## MEMBERS

### Program Members

Cryptography has become one of the most important areas in information technology.

With cryptography it is possible to construct many security protocols which are the basic infrastructure for secure communications like SSL, IPsec, TSL, WAP, iKP, ...

These security protocols provide us with different security applications like secure payment systems, secure IP Networks, secure mobile networks, and so on.
Two inevitable concepts for these attractive paradigms are public-key cryptosystem and digital signature. Without them we are not able to accomplish the above lucrative applications. The security of these concepts are underpinned by the difficulty of mathematical problems, for examples, a factoring problem, a discrete logarithm problem over elliptic curves, and lattice theory. Once the underlying problem is broken, the whole system using the problem is no longer secure. One of the main research subjects is to investigate the security of these problems and its implication to cryptographic protocols. In order to achieve these security applications in practice, we have to implement the security concept on a security device (like a smartcard). If the implementation on the device is careless, the attacker can easily break the secret information on it. The secure implementation on security devices is another important research subject.

##### (1)Pairing-Based Cryptography

Bilinear pairings on elliptic curves over finite fields have attracted much attention in cryptography, since pairing-based cryptosystems can provide manynovel applications, such as ID-based cryptosystems, keyword-searchable encryption, efficient broadcast encryption, and so on. We investigate to develop efficient algorithms for pairing-based cryptography and to analyze its security by number theoretic approach.

##### (2)Provable Security

In order to correctly judge the security level of cryptographic protocols, security models are needed. One of these standard models is the so called semantic security against the chosen ciphertext attack. A provably secure cryptosystem is a cryptosystem whose security can be mathematically verified in a security model. The provable security is not only theoretically but also practically meaningful, because we have a guarantee that there is no attack in the security model. We are engaged with the security of present and future cryptographic protocols.

##### (3)Efficient Algorithms

We are standing to the beginning of the ubiquitous computing era. It is expected that we can accomplish lucrative applications by effectively synthesizing the ubiquitous computer with cryptography. The ubiquitous computer only has scarce computational resources (like Smartcards or RFID), so that we have to make an effort to optimize the memory and efficiency of the security system. This research group is engaged with the development of new efficient cryptographic algorithms.