Similar to device-independent quantum key distribution （DI-QKD）, semi-device-independent quantum key distribu- tion （SDI-QKD） provides secure key distribution without any assumptions about the internal workings of the QKD devices. The only assumption is that the dimension of the Hilbert space is bounded. But SDI-QKD can be implemented in a one- way prepare-and-measure configuration without entanglement compared with DI-QKD. We propose a practical SDI-QKD protocol with four preparation states and three measurement bases by considering the maximal violation of dimension witnesses and specific processes of a QKD protocol. Moreover, we prove the security of the SDI-QKD protocol against collective attacks based on the min-entropy and dimension witnesses. We also show a comparison of the secret key rate between the SDI-QKD protocol and the standard QKD.
Information reconciliation is a significant step for a continuous-variable quantum key distribution（CV-QKD） system.We propose a reconciliation method that allows two authorized parties to extract a consistent and secure binary key in a CV-QKD protocol,which is based on Gaussian-modulated coherent states and homodyne detection.This method named spherical reconciliation is based on spherical quantization and non-binary low-density parity-check（LDPC） codes.With the suitable signal-to-noise ratio（SNR） and code rate of non-binary LDPC codes,spherical reconciliation algorithm has a high efficiency and can extend the transmission distance of CV-QKD.
In this paper, for the unbalanced Feistel network which employs diffusion matrices in a switching way, we study the fixed number of its differential active S-boxes. Firstly we obtain some lower bounds of the differential active S-boxes for m, 2m and 3m rounds of Feistel structure, respectively. By concatenating these rounds, a fixed number of differential active S-boxes for arbitrary round number is derived. Our results imply that the unbalanced Feistel network using DSM is more secure than the traditional structure.
