Hirokazu Ishizuka

Secure Hyperelliptic Cryptosystems and Their Performances

We investigate the discrete logarithm problem over jacobian varieties of hyperelliptic curves suitable for public-key cryptosystems, and clarify practical advantages of hyperelliptic cryptosystems compared to the elliptic cryptosystems and to RSA. We focus on the curves defined over the ground field of characteristic 2, and we present hyperelliptic cryptosystems from the jacobian associated with curves C : v 2 + v=u 2g+1 of genus g=3 and 11, which are secure against the known attacks. We further discuss the efficiency in implementation of such secure hyperelliptic cryptosystems.

How much security does Y-00 protocol provide us?

Abstract New quantum cryptography, often called Y-00 protocol, has much higher performance than the conventional quantum cryptographies. It seems that the conventional quantum cryptographic attacks are inefficient at Y-00 protocol as its security is based on the different grounds from that of the conventional ones. We have, then, tried to cryptoanalyze Y-00 protocol in the view of cryptographic communication system. As a result, it turns out that the security of Y-00 protocol is equivalent to that of classical stream cipher.

Error Detection and Authentication in Quantum Key Distribution

Detecting errors in a raw key and authenticating a private key are crucial for quantum key distribution schemes. Our aim is to propose practical methods for error detection and authentication in quantum key distribution schemes. We introduce several concepts about neighborhood collision free properties of Boolean functions, which are closely related to hash functions, and propose methods based on neighborhood collision free functions and error correcting codes such as Reed-Solomon code. We also examine whether or not widely used cryptographic hash functions SHA-1 and MD5 satisfy the neighborhood collision free property by computation experiments.