一种基于像素值偏移编解码技术的屏摄隐通道研究

屏摄隐通道通过摄像机拍摄显示器进行隐蔽通信.现有屏摄隐通道技术对摄像机的拍摄角度有严格要求.针对这种情况,文章提出了一种基于像素值偏移编解码技术的屏摄隐通道方法.该方法对显示图像的像素值进行偏移,把二维码(QR码)嵌入显示帧.利用人眼对于对比度、亮度相近的图像分辨能力差的特点,秘密地将显示帧发送给摄像机.在解码时提取加...     

Estimating sewer leakage from continuous tracer experiments

Direct measurements of sewer leakage with continuous dosing of tracers are often considered too imprecise for practical applications. However, no mathematical framework for data analysis is reported in literature. In this paper, we present an improved experimental design and data analysis procedure together with a comprehensive framework for uncertainty assessment. Test runs in a 700 m-long watertight sewer showed no significant bias and a very high precision of the methodology. The standard error in the results was assessed to 2.6% of the labeled flow with a simplified model. It could be reduced to 1.2% when a dynamic data analysis procedure was applied. The major error contribution was caused by transient transport phenomena, which suggests that careful choosing of the experimental time is more important than the choice of a very specific tracer substance. Although the method is not intended to replace traditional CCTV inspections, it can provide complementary information for rational rehabilitation planning.     

一种无监督的窃密攻击及时发现方法

近年来,窃密攻击成为了最严重的网络安全威胁之一.除了恶意软件,人也可以成为窃密攻击的实施主体,尤其是组织或企业的内部人员.由人实施的窃密很少留下明显的异常痕迹,给真实场景中攻击的及时发现和窃密操作的分析还原带来了挑战.提出了一个方法,将每个用户视为独立的主体,通过对比用户当前行为事件与其历史正常行为的偏差检测异常,以会话为单元的检测实现了攻击发现的及时性,采用无监督算法避免了对大量带标签数据的依赖,更能适用于真实场景.对算法检测为异常的会话,进一步提出事件链构建方法,一方面还原具体窃密操作,另一方面通过与窃密攻击模式对比,更精确地判断攻击.在卡内基梅隆大学的CERT内部威胁数据集上进行了实验,结果达到99%以上的准确率,且可以做到无漏报、低误报,证明了方法的有效性和优越性.     

面向AI模型训练的DNS窃密数据自动生成

近年来,借助DNS协议良好的隐蔽性和穿透性实施数据窃取已成为诸多APT组织青睐的TTPs,在网络边界监测DNS流量进而精准发现潜在攻击行为已成为企事业单位急需建立的网络防御能力。然而,基于DNS的APT攻击所涉及的恶意样本存在难获取、数量少、活性很低等现实问题,且主流的数据增强技术不适合移植到网络攻防这个语义敏感领域,这些问题制约了AI检测模型训练。为此,本文基于DNS窃密攻击机理分析,并结合了大量真实APT案例和DNS工具,提出了一种基于攻击TTPs的DNS窃密流量数据自动生成及应用方法,设计并实现了DNS窃密流量数据自动生成系统—MalDNS,以生成大规模、高逼真度、完备度可调的DNS窃密数据集。最后,通过实验验证了生成流量数据的有效性,以及对检测模型训练的有效支撑。     

Sources and transport of selected organic micropollutants in urban groundwater underlying the city of Halle (Saale), Germany

In this study, we used isotopic (delta18O, delta2H, delta34S-SO4) and chemical tracers (boron) to assess the sources and transport processes of the micropollutants carbamazepine, galaxolide, and bisphenol A in groundwater underlying the city of Halle (Saale), Germany. Their ubiquitous presence in urban groundwater results from a combination of local river water infiltration, sewer exfiltration, and urban stormwater recharge. Attenuation during transport with infiltrating river water increased from carbamazepine (0-60%) to galaxolide (60-80%) in accordance with their increasing sorption affinity and decreasing recalcitrance against biodegradation. Distinctly higher attenuation during transport was found for carbamazepine (85-100%) and galaxolide (95-100%) if micropollutants originated from sewer exfiltration. Most likely, this is related to higher contents of organic matter and higher transit times of the respective flow paths. Although attenuation undoubtedly also affects the transport of bisphenol A, quantification is limited due to additional contributions from the urban stormwater recharge. As a consequence, micropollutant loads in groundwater indicate that groundwater discharge may dominate the export of bisphenol A from urban areas.     

美国战术星发展研究

美国战术星项目是美国国防部作战响应空间试验计划的主要技术验证项目。作为目前唯一在轨运行的卫星,TacSat-4卫星为实现作战响应空间提供了“动中通”通信、数据暗渡和蓝军跟踪等相关先进能力,从而提高了作战响应空间系统的通信与覆盖能力、改进了卫星通信需求的能力和体系结构,并且为未来作战响应空间项目的采办提供了依据。另一方面,美国的战术星项目还需要面对军事效果评估和商业策略的挑战。然而,美国战术星的先进技术及军事效果评估结论也为我国未来卫星通信系统的建设以及卫星通信系统对抗装备的发展带来新的思考。     

洁净室阻漏送风末端装置性能与评价

本文从洁净室送风末端装置的发展着眼,认为许钟麟教授提出的“主流区”理论和德国艾思东教授提出的评价指标促进了送风末端装置早期的发展,近年来许钟麟教授提出阻漏层DEL理论以及阻漏送风天花DSC突破了传统理论和产品模式,使送风末端装置综合性能有了很大的提高。     

高层建筑的一个渗风计算模型

本文提出一个适用于具有两个不同区段且迎风及背风侧的渗风面积可以不对称的高层建筑渗风计算模型。论证了这个模型的两个基本的建筑总体特性值,即在纯热压作用下的中和界位置及在纯风压作用下的室内余压值,并给出了相应的数据及应用说明。