Undeniable signature scheme, devised by Chaum and van Antwerpen [CV90][CV92], are non-self-authenticating signature schemes, where signatures can only be verified with the signer's consent. However, if a signature is only verifiable with the aid of a signer, a dishonest signer may refuse to authenticate a genuine document. Undeniable signatures solve this problem by adding a new component called the disavowal protocol in addition to the normal components of signature and verification.