Does South Korea Have the Right to Blockade North Korea?

What should South Korea do if it confirms the responsibility of North Korea for the sinking of a South Korean naval vessel?  This article quotes a Korean law professor offering three options:

Writing in JoongAng Daily, Kim Hyun-soo, professor of international law at Inha University, said Lee has three options if he wishes to avoid risking all-out war on the peninsula. He could demand concerted action by the UN security council; he could take his case to the international court of justice; or, failing that, he could impose a maritime blockade, as the US did against Cuba in 1962.

The first option seems no problem, except that it is hard to get the Security Council to do anything.  The second option is a problem since, well, North Korea has not accepted the compulsory jurisdiction of the ICJ.  The third option seems the most interesting, but it is also the most complicated one legally.  The Koreas are in a state of cease-fire.  But blockades, at least in theory, are not permitted under the U.N. Charter except when authorized by the Security Council (see U.N. Charter Art. 42). The 1962 U.S. “quarantine” of Cuba was carefully not called a blockade to avoid this legal problem.  I suppose South Korea could end the cease-fire, initiate hostilities, and institute the blockade as part of its right of self-defense.  Now that would be legally defensible, although it would probably start an all out (maybe even nuclear) war. So let’s hope they go with option 1.