The quantum key distribution (QKD) protocol provides an absolutely secure way to distribute secret keys, where security can be guaranteed by quantum mechanics. To raise the key generation rate of classical BB84 QKD protocol, Hwang et al. (Phys Lett A 244(6):489–494, 1998) proposed a subtle variation (Hwang protocol), in which a pre-shared secret string is used to generate the consistent basis. Although the security of Hwang protocol has been verified in ideal condition, its practicality is still being studied in more depth. In this work, we propose a simple attack strategy to obtain all preparation basis by stealing partial information in each round. To eliminate this security threat, we further propose an improved QKD protocol using the idea of iteratively updating the basis. Furthermore, we apply our improved method to decoy-state QKD protocol and double its key generation rate.

量子密钥分发（QKD）协议提供了一种绝对安全的密钥分发方式，其中量子机制可以保证安全性。为了提高经典的BB84 QKD协议的密钥生成率，Hwang等人。（Phys Lett A 244（6）：489–494，1998）提出了一种微妙的变化（Hwang协议），其中使用了预共享的秘密字符串来生成一致的基础。尽管Hwang协议的安全性已在理想条件下得到验证，但其实用性仍在深入研究中。在这项工作中，我们提出一种简单的攻击策略，通过在每一轮中窃取部分信息来获得所有准备基础。为了消除这种安全威胁，我们进一步提出了一种改进的QKD协议，它使用了迭代更新基础的思想。此外，