How will quantum computing affect current cryptography practices?

A large-scale, fault-tolerant quantum computer poses an existential threat to our current cryptographic standards.

Threat to Asymmetric Encryption (e.g., RSA/ECC):

This is the encryption that protects almost everything online (HTTPS, e-commerce, VPNs, banking). It relies on the fact that it's easy for a classical computer to multiply two large prime numbers but impossibly hard to factor the result.

Shor's Algorithm, designed for a quantum computer, can solve this factoring problem with ease, effectively breaking this type of encryption.35 This is an "all-or-nothing" threat; when it happens, RSA will be completely insecure.

Threat to Symmetric Encryption (e.g., AES-256):

This is the encryption that protects files on your hard drive. A quantum algorithm called Grover's Algorithm can speed up the search for the correct key.

This is not a "world-ending" threat. It simply means we need to use longer keys. For example, AES-256 is considered secure against Grover's Algorithm, as it would still take an impossibly long time to crack.

The Solution (Already in Progress):

The solution is Post-Quantum Cryptography (PQC). PQC refers to new, classical encryption algorithms that are believed to be secure against attacks from both classical and quantum computers.

The U.S. National Institute of Standards and Technology (NIST) finalized its first set of PQC standards in 2024 (e.g., CRYSTALS-Kyber and CRYSTALS-Dilithium). The world is now in a "migration period," where companies are beginning the multi-year process of upgrading their systems to be "quantum-resistant."