Quantum key distribution (QKD) offers a practical solution for secure communication between two distinct parties via a quantum channel and an authentic public channel. In this work, we consider different approaches to the quantum bit error rate (QBER) estimation at the information reconciliation stage of the post-processing procedure. For reconciliation schemes using LDPC codes we develop a novel syndrome-based QBER estimation algorithm. The suggested algorithm is suitable for irregular LDPC-codes, and takes into account punctured and shortened bits. With testing our approach in the real QKD setup, we show that an approach combining the proposed algorithm with conventional QBER estimation techniques allows improving accuracy of the QBER estimation.

Quantum key distribution (QKD) enables unconditionally secure communication between distinct parties using a quantum channel and an authentic public channel. Reducing the portion of quantum-generated secret keys, that is consumed during the authentication procedure, is of significant importance for improving the performance of QKD systems. In the present work, we develop a lightweight authentication protocol for QKD based on a 'ping-pong' scheme of authenticity check for QKD. An important feature of this scheme is that the only one authentication tag is generated and transmitted during each of the QKD post-processing rounds. For the tag generation purpose, we design an unconditionally secure procedure based on the concept of key recycling. The procedure is based on the combination of almost universal2 polynomial hashing, XOR universal2 Toeplitz hashing, and one-time pad (OTP) encryption. We also demonstrate how to minimize both the length of the recycled key and the size of the authentication key, that is required for OTP encryption. Finally, we provide a security analysis of the full key growing process in the framework of universally composable security.