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A confidential reporting system (CRS) allows reporters to report concerns or problems in confidence without the fear of blame or reprisals. Nevertheless, privacy has been the primary concern of reporters. In this paper, we propose a privacy-preserving confidential reporting system with designated reporters (PPCRS-DR) to protect the privacy of reporters and the confidentiality of reports. Our PPCRS-DR provides the following interesting features: (1) for an event, an auditor can designate a reporter to report; (2) an auditor can neither see the report nor know the reporter's identity from an encrypted report if the reporter is not the designated one; (3) when an auditor is unavailable, he/she can temporarily designate a delegatee to collect and review reports on behalf of him/her. We formalize both the definition and security model of our PPCRS-DR, and propose a concrete construction. Furthermore, the security of the proposed PPCRS-DR is formally proven. The implementation shows that it is efficient. The novelty is to implement flexible decryption delegation of CRSs and protect reporters' privacy. [ABSTRACT FROM AUTHOR]

Homomorphic signature (HS) is a novel primitive that allows an agency to carry out arbitrary (polynomial time) computation f on the signed data m → and accordingly gain a signature σ h for the computation result f (m →) with respect to f on behalf of the data owner (DO). However, since DO lacks control of the agency's behavior, receivers would believe that DO did authenticate the computation result even if the agency misbehaves and applies a function that the DO does not want. To address the problem above, in this paper we introduce a new primitive called authorized function homomorphic signature (AFHS). In AFHS, the agency has to obtain a confidence key sk f from DO in order to evaluate a function f on the data m → and to obtain a signature with which one can check whether the agency acts in accordance with DO's instructions. A black-box construction of AFHS based on HS is given in this paper, and we show that if the underlying primitives are secure, so is our construction under the given security model. Moreover, we provide a somewhat concrete construction that offers stronger security guarantee. [ABSTRACT FROM AUTHOR]

As a basic and important primitive, hash proof system can be used to construct many cryptographic schemes and protocols. Therefore, it is significant to instantiate more efficient hash proof systems from various assumptions. Although there are many hash proof systems based on various classical assumptions, only a handful of efficient hash proof systems are known based on post-quantum assumptions. In this paper, we present several new hash proof systems based on the standard learning with errors (LWE) problem, which is at least as hard as standard worst-case lattice problems. Comparing with other existing constructions based on lattices, our main advantages are 2-fold: much simpler and more efficient. And our constructions can be easily extended to be identity-based ones and updatable ones. Throughout the paper, our main idea is to base hash proof systems on a new subset indistinguishability problem related to LWE, and employ the property of smooth parameter of q-ary orthogonal lattices to ensure smoothness. [ABSTRACT FROM AUTHOR]

With the progress of cloud computing, many users hope in time to upload their data into cloud for sharing. For sensitive data, the owner must encrypt it before sending it to cloud server. The state of the art method for fine-grained access control on encrypted data is attribute-based encryption (ABE). Though ABE is believed to be an outstanding technique for secure data sharing, it has many efficiency drawbacks. For example, its ciphertext size and decryption time increase linearly with the number of attributes used during encryption and decryption, and it is hard to revoke a user’s access ability. In this paper, we propose a method to outsource the decryption of ABE via public cloud computing, and to control a user’s decryption capacity through a bounded revocation technique. The public cloud server can transform any user’s ABE ciphertexts into short ElGamal-type ciphertexts via the user’s public transformation key. The transformed ciphertexts are actually ElGamal-type identity-based ciphertexts obtained through a bounded-collision identity-based encryption scheme, and the decryption time only requires one exponentiation. Our scheme can revoke user’s decryption ability. But it limits to scenario with bounded number of revocation. [ABSTRACT FROM AUTHOR]

Certificateless signcryption (CLSC) has attracted much attention from the research community since it provides both confidentiality and unforgeability, and, at the same time, it does not suffer from the certificate management problem in traditional public key cryptography and the key escrow problem in identity-based cryptography. However, most CLSC schemes are based on the bilinear pairing which is still a time-costing operation although many efforts have been made to improve its efficiency. Recently, Yu et al. proposed a pairing-free CLSC scheme and proved its security. In this paper, we point out that their scheme can be totally broken since confidentiality and unforgeability actually are not captured. [ABSTRACT FROM AUTHOR]

In recent times, there has been increasing interest in storing data securely in the cloud environment. To provide owners of data stored in the cloud with flexible control over access to their data by other users, we propose a role-based encryption (RBE) scheme for secure cloud storage. Our scheme allows the owner of data to store it in an encrypted form in the cloud and to grant access to that data for users with specific roles. The scheme specifies a set of roles to which the users are assigned, with each role having a set of permissions. The data owner can encrypt the data and store it in the cloud in such a way that only users with specific roles can decrypt the data. Anyone else, including the cloud providers themselves, will not be able to decrypt the data. We describe such an RBE scheme using a broadcast encryption algorithm. The paper describes the security analysis of the proposed scheme and gives proofs showing that the proposed scheme is secure against attacks. We also analyse the efficiency and performance of our scheme and show that it has superior characteristics compared with other previously published schemes. [ABSTRACT FROM AUTHOR]

A proxy re-encryption (PRE) allows a data owner to delegate the decryption rights of some encrypted data stored on the cloud without revealing the data to an honest-but-curious cloud service provider (i.e. the PRE proxy). Furthermore, the data owner can offload most of the computational operations to the cloud service provider and hence, usingPREfor encrypted cloud data sharing can be very effective even for data owners using limited resource devices (e.g. mobile devices). However, PRE schemes only enables data owners to delegate the decryption rights of all their encrypted data. A more practical notion is a conditional PRE (CPRE) that allows us to specify under what condition the decryption of an encrypted data can be delegated, for example, only sharing all the encrypted files under a directory called 'public'. In this paper, we provide an affirmative result on the long-standing question of building a full chosen-ciphertext attacks (CCA)-secure CPRE system in the standard model and for the first time, we show that a class of Hierarchical Identity-Based Encryption (HIBE) schemes can be transferred to building a CCA-secure CPRE in the standard model.We also list out some concrete HIBE schemes which fall into this class, e.g., Lewko-Waters HIBE. All existing CCA-securePRE schemes in the standard model are not conditional while all existing CPRE schemes are either not CCA secure or not in the standard model. By instantiating our generic HIBE-based transformation, we show that an efficient and concrete CPRE scheme which is both CCA secure in the standard model and conditional can be built. [ABSTRACT FROM AUTHOR]

Cloud computing is a new promising technology paradigm that can provide clients from the whole network with scalable storage resources and on-demand high-quality services. However, security concerns are raised when sensitive data are outsourced. Searchable encryption is a kind of cryptographic primitive that enables clients to selectively retrieve encrypted data, the existing schemes that support for sub-linear boolean queries are only considered in symmetric key setting, which makes a limitation for being widely deployed in many cloud applications. In order to address this issue, we propose a novel searchable asymmetric encryption scheme to support for sub-linear boolean query over encrypted data in a multi-client model that is extracted from an important observation that the outsourced database in cloud is continuously contributed and searched by multiple clients. For the purpose of introducing the scheme, we combine both the ideas of symmetric searchable encryption and public key searchable encryption and then design a novel secure inverted index. Furthermore, a detailed security analysis for our scheme is given under the simulation-based security definition. Finally, we conduct experiments for our construction on a real dataset (Enron) along with a performance analysis to show its practicality. [ABSTRACT FROM AUTHOR]

We propose a fully homomorphic encryption (FHE) scheme that encrypts matrices. Our scheme supports homomorphic matrix addition, multiplication and Hadamard product. In PKC 2015, Hiromasa et al. constructed the only FHE scheme that encrypts matrices and supports homomorphic matrix addition and multiplication. Compared with their work, the advantages of our scheme are the following: (1) Small ciphertext size : For a plaintext matrix M ∈ {0,1} r × r ⁠, the size of ciphertext matrix is r × (n + r) ⁠, in contrast to (n + r) × (n + r) ⌈ log q ⌉ in their work. (2) Standard assumption : The security is based on LWE assumption merely, while the security of scheme in their work depends additionally on some special kind of circular security assumption. (3) Supporting homomorphic matrix Hadamard product. We show how to apply the proposed scheme to optimize the bootstrapping procedure of Alperin-Sheriff and Peikert, in a way similar to the work of Hiromasa, Abe and Okamoto. Due to smaller ciphertext matrices, the bootstrapping key of our optimized bootstrapping procedure is smaller than that in the work of Hiromasa, Abe and Okamoto by a factor of (n / r + 1) ⌈ log q ⌉ ⁠. [ABSTRACT FROM AUTHOR]

We present a new type of public-key encryption called Criteria-based Encryption (or CE, for short). Different from Attribute-based Encryption, in CE, we consider the access policies as criteria carrying different weights. A user must hold some cases (or answers) satisfying the criteria and have sufficient weights in order to successfully decrypt a message. We then propose two CE Schemes under different settings: the first scheme requires a user to have at least one case for a criterion specified by the encryptor in the access structure, while the second scheme requires a user to have all the cases for each criterion. We prove that both schemes are secure under the Decisional q-Bilinear Diffie Hellman Exponent assumption without random oracles. In addition, we also present two special CE schemes for the above two settings without considering the weight requirement. We show that under this special case CE schemes can be constructed much more efficiently. [ABSTRACT FROM AUTHOR]

Functional encryption (FE) systems provide a flexible and expressive encryption mechanism that private keys and ciphertexts are associated with attributes ... and predicate formulae Γ and decryption are possible whenever keys and ciphertexts are related, i.e. Γ(...) = 1. In this work, we put forward a leakage-resilient FE scheme against the amount of leakage output over a hard-to-invert function family. In our scheme, the encryption policy is specified as an arbitrary monotonic formula, and the adversary can learn the arbitrary length output of the master key and the private key from any computationally irreversible function with the input (master) keys. To improve the efficiency, we employ the set of minimal sets to describe the predicate formula or access structure, and initiate the formal model of leakage-resilient FE, which is a generic extension of identity-based encryption and attribute-based encryption in the presence of key leakage with auxiliary inputs.We provide the concrete construction in bilinear groups of composite order, and prove the adaptively leakage-resilient security in the standard model based on static assumptions. Our hard-to-invert leakage resilience employs the Goldreich-Levin theorem and its extension as a hard-core value over large fields.We also give an extensional construction in the case of obtaining the hard-to-invert randomness leakage of the encryption, which uses a strong extractor to prevent leakage of randomness and a hard-to-invert encryption to prevent the leakage of the key. Finally, we analyze and discuss the stepped-up security on master leakage and continual leakage, and the lower bound of the irreversible leakage function. [ABSTRACT FROM AUTHOR]

We revisit the concept of public key encryption with delegated search (PKEDS), a concept proposed by Ibraimi et al. A PKEDS scheme allows a receiver to authorize a third-party server to search in two ways: either according to a message chosen by the server itself or according to a trapdoor sent by the receiver. We first show some observations on the primitive formulation and the proposed PKEDS scheme by Ibraimi et al. and point out that the single-server setting may limit the application of this primitive. We then extend the concept to the multiple-server setting and present a new security model. We finally propose a new PKEDS scheme, which is proven secure, and compare it with that by Ibraimi et al. [ABSTRACT FROM AUTHOR]