'Key' in the Bible

And to the angel of the assembly in Philadelphia write: These things saith the holy, the true; he that has the key of David, he who opens and no one shall shut, and shuts and no one shall open:

And the fifth angel sounded his trumpet: and I saw a star out of the heaven fallen to the earth; and there was given to it the key of the pit of the abyss.

And I saw an angel descending from the heaven, having the key of the abyss, and a great chain in his hand.