cephas is aramic for rock, and the strong's greek indicate is as masculine.
Jesus asked them all, "But what about you (plural)? Who do you (plural) say that I am?" Although it is Simon that answers, it is not that the others did not know that He is "the Christ, the Son of the living God," since in v. 20 He admonishes (them) not to tell anyone that He was the Christ. If anyone believes that He is the Christ, the Son of the living God, it has been revealed to him by His Father in heaven (v.17) and not by flesh and blood. Jesus has the keys to death and hades so access to any keys at all is through Him, not Peter.
Jesus asked them all, "But what about you (plural)? Who do you (plural) say that I am?" Although it is Simon that answers, it is not that the others did not know that He is "the Christ, the Son of the living God," since in v. 20 He admonishes (them) not to tell anyone that He was the Christ. If anyone believes that He is the Christ, the Son of the living God, it has been revealed to him by His Father in heaven (v.17) and not by flesh and blood. Jesus has the keys to death and hades so access to any keys at all is through Him, not Peter.
Jesus is the king who has the keys, he made Peter his stewart. Isiah 22 has a parallel idea to this. A king gives the keys to his stewart, and those keys are passed down to his descendants. The stewart is NOT the king, and all of the authority the keys hold is still tied to the king, but that doesn't change the fact that the stewart has the special keys that nobody else except the king has.