Cryptographic Systems Laboratory

A. Fujioka

A. Fujioka

Atsushi Fujioka

Office: 23-524 Ext.: 3772


03/1990, D.Eng., Tokyo Institute of Technology

03/1987, M.Eng., Tokyo Institute of Technology

T. Sasaki

T. Sasaki

Taroh Sasaki
(Research Associate)

Laboratory: 23-802 Ext.: 3871


03/1994, Ph.D., Yokohama National University

03/1991, M.Eng., Yokohama National University

Research Field

Cryptography, Complexity Theory, Information Theory.

Research Overview

Investigating cryptographic systems, security management, computer security, and information theory.

Research Subjects

  • 1. Theoretical research on algorithms in cryptography and information theory.
  • 2. Systems research on security policy and computer management.


Cryptography may bring to mind mystery or spy novels, but cryptographic technologies are essential in many everyday activities. When we use smartphones, pay in digital cash, or buy something on the net, cryptographic technologies make these activities secure. However, there is no perfect and convenient cryptographic technology. Therefore, it is important to devise secure systems while preserving convenience, and we must define acceptable levels of security to design systems. Similar to cryptographic technologies, error-controlling and data compression technologies in information theory are also important for digital communication. By correcting or detecting errors on a communication channel, each entity will receive the correct data, and compressing the data reduces the cost and time required to download the data. Combining all these technologies allows us to use devices, including mobile phones, music players, and digital TVs, on the net safely and conveniently. In addition, even when these technologies are theoretically effective, implementing them improperly will also diminish the safety and reliability of devices. Therefore, evaluating and improving implementation and system administration are also challenging research topics. We are studying theoretical and practical aspects of cryptography and information theory. Cryptographic theory is the basis of secure information systems, and research on system security, such as establishing consistent administration policy and safe system administration, is of considerable practical importance.

  • 1) A. Fujioka, "Generalized Key Substitution Attacks on Message Recovery Signatures," Tatra Mountains Mathematical Publications, vol. 70(3), pp.119--138 (2017).
  • 2) A. Fujioka et al., “Strongly secure authenticated key exchange from factoring, codes, and lattices,” Designs, Codes and Cryptography, vol. 76(3), pp. 469–504 (2015).
  • 3) A. Fujioka et al., “Non-malleable multiple public-key encryption,” IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences, vol. E97-A(6), pp. 1318–1334 (2014).
  • 4) A. Fujioka, “Characterization of strongly secure authenticated key exchanges without NAXOS technique,” IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences, vol. E96-A(6), pp. 1088–1009 (2013).
Affiliated Academic Organizations

A. Fujioka:
Institute of Electronics, Information and Communication Engineers (IEICE), Information Processing Society of Japan (IPSJ), International Association of Cryptologic Research (IACR).

T. Sasaki:
Institute of Electronics, Information and Communication Engineers (IEICE), Institute of Electrical and Electronics Engineers (IEEE).

Current members
◯ Professors: 1 ◯ Research Associates: 1
◯ Postgraduates: 2 ◯ Undergraduates: 12

Number of alumni: Undergraduates: 38