Secret Keys from Parity Bits in the Satellite Setting

We consider a two-way secret key distribution protocol in the satellite setting, where Alice, Bob and Eve each decode bits from noisy signals received from a source in their environment. Alice and Bob perform advantage distillation to find a secret key. We apply a Two-way Protocol with Parity bit Reconciliation (TPPR) where secret keys are collected from parity bits in course of advantage distillation, not only from the final distilled bits. We analyze the mutual information acquired by Eve from exploiting the original eavesdropped information together with the information leaked during the distillation protocol, as well as TPPR secret key rate. Comparing to the ParityCheck Protocol (PCP) known in the literature, TPPR provides complementary performance. In operation regions where PCP fare badly as compared to one-way protocols, TPPR provides gains in key rate.