Research On Quantum Multi-agent Blind Signature Scheme

With the rapid development and popularization of Internet and computer, our modern society is stepping into the information era. Informatization makes people's life convenient and fast, it also triggers the issue of information security concerned increasingly by the world. Information security is not only involved with personal life and privacy, but also related to the security of economy, finance, politics and national defense. Therefore, information security has become one of the most press-ing problems in modern society. Cryptographic technique plays an important role in protecting information security.As an important branch of cryptography, digital signature is an effective way to guarantee the authentication, integrality and undeniability of messages. The se-curity of most digital signature schemes is based on some difficult mathematical problems, such as large integer factoring problem and discrete logarithm problem. Unfortunately, if quantum computer is built in the future, it will threaten the se-curity of the classical signature schemes. Nowadays, many researchers have paid attention to the quantum signature scheme whose security is guaranteed by the principle of quantum mechanics.This thesis combines the property of multi-proxy with blindness, and investi-gates two kinds of quantum multi-proxy blind signature scheme. The main results are as follows:1. A quantum multi-proxy blind signature scheme based on teleportation is proposed. In this scheme, a special type of non-maximally entangled three-qubit state is used, which can realize perfect teleportation and reduce the implementation complexity. A message owner blinds his message by means of preparing two groups of nonorthogonal single-photon states. According to the original signer's delegation message, each proxy signer implements corresponding operation to sign the blind-ed message. An arbitrator can help a receiver verify the signature, and prevent the receiver from doing any damage. Security analysis and discussion show that this scheme not only satisfies the security requirements, i.e., undeniability and un- forgeability, but also possesses the special properties of multi-proxy, blindness and untraceability, so it has certain application value in an e-voting system, e-payment system, etc. Meanwhile, this scheme can resist some common attacks.2. A quantum multi-proxy blind signature scheme based on symmetric key is proposed. Under the supervision of an arbitrator, an original signer delegates her signing authority to a group of proxy signers by using a classical warrant. A random factor is introduced by a message owner to blind a message, the anonymity of the message is guaranteed by the blind factor but not the blind method. Each proxy signer signs the blinded message via applying appropriate unitary operators. The signing unitary operators have no commutative and anticommutative relations with the Pauli matrices so that this scheme is free from the existential forgery under known message attack. The arbitrator can help a receiver verify the signature, and keep him from forging and denying. It is showed that this scheme not only satisfies undeniability and unforgeability that general signature scheme should possess, but also has the particular properties of multi-proxy, blindness and untraceability, so it could be applied to an e-voting system, e-payment system, etc. At the same time, this scheme can resist some common attacks.