Band 11, Heft 1

In 2015, Fukase and Kashiwabara proposed an efficient method to find a very short lattice vector. Their method has been applied to solve Darmstadt shortest vector problems of dimensions 134 to 150. Their method is based on Schnorr’s random sampling, but their preprocessing is different from others. It aims to decrease the sum of the squared lengths of the Gram–Schmidt vectors of a lattice basis, before executing random sampling of short lattice vectors. The effect is substantiated from their statistical analysis, and it implies that the smaller the sum becomes, the shorter sampled vectors can be. However, no guarantee is known to strictly decrease the sum. In this paper, we study Fukase–Kashiwabara’s method in both theory and practice, and give a heuristic but practical condition that the sum is strictly decreased. We believe that our condition would enable one to monotonically decrease the sum and to find a very short lattice vector in fewer steps.

In this paper, we study an important problem in secret sharing that determines the exact value or bound for the complexity. First, we use the induced subgraph complexity of the graph G with access structure Γ to obtain a lower bound on the complexity of the graph G . Then, applying decomposition techniques, we obtain an upper bound on the complexity of the graph G . We determine the exact values of the complexity for each of the ten graph access structures on seven participants. Also, we improve the value bound of the complexity for the six graph access structures with seven participants.

We construct an algorithm that permits a large group of individuals to reach consensus on a random number, without having to rely on any third parties. The algorithm works with high probability if there are less than 50 of colluding parties in the group. We describe also some modifications and generalizations of the algorithm.

In the past when only “paper and pencil” ciphers were in use, a mnemonic Bellaso’s method was applied to obtain a permutation from a meaningful phrase. It turns out that even nowadays this method and its variations are employed and provide a simple but at the same time efficient tool for some ciphers. To the best of our knowledge the security of such ciphers has not been evaluated yet in all respects. Therefore, in this paper we initiate a study of their security with respect to the probability distribution of permutations obtained by Bellaso’s method.