A Novel Adaptive Scanning Approach for Effective H.265/HEVC Entropy Coding

The block transform video coder of H.265/HEVC has been formulated for a more flexible content representation to satisfy various implementation demands. Here three coefficient-scanning methods of diagonal, horizontal and vertical scan are employed for mapping a 2-D array to a 1-D vector for further reducing redundancy in entropy coding. However, the fixation scanning pattern does not fully exploit the correlation among quantized coefficients and the coding redundancy still exists. In this paper, a new adaptive coefficient scanning (ACS) method is proposed for effective H.265/HEVC entropy coding. Here the characteristic of syntax elements of quantized coefficients is first studied and then the related context probability of symbol is estimated through combining local property. Guided by the principle of entropy coding, the scanning approach is established for higher coding performance. Experimental results demonstrate that a reduction of about 3.6%–4.2% in bit-rate can be observed with almost no loss in coding complexity.

A Hybrid-CPU-FPGA-based Solution to the Recovery of Sha256crypt-hashed Passwords

This paper presents an accelerator design for the password recovery of sha256crypt based on hybrid CPU-FPGA devices. By applying the brute-force attack computation model proposed in this paper, we decompose the sha256crypt function into two types of operations, namely the data dispatching and the block transforming. The data dispatching operation generates message blocks and the block transforming operation transforms message blocks into digests. These two operations are efficiently accelerated by the customized data dispatch unit and the pipelined block transform unit, respectively. Difficulties of adopting the pipeline technique are addressed also with the following techniques. The group scheduling is used to solve the data dependency that stalls the pipeline. The look-ahead execution eliminates the uncertainty of the execution path. The data path pruning and spatial-temporal multiplexing reduce the resource overhead of non-computing units.The proposed accelerator design is implemented and evaluated on the Xilinx Zynq-7000 XC7Z030-3 SoC. Our experimental results show that the proposed accelerator can improve energy efficiency by 2.54x over the state-of-the-art password recovery tool Hashcat running on an NVIDIA GTX1080Ti GPU. Compared with the pure FPGA-based implementation in John-the-Ripper, the proposed accelerator improves energy efficiency by 1.64x and improves resource efficiency by 1.69x.

CBC-Based Synthetic Speech Detection

In previous studies of synthetic speech detection (SSD), the most widely used features are based on a linear power spectrum. Different from conventional methods, this article proposes a new feature extraction method for SSD from octave power spectrum which is obtained from constant-Q transform (CQT). By combining CQT, block transform (BT) and discrete cosine transform (DCT), a new feature is obtained, namely, constant-Q block coefficients (CBC). In which, CQT is used to transform speech from the time domain into the frequency domain, BT is used to segment octave power spectrum into many blocks and DCT is used to extract principal information of every block. The experimental results on ASVspoof 2015 corpus shows that CBC is superior to other front-ends features that have been benchmarked on ASVspoof 2015 evaluation set in terms of equal error rate (EER).