
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How to justify post quantum encryption security?

This is essentially the realm of computational complexity classes. For example, the class BQP may crudely described as the set of all problems that can be efficiently solved on a quantum computer. The ...
DaftWullie's user avatar
  • 58.1k
6 votes

Density matrix after measurement on density matrix

So Alice sends Bob a qubit with the density matrix $$\rho = \frac{1}{2}|0\rangle\langle 0| + \frac{1}{2}|1\rangle\langle 1| = \begin{bmatrix} .5 & 0 \\ 0 & .5 \end{bmatrix}$$ as you said. (I'...
Dripto Debroy's user avatar
6 votes
Accepted

Is the BB84 protocol an example of "quantum supremacy"?

This is an interesting question that reflects a conflation of some concepts in quantum information sciences. TL/DR - there is no task in BB84 that corresponds to what we when we speak of quantum ...
Mark Spinelli's user avatar
6 votes
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What's the effective speed of quantum computers circa 2022?

A few things: The 128 bits of security of SHA-256 is the hardness of a collision search, and pre-image resistance is still (classically) 256 bits. Grover's algorithm only helps with pre-image ...
Sam Jaques's user avatar
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6 votes
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Has it been proved that true post-quantum cryptography protocols exist?

No. Proving this requires (among other things) proving that P$\ne$NP. [0001] We have not proven that a post-quantum cryptographic protocol, satisfying all reasonable definitions, necessarily exists. ...
Mark Spinelli's user avatar
5 votes
Accepted

Quantum Bitcoin Subdivision

Why can you not subdivide a quantum bitcoin? Anyone can create a Cryptocurrency, how it works is up to them, how well it is received is up to the public, generally it is decided by: Utility, Scarcity,...
Rob's user avatar
  • 2,307
5 votes

Quantum computing and blockchain technology

This answer assumes that you do not have a technical background in cryptography or quantum physics. Most current implementations of the blockchain rely on two math concepts: (1) Public key encryption....
QComp2018's user avatar

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