ABSTRACT
With the arrival of the age of big data, the amount and types of data in the process of information transmission have increased significantly, and the full-disk encryption mode used by traditional encryption algorithms has certain limitations of the times. In order to further improve the bandwidth efficiency of digital images in the transmission process and the information effectiveness of digital image transmission, this paper proposes an algorithm of high-quality restoration image encryption using DCT frequency-domain compression coding and chaos. Firstly, the image hash value is used for the generation of an encryption key with plaintext correlation, then lightweight chaos is generated based on the key to obtain a pseudo-random sequence. Secondly, the image is partitioned into subblock, and converted from time domain into frequency domain by employing Discrete Cosine Transform (DCT) on each block, then perform quantization operation based on frequency domain information to obtain DCT coefficient matrix. Thirdly, the direct current (DC) coefficients and alternating current (AC) coefficients are extracted in the DCT coefficient matrix and compressed by different encoding methods to obtain two sets of bitstream containing DC coefficient and AC coefficient information. Fourthly, permute the DC coefficient bit stream by the chaotic sequence, and reconstruct it with the AC coefficient bit stream to obtain the frequency domain ciphertext image. Finally, the chaotic sequence is used to diffuse ciphertext, and the processed hash value is hidden in the ciphertext to obtain the final ciphertext. The theoretical and experimental analysis showed that the key length reaches 341 bits, and the PSNR value of the restored image is close to 60, all of which satisfy the theoretical value. Therefore, the algorithm has the characteristics of high compression rate, high-quality image restoration large key space, strong plaintext sensitivity, strong key sensitivity and so on. Our method proposed in this paper is expected to provide a new idea for confidential and secure communication in the age of big data.
ABSTRACT
In order to further improve the information effectiveness of digital image transmission, an image-encryption algorithm based on 2D-Logistic-adjusted-Sine map (2D-LASM) and Discrete Wavelet Transform (DWT) is proposed. First, a dynamic key with plaintext correlation is generated using Message-Digest Algorithm 5 (MD5), and 2D-LASM chaos is generated based on the key to obtain a chaotic pseudo-random sequence. Secondly, we perform DWT on the plaintext image to map the image from the time domain to the frequency domain and decompose the low-frequency (LF) coefficient and high-frequency (HF) coefficient. Then, the chaotic sequence is used to encrypt the LF coefficient with the structure of "confusion-permutation". We perform the permutation operation on HF coefficient, and we reconstruct the image of the processed LF coefficient and HF coefficient to obtain the frequency-domain ciphertext image. Finally, the ciphertext is dynamically diffused using the chaotic sequence to obtain the final ciphertext. Theoretical analysis and simulation experiments show that the algorithm has a large key space and can effectively resist various attacks. Compared with the spatial-domain algorithms, this algorithm has great advantages in terms of computational complexity, security performance, and encryption efficiency. At the same time, it provides better concealment of the encrypted image while ensuring the encryption efficiency compared to existing frequency-domain methods. The successful implementation on the embedded device in the optical network environment verifies the experimental feasibility of this algorithm in the new network application.
ABSTRACT
BACKGROUND: Fresh Agaricus bisporus is popular and consumed throughout the world because of its taste, as well as its nutritional and medicinal properties, but it is also prone to microbial growth. There is very limited information about the dynamic changes of microbial communities during storage. The present study aimed to analyze the microbial diversity of button mushroom during cold storage using Illumina HiSeq sequencing. Bacteria isolated from the later storage period were identified by MALDI-TOF mass spectrometry and a bioassay of pathogenicity was carried out. RESULTS: High-throughput sequencing showed that Pseudomonas was the predominant genus throughout the storage period. Pedobacter and Flavobacterium grew prolifically on the eighth day, while the relative abundance of Oscillospira continued to decrease. Pseudomonas, Ewingella and Chryseobacterium were isolated at the later period of mushroom storage. A pathogenicity bioassay on the cap of mushrooms showing brown blotch indicated an infection by Pseudomonas tolaasii. However, Ewingella americana did not have a pathogenic effect in our study. CONCLUSION: Bacterial communities of fresh Agaricus bisporus during cold storage were characterized by high-throughput sequencing. MALDI-TOF MS provides a good analytical procedure, in addition to 16S rRNA gene sequencing. © 2019 Society of Chemical Industry.
