Iran does not have full sovereignty over the strait of Hormuz. Ownership of the the strait is split between Iranian and Omani territorial waters. Iran has sovereignty over the waters on its side, but Iran does not have sovereignty over the Omani side.
Iran maintains a blockade on the strait by placing mines in Omani waters, and firing missiles at civilian ships that attempt to pass in Omani waters. It has no legal basis to do either of those.
