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Database encryption is essential for cloud database systems. For a large database, decryption could take a lot of computational time. Therefore, verifying an encryption that contains a correct plaintext without decryption becomes significant for a large database system. Plaintext-checkable encryption (PCE) is a potential tool for such database systems, which is first proposed by Canard et al. in CT-RSA 2012. Although the generic PCE in the random oracle model has been studied intensively, the generic PCE in the standard model and its efficient implementation are still challenging problems. This paper presents the first generic PCE in the standard model using smooth projective hash function (SPHF) and prove its s-priv1-cca security, which is independent of current unlink security. Based on the instantiated SPHF from DDH assumption, we obtain the most efficient PCE in the standard model, without any pairing operation. Finally, we improve two existing generic constructions in the random oracle model so that they are secure under chosen ciphertext attack.

Identity-based broadcast encryption (IBBE) is an important type of broadcast encryption. In the paper, we put forward the formal definition and security model of IBBE with leakage-resilience. Furthermore, we propose an IBBE scheme with continuous leakage-resilience. The presented scheme is resilient to private key leakage. By refreshing the private key, our scheme can resist continuous private key leakage. Based on dual system encryption technique, we prove the security of the proposed scheme under subgroup decisional assumptions. We give the specific performance analysis of leakage-resilience. The relative leakage ratio can amount to 1/3.

Public key encryption with equality test (PKEET), which was first introduced by Yang et al. (CT-RSA, 2010), has various applications including facilitating keyword search on encrypted data and partitioning encrypted data on the cloud. It can be also applied to manage personal health records on the internet. For these reasons, there have been improvements on earlier PKEET schemes in terms of performance and functionality. We present a semi-generic method for PKEET constructions, assuming only the existence of IND-CCA2 secure traditional public key encryption (PKE) schemes, the hardness of Computational Diffie-Hellman (CDH) problems, and random oracles. Our approach has several advantages; it enables us to understand requirements for the equality test functionality more clearly. Furthermore, our approach is quite general, in that if we change the underlying PKE scheme with the identity-based encryption (IBE) scheme (and we assume the hardness of Bilinear Diffie-Hellman problems instead of CDH), then we obtain the first IBE scheme with equality test (IBEET) satisfying analogous security arguments to those of PKEET. Although an IBEET construction was recently proposed, but we note that it satisfies only weak security requirements. MOE (Min. of Education, S’pore) Accepted version

Encryption schemes are generally considered to be secure in an ideal environment, where the adversary cannot obtain the secret internal state of schemes. However, in the realistic environment, the adversary can gain partial information about decryption private key through various types of side channel attacks. In order to capture these attacks, it is crucial to design encryption schemes which are resilient to leakage. In this article, we first formalize a continuous leakage-resilient security model of certificate-based encryption. In the model, the adversary continuously obtains partial information about the secret states through the continuous leakage attacks. Furthermore, we construct a continuous leakage-resilient certificate-based encryption (CLR-CBE) scheme which is resilient to continuous leakage, and it is secure against adaptive chosen ciphertext attacks under the bilinear Diffie-Hellman inversion (BDHI) hardness assumption. Lastly, we show the bound on leakage and make comparison between proposed and existing schemes in terms of security properties and efficiency.

In order to limit the damage of key exposure for identity-based encryption, we propose a new paradigm called intrusion-resilient identity-based encryption (IRIBE) in this paper. Compared with key-insulated identity-based encryption and forward-secure identity-based encryption, IRIBE can achieve a stronger level of security. In our proposed scheme, the ciphertexts in any other time periods are secure even after arbitrarily many compromises of the base and the user, as long as compromises do not happen simultaneously. Furthermore, the intruder cannot decrypt the ciphertexts pertaining to previous time periods, even if it compromises the base and the user simultaneously. Therefore, our IRIBE scheme can greatly enhance the security of identity-based encryption. We also formalize the definition and the security notions of this paradigm. The proposed scheme is proven secure in the standard model.

It is the first time to integrate identity-based encryption into public key encryption with equality test.It extends identity-based encryption with keyword search to yield a general function: equality test.It is proven to be one-way chosen-ciphertext security against a chosen identity attack as a desirable security.Unlike PEKS or IBEKS, it can be used alone since it contains decryption algorithm besides encryption algorithm. We firstly combine the concepts of public key encryption with equality test (PKEET) and identity-based encryption (IBE) to obtain identity-based encryption with equality test (IBEET). Inheriting the advantage of IBE, IBEET can simplify the certificate management of PKEET with all messages encrypted with the receiver's public identity. In the IBEET scheme, the receiver computes a trapdoor using the secret value for the identity and then sends it to a cloud server for equality test on its ciphertexts with others' ciphertexts. Using this primitive someone with the trapdoor for its identity can delegate out the capability of equality test on its ciphertexts without requiring a central authority to act as a delegator. So it is very suitable for the client with minimal computation resource, e.g, mobile phone. Furthermore, compared with PKEET, it has security improvement since not anyone can perform the test. Therefore, IBEET may have interesting applications in cloud computing, e.g., partition of encrypted emails. We define one-way chosen-ciphertext security against a chosen identity attack (OW-ID-CCA) and propose a construction in bilinear pairing. Finally, extensive security analysis and comparison with related works show that the proposed scheme is proven secure and useful.

An authenticated encryption scheme is a message transmission scheme, which can send a message in a secure and authentic way, and allows the specified recipient to simultaneously recover and verify the validity of a message. In the large message transmission, traditional authenticated encryption schemes have the disadvantages that communication overheads and the computation costs are too high. In this work, we propose a secure authentication encryption scheme and show that the scheme is secure in the random oracle model. In comparison with Lv et al.'s scheme and Li et al.'s scheme, our proposed scheme is the most efficient one in terms of computation complexity and communication cost. Finally, we extend our proposed scheme to adapt to the authenticated encryption for a large message, which is secure against the message block being reordered, replicated or partially deleted during transmission.

Anonymous encryption provides the decrypter’s identity privacy preservation as well as plaintext confidentiality. Spatial encryption, which is a kind of functional encryption, provides a generalized framework for special property encryption schemes such as broadcast encryption, predicate encryption, forward secure encryption, (hierarchical) identity-based encryption, delegatable attribute-based encryption etc. In this paper, we propose an anonymous spatial encryption scheme that deploys an affine subspace delegation mechanism. Our proposed scheme captures the message confidentiality , recipient anonymity , adaptive security , partial-order delegation and short ciphertext , simultaneously. To the best of our knowledge, the proposed scheme is the first anonymous spatial encryption that provides the anonymity property in adaptive security model, whose construction is based on a dual system encryption mechanism in bilinear composite-order groups. We also give a conversion construction to move into a prime-order setting with canceling property , whose security is based on the Decision Linear Problem. Finally, we provide a transformation methodology to obtain a CCA-secure scheme that combines a one-time signature, delegation functionality and the CPA-secure scheme.

Ciphertext-Policy Attribute-Based Encryption (CP-ABE) allows to encrypt data under an access policy, specified as a logical combination of attributes. Such ciphertexts can be decrypted by anyone with a set of attributes that satisfy the access policy. We propose a Ciphertext-Policy Attribute-Based Encryption, which is based on a recent secret sharing method called Linear Integer Secret Sharing Scheme (LISS). In this scheme, the encryptor can specify the access policy in terms of LISS matrix M, over the attributes in the system. The scheme is selectively secure under Decisional Bilinear Diffie-Hellman (DBDH) assumption.

Searching on remote encrypted data (commonly known as searchable encryption) has become an important issue in secure data outsourcing, since it allows users to outsource encrypted data to an untrusted third party while maintains the capability of keyword search on the data. Searchable encryption can be achieved using the classical method called oblivious RAM, but the resultant schemes are too inefficient to be applied in the real-world scenarios (e.g., cloud computing). Recently, a number of efficient searchable encryption schemes have been proposed under weaker security guarantees. Such schemes, however, still leak statistical information about the users' search pattern. In this paper, we first present two concrete attack methods to show that the search pattern leakage will result in such a situation: an adversary who has some auxiliary knowledge can uncover the underlying keywords of user queries. To address this issue, we then develop a grouping-based construction (GBC) to transform an existing searchable encryption scheme to a new scheme hiding the search pattern. Finally, experiments based on the real-world dataset demonstrate the effectiveness of our attack methods and the feasibility of our construction.

Threshold public-key encryption is a cryptographic primitive allowing decryption control in group-oriented encryption applications. Existing TPKE schemes suffer from long ciphertexts with size linear in the number of authorized users or can only achieve non-adaptive security, which is too weak to capture the capacity of the attackers in the real world. In this paper, we propose an efficient TPKE scheme with constant-size ciphertexts and adaptive security. Security is proven under the decision Bilinear Diffie-Hellman Exponentiation assumption in the standard model. Then we extend our basic construction with efficient trade-offs between the key size and the ciphertext size. Finally, we illustrate improvements to transmit multiple secret session keys in one session with almost no extra cost.

This paper provides two generic transformations to construct a designated tester public-key encryption with keyword search scheme using two identity-based encryption schemes. We also identify the properties of identity-based encryption that are sufficient to provide the confidentiality and consistency in designated tester public-key encryption with keyword search. The anonymity and confidentiality of identity-based encryption are sufficient for achieving confidentiality of designated tester public-key encryption with keyword search, and the confidentiality of identity-based encryption is sufficient for achieving consistency of designated tester public-key encryption with keyword search. Our constructions do not need any global set-up for the public parameters. We further extend our generic method to construct designated tester identity-based encryption with keyword search, where encryption is performed under the identity of a recipient instead of a public key.

Since the first practical and secure public-key encryption scheme without random oracles proposed by Cramer and Shoup in 1998, Cramer-Shoup's scheme and its variants remained the only practical and secure public-key encryption scheme without random oracles until 2004. In 2004, Canetti et al. proposed a generic transformation from a selective identity-based encryption scheme to a public-key encryption by adding a one-time strongly signature scheme. Since then, some transformation techniques from a selective identity-based encryption scheme to a public-key encryption have been proposed to enhance the computational efficiency, for example, Boneh-Katz's construction and Boyen-Mei-Waters' scheme. These transformations have either traded-off the publicly verifiable properties or tightness of security reduction. In 2007, Zhang proposed another generic transformation by adding Chameleon hash functions. In this paper, we introduce another technique from the Boneh-Boyen's selective identity-based encryption scheme to a public-key encryption which is publicly verifiable and is slightly more efficient than Zhang's transformation. The proposed public-key encryption scheme is based on the decisional bilinear Diffie-Hellman assumption and the target collision resistant hash functions.