Blockchain is a distributed database which is cryptographically protected against malicious modifications. While promising for a wide range of applications, current blockchain platforms rely on digital signatures, which are vulnerable to attacks by means of quantum computers. The same, albeit to a lesser extent, applies to cryptographic hash functions that are used in preparing new blocks, so parties with access to quantum computation would have unfair advantage in procuring mining rewards. Here we propose a possible solution to the quantum-era blockchain challenge and report an experimental realization of a quantum-safe blockchain platform that utilizes quantum key distribution across an urban fiber network for information-theoretically secure authentication. These results address important questions about realizability and scalability of quantum-safe blockchains for commercial and governmental applications.

We report the results of the implementation of a quantum key distribution (QKD) network using standard fibre communication lines in Moscow. The developed QKD network is based on the paradigm of trusted repeaters and allows a common secret key to be generated between users via an intermediate trusted node. The main feature of the network is the integration of the setups using two types of encoding, i.e. polarisation encoding and phase encoding. One of the possible applications of the developed QKD network is the continuous key renewal in existing symmetric encryption devices with a key refresh time of up to 14 s.

Quantum key distribution (QKD) provides information-theoretic security in communications based on the laws of quantum physics. In this work, we report an implementation of quantumsecured data transmission in the infrastructure of Sberbank of Russia in standard communication lines in Moscow The experiment is realized on the basis of the already deployed urban fibre-optic communication channels with significant losses. We realize the decoy-state BB84 QKD protocol using the one-way scheme with polarization encoding for generating keys. Quantum-generated keys are then used for continuous key renewal in the hardware devices for establishing a quantum-secured VPN Tunnel between two offices of Sberbank. The used hybrid approach offers possibilities for longterm protection of the transmitted data, and it is promising for integrating into the already existing information security infrastructure.

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.