Blockchain is a revolutionary technology that has reshaped the trust model among mutually distrustful peers in a distributed network. While blockchain is well-known for its initial usage in a public manner, such as the cryptocurrency of Bitcoin, consortium blockchain, which requires authentication of all involved participants, has also been widely adopted in various domains. Nevertheless, there is a lack of comprehensive study of consortium blockchain in terms of its architecture design, consensus mechanisms, comparative performance, etc. In this study, we aim to fill this gap by surveying the most popular consortium blockchain platforms and assessing their core designs in a layered fashion. Particularly, Byzantine fault tolerant (BFT) state machine replication (SMR) is introduced to act as a basic computational model of consortium blockchain. Then the consortium blockchain is split into the hardware layer, layer-0 (network layer), layer-I (data layer, consensus layer and contract layer), layer-II protocols, and application layer. Each layer is presented with closely related discussion and analysis. Furthermore, with the extraction of the core functionalities, i.e., robust storage and guaranteed execution, that a consortium blockchain can provide, several typical consortium blockchain-empowered decentralized application scenarios are introduced. With these thorough studies and analyses, this work aims to systematize the knowledge dispersed in the consortium blockchain, highlight the unsolved challenges, and also indicate the propitious avenues of future work.

Blockchain technology has been increasingly used for decentralizing cloud-based Internet of Things (IoT) architectures to address limitations faced by centralized systems. While many existing efforts are successful in decentralization with multiple servers (i.e., full nodes) to handle faulty nodes, an important issue has arisen that external clients have to rely on a relay node to communicate with the full nodes in the blockchain. Compromization of such relay nodes may result in a security breach and even a blockage of IoT sensors from the network. We propose blockchain-based decentralized IoT management systems for censorship resistance, which include a “diffusion” function to deliver all messages from sensors to all full nodes and an augmented consensus protocol to check data losses, replicate processing outcome, and facilitate opportunistic outcome delivery. We also leverage public key aggregation to reduce communication complexity and signature verification. The experimental results from proof-of-concept implementation and deployment in a real distributed environment show the feasibility and effectiveness in achieving censorship resistance.

Peer-to-peer (P2P) content delivery is up-and-coming to provide benefits comprising cost-saving and scalable peak-demand handling compared with centralized content delivery networks (CDNs), and also complementary to the popular decentralized storage networks such as Filecoin. However, reliable P2P delivery demands proper enforcement of delivery fairness, i.e., the deliverers should be rewarded in line with their in-time delivery. Unfortunately, most existing studies on delivery fairness are on the basis of non-cooperative game-theoretic assumptions that are arguably unrealistic in the ad-hoc P2P setting. We propose an expressive yet still minimalist security requirement for desired fair P2P content delivery, and give two efficient blockchain-enabled and monetary-incentivized solutions ${\mathsf {FairDownload}}$ and ${\mathsf {FairStream}}$ for P2P downloading and P2P streaming scenarios, respectively. Our designs not only ensure delivery fairness where deliverers are paid (nearly) proportional to their in-time delivery, but also guarantee exchange fairness where content consumers and content providers are also fairly treated. The fairness of each party can be assured even when other two parties collude to arbitrarily misbehave. Our protocols provide a general design of fetching content chunk from any specific position so the delivery can be resumed in the presence of unexpected interruption. Further, our systems are efficient in the sense of achieving asymptotically optimal on-chain costs and optimal delivery communication. We implement the prototype and deploy on the Ethereum Ropsten network. Extensive experiments in both LAN and WAN settings are conducted to evaluate the on-chain costs as well as the efficiency of downloading and streaming. Experimental results show the practicality and efficiency of our protocols.

Image anomaly detection and localization have received widespread interest in the community, and knowledge distillation (KD) has been widely explored. Recently, the reverse distillation (RD) paradigm has successfully mitigated the homogenization of anomaly representations in traditional KD arising from identical or similar teacher-student (T-S) architecture. However, in RD, the lack of an effective means to prevent anomalous patterns in the teacher encoder from being leaked into the student decoder undermines potential modeling discrepancies between the T-S model in anomaly representations. To settle this problem, we propose REverse distillation with latent Anomaly SuppressiON (REASON) method, preventing the student decoder from receiving anomalous patterns by extra means of anomaly filtering during the inference phase, and thus, the student model can only restore representations of anomaly-free images. Specifically, we construct a Siamese teacher encoder architecture, with one branch extracting features from anomaly-free samples and the other synthesizing anomaly features with spatial noise injection from the latent feature level. Next, we design a latent anomaly suppression module to recover normal features from perturbed anomalous features. In this sense, the follow-up student decoder will receive input without abnormal patterns. Thus, representations of the anomaly-free images can be described well, while those of the anomalous images can be well-differentiated between the T-S model. Furthermore, to enhance the model’s anomaly detection and localization capabilities, we propose multi-granularity KD loss to optimize the student decoder to focus on context and local details. Extensive experiments are performed on three benchmark datasets, i.e., MVTec AD, AeBAD, and OCT2017, and the results show the effectiveness and robustness of our proposed approach, which achieves superiority over the current state-of-the-art methods.

Time series are widely used in many classification and regression tasks. However, numerous time series contain unavoidable missing data, making it challenging to model the temporal dynamics of sequential data. Various data imputation methods have been proposed to infer missing values in time series. Although sequences recorded at fixed time intervals are presented in discrete form, they possess an inherent temporal continuity, which is ignored in most existing approaches. In this paper, we propose an end-to-end Attentive Continuous-Time Generative Adversarial Network (ACGANet) to estimate unobserved values in irregular sequences. ACGANet captures the temporal dynamics by transforming the discrete sequence into the continuous-time flow, thereby modeling the underlying distribution of the real data. Furthermore, ACGANet employs an adversarial learning strategy to alleviate the error introduced by imputed values, with the discriminator distinguishing between real and generated samples. Additionally, ACGANet introduces the log-density of hidden temporal states as an auxiliary loss to further optimize the generator. This allows the model to simultaneously focus on the overall temporal dynamics of the time series and the underlying distribution of the missing data. Extensive experiments on three publicly available real-world datasets demonstrate that ACGANet achieves state-of-the-art performance in imputing incomplete time series. Moreover, both qualitative and quantitative analyses validate the effectiveness of the proposed model.