The CAPTCHA has become an important issue in multimedia security. Aimed at a commonly used text-based CAPTCHA, this paper outlines some typical methods and summarizes the technological progress in text-based CAPTCHA breaking. First, the paper presents a comprehensive review of recent developments in the text-based CAPTCHA breaking field. Second, a framework of text-based CAPTCHA breaking technique is proposed. And the framework mainly consists of preprocessing, segmentation, combination, recognition, postprocessing, and other modules. Third, the research progress of the technique involved in each module is introduced, and some typical methods of segmentation and recognition are compared and analyzed. Lastly, the paper discusses some problems worth further research.
Fingerprinting attacks are one of the most severe threats to the security of networks. Fingerprinting attack aims to obtain the operating system information of target hosts to make preparations for future attacks. In this paper, a fingerprint hopping method (FPH) is proposed based on software-defined networks to defend against fingerprinting attacks. FPH introduces the idea of moving target defense to show a hopping fingerprint toward the fingerprinting attackers. The interaction of the fingerprinting attack and its defense is modeled as a signal game, and the equilibriums of the game are analyzed to develop an optimal defense strategy. Experiments show that FPH can resist fingerprinting attacks effectively.
Sniffer attack has been a severe threat to network communication security. Traditional network usually uses static network configuration, which provides convenience to sniffer attack. In this paper, an SDN-based double hopping communication (DHC) approach is proposed to solve this problem. In DHC, ends in communication packets as well as the routing paths are changed dynamically. Therefore, the traffic will be distributed to multiple flows and transmitted along different paths. Moreover, the data from multiple users will be mixed, bringing difficulty for attackers in obtaining and recovering the communication data, so that sniffer attack will be prevented effectively. It is concluded that DHC is able to increase the overhead of sniffer attack, as well as the difficulty of communication data recovery.
Existing algorithms experience difficulty resisting additive and subtractive attacks because the embedded watermarks are independent of the carrier programs. A dynamic software watermarking algorithm based on exception handling is proposed in this paper. The algorithm considers the fact that exception handling, which is difficult to remove, commonly exists in the programs to ensure the normal program operation. First, an exception type table is constructed, and the binary watermark to be embedded is mapped to a sequence of exception types by scrambling encoding. Second, corresponding trigger conditions and exception handlers are constructed, and watermark embeddable points are acquired in execution paths under secret inputs. Finally, the code segment of the constructed trigger conditions and exception handlers are inserted into the program with several meticulously designed identifiers. For watermark extraction, the triggered exception types can be obtained with the identifiers by executing the watermarked executable program under secret inputs. The mapping relationship between the exception type and watermark is utilized to decode the binary watermark. The algorithm analysis and experimental results show that the proposed algorithm can embed a watermark in the source code and extract it in an executable program. The algorithm demonstrates good performance against additive and subtractive attacks.INDEX TERMS Software watermarking, dynamic software watermarking, exception handling, watermark encoding.
3D steganalysis aims to find the changes embedded through steganographic or information hiding algorithms into 3D models. This research study proposes to use new 3D features, such as the edge vectors, represented in both Cartesian and Laplacian coordinate systems, together with other steganalytic features, for improving the results of 3D steganalysers. In this way the local feature vector used by the steganalyzer is extended to 124 dimensions. We test the performance of the extended local feature set, and compare it to four other steganalytic features, when detecting the stego-objects watermarked by six information hiding algorithms.
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