Universally composable and customizable post-processing for practical quantum key distribution

In quantum key distribution (QKD), a secret key is generated between two distant parties by transmitting quantum states. Experimental measurements on the quantum states are then transformed to a secret key by classical post-processing. Here, we propose a construction framework in which QKD classical post-processing can be custom made. Though seemingly obvious, the concept of concatenating classical blocks to form a whole procedure does not automatically apply to the formation of a quantum cryptographic procedure since the security of the entire QKD procedure rests on the laws of quantum mechanics and classical blocks are originally designed and characterized without regard to any properties of these laws. Nevertheless, we justify such concept of concatenating classical blocks in constructing QKD classical post-processing procedures, along with a relation to the universal-composability-security parameter. Consequently, effects arising from an actual QKD experiment, such as those due to the finiteness of the number of signals used, can be dealt with by employing suitable post-processing blocks. Lastly, we use our proposed customizable framework to build a comprehensive generic recipe for classical post-processing that one can follow to derive a secret key from the measurement outcomes in an actual experiment.