The efficient multipurpose convertible undeniable signature scheme

The digital signature can be verified and disavowed only with cooperation of the signer in undeniable signature scheme. A signed confidential document of a company can be copied and delivered to a rival company. If a conventional signature scheme is used to sign the document, it can be confirmed as authentic by verifying the signature without the signer's cooperation. However, if the company doesn't want the document to be verified as authentic by the rival company, it is recommended to use the undeniable signature scheme. Convertible undeniable signature scheme has additional property that the signer can convert undeniable signature to the ordinary one. The document signed by undeniable signature scheme that is no longer confidential can be opened to public use by converting the signature to the ordinary one. In this study, the efficient multipurpose convertible undeniable signature scheme based on El-Gamal signature scheme is proposed. The proposed scheme satisfies undeniable property and can convert undeniable signature to the ordinary one. The number of public keys and signatures are less than those of Boyar's convertible signature scheme[4]. It also reduces the number of communication steps of the signature confirmation protocol.