Many cryptographic schemes are based on computationally hard problems. The computational Diffie–Hellman problem is the most well-known hard problem and there are many variants of it. Two of them are the square Diffie–Hellman problem and the square root Diffie–Hellman problem. There have been no known reductions from one problem to the other in either direction. In this paper we show that these two problems are polynomial time equivalent under a certain condition. However, this condition is weak, and almost all of the parameters of cryptographic schemes satisfy this condition. Therefore, our reductions are valid for almost all cryptographic schemes.

Electroencephalography amplitude, phase synchronization, and directionality of phase coupling within and between hemispheres were compared for different frequency components in 27 healthy individuals before and after 5 days of daily 1 Hz repetitive transcranial magnetic stimulation (rTMS), and at 2 weeks after the last session. Instantaneous amplitudes of α (8–13 Hz) and β (13–30 Hz) frequency components were increased after daily rTMS, the effects of which were declining over time, suggesting an adapting response with repeated rTMS sessions. The phase synchronization of electroencephalography increased significantly in the α frequency, especially the upper-α band (11–13 Hz), in both the frontal and the temporal areas, predominantly in the ipsilateral hemisphere. Asymmetric directional interactions of the upper-α band were stronger from the stimulated area to the contralateral hemisphere. No significant differences were found at 2 weeks after rTMS in any of these values. Focal 1 Hz rTMS induces an enhancement in the ipsilateral dominant corticocortical interaction drastically by interhemispheric asymmetric coupling from the stimulated cortical area with an adapting response with repeated sessions. This kind of method can be valuable for possible clinical applications in various neuropsychiatric conditions to study the therapeutic mechanisms of 1 Hz rTMS.

Redactable signature schemes permit deletion of arbitrary substrings of a signed document while preserving the authenticity of the remaining document. Most of known redactable signatures based on pairing have large­sized signatures and the sizes depend on the product of security parameter and the number of blocks of the redacted document. In this paper, we present a short redactable signature scheme based on pairing. We modify Waters signature scheme to obtain an underlying standard signature defined on composite­order bilinear group. The modified scheme satisfies the unforgeability under the known message attack based on the Computational Diffie–Hellman assumption. Based on the modified Waters signature, we propose a short redactable signature that is existentially unforgeable under random message attack and weakly private. The size of the proposed scheme is 20% of known redactable signatures using aggregated pairing­based signatures when half of the message blocks are deleted. Copyright © 2011 John Wiley & Sons, Ltd.

Since the publication of Hwang-Li's password-based remote user authentication scheme with smart cards, a number of password-based authentication schemes with smart cards have been proposed to meet a variety of desirable security and performance requirements. In this paper, security flaws in three password-based remote user authentication schemes with smart cards are pointed out. These results demonstrate that no more password-based authentication schemes with smart cards should be constructed with such ad-hoc methods, i.e., the formal design methodology with provable security approach should be employed in future design.

A large number of technologies are used in a satellite because it is hard difficult to repair and replace its components after it has been launched. Furthermore, there are many threats to the satellite such as software aging, environmental problems and network attacks. Because of this nature, it is important that the satellite operates well in spite of the occurrence of hardware and/or software faults. In particular, software aging in the on-board computer (OBC) causes unavailability of a whole satellite system. In this paper, we propose to adopt software rejuvenation for OBC in conjunction with cold, hot and warm standby redundancy in a satellite system. We use stochastic reward nets (SRN) to model OBC with cold, hot and warm standby redundancy and model OBC with that redundancy with software rejuvenation. We compare the models in terms of steady state availability and downtime cost. Sensitivity analysis with respect to some parameters is used to find bottlenecks of the models. Finally, we present a reliability model and analysis with cost consideration.

One of the main problems of existing approaches in anomaly detection in intrusion detection system (IDS) is that IDSs provide only binary detection result: intrusion (attack) or normal. If some attack data or normal data is belonged to boundary, they may be classified wrongly. That is a main cause of high false rates and inaccurate detection rates in IDS. We propose a new approach named Quantitative Intrusion Intensity Assessment (QIIA) that exploits proximity metrics computation so that it provides intrusion (or normal) quantitative intensity value. It is capable of representing how an instance of audit data is proximal to intrusion or normal in a numerical value. This can identify unknown intrusion and normal pattern more accurately. Prior to applying QIIA to audit data, we perform feature selection and parameter optimization of detection models to decrease the overheads to process audit data and to enhance detection rates. Random Forests is used to generate proximity metrics that represent the intrusion intensity (and normal instance intensity) in a numerical way. The numerical value is used to determine whether unknown audit data are intrusion or normal. We carry out several experiments on KDD 1999 dataset and the experimental results show the feasibility of our approach. Copyright © 2012 John Wiley & Sons, Ltd.

Given a graph G, the m-step graph of G, denoted by S _m (G), has the same vertex set as G and an edge between two distinct vertices u and v if there is a walk of length m from u to v. The line graph of G, denoted by L(G), is a graph such that the vertex set of L(G) is the edge set of G and two vertices u and v of L(G) are adjacent if the edges corresponding to u and v share a common end vertex in G. We characterize connected graphs G such that S _m (G) and L(G) are isomorphic.