Non-monotone Access Structures Research Articles

Hierarchical and non-monotonic key-policy attribute-based encryption and its application

Hierarchical-authority attribute-based encryption (HABE) can resolve the performance bottleneck of the key generation center in the traditional attribute-based encryption (ABE) system. HABE has numerous applications, such as cloud computing and smart grid systems. Nevertheless, almost all of the existing HABE schemes are in the ciphertext-policy setting and do not support non-monotonic access structures. In this work, we propose the first key-policy hierarchical-authority ABE with non-monotonic access structures, dubbed KP-HABE-NMaCS, which supports the authority key delegation, constant size ciphertexts and the large universe simultaneously. We further define the security model of KP-HABE-NMaCS and prove the selective security of it in the standard model. Then we optimize our scheme to realize the outsourced decryption. Subsequently, we present the detailed theoretical analysis of our constructions and the existing HABE constructions in computation and storage costs, and meanwhile implement ours and conduct a series of experiments. Both results indicate that our KP-HABE-NMaCS construction makes improvements in expressiveness and features, and achieves efficiency comparable to the previous HABE constructions. Furthermore, they also show that our extension construction is suitable for resource-limited applications. Eventually, we explore how to apply our KP-HABE-NMaCS to build an ABE with equality test and time-based authorization.

Fully Secure Functional Encryption with a Large Class of Relations from the Decisional Linear Assumption

This paper presents a fully secure (adaptively secure) practical functional encryption scheme for a large class of relations, that are specified by non-monotone access structures combined with inner-product relations. The security is proven under a standard assumption, the decisional linear assumption, in the standard model. Our scheme is constructed on the concept of dual pairing vector spaces and a hierarchical reduction technique on this concept is employed for the security proof. The proposed functional encryption scheme covers, as special cases, (1) key-policy, ciphertext-policy and unified-policy attribute-based encryption with non-monotone access structures, (2) (hierarchical) attribute-hiding functional encryption with inner-product relations and functional encryption with nonzero inner-product relations and (3) spatial encryption and a more general class of encryption than spatial encryption.

Decentralised Functional Signatures

With the rapid development of the Internet of Things (IoT) a lot of critical information is shared however without having guarantees about the origin and integrity of the information. Digital signatures can provide important integrity guarantees to prevent illegal users from getting access to private and sensitive data in various IoT applications. Functional signatures, introduced by Boyle, Goldwasser and Ivan (PKC 2014) as signatures with a finegrained access control, allow an authority to generate signing keys corresponding to various functions such that a user with a signing key for a function f, can sign the image of the function f on a message mi.e., can sign f(m). Okamoto and Takashima (PKC 2013) firstly proposed the notion of a decentralized multi-authority functional signature (DMA-FS) scheme, which supports non-monotone access structures combined with inner-product relations. In this paper, we generalise the definition of DMA-FS proposed by Okamoto et al. (PKC13) for even more general policy functions, which support any polynomial-size boolean predicates other than the inner product relation and allow modifications of the original message. In our multi-authority functional signature (MAFS), there are multiple authorities and each one is able to certify a specific function and issue a corresponding functional signing key for each individual with some property, rendering them very useful in application settings such smart homes, smart cities, smart health care etc. We also provide a general transformation from a standard signature scheme to a MAFS scheme. Moreover, we present a way to build a function private MAFS from a FS without function privacy together with SNARKs.

Attribute-based Encryption with Non-Monotonic Access Structures Supporting Fine-Grained Attribute Revocation in M-healthcare.

By sharing the personal health information (PHI) in the healthcare provider (HP) which is equipped with cloud servers, mobile-healthcare (m-healthcare) significantly promotes a huge revolution of medical consultation. Nonetheless there is a series of challenges such as PHI confidentiality and the attribute revocation. To deal with these problems, we propose a scheme based on the attribute-based encryption. The scheme which supports non-monotonic access structures and fine-grained attribute revocation is established over the composite order bilinear groups. By utilizing this scheme, we can well protect PHI and achieve the goal of revocation. Furthermore, the security analysis and comparison show that our scheme is more expressive despite of the lower efficiency.

Attribute-based encryption schemes with constant-size ciphertexts

Attribute-based encryption (ABE), as introduced by Sahai and Waters, allows for fine-grained access control on encrypted data. In its key-policy flavor (the dual ciphertext-policy scenario proceeds the other way around), the primitive enables senders to encrypt messages under a set of attributes and private keys are associated with access structures that specify which ciphertexts the key holder will be allowed to decrypt. In most ABE systems, the ciphertext size grows linearly with the number of ciphertext attributes and the only known exception only supports restricted forms of access policies. This paper proposes the first attribute-based encryption (ABE) schemes allowing for truly expressive access structures and with constant ciphertext size. Our first result is a ciphertext-policy attribute-based encryption (CP-ABE) scheme with O(1)-size ciphertexts for threshold access policies and where private keys remain as short as in previous systems. As a second result, we show that a certain class of identity-based broadcast encryption schemes generically yields monotonic key-policy attribute-based encryption (KP-ABE) systems in the selective set model. Our final contribution is a KP-ABE realization supporting non-monotonic access structures (i.e., that may contain negated attributes) with short ciphertexts. As an intermediate step toward this result, we describe a new efficient identity-based revocation mechanism that, when combined with a particular instantiation of our general monotonic construction, gives rise to the most expressive KP-ABE realization with constant-size ciphertexts. The downside of our second and third constructions is that private keys have quadratic size in the number of attributes. On the other hand, they reduce the number of pairing evaluations to a constant, which appears to be a unique feature among expressive KP-ABE schemes.