Advance in Security Proofs of Quantum Key Distribution and Its Challenges towards Practical Implementation

This paper provides an overview of advancements in the security proof of quantum key distribution (QKD) while discussing the rationale and challenges of its practical implementation. QKD ensures information-theoretic security, meaning even eavesdroppers with unlimited computational power cannot decipher the transmitted data. As a result, it is resilient against various attacks, including eavesdropping and harvest-now-decrypt-later attacks strategies, where ciphertext is stored for future decryption attempts. QKD encompasses a range of methodologies, each supported by corresponding security proofs. Since the introduction of the first QKD protocol, BB84, in 1984, significant theoretical progress has been made to address evolving technologies and counter implementation attacks that exploit device imperfections. In 2020, the first security proof for continuous-variable QKD (CV-QKD) was established. This method offers greater compatibility with existing optical fiber networks. Despite its advantages, QKD requires specialized devices, resulting in high costs for network construction. Currently, QKD is primarily suitable for transmitting highly confidential information across multiple hubs. To encourage its adoption, several challenges must be addressed, including advancing quantum relay technologies, enhancing performance, establishing protocol standards, and creating institutional frameworks for verifying and certifying device security.