keyrate

Keyrate, in cryptography, refers to the rate at which secure cryptographic keys are produced by a key distribution protocol. It is typically measured in bits per second (bps) or, in some analyses, as bits per transmitted signal. In quantum key distribution (QKD), the keyrate is a central performance metric because it captures how quickly fresh secret keys can be supplied to users after accounting for security requirements.

In a QKD workflow, several stages affect the final keyrate. Quantum signals generate a raw key, which after measurement basis choices undergoes sifting to produce a sifted key. Error reconciliation (or information reconciliation) corrects discrepancies, and privacy amplification reduces any information potentially known to an eavesdropper. The remaining bits constitute the secret key. Thus the secret-key rate is typically lower than the raw or sifted key rate.

Expressed conceptually, the secret-key rate R is the amount of secret information obtained per channel use or per unit time after removing the costs of error correction and privacy amplification. A common informal relation is R ≈ R_sifted − leak_EC − PA, where leak_EC accounts for the information disclosed during error correction and PA represents bits sacrificed to bound an adversary’s knowledge. In practice, R depends on factors such as the quantum bit error rate (QBER), channel loss, detector efficiency, the presence of multi-photon pulses, protocol specifics (for example, decoy-state methods), and finite-size security analyses.

Beyond QKD, keyrate also appears in classical key-exchange settings as the throughput of generating usable keys, emphasizing the distinction between key provisioning and data transmission.