# Quantum computer threats to modern cryptography

I am having a university assignment that requires me to study on the threats that quantum computer poses to modern cryptography.

At the moment, I know that modern symmetric encryption will reduce their key size strength in half through Grover's algorithm. It can also break existing standardized RSA, Curve448 and Curve25519 (Not Grover's algorithm).

Can I have the papers or some layman's reference link to those kinds of attacks? Other than the listed attacks, is there any other threats that quantum computer poses to modern cryptography?

• Shor's algorithm is what is used for breaking public key cryptography, not Grover's algorithm. Commented Nov 11, 2022 at 3:00
• @forest Does shor's algorithm also applies to named elliptic curve448 and curve25519? Due to my limited understanding, I only know shor's algorithm poses a great threat to RSA by simply ignoring the prime numbers factorization, a form of solving discrete logarithm problem.
– Hern
Commented Nov 11, 2022 at 3:07
• @Hern, Shor's algorithm is also applicable to discrete algorithm, regardless the form of the underlying group, so Curve448 and Curve25519 are also breakable by Shor's algo. Commented Nov 11, 2022 at 5:22
• How about the entropy generation for cryptography keys generation? Is there any papers out there that states current cryptography keys generation could poses a problem to quantum computing(I don't really know about this one that's why I asked)
– Hern
Commented Nov 11, 2022 at 5:54
• "modern symmetric encryption will reduce their key size strength in half through Grover's algorithm" is a pessimistic worst-case scenario. See this for a more nuanced view. Independently: "entropy generation for cryptography keys generation" is a possible application of quantum physics to cryptography; not a "threat to modern cryptography"; the many failures of RNGs are typically attributable to inappropriate design, rather than to use of a not-enough-quantuim source.
– fgrieu
Commented Nov 11, 2022 at 9:10