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Does a quantum computer crack every password in seconds?

Movie · Hacking thrillers, from the 1990s on

Stretched. The mechanism is real, and the scene pushes it past what it does.

What the scene or the claim says

A quantum machine is plugged in and every lock in the building opens.

What is real

Shor's algorithm (1994) factors integers and computes discrete logarithms efficiently, which would break RSA and elliptic-curve cryptography. Those protect web connections, software signatures and Bitcoin keys.

What stops it working that way

• It needs an error-corrected machine far larger than any built. Our Bitcoin page tracks the qubit estimates, which have fallen sharply on paper and still sit orders of magnitude above what exists.
• Passwords and symmetric ciphers such as AES face only Grover's square-root speedup, so a longer key answers it.
• A password guess usually needs the login server to reply to each try. The limit is the service, not the attacker's processor.

If you wanted it to work

The plausible danger is slower and quieter: record encrypted traffic today, open it years from now. That is why NIST published its first post-quantum standards in August 2024 (FIPS 203, 204 and 205) and why migration is under way now. What would change the timeline is a fault-tolerant machine arriving earlier than the estimates say, so the estimates are worth watching more than the headlines.

Learn the physics

• Can quantum break Bitcoin?
• Post-quantum, on the wire

Sources

• Shor 1994
• NIST's first three post-quantum standards

See it in the swipe deck, with the other cards.