Walter E. Block, Loyola University of New Orleans, College of Business, has published A Libertarian Theory of Blackmail. Here is the abstract.
Download the text from SSRN at the link.This article will attempt to analyze the law prohibiting blackmail from a libertarian perspective. Libertarianism is a political philosophy; as such, it is a theory of the just use of violence. From this viewpoint, the just use of violence is essentially defensive: one may employ force only to repel an invasion; only to protect one’s person or property from external threat, and for no other reason.