Information reconciliation for quantum key distribution

Quantum key distribution (QKD) relies on quantum and classical procedures in orderto achieve the growing of a secret random string --the key-- known only to the twoparties executing the protocol. Limited intrinsic efficiency of the protocol, imperfectdevices and eavesdropping produce errors and information leakage from which the set ofmeasured signals --the raw key-- must be stripped in order to distill a final, informationtheoretically secure, key. The key distillation process is a classical one in which basisreconciliation, error correction and privacy amplification protocols are applied to the rawkey. This cleaning process is known as information reconciliation and must be done in afast and efficient way to avoid cramping the performance of the QKD system. Brassardand Salvail proposed a very simple and elegant protocol to reconcile keys in the secret-key agreement context, known as Cascade, that has become the de-facto standard for allQKD practical implementations. However, it is highly interactive, requiring many com-munications between the legitimate parties and its efficiency is not optimal, imposing anearly limit to the maximum tolerable error rate. In this paper we describe a low-densityparity-check reconciliation protocol that improves significantly on these problems. Theprotocol exhibits better efficiency and limits the number of uses of the communicationschannel. It is also able to adapt to different error rates while remaining efficient, thusreaching longer distances or higher secure key rate for a given QKD system.