# Quantum Privacy Query Protocol Based on GHZ-like States
## 4 Functional Comparison and Security Analysis
### Functional Comparison  
The references [2; 19; 20; 21] implement different privacy query schemes. In ref. [2], the privacy protection protocol based on OT is designed for protecting [PERSON]'s privacy database, so the user does not know any information other than the type of disease which is corresponding to her symptoms. In addition, the protocol protects the privacy of user [PERSON], so [PERSON] does not know the address of the specific data which is queried by [PERSON]. But with the development of quantum computing, the traditional encryption algorithms are no longer secure. So, the quantum privacy query came up. There are two main methods for quantum key distribution in quantum privacy query: single particle distribution and entangled state distribution. When we use single-particle distribution for quantum privacy queries, users can still attack our protocol through joint measurements. So, some studies in the literature use EPR for quantum privacy queries, such as the ref. [19], and the user can use specific algorithms and iterative steps to obtain the final key. However, the ratio of the original  
Figure 2: The schematic figure of the proposed quantum privacy query based on the GHZ-like states.  
keys known by [PERSON] to the whole original key is surprisingly as high as \(1/6\). So, even if entangled states are used, the number of the key known by [PERSON] is not controlled to \(1\). In our protocol, we use the entangled nature of GHZ-like states so that [PERSON] can infer the original key from [PERSON]'s statement and the secret messages. In this process, we control the number of keys [PERSON] obtains by controlling the number of bits [PERSON] sends secretly. Therefore, our protocol is free from JM attacks and has a significant security improvement. In ref. [20], the protocol utilize w-state for privacy query. It can also evade JM attack, but the use of spurious entangled photons by dishonest third parties may pose a threat to the database and the privacy of the user. In comparison, GHZ-like states are easier to fabricate and remain robust for specific noise and interference. So, GHZ-like states are more suitable for quantum privacy queries. In realizing these QKD protocols, we must take into account the key rate, the quantum production cost, and the quantum robustness. What is more important is whether the protocols resist various security attacks.  
Compare with the above protocols that our protocol has four functions advantages (in Table 4). Firstly, our protocol uses quantum states which can withstand attacks from quantum computers, just like in the literature [19; 20]. Secondly, our protocol adds the detection of illegal eavesdroppers in Step 3. Thirdly, we precisely control the number of keys obtained by the querier in Step 5, which not only sufficiently resists participant's attacks and improves the security but also improves the efficiency of our efficiency of the protocol. Finally, we add authentication in Step 7, which makes our protocol sufficiently resistant to external attackers and improves the security of our protocol to a certain extent. This process not only protects the privacy of user [PERSON] but also protects the privacy of database [PERSON], so [PERSON] does not know the specific address of the data queried by [PERSON].