We give an abstraction of multisecret sharing based on Lagrange interpolating polynomial that is accessible to a fully mechanized analysis. This abstraction is formalized in the applied pi-calculus by using an equational theory that characterizes the cryptographic semantics of multisecret sharing based on Lagrange interpolating polynomial. We also present an encoding from the equational theory into a convergent rewriting system, which is suitable for the automated protocol verifier ProVerif. Finally, we verify the Yang–Chang–Hwang (YCH) protocol in ProVerif. Copyright © 2013 John Wiley & Sons, Ltd.