The Research Of Arbitrated Quantum Signature Schemes

The digital signature, which is an important branch of cryptography, plays a key role in the authentication and data integrity protection. However, with the development of quantum computation, it can be seen that the classical digital signature schemes based on hard mathematic problems, seem to be insecure. In order to ensure the security of digital signature in quantum environment, a new researching area named quantum signature has been proposed. Its idea is to directly apply quantum mechanics into the digital signature. In the current study of quantum signature, the arbitrated quantum signature (AQS) schemes provide the basic design and analyzing ideas to quantum signature. That is to say AQS is a significant topic of quantum signature in theory and practice.In this thesis, a detailed study of arbitrated quantum signature (AQS) has been provided. With the analysis of quantum encryption and specific schemes, some design defects and security loopholes existed in the previous schemes are pointed out. Furthermore, the secure schemes and improved strategies are proposed. The contents and main contributions of the thesis can be seen as follows.In the analysis of quantum encryption applied in AQS, the vulnerability "of Choi’s encryption is firstly analyzed. It can be seen that Choi’s encryption cannot prevent the receiver’s forgery attack. Then, from a more general perspective, it has been proved that the existing quantum encryptions whatever they are used to encrypt quantum messages or classical messages, cannot prevent the receiver’s forgery attack. These results show that the quantum encryption algorithms, which are used to make secure communication, should not be directly applied in AQS schemes to ensure their security.In the design and improvement of quantum encryption applied in AQS, the available conditions of Choi’s encryption are firstly pointed out. For the AQS schemes with rotation operations to generate signatures, Choi’s encryption can be improved to prevent the receiver’s forgery attack. Then, using the shared keys to encrypt multiple conditions, a series of general quantum encryptions have been designed to prevent the forgery attack, including the controlled assisted operation encryption, the relation encryption, the sequential encryption and the paralleled multiple operation encryption.In the design and analysis of specific AQS schemes, the security and availability of two arbitrated quantum group signature schemes are analyzed. Firstly, it can be verified that Wen et.al’s arbitrated quantum group signature scheme is a two-party quantum signature in essence, so the receivers can forge the signature and the signer can deny her signature in the scheme. In addition, the signer can disavow her signature successfully with the intercept-resend attack in Xu et.al’s arbitrated quantum group signature scheme. Furthermore, a more secure arbitrated quantum group signature scheme has been proposed utilizing the quantum entanglement swapping technique. At last, the unfeasibility of an arbitrated quantum proxy weak blind signature scheme has been pointed. Since the roles of the participants cannot be suitably controlled, the receiver can forge the signature as he wishes.