Technology

Anybody who believed that quantum computing posed a risk to symmetric encryption was fundamentally misunderstanding how encryption works and what quantum computing might be good at one day.

Asymmetric cryptography is primarily used for the secure exchanging of symmetric keys: use a public/private key pair to exchange secure messages of what symmetric key to use for their session, and then both sides switch to the symmetric key for actual communication of a real payload.

A public/private key pair is two keys that have some interesting mathematical relationship, such that it is easy to confirm that someone possesses the right private key using the public key or to encrypt something that only the correct private key can decrypt. And that mathematical relationship, relating to the product of two very large prime numbers, is at the core of modern asymmetric cryptography.

Quantum computing may make number factorization much, much easier. So once a product of two large primes becomes possible to factor, the public/private key pairs might not be as secure anymore.

But none of this has anything to do with symmetric encryption, or hash functions. Quantum doesn't move the needle on that particular math.

The real risk, though, is for an adversary to eavesdrop on an encrypted key exchange (which uses asymmetric cryptography) and then the message itself (which uses symmetric cryptography) and then be able to take the two steps of getting the secret symmetric key from the intercepted key exchange over a compromised asymmetric protocol, and being able to decrypt the symmetric portion of the communication too.