Last reviewed 10 November 2026
The quantum threat
A cryptographically relevant quantum computer, if one is built, would change the maths problems that protect today's public-key cryptography. This lesson names the main quantum algorithms involved and one confidentiality risk that does not wait for that machine to exist.
Authority recommendation: NIST IR 8547, October 2026, names Shor's algorithm as the quantum algorithm that threatens today's public-key key establishment and digital signatures. It names Grover's algorithm as the more limited threat, which does not by itself retire symmetric cryptography on the same timetable.
Harvest-now, decrypt-later means collecting ciphertext now and decrypting it later, when a breakthrough makes that possible. The risk applies to confidentiality: information that was meant to stay secret for years could be read later if the public-key cryptography that protected it is broken. Long-lived secrets therefore matter even before such a computer exists.
This page does not say that a cryptographically relevant quantum computer already exists.
Next: What post-quantum means.
Sources
- NIST IR 8547, Transition to Post-Quantum Cryptography Standards, October 2026. NIST IR 8547