Quantum Computing Stack Exchange
Quantum Computing Stack Exchange

Questions tagged [cryptography]

For questions about cryptography as it relates directly to quantum computing. Not for general cryptographic methods.

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

Reference: https://en.wikipedia.org/wiki/Quantum_cryptography

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How is quantum cryptography different from cryptography used nowadays?

Recent researches indicate that quantum algorithms are able to solve typical cryptology problems much faster than classic algorithms. Have any quantum algorithms for encryption been developed? I'm aware about BB84, but it only seems to be a partial…
Be Brave Be Like Ukraine
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Does quantum computing threaten blockchain?

As per Wikipedia, blockchains are a way to maintain "a continuously growing list of records, called blocks, which are linked and secured using cryptography [... and] inherently resistant to modification of the data." Blockchains are in current…
Daniel Tordera
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How to justify post quantum encryption security?

Is there some definition or theorem about what a quantum computer can achieve from which post-quantum cryptographic schemes (eg lattice cryptography, but not quantum cryptography) can justify their security? I know the period finding function is…
Joseph Johnston
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How can we reliably know if a key size is still safe to use as new quantum computers are created?

I've heard that quantum computers pose a major threat to 1024 bit and possibly even 2048 bit RSA public-private key cryptography. In the future however, bigger size keys will probably become at risk at one point or another, as newer, faster quantum…
Alex Jone
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Quantum computing and blockchain technology

It is popularly stated that quantum computing could destroy and disrupt blockchain technology completely. How is quantum computing a threat to blockchain technology?
Chetan Warke
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What measures can be taken against attacks on cryptosystems by quantum computers other than just classifying research?

If quantum computers advance to the point where they can defeat RSA, DSA, SHA (and really all existing classical public key encryption or and authentication) then it appears that it would be impossible to make secure transactions on the internet. …
user4574
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Has it been proved that true post-quantum cryptography protocols exist?

Post-quantum cryptography is the development of cryptographic protocols that are not easily crackable using a fault-tolerance quantum computer. I know that NIST has a competition to find the best post-quantum cryptography algorithm, and some of the…
Mauricio
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What's the effective speed of quantum computers circa 2022?

Obviously they do not correspond to classical clock speeds, but they still have a number of operations they can do per second. And it does really matter a lot. Suppose you are attacking an SHA256 hash. Because of rainbow tables, you only have about…
Steve
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How is it possible for Quantum computers to handle encryption if their states are unstable?

I've been doing research on quantum computers and encryption. How is it possible for quantum computers to solve complex encryption algorithms while their qubit states are not even predictable? How is it even possible for them to implement vectoring?…
Daniel Jerome
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Theoretical obstacles for a BZK-like quantum algorithm instantiated with a subroutine operates at small block size?

Obviously this specific topic had not been thoroughly studied, and the best we can do are empirical deductions based on past experience with quantum algorithms. The security of lattice-based public-key encryption and digital signature schemes are…
DannyNiu
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(Why) does unconditionally secure multi-party quantum computation imply quantum bit commitment?

I have read in several papers now that information-theoretically secure multi-party quantum computation (MQPC) with a dishonest majority ($t \geq n/2$) is impossible because of the impossibility of unconditionally secure quantum bit commitment.…
jgerrit
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Will post quantum crypto come soon enough?

The main reason to start with Post Quantum Crypto (PQC) right now is because creating strong crypto, good implementation and accepted standards takes very long. Right now, most PQC is in the 'crypto' stage or starting to enter 'implementation'…
Discrete lizard
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Clarifying Mosca's Inequality Theorem - parallel vs additive

I wonder if anyone might have some insight into Mosca’s Inequality "Theorem". It states when users need to be worried about quantum computers factoring traditional cryptography. Mosca’s theorem says, “We need to start worrying about the impact of…
Roger A. Grimes
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Are there any examples of "harvest now, decrypt later" that we know of?

It seems like all the worry about quantum computers breaking encryption is based on speculation that someday quantum computers will break modern encryption. I think we can all agree it will happen at some point, but I have yet to find any credible…
Rydberg
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Clarification on the definition of cipherstate in the quantum one-time pad

I was reading the paper “Optimal Encryption of Quantum Bits ” (quantum one-time pad) and came across the following paragraph: The input state, $\rho$, is called the message state, and the output state, $\rho_c$, is called the cipherstate. The…
Josh
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