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Carbon dots (CDs), as an attractive zero-dimensional carbon nanomaterial with unique photoluminescent merits, have recently exhibited significant application potential in gas sensing as a result of their excellent optical/electronic characteristics, high chemical/thermal stability, and tunable surface states. CDs exhibit strong light absorption in the ultraviolet range and tunable photoluminescence characteristics in the visible range, which makes CDs an effective tool for optical sensing applications. Optical gas sensor based on CDs have been investigated, which generally responds to the target gas by corresponding changes in optical absorption or fluorescence. Moreover, electrical gas sensor and quartz crystal microbalance sensor whose sensing layer involves CDs have also been designed. Electrical gas sensor exhibits an increase or a decrease in electrical current, capacitance, or conductance once exposed to the target gas. Quartz crystal microbalance sensor responds to the target gas with a frequency shift. CDs greatly promote the absorption of the target gas and improve the sensitivity of both sensors. In this review, we aim to summarize different types of gas sensors involving CDs, and sensing performances of these sensors for monitoring diverse gases or vapors, as well as the mechanisms of CDs in different types of sensors. Moreover, this review provides the prospect of the potential development of CDs based gas sensors.

Recently, researchers are no longer satisfied with the investigation of the fluorescence properties of carbon dots (CDs), but instead focus on the more attractive afterglow luminescence, especially room temperature phosphorescence (RTP) and thermal activation delayed fluorescence (TADF). Numerous attempts have been made to construct CD-based afterglow materials, including embed CDs in various rigid matrices or construct self-protective structures. Because of the diversity of construction methodologies, different mechanisms and effects would be produced, thus resulting in distinguishing afterglow characteristics. Afterglow of CDs in organic matrices is mainly due to the formation of hydrogen bonds, which can suppress intramolecular vibration and stabilize triplet states, thus generating afterglow emission. Afterglow of CDs in diverse inorganic matrices are completely different because the multifarious interactions between CDs and different matrices are generated (e.g., rigid structure covalent bonds, structural confinement, energy transform, etc). The self-protective CDs always possess polymer-like structure or polymer-chains on their surface, which can act as rigid matrix to activating afterglow emission. This review aims to sum up the relationships between structure construction and afterglow characteristics, and the mechanism of afterglow generation, which are of great significance for stimulating more exciting progress in the purposeful design of afterglow materials.

Stimuli-responsive shape-memory materials are a category of fascinating smart materials, which undergo reversible shape transformation with environmental changes. Among a large number of stimuli-responsive shape-memory materials, light-driven materials have sparked tremendous attention because of their stability, remote operability and environmentally friendly. Herein, we report a novel strategy for the synthesis of a light-responsive shape-memory polymer that is made from carbon dots and polyvinyl alcohol. The as-prepared carbon dots are endowed with good visible light absorption and excellent photothermal conversion, which enable the carbon dot/polyvinyl alcohol composite polymer to serve as a light-responsive shape-memory polymer. The carbon dots not only work as photothermal agents but also offer additional hydrogen bond interaction, which accelerates the shape-memory recovery rate. The results show that the composite polymer can realize shape recovery using relatively low laser power. Most importantly, the as-prepared carbon dot/polyvinyl alcohol composite polymer not only possesses great research potential in different types of fields, such as medical and sensing, but also provides a effective and economic strategy for taking the advantage of light.

Afterglow including thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) has stimulated considerable attention owing to bright potential applications in optoelectronic devices, sensing, and security systems. However, previously reported afterglow materials are mostly single-mode (one of RTP or TADF only), a tunable multi-mode afterglow emission is still rarely achieved. Herein, we report the temperature-responsive conversion characteristics of TADF and RTP of carbon dots in silica (CDs@SiO2) for the first time. The unique temperature-responsive afterglow characteristics, that is, phosphorescence and TADF can be mutually transformed as the temperature changes, resulting in the free conversion of the RTP/TADF ratio as well as the afterglow color change through simple temperature control. The Si–O network plays multiple roles to strengthen and confine the embedded CDs, thus resulting in ultralong RTP emission and unique afterglow characteristics. Furthermore, CDs@SiO2 exhibited excellent stability against water, acid, alkali, salt and oxidants as well as polar solvents. CDs@SiO2 with unique afterglow characteristics and high stability can have multiple potential applications in rapid fingerprint detection and temperature sensing, especially in advanced temperature-responsive multicolor anti-counterfeiting and encryption.

Biomimetic nanodevice is an important branch to expand the potential applications of artificial nanochannels. Here, we constructed nanochannels for cascade response of borate and cis-hydroxyl compounds by modifying the nanochannels of track-etched polycarbonate (TEPC) membranes with polyvinyl alcohol (PVA). Firstly, borate bound to PVA and increased the negative charge density on the surface of the nanochannels, which obstructed the transport of 1,5-naphthalene disulfonate (NDS2−). Subsequently, the addition of cis-hydroxyl compounds induced leaving of borate due to the stronger binding affinities between borate and cis-hydroxyl compounds, which reduced the negative charge density on nanochannels and then enhanced the transport of NDS2−. The cascade response of the nanochannels also accord with the properties of IMP (implication) logic gate. In addition, such nanochannels showed good reproducibility and reversibility. Therefore, this cascade response model based on nanochannels has the potential to be used as switches in area of actuators and biosensors, and is also expected to be used to understand the interaction of substances in nanoscale and simulate the physiological functions of boron.

UV absorbers are very effective in the fields of antiyellowing, resistance of photocatalytic degradation, and sunscreen cosmetics. However, commercialized UV absorbers have the drawbacks of toxicity, low absorption efficiency, transparency, etc. Here, we report for the first time silicon quantum dots as full-band UV absorbers. The NH-refunctionalized silicon quantum dots with high-performance UV absorption were successfully synthesized under the synergistic effect of sodium citrate and ethanediamine, and the (NH, OH)-functionalized silicon quantum dots (SiQDs) with full-band UV absorption can be achieved by reregulating -NH2 and -OH groups on the surface. The as-prepared (NH, OH)-functionalized SiQDs exhibited good stability and underwent treatment of varying pH and temperature. Furthermore, experimental results demonstrated that compared to commercial water-soluble organic UV absorbers, the (NH, OH)-functionalized SiQDs showed better antiyellowing performance for polyurethane and resistance of photocatalytic degradation for rhodamine B, and presented huge application potential in sunscreen cosmetics. Finally, the UV absorption mechanism of SiQDs was explained to be mainly related to Γ → Γ direct band gap transition, which absorb UV light and release it as thermal radiation.

All-inorganic perovskite CsPbBr3 quantum dots (QDs) are becoming the most popular narrow-band green emitter for use as a critical material in next generation wide-color-gamut backlight displays. However, their intrinsic poor stability greatly hinders their development for practical applications. Herein, CsPbBr3 QDs were successfully precipitated in boro-germanate glass (CsPbBr3 QDs@glass) with well-designed compositions, not only retaining a high photoluminescence quantum yield (PLQY of 43% upon 450 nm excitation) and narrow bandwidth (FWHM of 22 nm), but also showing significantly enhanced stability in relation to water, heat, and UV/blue irradiation. The relative PL intensity of CsPbBr3 QDs@glass was maintained at 60% or 85% after being immersed in water for 22 days or exposed to UV light for 100 hours, respectively. Moreover, CsPbBr3 QDs@glass samples present impressive recovery abilities in thermal cycling experiments or upon intermittent blue light irradiation. Finally, an all-inorganic white light-emitting diode (white LED) achieving 125% of National Television Standards Committee (NTSC) performance was fabricated through employing green-emitting CsPbBr3 QDs@glass and red-emitting Cs2SiF6:Mn4+ phosphor-in-glass (PiG) plates as color convertors. The design rules established here could initiate the further exploration of other glass systems with moderate halide solubilities and low melting temperatures to precipitate highly efficient and stable CsPbX3 (X = Cl, Br, I) QDs.

Internet-of-Things (IoT) devices deployed in smart homes expose users to cyber threats that can cause privacy leakage (e.g., smart TV eavesdropping) or physical hazards (e.g., smart stove causing fire). Prior work has argued that to effectively detect and prevent such threats, contextual policies are needed to decide if an access to an IoT device should be allowed. Today, however, such contextual access control policies need to be manually generated by IoT developers or users via preinstallation or runtime prompts. Both approaches suffer from potential misconfigurations and often fail to provide coverage over the space of policies. In this paper, our goal is to build a machine learning framework to automatically learn the contextual access control policies from the observed behavioral patterns of users in smart homes. Designing such a learning framework is challenging on two fronts. First, the accuracy is constrained by insufficient data in some smart homes and the diversity of IoT access patterns across different smart homes. Second, since we rely on usage patterns of IoT devices, users will have privacy concerns. We address these challenges in designing LoFTI, a federated multi-task learning framework that learns customized context-aware policies from multiple smart homes in a privacy-preserving manner. Based on prior user studies, we identify six general types of features to capture contextual access patterns. We build a simple machine learning model with temporal structure to achieve a good trade-off between accuracy and communication/computation cost. We design a custom data augmentation mechanism to address the issue of unbalanced data in learning (i.e., few negative vs. normal samples). We show that LoFTI can achieve low false positives/false negatives, reducing the false negative rate by 24.2% and false positive rate by 49.5%, comparing with the state-of-the-art single-home learning and all-home learning mechanism.

Room temperature phosphorescence materials have inspired extensive attention owing to their great potential in optical applications. However, it is hard to achieve a room temperature phosphorescence material with simultaneous long lifetime and high phosphorescence quantum efficiency. Herein, multi-confined carbon dots were designed and fabricated, enabling room temperature phosphorescence material with simultaneous ultralong lifetime, high phosphorescence quantum efficiency, and excellent stability. The multi-confinement by a highly rigid network, stable covalent bonding, and 3D spatial restriction efficiently rigidified the triplet excited states of carbon dots from non-radiative deactivation. The as-designed multi-confined carbon dots exhibit ultralong lifetime of 5.72 s, phosphorescence quantum efficiency of 26.36%, and exceptional stability against strong oxidants, acids and bases, as well as polar solvents. This work provides design principles and a universal strategy to construct metal-free room temperature phosphorescence materials with ultralong lifetime, high phosphorescence quantum efficiency, and high stability for promising applications, especially under harsh conditions., For room temperature phosphorescence (RTP) materials to reach their potential for optical applications, new materials with improved performance must be realized. Here, the authors report multi-confined carbon dots as high stability RTP materials with long afterglow lifetime & high efficiency.

The outbreak of the COVID-19 pandemic in 2020 has posed unprecedented challenges for fish trade worldwide. This study examines these challenges through an observation of China’s fish import and export activities and a qualitative study on evolving policies in the first nine months of 2020. The results indicate that control measures responding to uncertainty regarding the source of the disease and transmission path, the pressing need for restriction of the movement of people and goods, and fear of a second wave of outbreaks have substantially disrupted fish trade. To meet these challenges, certain coping measures are adopted to offset negative effects in the short term. These measures indicate the government’s pivotal role in stabilizing the supply chain and striking a balance between control requirements and efficiency required in trading activities, as well as the importance to find alternative markets to mitigate risks brought by the delayed supply and the plummeting consumption market. It concludes with some suggestions on improving international cooperation and domestic regulation for building resilience in long run.

Carbon dots as an emerging photoluminescent material has attracted growing attention. Hence, there is a highly urgent to develop kinds of multicolor emission carbon dots materials. Here, we report a new kind of dual-emissive carbon dots which display two emission band located at 457 and 643 nm (blue and red) in alcohols solvent, respectively. In particular, the red emission band of carbon dots independent of the excitation wavelength can be manipulated by changing the polarity of the solvent, which is called solvatochromic phenomenon. It is incredibly rare for bare carbon dots to have both dual-emission and solvatochromic phenomenon at the same time. The temperature-dependent emission spectra of synthesized carbon dots have been measured to go insight into the hydrogen bond interaction, and the aggregation in microscale is observed by transmission electron microscopy. Results indicates that the special dual-emission and solvatochromic phenomenon stem from partially nanoparticle agglomerates which caused by intermolecular hydrogen bond (between solvents and carbon dots). Benefiting from the special optical characteristics, the applications of ratiometric detecting water in ethanol was carried out.

The shell/core structure of CDs@CaF

Recombinant proteins have shown several benefits compared with their non-recombinant counterparts in protein therapeutics. However, there are still some problems with the storage and distribution of recombinant proteins, owing to their temperature sensitivity. Microfluidic chips can integrate different functional modules into a single device because of the advantages of integration and miniaturization, which have the special potential to synthesize drugs when and where they are needed most. Here, we integrated cell-free protein synthesis and purification into a microfluidic chip for the production of recombinant protein. The chip consisted of a main channel and a branch channel. The main channel included two pinches, which were filled with template DNA-modified agarose microbeads and nickel ion-modified agarose beads as the cell-free protein synthesis unit and protein purification unit, respectively. The reaction mixture for protein synthesis was introduced into the main channel and first passed through the protein synthesis unit where the target protein was synthesized; next, the reaction mixture passed through the protein purification unit where the target protein was captured; and, finally, pure protein was collected at the outlet when washing buffer and eluting buffer were sequentially introduced into the branch channel. Enhanced green fluorescent protein (EGFP) was used as the model to investigate the performance of our chip. One chip could produce 70 μl of EGFP solution (144.3 μg/ml, 10.1 μg) per batch, and another round of protein synthesis and purification could be performed after replacing or regenerating nickel ion-modified agarose beads. It should be possible to produce other recombinant proteins on demand with this chip by simply replacing the template DNA.

Light-up aptamers have attracted growing attention due to their advantages of being label-free and having low fluorescence background. In this work, we developed a light-up fluorescence assay for label-free detection of tumor cells based on a bifunctional split aptamer (BFSA) that contained two DNA strands (BFSA-a and BFSA-b). BFSA-a and BFSA-b were constructed by combining aptamers ZY11 and ThT.2-2, which could specifically bind to the tumor cell SMMC-7721 and activate the fluorescence of thioflavin T (ThT). A Helper strand was introduced to hybridize with BFSA-b, and then BFSA-a and BFSA-b were separated if the target cell was absent. Only when the target cell is present can BFSA-a approach and hybridize with BFSA-b due to the 'induced-fit effect', which made the Helper strand dissociate. Then ThT bound to BFSA and the fluorescence of ThT was activated. The results indicated that this fluorescence assay had a good linear response to the target cells in the range of 250-20 000 cells in 100 μL binding buffer; the lowest cell number actually detected was 125 cells in 100 μL buffer. This assay also displayed excellent selectivity and was successfully applied to detect target cells in 20% human serum samples. The design of bifunctional split aptamers realized no-washing, label-free, low-cost, one-step detection of tumor cells, which could generate detectable fluorescence signals just by mixing nucleic acid aptamers and fluorescent reporter molecules with target cells. Such a design of aptamer probes also has the potential to construct stimuli-responsive controlled drug delivery systems.

Cell-surface glycosylation contains abundant biological information that reflects cell physiological state, and it is of great value to image cell-surface glycosylation to elucidate its functions. Here we present a hybridization chain reaction (HCR)-based multifluorescence resonance energy transfer (multi-FRET) method for specific imaging of cell-surface glycosylation. By installing donors through metabolic glycan labeling and acceptors through aptamer-tethered nanoassemblies on the same glycoconjugate, intramolecular multi-FRET occurs due to near donor-acceptor distance. Benefiting from amplified effect and spatial flexibility of the HCR nanoassemblies, enhanced multi-FRET imaging of specific cell-surface glycosylation can be obtained. With this HCR-based multi-FRET method, we achieved obvious contrast in imaging of protein-specific GalNAcylation on 7211 cell surfaces. In addition, we demonstrated the general applicability of this method by visualizing the protein-specific sialylation on CEM cell surfaces. Furthermore, the expression changes of CEM cell-surface protein-specific sialylation under drug treatment was accurately monitored. This developed imaging method may provide a powerful tool in researching glycosylation functions, discovering biomarkers, and screening drugs.

Highly sensitive detection of cancer cells with high signal-to-background ratio (SBR) is still urgently needed. Here, a self-assembling activatable probe (SAAP) based on split aptamers was developed to meet this purpose. The SAAP is formed with quenched fluorescence; only when target cells are present would the split aptamers self-assemble together and thus activate fluorescence by intramolecular and intermolecular fluorescence quenching strategies. As proof of concept, a split aptamer pair stemming from an intact aptamer, ZY11, developed by our lab was selected to construct SAAP. Owing to the design of self-assembly and activation strategy, the SBR of our approach could be raised to ∼40 and achieved a very low detection limit of seven target 7721 cells in 100 μL of binding buffer. Meanwhile, one-step detection of target cells was achieved within 15 min without any washing steps and pretreatment, which shows potential for point-of-care detection. Moreover, we succeeded in the specific recognition of target cells in 50% human serum and mixed cell samples, which indicated this strategy had great advantages in detection in complex biological samples. In addition, dual-signal detection was also successfully implemented, which may be helpful for accurate detection of target cells. Therefore, this rapid, facile, specific, and highly sensitive detection method for cancer cells may provide convenience in cancer research and medical diagnosis.

The shell/core structure of CDs@CaF2 nanocomposites (CCNCs) were prepared by assembling fluorescent carbon dots (CDs) inside the inorganic CaF2 substrates using co-precipitation interaction. CDs endow CaF2 with properties of good UV-absorbing behavior and efficient blue light emission instead of rare-earth such as Eu that is expensive and susceptible to polluting the environment during the mining process. Due to the nanometer size and surface effect of nano CaF2, and the approximate refractive index between CaF2 and polyethylene (PE), CCNC/PE film exhibits better elongation at the break than pure PE film while maintaining high transparency and visible light transmittance. Simultaneously, the CCNC/PE film was experimentally demonstrated to have outstanding performance of anti-UV and blue light conversion, which shows that CCNCs can be a novel and promising multifunctional additive applied in polymers especially for greenhouse film.

Cloud computing platforms are now constructed as distributed, modular systems of cloud services, which enable cloud users to manage their cloud resources. However, in current cloud platforms, cloud services fully trust each other, so a malicious user may exploit a vulnerability in a cloud service to obtain unauthorized access to another user's data. To date, over 150 vulnerabilities have been reported in cloud services in the OpenStack cloud. Research efforts in cloud security have focused primarily on attacks originating from user VMs or compromised operating systems rather than threats caused by the compromise of distributed cloud services, leaving cloud users open to attacks from these vulnerable cloud services. In this paper, we propose the Pileus cloud service architecture, which isolates each user's cloud operations to prevent vulnerabilities in cloud services from enabling malicious users to gain unauthorized access. Pileus deploys stateless cloud services "on demand" to service each user's cloud operations, limiting cloud services to the permissions of individual users. Pileus leverages the decentralized information flow control (DIFC) model for permission management, but the Pileus design addresses special challenges in the cloud environment to: (1) restrict how cloud services may be allowed to make security decisions; (2) select trustworthy nodes for access enforcement in a dynamic, distributed environment; and (3) limit the set of nodes a user must trust to service each operation. We have ported the OpenStack cloud platform to Pileus, finding that we can systematically prevent compromised cloud services from attacking other users' cloud operations with less than 3% additional latency for the operation. Application of the Pileus architecture to Open-Stack shows that confined cloud services can service users' cloud operations effectively for a modest overhead.

In this paper, a modified active disturbance rejection control (ADRC) structure composed of a linear extended state observer (LESO) and a composite nonlinear feedback controller (CNFC) is developed to improve the transient performance of the micro/nano-manipulating systems. In particular, the controller adopts the LESO to estimate the “total disturbance” and then compensates it through the CNFC. The linear feedback part is designed with a small damping ratio such that the closed-loop system yields a fast response. The nonlinear feedback controller composed of the specific structure of the augmented system is exploited to eliminate the overshoot of the closed-loop system as the system output approaches the target reference. The proposed control architecture is deployed on a customize-designed nano-stage driven by a piezoelectric (PZT) actuator, where real time experiments demonstrate good transient performance and stead-state accuracy in high precision positioning.

Voice control is a popular way to operate mobile devices, enabling users to communicate requests to their devices. However, adversaries can leverage voice control to trick mobile devices into executing commands to leak secrets or to modify critical information. Contemporary mobile operating systems fail to prevent such attacks because they do not control access to the speaker at all and fail to control when untrusted apps may use the microphone, enabling authorized apps to create exploitable communication channels. In this paper, we propose a security mechanism that tracks the creation of audio communication channels explicitly and controls the information flows over these channels to prevent several types of attacks.We design and implement AuDroid, an extension to the SELinux reference monitor integrated into the Android operating system for enforcing lattice security policies over the dynamically changing use of system audio resources. To enhance flexibility, when information flow errors are detected, the device owner, system apps and services are given the opportunity to resolve information flow errors using known methods, enabling AuDroid to run many configurations safely. We evaluate our approach on 17 widely-used apps that make extensive use of the microphone and speaker, finding that AuDroid prevents six types of attack scenarios on audio channels while permitting all 17 apps to run effectively. AuDroid shows that it is possible to prevent attacks using audio channels without compromising functionality or introducing significant performance overhead., 2015 Annual Computer Security Applications Conference

This paper presents analysis and testing of a novel 2-DOF nanopositioner driven by piezoelectric-actuators. In order to achieve long travel range, the nanopositioner employs amplification mechanisms to overcome the small displacement of the stack-type piezoelectric element. A modified level displacement amplifier is proposed in the present paper, which has a mutually perpendicular structure for the input displacement and output displacement To achieve a better decoupling performance for the motions in two axes, a fully symmetric configuration is introduced for the parallelogram flexures. According to the analysis results, the mechanical parameters are optimized to achieve a relatively large stroke for the nanopositioner. The prototype testing results show that the first natural frequency of the proposed stage is around 330 Hz, with the amplification ratio of the displacement in each axes about 5.3. The nanopositioner achieves an overall workshapce of 65 × 67 µm, while the cross coupling between the two axes is minimized to the level of less than 2%. Ultra high precision positioning and tracking capabilities are also demonstrated with some preliminary closed loop control tests.

Microservice architecture allows different parts of an application to be developed, deployed and scaled independently, therefore becoming a trend for developing cloud applications. However, it comes with challenging security issues. First, the network complexity introduced by the large number of microservices greatly increases the difficulty in monitoring the security of the entire application. Second, microservices are often designed to completely trust each other, therefore compromise of a single microservice may bring down the entire application. The problems are only exacerbated by the cloud, since applications no longer have complete control over their networks. In this paper, we propose a design for security-as-a-service for microservices-based cloud applications. By adding a new API primitive FlowTap for the network hypervisor, we build a flexible monitoring and policy enforcement infrastructure for network traffic to secure cloud applications. We demonstrate the effectiveness of our solution by deploying the Bro network monitor using FlowTap. Results show that our solution is flexible enough to support various kinds of monitoring scenarios and policies and it incurs minimal overhead (~6%) for real world usage. As a result, cloud applications can leverage our solution to deploy network security monitors to flexibly detect and block threats both external and internal to their network.

Infrastructure-as-a-Service (IaaS) clouds can be viewed as distributed systems of cloud services that are entrusted to execute users' cloud commands to provision and manage clouds computing resources (e.g., VM). However, recent vulnerabilities found in cloud services show that this trust is often misplaced. By exploiting a vulnerability in a cloud service, an adversary can hijack or forge commands to modify user VMs, exfiltrate sensitive information, and even modify other service hosts. This paper introduces Cloud Armor, a system that detects and blocks the tampering of user commands without the need for modifications to cloud services. Our insight is that we can construct state machine models to limit the system call sequences executed by cloud services. By applying constraints over system call arguments, we can restrict the way user commands are executed, blocking unauthorized operations from compromised cloud services. We implemented a prototype Cloud Armor system for Open Stack, a widely adopted open source cloud platform. Results show that Cloud Armor can greatly limit attack options available for adversaries while imposing less than 1% overhead for user VMs. As a result, cloud users can leverage Cloud Armor to execute user commands safely even in presence of compromised cloud services.

IaaS clouds offer customers on-demand computing resources such as virtual machine, network and storage. To provision and manage these resources, cloud users must rely on a variety of cloud services. However, a wide range of vulnerabilities have been identified in these cloud services that may enable an adversary to compromise customers' computations or even the cloud platform itself. Using the motivation for adding mandatory access to commercial operating systems, we argue for the development of a secure cloud operating system (SCOS) to enforce mandatory access control (MAC) over cloud services and customer instances. To better understand the concrete challenges of building a SCOS, we examine the OpenStack cloud platform from two perspectives: (1) how attacks propagate across cloud services and (2) how adversaries leverage vulnerabilities in cloud services to attack hosts. Using this information, we review the application of three MAC approaches employed by "secure" commercial systems to evaluate their practical effectiveness for controlling cloud services. While MAC enforcement can improve security for cloud services, several threats remain unchecked. We outline a set of additional security policy goals that a SCOS must enforce to control threats from potentially compromised cloud services comprehensively. While we do not actually construct a SCOS in this paper, we hope that this study will initiate discussions that may lead to practical designs.

Cloud computing has commoditized compute, storage, and networking resources creating an on-demand utility. Despite the attractiveness of this new paradigm, its adoption has been stymied by cloud platform's lack of transparency, which leaves customers unsure if their sensitive data and computation can be entrusted to the cloud. While techniques like encryption can protect customers' data at rest, clouds still lack mechanisms for customers to verify that their computations are being executed as expected, a guarantee one could obtain if they were running the computation in their own data center. In this paper, we present the cloud verifier (CV), a flexible framework that cloud vendors can configure to provide cloud monitoring services for customers to validate that their computations are configured and being run as expected in Infrastructure as a Service (IaaS) clouds. The CV builds a chain of trust from the customer to their hosted virtual machine (VM) instances through the cloud platform, enabling it to check customer-specified requirements against a comprehensive view of both the VM's load-time and run-time properties. In addition, the CV enables cloud vendors to provide more responsive remediation techniques than traditional attestation mechanisms. We built a proof of concept CV for the OpenStack cloud platform whose evaluation demonstrates that a single CV enables over 20,000 simultaneous customers to verify numerous properties with little impact on cloud application performance. As a result, the CV gives cloud customers a low-overhead method for assuring that their instances are running according to their requirements.

In current Xen environment, platform attests its integrity to remote customer through signing the measurements of itself by Attestation Identity Key (AIK) from virtual TPM instance. They believe that this evidence of the platform is credible since the signature of AIK can not be faked. However, this approach ignores the privileged domain and its administrator. Since they could access arbitrary memory address of the platform, they could steal the AIK and forge the measurements therefore cheats the customer. In this paper, we design and implement a dual AIK signing scheme which makes use of the AIK from hardware TPM. Through signing the measurements of platform and upper-level virtual machine separately, rogue platform could not tamper with the integrity evidence of the platform. We also present a virtual AIK certificate mechanism and a new remote integrity attestation protocol for this dual AIK signing scheme. Finally, we perform a security analysis of our approach to show that it has built a correct trust model in the trusted virtualization platform and it is truly secure.

In this paper, we present a periodic authentication scheme of integrity measurements based on TNC architecture. In TNC architecture, server authenticates security posture of endpoint before an endpoint is allowed to access the network. After connected, the endpoint will not be supervised any more. Our scheme is the first to extend this before-access authentication to all-time authentication over endpoints. In fact, we show that by our scheme, the security posture of endpoint would be always monitored therefore the security of network can be improved greatly by cutting off malicious endpoint's connection. We also optimize this scheme to limit its impact on network's performance. Results show that these optimizations make the scheme more efficient and the scheme achieves a desirable effect in practical network.