Quantum Secure Communication Protocols Based On W States

Quantum cryptography is a new cross subject with the combination of classic cryptography and quantum mechanics, compared with the classical cryptography. The basic principles of quantum mechanics ensures its unconditional security, it also has the character that can detect eavesdropping. therefore, quantum cryptography can solve the problem that classical cryptography relies on mathematical difficulties of computational complexity to ensure the safety, it has developed rapidly both in theory and experiment.This paper mainly involved two fields including quantum secret sharing and quantum secure direct communication. Quantum secret sharing, namely, divide the secret information into several parts, any of the participants can’t get the secret, only all of them who work together can recover the secret; Quantum secure direct communication is which both the communication sides don’t need to share a secret in advance, use the quantum channel to shared secret messages directly. This paper proposes a quantum secret sharing scheme based on W states, the secret information is encoding on the W states by Pauli matrix, and to ensure the safety of the quantum channel, the nonorthogonal states are insert randomly into the W states. in addition, to recover the secret, the participants only need to perform 3 particle projection measurements. In quantum secure direct communication, a QSDC protocol based on symmetric W state is proposed, Alice splits the W state particles, and encrypts the shared secret information on the quantum state through certain local operations, then Bob can get Alice’s secret information through choosing suitable measurement bases to measure the two particles in her hand according to Alice’s measurement result. Bell states are inserted into the transmission of particle sequences in order to detect the hacking in the quantum channel. The analysis proves that the scheme is secure and efficient, the quantum efficiency is 67% in theory.