Conditional Attribute-Based Proxy Re-Encryption

Proxy re-encryption (PRE) is a cryptographic primitive that allows a semi-trusted proxy to transfer the decryption rights of ciphertexts in a secure and privacy-preserving manner. This versatile primitive has been extended to several powerful variants, leading to numerous applications, such as e-mail forwarding and content distribution. One such variant is attribute-based PRE (AB-PRE), which provides an expressible access control mechanism by allowing the proxy to switch the underlying policy of an attribute-based encryption (ABE) ciphertext. However, the function of AB-PRE is to convert the underlying policies of all ciphertexts indiscriminately, which lacks the flexibility of ciphertext transformation. Therefore, AB-PRE needs to support the property of conditional delegation. Among the other variants of PRE, there is a variant called conditional PRE (C-PRE), which allows fine-grained delegations by restricting the proxy to performing valid re-encryption only for a limited set of ciphertexts. Unfortunately, existing PRE schemes cannot simultaneously achieve expressible access control mechanisms and fine-grained delegations. Specifically, we require a PRE scheme, via which the proxy can convert the underlying policies of an ABE ciphertext only if this ciphertext is in the set of ciphertexts allowing the proxy to perform valid transformations. To address this problem, we formalize the notion of conditional attribute-based PRE (CAB-PRE) in the honest re-encryption attacks (HRA) model, which is more robust and implies chosen-plaintext attacks (CPA) security, and propose the first CAB-PRE scheme. To construct such a scheme, we design as a building block, the first adaptively HRA-secure (ciphertext-policy) AB-PRE based on the learning with errors (LWE) problem. This scheme solves the open problem left by Susilo et al. in ESORICS\u2721 about how to construct an HRA-secure (ciphertext-policy) AB-PRE scheme, and it should be of independent interest. Then, we introduce a well-matched conditional delegation mechanism for this AB-PRE scheme to derive our adaptively HRA-secure CAB-PRE scheme

Survey on Fully Homomorphic Encryption, Theory, and Applications

Data privacy concerns are increasing significantly in the context of Internet of Things, cloud services, edge computing, artificial intelligence applications, and other applications enabled by next generation networks. Homomorphic Encryption addresses privacy challenges by enabling multiple operations to be performed on encrypted messages without decryption. This paper comprehensively addresses homomorphic encryption from both theoretical and practical perspectives. The paper delves into the mathematical foundations required to understand fully homomorphic encryption (FHE). It consequently covers design fundamentals and security properties of FHE and describes the main FHE schemes based on various mathematical problems. On a more practical level, the paper presents a view on privacy-preserving Machine Learning using homomorphic encryption, then surveys FHE at length from an engineering angle, covering the potential application of FHE in fog computing, and cloud computing services. It also provides a comprehensive analysis of existing state-of-the-art FHE libraries and tools, implemented in software and hardware, and the performance thereof