Abstract-Quantum key distribution (QKD) is the future of the cryptography world. The QKD was invented to increase the security rate when exchanging a private key. Since 1984, several experimental attempts to design protocols have been developed based upon the rule of physics. These QKD protocols were represented by different algorithms with limited ability to stand up against quantum attacks. This paper evaluates the most functional QKD protocols in the cryptography field and explains every QKD protocol as well illustrates the features that were utilized in each protocol.