Table 2.

Trustworthiness levels of TP.

Trustworthiness level	Definition
Honest TP	The TP has to follow the procedure of the protocol honestly and the participants can completely trust it. Therefore, the participants can share their secret information with the TP. However, the assumption of a trustworthy TP may be impractical
Semi-honest TP	The TP has to execute the protocol loyally, but it may try to obtain the participants’ secret information passively using the records of all intermediate transmissions and computations by the participants
Almost dishonest TP	To extract the participants’ secret information, the TP may perform any possible attacks except collaborating with other participants. This assumption is only suitable for some applications such as a quantum private comparison protocol
Untrusted/dishonest TP	The TP may perform any possible attacks