Efficient privacy preserving predicate encryption with fine-grained searchable capability for cloud storage

With the fast development in Cloud storage technologies and ever increasing use of Cloud data centres, data privacy and confidentiality has become a must. Indeed, Cloud data centres store each time more sensitive data such as personal data, organizational and enterprise data, transactional data, etc. However, achieving confidentiality with flexible searchable capability is a challenging issue. In this article, we show how to construct an efficient predicate encryption with fine-grained searchable capability. Predicate Encryption (PEPE) can achieve more sophisticated and flexible functionality compared with traditional public key encryption. We propose an efficient predicate encryption scheme by utilizing the dual system encryption technique, which can also be proved to be IND-AH-CPA (indistinguishable under chosen plain-text attack for attribute-hiding) secure without random oracle. We also carefully analyse the relationship between predicate encryption and searchable encryption. To that end, we introduce a new notion of Public-Key Encryption with Fine-grained Keyword Search (PEFKSPEFKS). Our results show that an IND-AH-CPA secure PE scheme can be used to construct an IND-PEFKS-CPA (indistinguishable under chosen plain-text attack for public-key encryption with fine-grained keyword search) secure PEFKSPEFKS scheme. A new transformation of PE-to-PEFKS is also proposed and used to construct an efficient PEFKSPEFKS scheme based on the transformation from the proposed PEPE scheme. Finally, we design a new framework for supporting privacy preserving predicate encryption with fine-grained searchable capability for Cloud storage. Compared to most prominent frameworks, our framework satisfies more features altogether and can serve as a basis for developing such frameworks for Cloud data centres.Peer ReviewedPostprint (author's final draft

Anonymous deniable predicate authentication scheme with revocability

In authentication protocols, anonymity is for privacy, while deniability is for anti-forensics after completion of the protocols. We propose a syntax and security definitions of an anonymous deniable predicate authentication scheme with revocability (rADPA). This new cryptographic primitive is to attain revocation function and strong privacy guarantee with predicate authentication, where a predicate is a boolean function over attributes of participants. We also give a generic construction of our rADPA scheme. Our approach is to build-in the revocable attribute-based encryption scheme proposed by K.Yamada et al. (ESORICS2017) into the anonymous deniable predicate authentication scheme proposed by S.Yamada et al. (PKC2012). Finally, we discuss how our rADPA scheme can be instantiated by employing concrete building blocks in our generic construction

Private Ciphertext-Policy Attribute-based Encryption Schemes With Constant-Size Ciphertext Supporting CNF Access Policy

Attribute-based encryption (ABE) is an extension of traditional public key encryption in which the encryption and decryption phases are based on user\u27s attributes. More precisely, we focus on cipher-text-policy ABE (CP-ABE) where the secret-key is associated to a set of attributes and the ciphertext is generated with an access policy. It then becomes feasible to decrypt a ciphertext only if one\u27s attributes satisfy the used access policy. In this paper, we give the first private CP-ABE constructions with a constant-size ciphertext, supporting CNF (Conjunctive Normal Form) access policy, with the simple restriction that each attribute can only appear $k_{max}$ times in the access formula. Our two constructions are based on the BGW scheme at Crypto\u2705. The first scheme is basic selective secure (in the standard model) while our second one reaches the selective CCA security (in the random oracle model)

Unbounded Dynamic Predicate Compositions in ABE from Standard Assumptions

At Eurocrypt\u2719, Attrapadung presented several transformations that dynamically compose a set of attribute-based encryption (ABE) schemes for simpler predicates into a new ABE scheme for more expressive predicates. Due to the powerful unbounded and modular nature of his compositions, many new ABE schemes can be obtained in a systematic manner. However, his approach heavily relies on $q$-type assumptions, which are not standard. Devising such powerful compositions from standard assumptions was left as an important open problem. In this paper, we present a new framework for constructing ABE schemes that allow unbounded and dynamic predicate compositions among them, and show that the adaptive security of these composed ABE will be preserved by relying only on the standard matrix Diffie-Hellman (MDDH) assumption. This thus resolves the open problem posed by Attrapadung. As for applications, we obtain various ABEs that are the first such instantiations of their kinds from standard assumptions.These include the following adaptively secure large-universe ABEs for Boolean formulae under MDDH: - The first completely unbounded monotone key-policy (KP)/ciphertext-policy (CP) ABE. Such ABE was recently proposed, but only for the KP and small-universe flavor (Kowalczyk and Wee, Eurocrypt\u2719). - The first completely unbounded non-monotone KP/CP-ABE. Especially, our ABEs support a new type of non-monotonicity that subsumes previous two types of non-monotonicity, namely, by Ostrovsky et al. (CCS\u2707) and by Okamoto and Takashima (CRYPTO\u2710). - The first (non-monotone) KP and CP-ABE with constant-size ciphertexts and secret keys, respectively. - The first KP and CP-ABE with constant-size secret keys and ciphertexts, respectively. At the core of our framework lies a new partially symmetric design of the core 1-key 1-ciphertext oracle component called Key Encoding Indistinguishability, which exploits the symmetry so as to obtain compositions

Registered (Inner-Product) Functional Encryption

Registered encryption (Garg et al., TCC\u2718) is an emerging paradigm that tackles the key-escrow problem associated with identity-based encryption by replacing the private-key generator with a much weaker entity known as the key curator. The key curator holds no secret information, and is responsible to: (i) update the master public key whenever a new user registers its own public key to the system; (ii) provide helper decryption keys to the users already registered in the system, in order to still enable them to decrypt after new users join the system. For practical purposes, tasks (i) and (ii) need to be efficient, in the sense that the size of the public parameters, of the master public key, and of the helper decryption keys, as well as the running times for key generation and user registration, and the number of updates, must be small. In this paper, we generalize the notion of registered encryption to the setting of functional encryption (FE). As our main contribution, we show an efficient construction of registered FE for the special case of ({\it attribute hiding}) inner-product predicates, built over asymmetric bilinear groups of prime order. Our scheme supports a {\it large} attribute universe and is proven secure in the bilinear generic group model. We also implement our scheme and experimentally demonstrate the efficiency requirements of the registered settings. Our second contribution is a feasibility result where we build registered FE for P/poly based on indistinguishability obfuscation and somewhere statistically binding hash functions

Attribute-Based Signatures for Unbounded Languages from Standard Assumptions

Attribute-based signature (ABS) schemes are advanced signature schemes that simultaneously provide fine-grained authentication while protecting privacy of the signer. Previously known expressive ABS schemes support either the class of deterministic finite automata and circuits from standard assumptions or Turing machines from the existence of indistinguishability obfuscations. In this paper, we propose the first ABS scheme for a very general policy class, all deterministic Turin machines, from a standard assumption, namely, the Symmetric External Diffie-Hellman (SXDH) assumption. We also propose the first ABS scheme that allows nondeterministic finite automata (NFA) to be used as policies. Although the expressiveness of NFAs are more restricted than Turing machines, this is the first scheme that supports nondeterministic computations as policies. Our main idea lies in abstracting ABS constructions and presenting the concept of history of computations; this allows a signer to prove possession of a policy that accepts the string associated to a message in zero-knowledge while also hiding the policy, regardless of the computational model being used. With this abstraction in hand, we are able to construct ABS for Turing machines and NFAs using a surprisingly weak NIZK proof system. Essentially we only require a NIZK proof system for proving that a (normal) signature is valid. Such a NIZK proof system together with a base signature scheme are, in turn, possible from bilinear groups under the SXDH assumption, and hence so are our ABS schemes

Designated Verifier/Prover and Preprocessing NIZKs from Diffie-Hellman Assumptions

In a non-interactive zero-knowledge (NIZK) proof, a prover can non-interactively convince a verifier of a statement without revealing any additional information. Thus far, numerous constructions of NIZKs have been provided in the common reference string (CRS) model (CRS-NIZK) from various assumptions, however, it still remains a long standing open problem to construct them from tools such as pairing-free groups or lattices. Recently, Kim and Wu (CRYPTO\u2718) made great progress regarding this problem and constructed the first lattice-based NIZK in a relaxed model called NIZKs in the preprocessing model (PP-NIZKs). In this model, there is a trusted statement-independent preprocessing phase where secret information are generated for the prover and verifier. Depending on whether those secret information can be made public, PP-NIZK captures CRS-NIZK, designated-verifier NIZK (DV-NIZK), and designated-prover NIZK (DP-NIZK) as special cases. It was left as an open problem by Kim and Wu whether we can construct such NIZKs from weak paring-free group assumptions such as DDH. As a further matter, all constructions of NIZKs from Diffie-Hellman (DH) type assumptions (regardless of whether it is over a paring-free or paring group) require the proof size to have a multiplicative-overhead $|C| \cdot \mathsf{poly}(\kappa)$, where $|C|$ is the size of the circuit that computes the $\mathbf{NP}$ relation. In this work, we make progress of constructing (DV, DP, PP)-NIZKs with varying flavors from DH-type assumptions. Our results are summarized as follows: 1. DV-NIZKs for $\mathbf{NP}$ from the CDH assumption over pairing-free groups. This is the first construction of such NIZKs on pairing-free groups and resolves the open problem posed by Kim and Wu (CRYPTO\u2718). 2. DP-NIZKs for $\mathbf{NP}$ with short proof size from a DH-type assumption over pairing groups. Here, the proof size has an additive-overhead $|C|+\mathsf{poly}(\kappa)$ rather then an multiplicative-overhead $|C| \cdot \mathsf{poly}(\kappa)$. This is the first construction of such NIZKs (including CRS-NIZKs) that does not rely on the LWE assumption, fully-homomorphic encryption, indistinguishability obfuscation, or non-falsifiable assumptions. 3. PP-NIZK for $\mathbf{NP}$ with short proof size from the DDH assumption over pairing-free groups. This is the first PP-NIZK that achieves a short proof size from a weak and static DH-type assumption such as DDH. Similarly to the above DP-NIZK, the proof size is $|C|+\mathsf{poly}(\kappa)$. This too serves as a solution to the open problem posed by Kim and Wu (CRYPTO\u2718). Along the way, we construct two new homomorphic authentication (HomAuth) schemes which may be of independent interest

LIPIcs, Volume 261, ICALP 2023, Complete Volume

LIPIcs, Volume 261, ICALP 2023, Complete Volum