Twoparty quantum key agreement against collective noisy channel Quantum key agreement (QKA) permits participants to constitute a shared key on a quantum channel, and no participants are able to independently determine the shared key. In fact, particles are frequently affected by channel noise in the transmission process of quantum channel. Under the cover of noise, attackers can launch malicious attacks. In this thesis, on account of the usage of entanglement swapping of GHZ state and logical Bell states, we design two twoparty QKA protocols which are immune to collectivedephasing noise and collectiverotation noise, respectively. In comparison with the existing QKA protocols of two parties, the proposed protocols have better quantum resource cost and the qubit efficiency in the global scope. Security analysis reveals that they can resist not only attacks by participants but also external attacks.

Semiquantum cryptography Semiquantum communication, a model introduced by Boyer et al. (Phys Rev Lett 99:140501, 2007), involves the use of fully quantum users and semiquantum, or xe2x80x9cclassicalxe2x80x9d users. These restricted users are only allowed to interact with the quantum channel in a limited manner. Originally introduced to study the keydistribution problem, semiquantum research has since expanded, and continues to grow, with new protocols, security proof methods, experimental implementations, and new cryptographic applications beyond key distribution. Research in the field of semiquantum cryptography requires new insights into working with restricted protocols and, so, the tools and techniques derived in this field can translate to results in broader quantum information science. Furthermore, other questions such as the connection between quantum and classical processing, including how classical information processing can be used to counteract a quantum deficiency in a protocol, can shed light on important theoretical questions. This work surveys the history and current state of the art in semiquantum research. We discuss the model and several protocols offering the reader insight into how protocols are constructed in this realm. We discuss security proof methods and how classical postprocessing can be used to counteract usersxe2x80x99 inability to perform certain quantum operations. Moving beyond key distribution, we survey current work in other semiquantum cryptographic protocols and current trends. We also survey recent work done in attempting to construct practical semiquantum systems including recent experimental results in this field. Finally, as this is still a growing field, we highlight, throughout this survey, several open problems that we feel are important to investigate in the hopes that this will spur even more research in this topic.