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We present a new quantum protocol for comparing the equal information with the help of a semi-honest third party (TP). Different from previous protocols, we utilize the four-particle χ -type states as the information carriers. Various kinds of outside attacks and participant attacks are discussed in detail. One party cannot learn the other's private information. The TP cannot learn any information about the private information, even about the comparison result or the length of secret inputs.

We present a new quantum private comparison protocol based on the four-particle χ -type states. Different from previous protocols using the four-particle χ -type states, our protocol have some advantages. Without using the entangled character, we only need to prepare one type of χ -type state and N χ-type states. And we use the Pauli local unitary operation on particles to encode the information and to extract information by measurement. We also discuss that our protocol can withstand all various kinds of outside attacks and participant attacks.

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