| dc.description.abstract | Being a digital alternative of a hand-written signature, an ordinary digital signature provides better protections in security aspects but unfortunately achieves no significant improvement in functional aspects. Many recent researches try to enrich digital signatures by introducing a diversity of novel and practical functionalities over the ordinary ones. Duo to the variety of application scenarios digital signatures can be applied to, privacy-related issues of digital signatures should never be overlooked; hence a large part of those new signature developments involves privacy enhancement. In this dissertation, privacy-related issues of digital signatures are extensively discussed from the view points of different participants of a digital signature scheme.
For the privacy of the signer, some signature schemes with signer-ambiguity are discussed. First of all, a designated verifier signature scheme with secure disavowability is suggested; the suggested scheme keeps the identity of the signer ambiguous to third-party observers while maintains the signature non-repudiation property. Secondly, by using concurrent signatures, a fair and practical transaction model for online shopping applications is introduced; and thirdly, by using ring signatures, a mobile agent price survey protocol which simultaneously achieves publicly verifiable forward integrity and forward privacy is proposed.
For the privacy of the verifier, the security of a previous nominative signature scheme is reconsidered. It is showed that the previous scheme survives after a recent cryptanalysis against the designated verifier’’s privacy, since the recent cryptanalysis neglects a subtle difference between two related security notions, namely, verification and screening. This dissertation also points out that this subtle difference is neglected in some research works of signature batch verification as well.
In some signature schemes with sophisticated functionalities, a third participant might be involved. For the privacy of the possible third participant in a digital signature scheme, proxy signatures are taken as an example and a new proxy signature scheme with privacy enhancement to proxy signers is proposed. More precisely, the proposed scheme provides anonymity and unlinkability to proxy signers; in some applications, these two properties also enhance the privacy of the original signer. | en_US |