Even though meet-in-the-middle preimage attack framework has been successfully applied to attack most of narrow-pipe hash functions, it seems difficult to apply this framework to attack double-branch hash functions. Only few results have been published on this research. This paper proposes a refined strategy of applying meet-in-the-middle attack framework to double-branch hash functions. The main novelty is a new local-collision approach named one-message-word local collision. We have applied our strategy to two double-branch hash functions RIPEMD and RIPEMD-128, and obtain the following results.·On RIPEMD. We find a pseudo-preimage attack on 47-step compression function, where the full version has 48 steps, with a complexity of 2119. It can be converted to a second preimage attack on 47-step hash function with a complexity of 2124.5. Moreover, we also improve previous preimage attacks on (intermediate) 35-step RIPEMD, and reduce the complexity from 2113 to 296. ·On RIPEMD-128. We find a pseudo-preimage on (intermediate) 36-step compression function, where the full version has 64 steps, with a complexity of 2123. It canl be converted to a preimage attack on (intermediate) 36-step hash function with a complexity of 2126.5. Both RIPEMD and RIPEMD-128 produce 128-bit digests. Therefore our attacks are faster than the brute-force attack, which means that our attacks break the theoretical security bound of the above step-reduced variants of those two hash functions in the sense of (second) preimage resistance. The maximum number of the attacked steps on both those two hash functions is 35 among previous works based to our best knowledge. Therefore we have successfully increased the number of the attacked steps. We stress that our attacks does not break the security of full-version RIPEMD and RIPEMD-128. But the security mergin of RIPEMD becomes very narrow. On the other hand, RIPEMD-128 still has enough security margin.

We present pseudo-preimage attacks on Davis-Meyer mode of reduced rounds of the block ciphers ARIA, Camellia, and Serpent by using Sasaki's framework. They yield preimage or second-preimage attacks on PGV hashing modes. We develop proper initial structures for applying meet-in-the-middle techniques to the block ciphers, by considering their diffusion layers, and propose a method to find matching-check equations for indirect partial matching technique with a binary matrix. These works enable us to attack 5 rounds of ARIA, 7 rounds of Camellia, and 4 rounds of Serpent faster than brute force attack.

Recently, a novel approach to color image compression based on colorization has been presented. The conventional method for colorization-based image coding tends to lose the local oscillation of chrominance components that the original images had. A large number of color assignments is required to restore these oscillations. On the other hand, previous studies suggest that an oscillation of a chrominance component correlates with the oscillation of a corresponding luminance component. In this paper, we propose a new colorization-based image coding method that utilizes the local correlation between texture components of luminance and chrominance. These texture components are obtained by a total variation regularized energy minimization method. The local correlation relationships are approximated by linear functions, and their coefficients are extracted by an optimization method. This key idea enables us to represent the oscillations of chrominance components by using only a few pieces of information. Experimental results showed that our method can restore the local oscillation and code images more efficiently than the conventional method, JPEG, or JPEG2000 at a high compression rate.

In multimedia communication, due to the limited computational capability of the personal information machine, a coder with low computational complexity is needed to integrate services from several media sources. This paper presents two efficient candidate schemes to simplify the most computationally demanding operation, the excitation codebook search procedure. For fast adaptive codebook search, we propose an algorithm that uses residual signals to predict the candidate gain-vectors of the adaptive codebook. For the fixed codebook, we propose a fast search algorithm using an energy function to predict the candidate pulses, and we redesign the codebook structure to twin multi-track positions architecture. Overall simulation results indicate that the average perceptual evaluation of speech quality (PESQ) score is degraded slightly, by 0.049, and our proposed methods can reduce total computational complexity by about 67% relative to the original G.723.1 encoder computation load, and with perceptually negligible degradation. Objective and subjective evaluations verify that the more efficient candidate schemes we propose can provide speech quality comparable to that using the original coder approach.

Short-range Multiple-Input-Multiple-Output (SR-MIMO) transmission is an effective technique for achieving high-speed and short-range wireless communication. With this technique, however, the optimum aperture size of array antennas grows when the transmission distance is increased. Thus, antenna miniaturization is an important issue in SR-MIMO. In this paper, we clarify the effectiveness of using dual-polarized planar antennas as a means of miniaturizing SR-MIMO array antennas by measurements and analysis of MIMO transmission characteristics. We found that even in SR-MIMO transmission, the use of dual-polarized transmission enables higher channel capacity. Dual-polarized antennas can reduce by two thirds the array area that is needed to obtain the same channel capacity. For a transmission distance of two wavelengths, the use of a dual-polarized antenna improved the channel capacity by 26 bit/s/Hz while maintaining the same number of transmitters and receivers and the same antenna aperture size. Moreover, dual-polarized SR-MIMO has a further benefit when zero-forcing (ZF) reception without transmit beamforming is adopted, i.e., it effectively simplifies hardware configuration because it can reduce spatial correlation even in narrow element spacing. In this work, we confirmed that the application of dual-polarization to SR-MIMO is an effective way to both increase channel capacity and enhance transceiver simplification.

T-function is a kind of cryptographic function which is shown to be useful in various applications. It is known that any function f on F2n or Z2n automatically deduces a unique polynomial fF ∈ F2n[x] with degree ≤ 2n-1. In this letter, we study an algebraic property of fF while f is a T-function. We prove that for a single cycle T-function f on F2n or Z2n, deg fF=2n-2 which is optimal for a permutation. We also consider a kind of widely used T-function in many cryptographic algorithms, namely the modular addition function Ab(x)=x+b ∈ Z2n[x]. We demonstrate how to calculate deg Ab F from the constant value b. These results can facilitate us to evaluate the immunity of the T-function based cryptosystem against some known attacks such as interpolation attack and integral attack.

The channel characteristics of IEEE 802.11 WLAN vary with time and this can affect packet transmission performance. For achieving robust and efficient transmission, the transmission rate is controlled by exploiting the multi-rate capability of the IEEE 802.11 physical layer (PHY) to respond to the time-varying channel condition. In this paper, we propose a novel rate adaptation scheme, called RA-MCE, in which the transmitter estimates channel quality in the MAC layer to enhance throughput performance without the need to use the RTS-CTS mechanism nor to modify the IEEE 802.11 standard. RA-MCE adaptively controls the transmission rate according to the estimated channel quality by the MAC layer channel quality estimator (MCE) that uses only local MAC layer measurements. Through extensive simulations, we validate the accuracy of MCE and evaluate the performance of RA-MCE to show that it achieves higher throughput performance than other rate adaptation schemes under various circumstances.

This letter proposes a novel TPC scheme that increases the energy efficiency of IEEE 802.11 WLAN users. It can determine whether to access the channel and with what level of transmit power given the current channel condition by comparing the expected energy efficiency to an adaptive threshold.

This paper deals with the diffraction of a transverse magnetic (TM) plane wave by a perfectly conductive periodic surface by an integral method. However, it is known that a conventional integral method does not work for a critical angle of incidence, because of divergence of a periodic Green's function (integral kernel). To overcome such a divergence difficulty, we introduce an image Green's function which is physically defined as a field radiated from an infinite phased array of dipoles. By use of the image Green's function, it is newly shown that the diffracted field is represented as a sum of radiation from the periodic surface and its image surface. Then, this paper obtains a new image integral equation for the basic surface current, which is solved numerically. A numerical result is illustrated for a very rough sinusoidal surface. Then, it is concluded that the method of image Green's function works practically even at a critical angle of incidence.

With the evolution of the P2P research field, new problems, such as those related with information security, have arisen. It is important to provide security mechanisms to P2P systems, since it has already become one of the key issues when evaluating them. However, even though many P2P systems have been adapted to provide a security baseline to their underlying applications, more advanced capabilities are becoming necessary. Specifically, privacy preservation and anonymity are deemed essential to make the information society sustainable. Unfortunately, sometimes, it may be difficult to attain anonymity unless it is included into the system's initial design. The JXTA open protocols specification is a good example of this kind of scenario. This work studies how to provide anonymity to JXTA's architecture in a feasible manner and proposes an extension which allows deployed services to process two-way messaging without disclosing the endpoints' identities to third parties.

The suffix tree is one of most widely adopted indexes in the application of genome sequence alignment. Although it supports very fast alignment, it has a couple of shortcomings, such as a very long construction time and a very large volume size. Loh et al. [7] proposed a suffix tree construction algorithm with dramatically improved performance; however, the size still remains as a challenging problem. We propose an algorithm by extending the one by Loh et al. to reduce the suffix tree size. As a result of our experiments, our algorithm constructed a suffix tree of approximately 60% of the size within almost the same time period.

A finite buffer shared by multiple packet queues is considered. Partitioning the buffer to maximize total throughput is formulated as a resource allocation problem, the solution is shown to be achieved by a greedy incremental algorithm in polynomial time. The optimal buffer allocation strategy is applied to different models for a wireless downlink. First, a set of parallel M/M/1/mi queues, corresponding to a downlink with orthogonal channels is considered. It is verified that at high load, optimal buffer partitioning can boost the throughput significantly with respect to complete sharing of the buffer. Next, the problem of optimal combined buffer allocation and channel assignment problems are shown to be separable in an outage scenario. Motivated by this observation, buffer allocation is considered in a system where users need to be multiplexed and scheduled based on channel state. It is observed that under finite buffers in the high load regime, scheduling simply with respect to channel state with a simply partitioned buffer achieves comparable throughput to combined channel and queue-aware scheduling.

The impact and benefits of channel state information (CSI) are analyzed in terms of degrees-of-freedom (DoFs) in a K-user interference network operating over time-selective channels, where the error variance of CSI estimation is assumed to scale with an exponent of the received signal-to-noise ratio (SNR). The original interference alignment (IA) scheme is used with a slight modification in the network. Then, it is shown that the DoFs promised by the original IA can be fully achieved under the condition that the CSI quality order, represented as a function of the error variance and the SNR, is greater than or equal to 1. Our result is extended to the case where the number of communication pairs, K, scales with the SNR, i.e., infinite K scenario, by introducing the user scaling order. As a result, this letter provides vital information to the system designer in terms of allocating training resources for channel estimation in practical cellular environments using IA.

The impact degree is a measure of the robustness of a metabolic network against deletion of single or multiple reaction(s). Although such a measure is useful for mining important enzymes/genes, it was defined only for networks without cycles. In this paper, we extend the impact degree for metabolic networks containing cycles and develop a simple algorithm to calculate the impact degree. Furthermore we improve this algorithm to reduce computation time for the impact degree by deletions of multiple reactions. We applied our method to the metabolic network of E. coli, that includes reference pathways, consisting of 3281 reaction nodes and 2444 compound nodes, downloaded from KEGG database, and calculate the distribution of the impact degree. The results of our computational experiments show that the improved algorithm is 18.4 times faster than the simple algorithm for deletion of reaction-pairs and 11.4 times faster for deletion of reaction-triplets. We also enumerate genes with high impact degrees for single and multiple reaction deletions.

This letter proposes a spread spectrum audio watermarking robust against playback speed modification (PSM) attack which introduces both time-scale modification and pitch shifting. Two important improvements are exploited to achieve this robustness. The first one is selecting an embedding region according to the stable characteristic of the audio energy. The second one is stretching the pseudo-random noise sequence to match the length of the embedding region before embedding and detection. Experimental results show that our method is highly robust to common audio signal processing attacks and synchronization attacks including PSM, cropping, trimming and jittering.

We propose a novel technique to grow the single-walled carbon nanotubes (SWNTs) with specific chirality at the desired position using free electron laser (FEL) irradiation during growth and surface treatment. As a result, only the semiconducting SWNTs grew at the area between triangle electrodes, where the ozone treatment was done to be hydrophilic when an alcohol chemical vapor deposition (ACCVD) process was carried out with the 800 nm FEL irradiation. Although the number of possible chiral index is 22 in the SWNTs grown without the FEL irradiation, the number is much reduced to be 8 by the FEL.

In recent Printed Circuit Boards (PCB), the design size and density have increased, and the improvement of routing tools for PCB is required. There are several routing tools which generate high quality routing patterns when connection requirement can be realized by horizontal and vertical segments only. However, in high density PCB, the connection requirements cannot be realized when only horizontal and vertical segments are used. Up to one third nets can not be realized if no non-orthogonal segments are used. In this paper, a routing method for a single-layer routing area that handles higher density designs in which 45-degree segments are used locally to relax the routing density is introduced. In the proposed method, critical zones in which non-orthogonal segments are required in order to realize the connection requirements are extracted, and 45-degree segments are used only in these zones. By extracting minimal critical zones, the other area that can be used to improve the quality of routing pattern without worry about connectivity issues is maximized. Our proposed method can utilize the routing methods which generate high quality routing pattern even if they only handle horizontal and vertical segments as subroutines. Experiments show that the proposed method analyzes a routing problem properly, and that the routing is realized by using 45-degree segments effectively.

In this paper, we introduce an LDPC decoder design for decoding a length-672 multi-rate code adopted in IEEE 802.15.3c standard. The proposed decoder features high performances in both data rate and power efficiency. A macro-layer level fully parallel layered decoding architecture is proposed to support the throughput requirement in the standard. For the proposed decoder, it takes only 4 clock cycles to process one decoding iteration. While parallelism increases, the chip routing congestion problem becomes more severe because a more complicated interconnection network is needed for message passing during the decoding process. This problem is nicely solved by our proposed efficient message permutation scheme utilizing exploited parity check matrix features. The proposed message permutation network features high compatibility and zero-logic-gate VLSI implementation, which contribute to the remarkable improvements in both area utilization ratio and total gate count. Meanwhile, frame-level pipeline decoding is applied in the design to shorten the critical path. To verify the above techniques, the proposed decoder is implemented on a chip fabricated using Fujitsu 65 nm 1P12L LVT CMOS process. The chip occupies a core area of 1.30 mm2 with area utilization ratio 86.3%. According to the measurement results, working at 1.2 V, 400 MHz and 10 iterations the proposed decoder delivers a 6.72 Gb/s data throughput and dissipates a power of 537.6 mW, resulting in an energy efficiency 8.0 pJ/bit/iteration. Moreover, a decoder of the same architecture but with no pipeline stage for low-profile application is also implemented and evaluated at post-layout level.

We developed a novel movement-imagery-based brain-computer interface (BCI) for untrained subjects without employing machine learning techniques. The development of BCI consisted of several steps. First, spline Laplacian analysis was performed. Next, time-frequency analysis was applied to determine the optimal frequency range and latencies of the electroencephalograms (EEGs). Finally, trials were classified as right or left based on β-band event-related synchronization using the cumulative distribution function of pretrigger EEG noise. To test the performance of the BCI, EEGs during the execution and imagination of right/left wrist-bending movements were measured from 63 locations over the entire scalp using eight healthy subjects. The highest classification accuracies were 84.4% and 77.8% for real movements and their imageries, respectively. The accuracy is significantly higher than that of previously reported machine-learning-based BCIs in the movement imagery task (paired t-test, p < 0.05). It has also been demonstrated that the highest accuracy was achieved even though subjects had never participated in movement imageries.

This paper proposes a precoding scheme for downlink multiuser MIMO-OFDM systems. The proposed precoding employs the minimum average bit error rate (MABER) criterion, and obtains precoding matrices by the steepest descent algorithm in order to minimize average BER of mobile stations. As the cost function of the proposed scheme, an upper bound of the average BER is derived from the pairwise error probability (PEP) and is averaged with respect to channel state information (CSI) errors. Thus, the MABER scheme is robust against imperfect CSI. Computer simulations under a frequency-selective fading condition demonstrate that the proposed precoder is more robust against the CSI errors than both the zero-forcing (ZF) precoder and a robust sum mean square error (SMSE) precoder, and that it is superior in BER to the conventional schemes.