Nonogram is one of logical games popular in Japan and Netherlands. Solving nonogram is a NP-complete problem. There are some related papers proposed. Some use genetic algorithm (GA), but the solution may get stuck in local optima. Some use depth first search (DFS) algorithm, the execution speed is very slow. In this paper, we propose a puzzle solving algorithm to treat these problems. Based on the fact that most of nonograms are compact and contiguous, some logical rules are deduced to paint some cells. Then, we use the chronological backtracking algorithm to solve those undetermined cells and logical rules to improve the search efficiently. Experimental results show that our algorithm can solve nonograms successfully, and the processing speed is significantly faster than that of DFS. Moreover, our method can determine that a nonogram has no solution.
Many password authentication schemes employ hash functions as their basic building blocks to achieve better efficiency. In 2000, Peyravian and Zunic proposed a hash-based password authentication scheme that is efficient and can be easily implemented. Recently, Lee, Li, and Hwang demonstrated that Peyravian-Zunic's hash-based password authentication scheme is vulnerable to the off-line guessing attack, and then proposed an improved version. In this article, we show that their improved scheme is still vulnerable to the of-line guessing attack, the denial-of-service attack, and the stolen-verifier attack.Password authentication is regarded as one of the simplest and most convenient authentication mechanisms. Conventional static password authentication methods can not resist direct wiretapping attacks, and thus, are unsuitable for open network environments. To meet today's security requirements, many password authentication methods using dynamic, or one-time, passwords have been proposed . Existing dynamic one-time password authentication schemes can be categorized into two types, one [3] employs cryptosystems, either public-key cryptosystems or secret-key cryptosystems, and the other [4,9,11,15,16,17] employs only simple operations, e.g., one-way hash function [12,14,18] and XOR (exclusive-or) operation. Although the latter type, the hash-based password authentication scheme, usually requires that users should choose strong passwords, which can not be easily guessed, however, it has the advantage over the former type in that its computation is lighter, design is simpler, and implementation is easier, and therefore is especially suitable for certain constrained environments.The first well-known hash-based password authentication scheme was proposed by Lamport [9] . This scheme allows the server to authenticate the user in a way that neither eavesdropping on an authentication exchange nor reading server's database enables someone to impersonate the user. However, high hash overhead and the necessity for password resetting decrease its suitability for practical use. Additionally, Lamport's scheme is vulnerable to the replay attack . Later, Haller [4]
Halftone images are commonly printed on books, newspapers, and magazines. How to protect the copyright of these printed halftone images becomes an important issue. Digital watermarking provides a solution for copyright protection. In this paper, we will propose a novel printable watermarking method for dithering halftone images. Based on downsampling and the property of a dispersed dithering screen, the method can resist cropping, tampering, and print-and-scan process attacks. In addition, comparing to Guo et al.’s method, the experimental results show that the proposed method provides higher robustness for the above-mentioned attacks and better visual quality in the high-frequency regions of halftone images.
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