With the popularization and rapid development of mobile intelligent terminals(MITs), the number of mobile applications, or apps, has increased exponentially. It is increasingly common for malicious code to be inserted...With the popularization and rapid development of mobile intelligent terminals(MITs), the number of mobile applications, or apps, has increased exponentially. It is increasingly common for malicious code to be inserted into counterfeit apps, which can cause significant economic damage and threaten the security of users. Code obfuscation techniques are a highly efficient group of methods for code security protection. In this paper, we propose a novel control flow obfuscation based method for Android code protection. First, algorithms to insert irrelevant code and flatten the control flow are employed that minimize the cost of obfuscation while ensuring its strength. Second, we improve the traditional methods of control flow flattening to further reduce the costs of obfuscation. Lastly, the use of opaque predicates is strengthened by establishing an access control strategy, which converts the identification of opaque predicates in the entire program into a graph traversal problem, and thereby increases the strength of the code protection. We did some experiments to evaluate our method, and the results show that the proposed method can work well.展开更多
This paper examines structural changes in China s exchange rate mechanism.For this purpose,we propose a predictive model incorporating three factors that influence the central parity rate:a smoothing factor,a market f...This paper examines structural changes in China s exchange rate mechanism.For this purpose,we propose a predictive model incorporating three factors that influence the central parity rate:a smoothing factor,a market factor,and a basket factor.We first apply the model to analyze the effects of 12 exchange rate reforms since 2005,treating these reforms as predetermined structural breaks.Among other results,we find that the main impact of introducing a“counter-cyclical factor”is to weaken the role of the basket factor.We estimate structural breaks in data,assuming that the number and dates of breaks are unknown,and we find that,although the majority of estimated breaks occur within the neighborhood of exchange rate reforms,there are breaks due to other external shocks such as the escalation of the China-US trade conflict in May 2019.It is suggested that our model may be used to guide future currency reforms in China.展开更多
基金supported by National Natural Science Foundation of China (CN) Project (U153610079,61401038, 61762086)
文摘With the popularization and rapid development of mobile intelligent terminals(MITs), the number of mobile applications, or apps, has increased exponentially. It is increasingly common for malicious code to be inserted into counterfeit apps, which can cause significant economic damage and threaten the security of users. Code obfuscation techniques are a highly efficient group of methods for code security protection. In this paper, we propose a novel control flow obfuscation based method for Android code protection. First, algorithms to insert irrelevant code and flatten the control flow are employed that minimize the cost of obfuscation while ensuring its strength. Second, we improve the traditional methods of control flow flattening to further reduce the costs of obfuscation. Lastly, the use of opaque predicates is strengthened by establishing an access control strategy, which converts the identification of opaque predicates in the entire program into a graph traversal problem, and thereby increases the strength of the code protection. We did some experiments to evaluate our method, and the results show that the proposed method can work well.
基金the Natural Science Foundation of China(No.71673183).
文摘This paper examines structural changes in China s exchange rate mechanism.For this purpose,we propose a predictive model incorporating three factors that influence the central parity rate:a smoothing factor,a market factor,and a basket factor.We first apply the model to analyze the effects of 12 exchange rate reforms since 2005,treating these reforms as predetermined structural breaks.Among other results,we find that the main impact of introducing a“counter-cyclical factor”is to weaken the role of the basket factor.We estimate structural breaks in data,assuming that the number and dates of breaks are unknown,and we find that,although the majority of estimated breaks occur within the neighborhood of exchange rate reforms,there are breaks due to other external shocks such as the escalation of the China-US trade conflict in May 2019.It is suggested that our model may be used to guide future currency reforms in China.
