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My main research topics are the followings:

- Digital content protection
- Pseudorandom number generators and physical random number generators; generation, application and evaluation
- Quantum information theory
- Applications of mathematics to information security

I have been studying on digital fingerprint technology, that enables digital content servers to embed user identification information into the contents (movies, musics, etc.) before distribution, and thus to detect the guilty user when illegally copied/redistributed contents are found.
In particular, I am currently interested in such techniques based on collusion-secure codes, from the following points of view:

(See also: RCIS Research Topics Secure fingerprinting codes for digital watermarking

)

- Development of collusion-secure codes with high security performance, together with their theoretical evaluation
- Development of good schemes concerning
implementation problems

, such as execution time, memory amount, etc. - Research on new applications of collusion-secure codes
- ...

- Koji Nuida, Satoshi Fujitsu, Manabu Hagiwara, Takashi Kitagawa, Hajime Watanabe, Kazuto Ogawa, Hideki Imai, An improvement of discrete Tardos fingerprinting codes, Designs, Codes and Cryptography, vol.52, no.3, 2009, pp.339--362
- Koji Nuida, Satoshi Fujitsu, Manabu Hagiwara, Hideki Imai, Takashi Kitagawa, Kazuto Ogawa, Hajime Watanabe, An efficient 2-secure and short random fingerprint code and its security evaluation, IEICE Trans. Fundamentals, vol.E92-A, no.1, Special Section on Cryptography and Information Security, IEICE, January 2009, pp.197--206
- Koji Nuida, An error-tolerant variant of a short 2-secure fingerprint code and its security evaluation, to appear in: The 4th International Workshop on Security (IWSEC 2009) (regular paper), Toyama, Japan, October 28--30, 2009
- Koji Nuida, An improvement of short 2-secure fingerprint codes strongly avoiding false-positive, 11th Information Hiding (IH 2009), Darmstadt, Germany, June 9, 2009
- Koji Nuida, Manabu Hagiwara, Hajime Watanabe, Hideki Imai, Optimization of Tardos's fingerprinting codes in a viewpoint of memory amount, in: T. Furon, F. Cayre, G. Doerr, P. Bas (Eds.), Information Hiding (IH 2007), LNCS 4567, June 2007, pp.279--293
- Koji Nuida, Manabu Hagiwara, Takashi Kitagawa, Hajime Watanabe, Kazuto Ogawa, Satoshi Fujitsu, Hideki Imai, A tracing algorithm for short 2-secure probabilistic fingerprinting codes strongly protecting innocent users, in: 4th IEEE Consumer Communications and Networking Conference (IEEE CCNC 2007), IEEE, January 2007, pp.1068--1072
- (requested talk, in Japanese) Koji Nuida, Fingerprinting Codes: Past, Present, and Future, the 31st Symposium on Information Theory and Its Applications (SITA2008) Workshop, Nikko-si, Japan, October 8, 2008

Many information security schemes are implemented by using pseudorandom numbers

instead of theoretically complete random numbers.
Thus it is important for preventing vulnerability to choose appropriately the pseudorandom numbers we use.
In my research, I am analyzing performances of existing pseudorandom number generators mainly by mathematical methods.

- Koji Nuida, Bounds of asymptotic occurrence rates of some patterns in binary words related to integer-valued logistic maps, to appear in: 21st International Conference on Formal Power Series and Algebraic Combinatorics (FPSAC'09) (poster session), Hagenberg, Austria, July 20--24, 2009

Many information security schemes are implemented by using pseudorandom numbers

instead of theoretically complete random numbers.
Thus it is important for preventing vulnerability to choose appropriately the pseudorandom numbers we use.
I am investigating methods of implementing theoretically secure (by use of true random numbers) information security schemes by using pseudorandom numbers, mainly from a viewpoint of security evaluation methods of such implemented systems.

There have been proposed random number generation methods based on several physical phenomena that may achieve ideal accuracy in theory. However, in practice even such physical random number generators in general possess some biases due to implementation errors, that may lead some problems in sensitive applications such as cryptography. I am investigating mathematical post-processing methods to reduce the biases of physical random numbers.

- Koji Nuida, Bounds on fixed-length post-processing functions for stationary biased random number generators, in: Proceedings of International Symposium on Information Theory and its Applications (ISITA 2008), SITA, December 2008 (CD-ROM)

It is a common belief, and also a security base of most of the present cryptosystems, that certain mathematical problems (such as Integer Factoring) cannot be solved efficiently by any computer of current type.
However, quantum computers

, which are essentially new computers and are well investigated recently toward realization, will be able to solve some of such problems (including Integer Factoring) very efficiently; this means that many of present cryptosystems will turn into insecure once quantum computers are realized.
Nowadays cryptosystems based on problems difficult even for quantum computers have been investigated in researches on cryptography.

My research has analyzed which problems will in fact be efficiently solvable by quantum computers.
In particular, I have been trying to establish new algorithms for quantum computers, by using certain method different from preceding researches.

- (in Japanese) Koji Nuida, Hideki Imai,
An Approach to Hidden Subgroup Problem Based on Orbit Decomposition

, in: Proceedings of the 29th Symposium on Information Theory and Its Applications (SITA2006), SITA (Society of Information Theory and its Applications), November 2006, pp.771--774

For unconditionally secure

quantum cryptography (quantum key distribution) that is expected as a new-generation cryptographic scheme, its security is assured by theory of quantum mechanics.
Recently, many works have been done on axiomatic and operational approaches to quantum information theory.
In my research, I am mainly working on preparation and development of mathematical foundation of such research activities.

- Koji Nuida, Gen Kimura, Takayuki Miyadera, Optimal observables for minimum-error state discrimination in general probabilistic theories, e-print arXiv:0906.5419, preprint, http://arxiv.org/abs/0906.5419
- Koji Nuida, Gen Kimura, Takayuki Miyadera, Hideki Imai, On minimum-error state discrimination problems in generic probability models, The Twelfth Workshop on Quantum Information Processing (QIP 2009) (poster session), New Mexico, USA, January 14, 2009

I have applied, or intended to apply, some advanced mathematics to several topics of information security, including the above-mentioned ones.

Last Modified: April 3, 2012

(c) Koji NUIDA 2009: All Rights Reserved

Note: The following E-mail address is modified for avoiding spams. You can obtain my correct address by moving the first two letters to the end.

I am sorry to trouble you. Thank you for your kind cooperation.

E-mail: jpk.nuida@aist.go.

Note: The following E-mail address is modified for avoiding spams. You can obtain my correct address by moving the first two letters to the end.

I am sorry to trouble you. Thank you for your kind cooperation.

E-mail: jpk.nuida@aist.go.