Federated learning (FL) faces challenges in ensuring personalized model performance while maintaining strong privacy protection. Combined with knowledge distillation, federated learning enhanced by differential privacy has garnered increased attention. However, existing privacy-preserving federated distillation methods often apply a uniform privacy budget, neglecting the varying privacy needs across heterogeneous clients. In this letter, we propose PDP-FedKD, aPersonalizedDifferentialPrivacy-basedFederatedKnowledgeDistillationapproach. PDP-FedKD allows clients to self-select their privacy budgets using a nonuniform sampling strategy and introduces tailored noise into distillation models across heterogeneous clients. Our approach ensures global model generalization and local model personalization while preserving the global privacy budget. We further analyze tight privacy accounting based on Rényi differential privacy to optimize the trade-off between privacy and model accuracy. Experimental results in non-IID settings show that PDP-FedKD improves model performance by 4.06% over LDP-FedAKD with a uniform privacy budget and by 7.73% over DP-FedAvg without optimizing heterogeneity.

Recently, redactable blockchains have attracted attention owing to enabling the contents of blocks to be re-written. The existing redactable blockchain solutions can be classified as two categories, the centralized one and decentralized one. In centralized solutions, a single blockchain node possessing the trapdoor conducts redaction operations. However, they suffer from the issue of single point of failure. In decentralized solutions, redaction operations are performed by numerous blockchain nodes cooperatively. But there also exists the issue of inefficiency or requiring a trusted party in these solutions. Subsequently, Jia et al. proposed a redactable blockchain solution from a decentralized chameleon hash function (DCH) they designed, which supports the threshold redaction, traceability and consistency check. Nevertheless, after carefully analyzing their solution, we find that it fails to achieve the security they claimed by presenting a concrete attack. To resolve this security issue, we propose a novel chameleon hash function scheme that achieves strong collision-resistant security while maintaining simple and efficient as the building block. Based on it, we then present an improved DCH scheme with sufficient security, so that the redactable blockchain from it can resist the presented attack. Theoretical and experimental analyses demonstrate that improved DCH achieves efficiency comparable to DCH.

Online/offline identity-based signature (OO-IBS) is a versatile cryptographic tool to provide the message authentication and integrity in mobile devices, since it lightens the computational burden after the signer receiving the message and eliminates the overhead of certificate management. It has several valuable applications, for instance, wireless sensor networks. Identity-based chameleon hash (IB-CH), as an alternative building block to construct OO-IBS, has been explored in numerous literatures. Nevertheless, there still exist two major issues. 1) Nearly all of the previous IB-CH schemes with weak collision-resistance (W-CollRes) are with random oracles, which may lead to security risks in practicality. The only IB-CH scheme in the standard model suffers from the large size of public parameters and inefficient setup process. 2) The only IB-CH scheme without key exposure also relies on random oracles. In this paper, we propose two novel IB-CH schemes in the standard model. The first scheme is adaptive identity, W-CollRes secure and efficient, significantly reducing the computation costs of all algorithms and the size of public parameters compared with the existing scheme in the standard model. The second scheme is the first IB-CH achieving key exposure freeness without random oracles. Both theoretical and experimental analyses demonstrate the good performance of our proposed schemes. Furthermore, we apply our schemes to optimizing the existing generic OO-IBS construction. The optimized generic constructions reduce computational overhead by 50.0% in the online phase and enable the hash value/signature tuple generated in the offline phase to be reusable, respectively.

Federated learning (FL) allows different participants to collaborate on model training without transmitting raw data, thereby protecting user data privacy. However, FL faces a series of security and privacy issues (e.g. the leakage of raw data from publicly shared parameters). Several privacy protection technologies, such as homomorphic encryption, differential privacy and functional encryption, are introduced for privacy enhancement in FL. Among them, the FL frameworks based on functional encryption better balance security and performance, thus receiving increasing attention. The previous FL frameworks based on functional encryption suffer from several security issues, including attacks by combining multiple rounds of ciphertexts and keys, and leakage of global parameters to the central server. To tackle these issues, we propose a novel multi-input functional proxy re-encryption (MI-FPRE) scheme and further design a new FL framework with better privacy based on MI-FPRE. Our framework allows a semi-trusted central server to aggregate the parameters without knowing the intermediate parameters and the result of aggregation, thus achieves better privacy in FL training. The experimental results indicate that our framework achieves less communication overhead and higher computational efficiency without losing accuracy.

The rise of new industries, such as the Internet of Things and Smart Healthcare, has brought many cross-cloud business opportunities for cloud computing and posed new challenges to the cloud security. Traditionally, security can be assessed by compliance checking when selecting cloud services. However, when facing cross-cloud security requirements, even if passing the compliance checking, it cannot prove that different clouds have the same security level since they pass different standards. Therefore, security equivalence assessment of different security standards is a fundamental issue. In order to solve the issue automatically, we first transform it into the problem of mapping between control items with respect to different standards. Then, we define three tasks to work out the mapping problem: a task for mapping searching and two for new mapping establishing. Next, we collect, organize, and expand a dataset of mappings between control items containing 21 standards and more than 100,000 pieces of mapping data. Subsequently, we experiment with four well-known models for each task to test their performance on the dataset of mappings: TF-IDF, Word2vec, BERT, and GPT-Neo. Experimental results indicate that the current models can perform very well on the first two tasks but need to be better on the last task.

Representation learning frameworks in unlabeled time series have been proposed for medical signal processing. Despite the numerous excellent progresses have been made in previous works, we observe the representation extracted for the time series still does not generalize well. In this paper, we present a Time series (medical signal) Representation Learning framework via Spectrogram (TRLS) to get more informative representations. We transform the input time-domain medical signals into spectrograms and design a time-frequency encoder named Time Frequency RNN (TFRNN) to capture more robust multi-scale representations from the augmented spectrograms. Our TRLS takes spectrogram as input with two types of different data augmentations and maximizes the similarity between positive ones, which effectively circumvents the problem of designing negative samples. Our evaluation of four real-world medical signal datasets focusing on medical signal classification shows that TRLS is superior to the existing frameworks. We will open-source our code when the paper is accepted.

Due to the rapid growth of mobile internet, massive multimedia data (e.g., movies, photos, notes, etc.) on mobile devices is synchronized and shared through the cloud. During this process, public key encryption plays an important role in ensuring the confidentiality of data. However, due to the bottleneck of computing and storage resources in mobile devices, it is difficult to execute complex cryptographic algorithms on them. In this paper, we present a novel Hybrid Proxy Reencryption (HyPRE) scheme for the sharing of multimedia data on mobile devices, which empowers a semi-trusted proxy to convert a ciphertext under an identity to a new one under an expressive policy without revealing the underlying plaintext. Our scheme allows mobile devices with limited resources to encrypt data efficiently, and then to share the encrypted data to multiple entities securely. We define the HRA security for our HyPRE scheme to improve the incompleteness of the security under chosen plaintext attacks (CPA) in traditional proxy re-encryption schemes and prove it selectively secure under HRA. Experimental analysis indicates that HyPRE achieves 2× to 3× improvement in terms of re-encryption performance compared with the state-of-the-art ones.

Federated learning is widely used in medical applications for training global models without needing local data access, but varying computational capabilities and network architectures (system heterogeneity) across clients pose significant challenges in effectively aggregating information from non-independently and identically distributed (non-IID) data (statistic heterogeneity). Current federated learning methods using knowledge distillation require public datasets, raising privacy and data collection issues. Additionally, these datasets require additional local computing and storage resources, which is a burden for medical institutions with limited hardware conditions. In this paper, we introduce a novel federated learning paradigm, named Model Heterogeneous personalized Federated Learning via Injection and Distillation (MH-pFLID). Our framework leverages a lightweight messenger model, eliminating the need for public datasets and reducing the training cost for each client. We also develops receiver and transmitter modules for each client to separate local biases from generalizable information, reducing biased data collection and mitigating client drift. Our experiments on various medical tasks including image classification, image segmentation, and time-series classification, show MH-pFLID outperforms state-of-the-art methods in all these areas and has good generalizability.

Abstract Federated learning (FL) as a privacy-preserving technology enables multiple clients to collaboratively train models on decentralized data. However, transmitting model parameters between local clients and the central server can potentially result in information leakage. Differentially private federated learning (DPFL) has emerged as a promising solution to enhance privacy. Nevertheless, existing DPFL schemes suffer from two issues: (i) most schemes that aim to achieve desired model accuracy may incur a high privacy budget. (ii) several schemes that consider the trade-off between privacy and accuracy by utilizing linear clipping bound may distort numerous model parameters. In this paper, we first propose FDP-FL, a flexible differential privacy approach for FL. FDP-FL introduces a novel series sum privacy budget allocation instead of uniform allocation and enables adaptive and nonlinear noise scale decay. In this way, a tight bound for cumulative privacy loss can be achieved while optimizing model accuracy. Then in order to mitigate gradient leakages caused by honest-but-curious clients and server, we further design client-level FDP-FL and record-level FDP-FL, respectively. Experimental results demonstrate that our FDP-FL improves model accuracy by $\sim $13.3% compared with the basic DP-FL under a fixed privacy budget and outperforms existing trade-off schemes with the same hyperparameter setting.

Nearly all of the previous attribute-based proxy re-encryption (ABPRE) schemes cannot support keyword search and keyword updating without the aid of private key generator (PKG) simultaneously. To resolve this problem, recently in IEEE Transactions on Dependable and Secure Computing (doi: 10.1109/TDSC.2020.2963978), Ge et al. proposed a ciphertext-policy ABPRE scheme with keyword search, dubbed CPAB-KSDS, which supports keyword updating without communicating with PKG. It also achieves indistinguishability against chosen-ciphertext attack (IND-CCA) security and indistinguishability against chosen-keyword attack (INDCKA) security in the random oracle model. In this paper, we carefully analyze the security of Ge et al.’s CPAB-KSDS scheme and find that they did not give a correct reduction from IND-CKA security of theirs to the underlying cryptographic assumption. Furthermore, we also give a concrete attack on IND-CKA security of the CPAB-KSDS scheme. Therefore, it fails to achieve IND-CKA security they claimed, which is an essential security requirement for the encryption scheme with keyword search.

Computer-aided diagnosis plays an increasingly important role in modern medical activities, relying largely on the deployment of medical machine learning models. Protecting the security of model parameters is crucial for model providers. However, the current schemes for protecting model parameters are mostly interactive. This interactive nature makes it difficult to support offline deployment of models and flexible authorization of prediction results, thus hindering the widespread application of computer-aided diagnosis. To address these limitations, we propose a new computer-aided medical diagnosis framework by designing a new identity-based inner product functional proxy re-encryption (IB-IPFPRE) scheme. Our framework supports private deployment of medical diagnostic models without compromising model parameters. It also enables access control of prediction results based on user identity. Compared to existing privacy-preserving prediction techniques, our framework significantly reduces communication overhead and does not require the model owner to be online in real-time. Furthermore, our scheme enables flexible delegation of prediction results, allowing users to authorize the sharing of prediction results with other entities as needed. We conducted extensive experiments for logistic regression on three medical datasets. The experiments demonstrate that our scheme achieved 40% to 7× performance improvement in LAN environment and 13× to 15× improvement in WAN environment, and did not require any communication overhead during the privacy preserving prediction phase.

With the popularity of the Internet of Things (IoT) applications, for instance, smart homes and smart medical, edge servers have become increasingly critical infrastructures. Nevertheless, the loose management puts the edge server under the threat of malicious administrators, which causes the leaking risks of the user’s data security. We first give a Data Sniffing Attack that malicious administrators can use live migration to complete without being discovered. To resist the attack, the transparency of live migration to users is the most severe difficulty, where there has not been an effective solution yet. In this paper, we propose a live migration detection model to simulate the migration process, namely observing the indicator values that can obtain without high authorities and calculating the possibility of state transition. Then through many migration experiments, we present the immediate indicators represented by the OS interrupts and the persistent indicators represented by the IO speed, and sort these indicator values into datasets. Next, we train ten frequently-used classifiers and show their accuracy. Eventually, we analyze the advantages and disadvantages of different algorithms in predicting migration and provide the weight recommendation if applied in the detection model.

At present, backdoor attacks attract attention as they do great harm to deep learning models. By poisoning the training data, the adversary makes the model trained based on this dataset being injected with a backdoor. In the field of text, however, existing works do not provide sufficient defense against backdoor attacks. In this paper, we propose a Noise-augmented Contrastive Learning (NCL) framework to defend against textual backdoor attacks when training models with untrustworthy data. With the aim of mitigating the mapping between triggers and the target label, we add appropriate noise perturbing possible backdoor triggers, augment the training dataset, and then pull homology samples in the feature space utilizing contrastive learning objective. Experiments demonstrate the effectiveness of our method in defending three types of textual backdoor attacks, outperforming the prior works.

Online/offline identity-based signature (OO-IBS) is an adequate cryptographic tool to provide the message authentication and integrity in mobile devices, since it lightens the computational burden after the signer receives the message and eliminates the overhead of certificate management. It has several valuable applications, such as wireless sensor networks and automatic dependent surveillance-broadcast systems. Identity-based chameleon hash (IB-CH), as an alternative building block to construct OO-IBS, has been explored in several literatures. Nevertheless, almost all of the prior IB-CH schemes are in the random oracle model, which may lead to security risks in practicality. The only IB-CH scheme in the standard model proposed by Xie et al. (ICC’21) suffers from the large size of public parameters and inefficient setup process. In this paper, we propose an efficient IB-CH scheme in the standard model, significantly reducing the computational costs of all the algorithms and the size of public parameters compared with Xie’s scheme. The security and experimental analyses demonstrate the security and good performance of our scheme. Furthermore, we applied our scheme to optimize the existing generic OO-IBS construction. Our optimized construction reduces computational overhead by 50.0% in the online phase compared with the original construction.

The rapid development of the mobile Internet makes it necessary to adopt efficient cryptographic primitives for the portable devices with limited computing resources. Online/offline identity-based signatures are suitable because of short response time of signature generation and being free from the cumbersome operations caused by public key infrastructures. In this paper, we propose the first identity-based chameleon hash which can be proved secure without the random oracle and show how to use it to translate any identity-based signature to an online/offline one.

Abstract Attribute-based encryption with equality test (ABEET) simultaneously supports fine-grained access control on the encrypted data and plaintext message equality comparison without decrypting the ciphertexts. Recently, there have been several literatures about ABEET proposed. Nevertheless, most of them explore the ABEET schemes in the random oracle model, which has been pointed out to have many defects in practicality. The only existing ABEET scheme in the standard model, proposed by Wang et al., merely achieves the indistinguishable against chosen-plaintext attack security. Considering the aforementioned problems, in this paper, we propose the first direct adaptive chosen-ciphertext security ciphertext-policy ABEET scheme in the standard model. Our method only adopts a chameleon hash function and adds one dummy attribute to the access structure. Compared with the previous works, our scheme achieves the security improvement, ciphertext validity check and large universe. Besides, we further optimize our scheme to support the outsourced decryption. Finally, we first give the detailed theoretical analysis of our constructions in computation and storage costs, then we implement our constructions and carry out a series of experiments. Both results indicate that our constructions are more efficient in Setup and Trapdoor and have the shorter public parameters than the existing ABEET ones do.

Summary We present a practical large universe hierarchical attribute‐based encryption (LU‐HABE) scheme, which supports monotone access structures. In our system, key generation centers (KGCs), any one in which is labeled by a unique identity, are organized as a hierarchical structure. Thus, all secret keys issued by the KGC contain 2 parts: the identity‐related one and the attribute‐related one. Once the data owner wants to encrypt his/her data, he/she needs to specify certain numbers of pairs according to his/her demand. The pair consists of an identity of a KGC and a policy of attributes managed by the corresponding KGC, eg, IDi and (Mi, ρi). If and only if an identity associated with user's secret key is equal to or is an ancestor of one of the identities appearing in ciphertext, and simultaneously a set of attributes belonging to the user satisfies the policy, the user can decrypt it successfully. Our scheme is proved to be selectively secure in the standard model under the modified “q‐type” assumption similar to the ones used in former works and is extended to support online/offline encryption. To show the efficiency of our construction, we implement our original scheme and the extended one in Charm. Analyses show that both of them are very practical.