In 1990, the present authors proposed the first ID-based non-interacrive key sharing scheme (ID-NIKS) based on the discrete logarithm problem (DLP) over a composite number $n$. With a rapid progress of computer system for the last two decades, ID-NIKS based on DLP over $n$ would have more chance to be applied practically. However, there existed no secure ID-NIKS based on DLP over $n$ against the square-root attack when $n$ is a product of three prime numbers. In this paper, we propose an ID-NIKS based on DLP over a product of three prime numbers which can circumvent the square-root attack.
The knapsack scheme is expected to be not only a light-weight public-key cryptosystem but also a post quantum cryptosystem. In this paper, we propose a new method for constructing knapsack PKC by using a random sequence. We also give two concrete knapsack schemes based on the proposed method. The scheme constructed the proposed method can be secure against the low-density attack because the density can be made as large as one desires. The scheme constructed the proposed method can be also secure against the attack of computing the secret key, because the public key is almost indistinguishable from a random numbers.
A dual fluidized bed process using CaO-based solid sorbent is considered to be a promising technology to separate CO2 from flue gas with low energy penalty. As reactor for CaO-looping cycle, both bubbling fluidized bed and “fast” fluidized bed are available, thus four possible combinations, (bubbling or fast absorber)x(bubbling or fast regenerator), are conceivable for this process. In this work, the authors discuss favorable combination of reactor type from viewpoints of heat removal from carbonation reactor and on energy penalty associated with dilution of pure oxygen by CO2 in the regenerator. As conclusion, suitable combination was found to be bubbling bed absorber and fast regenerator. Design of bench-scale experimental apparatus of the present system was also carried out. Bubbling bed absorber was designed to achieve 86 % CO2 removal efficiency from flue gas. Preliminary operating results of solid circulation at room temperature are also presented.
Abstract Recently, many applications of integer theory to cryptographic techniques have been observed. The discrete logarithm problem is one such case. Usually, the discrete logarithm problem is the determination of the logarithm for the given arbitrary element with a prime number as the modulus. However, the discrete logarithm problem can also be considered with a composite number as the modulus. It is anticipated that the discrete logarithm problem with a composite number as the modulus is a difficult problem if the prime factors of the composite number, which is used as the modulus, are unknown. Then the problem can be applied to the cryptography. In the general discrete logarithm problem with a composite number as the modulus, it is not always true that an arbitrary element has a logarithm. From such a viewpoint, this paper shows that the exponent of an arbitrary element belonging to the irreducible residue class with a composite number as the modulus has a logarithm. Then the necessary condition in the application to the cryptographic technique is presented. Finally, as an application example of the technique proposed in this paper, a cryptographic technique based on the discrete logarithm problem with the composite number as the modulus is shown.
