On the Security of Yuan et al.'s Undeniable Signature Scheme

Undeniable signatures were proposed to limit the publicverification property of ordinary digital signature. In fact, theverification of such signatures cannot be obtained without thehelp of the signer via the confirmation/disavowal protocols. Inthis paper, we reconsider the security of the undeniable signaturescheme proposed by Yuan et al. at ICICS 2007, and point out theirscheme does not satisfy the security model of invisibility theauthors presented.