Key sifting

Selecting the raw key rounds from announced measurement settings and other public acceptance data. Outcomes revealed for parameter estimation must be excluded from the secret raw key. Basis announcements follow receipt of the quantum systems; premature basis announcement in quantum key distribution can permit a memory attack.

In quantum key distribution, a raw key is an intermediate string of correlated bits obtained from measurement outcomes before the full reconciliation and privacy-processing stages are complete. Terminology varies about whether the name applies before or after key sifting, so a protocol description should state its stage explicitly. The bits can contain errors and may be partly known to an adversary. Information reconciliation aligns the parties' strings, while privacy amplification shortens them to a final key with a quantified secrecy property. A raw bit count alone is not a secure final key length.