Why are quantum computers a threat to encryption?
Because a large, fault-tolerant quantum computer running Shor's algorithm could break the public-key methods used today to agree keys and sign data: RSA and elliptic-curve cryptography (ECC). Those two protect the key exchange of almost every HTTPS, VPN and SSH connection, and the signatures on certificates, software updates and documents. An attacker with such a machine could read traffic recorded earlier and forge signatures. Symmetric encryption such as AES, which encrypts the data once the key is agreed, is weakened only modestly by Grover's algorithm and stays usable with 256-bit keys. No such computer exists today, and nobody can name the year one will. The risk is real for data that must stay secret for many years, and it is something to plan for, not an emergency. The fix is software, not hardware: new algorithms standardised by NIST in 2024, rolled out through updates.