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Lightweight devices in the Internet of Things (IoT) typically need to store massive data on a cloud server with strong processing and storage capabilities for later retrieval and usage. Since these data contain the participant’s sensitive information, they cannot be delivered directly to the cloud server. Public-key Encryption with Keyword Search (PEKS) allows customers to search for target encrypted files using keywords. However, the majority of PEKS implementations are unable to repel malicious quantum-capable attackers. And with regard to forward security, they must search for many rounds to obtain the necessary data. To resolve these concerns, we propose a comprehensive Inner Product Outsourcing PEKS system (IPO-PEKS) with forward security based on LWE assumptions, which raises search efficiency by allowing authorized clients to find the information they desire in a single round and achieves more fine-grained searches. Furthermore, we offer an inner product outsourcing calculation technique that allows the server to compute the inner product result without knowing the details of both parties in order to conceal the relevant privacy data of transmitting and decryption states. The paradigm can be utilized for efficient state transition through the use of parallel computing to accomplish the target of one round of iteration.

The security of several fully homomorphic encryption (FHE) schemes depends on the intractability assumption of the approximate common divisor (ACD) problem over integers. Subsequent efforts to solve the ACD problem as well as its variants were also developed during the past decade. In this paper, an improved orthogonal lattice (OL)-based algorithm, AIOL, is proposed to solve the general approximate common divisor (GACD) problem. The conditions for ensuring the feasibility of AIOL are also presented. Compared to the Ding–Tao OL algorithm, the well-known LLL reduction method is used only once in AIOL, and when the error vector r is recovered in AIOL, the possible difference between the restored and the true value of p is given. Experimental comparisons between the Ding-Tao algorithm and ours are also provided to validate our improvements.

Cloud computing with massive storage and computing capabilities has become widespread in actual applications. It is critical to ensure secure data sharing in cloud-based applications. Currently, numerous identity-based broadcast proxy re-encryption (IB-BPRE) schemes have been proposed to resolve the privacy issue. However, the existing IB-BPRE schemes cannot reach the transformation of the decryption right for outsourced encrypted data between the broadcast receiver sets (data user sets) delegated by the data owner (Alice) because it is difficult for the IB-BPRE to hold the character of multi-hop. Consequently, a new cryptographic primitive called autonomous path identity-based broadcast proxy re-encryption (APIB-BPRE) is presented to address the above issue. In an APIB-BPRE scheme, the delegator establishes an autonomous path involving preferred multiple broadcast receiver sets and the proxy can convert the decryption right for the broadcast receiver set into the decryption right for the next broadcast receiver set by the re-encryption key from the delegator. This solution is convenient and flexible for cloud users and utilizes the benefits of cloud computing. The evaluation and comparison indicate that our APIB-BPRE system is effective and practical.

Abstract Public key encryption scheme with keyword search is a promising technique supporting search on encrypted data without leaking any information about the keyword. In real applications, it’s critical to find an effective revocation method to revoke users in multi-user cryptosystems, when user’s secret keys are exposed. In this paper, we propose the first designated server-aided revocable identity-based encryption scheme with keyword search (dSR-IBKS) from lattice. The dSR-IBKS model requires each user to keep just one private key corresponding with his identity and does not need to communicate with the key generation center or the server during key updating. We have proved that our scheme can achieve chosen keyword indistinguishability in the standard model. In particular, our scheme can designate a unique tester to test and return the search results, therefore no other entity can guess the keyword embedded in the ciphertext by generating search queries and doing the test by itself. We provide a formal security proof of our scheme assuming the hardness of the learning with errors problem on the standard model.

Cloud computing has become popular in data sharing mainly because it has huge storage capacity and computing power. Securing the privacy of sensitive data for cloud-based data sharing is vital. Currently, there are various conditional proxy re-encryption (UPRE) schemes that have been proposed to resolve the privacy issue. Nevertheless, the existing UPRE schemes cannot allow the proxy (e.g., the cloud server) to transfer the outsourced encrypted data under the data owner’s public key of any homomorphic encryption scheme into the encrypted data under the data user’s public key of a homomorphic encryption scheme (possibly different from the data owner). The transformation of outsourced encrypted data between homomorphic encryption schemes is more suitable for the real data sharing in clouds. Consequently, we present the notion of universal conditional proxy re-encryption (UCPRE) to solve the issue of flexible transformation of outsourced encrypted data between homomorphic encryption schemes in cloud-based data sharing. UCPRE is lightweight in the sense that it only requires the re-encrypted key generation and re-encryption algorithms. We give the definition of UCPRE and prove that it is HRA secure without random oracle. Finally, we show that our UCPRE is efficient and rational compared to other existing CPRE schemes by instantiating our UCPRE.

In e-health systems, patients encrypt their personal health data for privacy purposes and upload them to the cloud. There exists a need for sharing patient health data with doctors for healing purposes in one’s own preferred order. To achieve this fine-gained access control to delegation paths, some researchers have designed a new proxy re-encryption (PRE) scheme called autonomous path proxy re-encryption (AP-PRE), where the delegator can control the whole delegation path in a multi-hop delegation process. In this paper, we introduce a certificateless autonomous path proxy re-encryption (CLAP-PRE) using multilinear maps, which holds both the properties (i.e., certificateless, autonomous path) of certificateless encryption and autonomous path proxy re-encryption. In the proposed scheme, (a) each user has two public keys (user’s identity and traditional public key) with corresponding private keys, and (b) each ciphertext is first re-encrypted from a public key encryption (PKE) scheme to an identity-based encryption (IBE) scheme and then transformed in the IBE scheme. Our scheme is an IND-CPA secure CLAP-PRE scheme under the k-multilinear decisional Diffie–Hellman (k-MDDH) assumption in the random oracle model.

With the development of privacy-preserving techniques, the increasing demand for secure multiparty computation (MPC) of mobile devices has become a significant challenge. Unfortunately, it is inapplicable for mobile devices to implement the existing secure multiparty computation schemes that rely on costly computation and communication overhead. To solve this problem, we propose an efficient two-party computation protocol secure against semi-honest adversary based on the Chinese remainder theorem (CRT). Our protocol utilizes CRT-based encryption and re-encryption techniques to realize additional and multiplicative homomorphic encryption, which can be transformed into a two-party secure computation scheme. Then, we extend our two-party LPCP protocol into a multiparty LPCP protocol, which is much faster and more space saving than the previous works. For practical purpose, we describe a distance measurement application for mobile devices based on LPCP. In the end, we implement LPCP codes and compare the experimental results to the state-of-the-art two-party and multiparty computation protocols. The experimental result shows that the high computation and communication efficiency of LPCP makes it possible for low computing-power mobile devices to implement multiparty secure computation protocols in reality.

RIPEMD-160 is a hash function published in 1996, which shares similarities with other hash functions designed in this time-period like MD4, MD5 and SHA-1. However, for RIPEMD-160, no (semi-free-start) collision attacks on the full number of steps are known. Hence, it is still used, e.g., to generate Bitcoin addresses together with SHA-256, and is an ISO/IEC standard. Due to its dual-stream structure, even semifree- start collision attacks starting from the first step only reach 36 steps, which were firstly shown by Mendel et al. at Asiacrypt 2013 and later improved by Liu, Mendel and Wang at Asiacrypt 2017. Both of the attacks are based on a similar freedom degree utilization technique as proposed by Landelle and Peyrin at Eurocrypt 2013. However, the best known semi-free-start collision attack on 36 steps of RIPEMD-160 presented at Asiacrypt 2017 still requires 255.1 time and 232 memory. Consequently, a practical semi-free-start collision attack for the first 36 steps of RIPEMD-160 still requires a significant amount of resources. Considering the structure of these previous semi-free-start collision attacks for 36 steps of RIPEMD-160, it seems hard to extend it to more steps. Thus, we develop a different semi-free-start collision attack framework for reduced RIPEMD-160 by carefully investigating the message expansion of RIPEMD-160. Our new framework has several advantages. First of all, it allows to extend the attacks to more steps. Second, the memory complexity of the attacks is negligible. Hence, we were able to mount semi-free-start collision attacks on 36 and 37 steps of RIPEMD-160 with practical time complexity 241 and 249 respectively. Additionally, we describe semi-free-start collision attacks on 38 and 40 (out of 80) steps of RIPEMD-160 with time complexity 252 and 274.6, respectively. To the best of our knowledge, these are the best semi-free-start collision attacks for RIPEMD-160 starting from the first step with respect to the number of steps, including the first practical colliding message pairs for 36 and 37 steps of RIPEMD-160.

Ciphertext-policy attribute-based encryption is a promising mechanism with fine-grained access control for cloud storage system. However, there is a long-lasting problem of key abuse that a user may share its decryption key and a semi-honest authority may illegally issue decryption keys for unauthorized users for profits. To address this problem, we propose an accountable ciphertext-policy attribute-based encryption scheme. In our construction, there are two authorities to issue keys for users, but they cannot decrypt any ciphertexts without collusion. A shared key can be effectively traced, and if the traced identity claims that it is innocent, an auditor can publicly audit who will be responsible for the shared key. Compared with existing accountable ciphertext-policy attribute-based encryption schemes, the proposed scheme is more practical from the two aspects: (1) a user can normally request for a decryption key along with a short signature, and no additional interaction between users and authorities is needed; and (2) the complexity of tracing a masked secret key is reduced to | U | exponent computation, where | U | denotes the number of users in the system. At last, we give the security and experimental analysis.