Kengo Mori

An implementation of a universally verifiable electronic voting scheme based on shuffling

This paper discusses the implementation of the voting scheme based on mix-net technology. The advantages of employing this technology are that voters can vote-and-go, and that it is flexible enough to be used for variety of vote-expression methods, while ensuring the privacy of votes and the elimination of faulty players. The most attractive security feature of this scheme is its universal verifiability; anyone can confirm the correctness of the result. Such verifiability is achieved by providing proofs on correct shuffling and decryption. The paper presents a new scheme for generating a single proof for shuffle-and-decrypt process. Compared to the combination of two separate proofs on shuffle and decryption, the new scheme is 150% faster with only 80% of the length. As a result, the system was able to produce results that were verified correct within twenty minutes following a vote participated in by ten thousand voters, with three shuffling centers being used. We believe this is the first implementation report of a voting scheme with universal verifiability.

Using group signatures for identity management and its implementation

We discuss the merits of using group signature technology in Identity Management. We propose a novel model of group signature scheme and introduce a new entity called User-Revocation manager. User-Revocation manager plays an independent role regarding user revocation which was previously covered by either Group manager or Issuing manager. We extend the idea of the Camenisch-Groth scheme and present an efficient revocation scheme where the cost of user revocation is smaller than that of the Camenisch-Groth scheme. We also discuss the details of our implementation.

An implementation of a mix-net based network voting scheme and its use in a private organization

We discuss an implementation of a network voting scheme based on mix-net technology. We employed the scheme presented at Financial Cryptography 2002, but replaced the numeric computations with those on a elliptic curve. As a result, we obtained three times speed up and data length shortening to one third. The system has been employed in a private organization with roughly 20,000 voters since 2004.

Privacy-Preserving Fingerprint Authentication Resistant to Hill-Climbing Attacks

This paper proposes a novel secure biometric authentication scheme that hides the biometric features and the distance between the enrolled and authenticated biometric features, and prevent impersonation. To confirm that the proposed scheme has such properties, we formally model secure biometric authentication schemes by generalizing the related and proposed schemes. As far as we know, the proposed scheme is the first one that has been proved to satisfy all the properties. In particular, the proposed scheme achieves security under the decisional Diffie-Hellman assumption.