No abstract

Reactive defense mechanisms, such as intrusion detection systems, have made significant efforts to secure a system or network for the last several decades. However, the nature of reactive security mechanisms has limitations because potential attackers cannot be prevented in advance. We are facing a reality with the proliferation of persistent, advanced, intelligent attacks while defenders are often way behind attackers in taking appropriate actions to thwart potential attackers. The concept of moving target defense (MTD) has emerged as a proactive defense mechanism aiming to prevent attacks. In this work, we conducted a comprehensive, in-depth survey to discuss the following aspects of MTD: key roles, design principles, classifications, common attacks, key methodologies, important algorithms, metrics, evaluation methods, and application domains. We discuss the pros and cons of all aspects of MTD surveyed in this work. Lastly, we highlight insights and lessons learned from this study and suggest future work directions. The aim of this paper is to provide the overall trends of MTD research in terms of critical aspects of defense systems for researchers who seek for developing proactive, adaptive MTD mechanisms.

No abstract

The cobalt(II) complexes of D2-symmetric chiral porphyrins, such as 3,5-Di(t)Bu-ChenPhyrin P5, can catalyze asymmetric olefin aziridination with diphenylphosphoryl azide (DPPA) as a nitrene source. Acceptable asymmetric inductions were observed for the [Co(P5)]-based catalytic system, forming the desired N-phosphorus-substituted aziridines in moderate to high yields and good enantioselectivities.