Key-homomorphic Pseudorandom Function Research Articles

Backward private dynamic searchable encryption with update pattern

Symmetric Searchable Encryption (SSE) realizes to outsource data to an untrusted server privately. Dynamic SSE (DSSE) is a practical application which supports data addition and deletion. However, these update operations incur leakage during search and update queries. Therefore, forward and backward privacy were introduced to address the update and search operation leakage in DSSE. Forward privacy was extensively studied in the literature. Backward privacy with three types of revealing level was studied little. The strongest backward privacy was achieved by the expensive tools, impractical! Wheras the practical DSSEs gained weak backward privacy only. In this paper, we present a practical DSSE scheme to achieve stronger backward security—backward privacy with update pattern. We take advantage of key-homomorphic pseudorandom functions and our scheme requires only 1 roundtrip to get search result.

OrgAn: Organizational Anonymity with Low Latency

There is a growing demand for network-level anonymity for delegates at global organizations such as the UN and Red Cross. Numerous anonymous communication (AC) systems have been proposed over the last few decades to provide anonymity over the internet; however, they introduce high latency overhead, provide weaker anonymity guarantees, or are difficult to deploy at the organizational networks. Recently, the PriFi system introduced a client/relay/server model that suitably utilizes the organizational network topology and proposes a low-latency, strong-anonymity AC protocol. Using an efficient lattice-based (almost) keyhomomorphic pseudorandom function and Netwon’s power sums, we present a novel AC protocol OrgAn in this client/relay/server model that provides strong anonymity against a global adversary controlling the majority of the network. OrgAn’s cryptographic design allows it to overcome several major problems with any realistic PriFi instantiation: (a) unlike PriFi, OrgAn avoids frequent, interactive, slot-agreement protocol among the servers; (b) a PriFi relay has to receive frequent communication from the servers, which can not only become a latency bottleneck but also reveal the access pattern to the servers and increases the chance of server collusion/coercion, while OrgAn servers are absent from any real-time process. We demonstrate how to make this public-key cryptographic solution scale equally well as the symmetric-cryptographic PriFi with practical pre-computation and storage requirements. Through a prototype implementation, we show that OrgAn provides similar throughput and end-to-end latency guarantees as PriFi, while still discounting the setup challenges in PriFi.

Private Stream Aggregation with Labels in the Standard Model

Abstract A private stream aggregation (PSA) scheme is a protocol of n clients and one aggregator. At every time step, the clients send an encrypted value to the (untrusted) aggregator, who is able to compute the sum of all client values, but cannot learn the values of individual clients. One possible application of PSA is privacy-preserving smart-metering, where a power supplier can learn the total power consumption, but not the consumption of individual households. We construct a simple PSA scheme that supports labels and which we prove to be secure in the standard model. Labels are useful to restrict the access of the aggregator, because it prevents the aggregator from combining ciphertexts with different labels (or from different time-steps) and thus avoids leaking information about values of individual clients. The scheme is based on key-homomorphic pseudorandom functions (PRFs) as the only primitive, supports a large message space, scales well for a large number of users and has small ciphertexts. We provide an implementation of the scheme with a lattice-based key-homomorphic PRF (secure in the ROM) and measure the performance of the implementation. Furthermore, we discuss practical issues such as how to avoid a trusted party during the setup and how to cope with clients joining or leaving the system.

Private Predicate Encryption for Inner Product from Key-Homomorphic Pseudorandom Function

Predicate encryption (PE), formalized by Katz et al., is a new paradigm of public-key encryption that conceptually captures the public-key encryption that supports fine-grained access control policy. Because of the nature of PE, it is used for cloud storage so that users can retrieve encrypted data without revealing any information about the data to cloud servers and other users. Although lots of PE schemes have been studied, the predicate-hiding security is seldom considered; that is, the user’s secret key may leak sensitive information of the predicate. Additionally, the security of the current predicate-hiding PE schemes relies on the discrete logarithm assumption which cannot resist the quantum attacks in the future. In this paper, we propose a generic PE for inner product under symmetric-key setting, called private IPE, from specific key-homomorphic pseudorandom function (PRF). The rigorous proofs are provided to show that the construction is payload-hiding, attribute-hiding, and predicate-hiding secure. With the advantage of the generic construction, if the underlying PRF can resist quantum attacks, then, through our proposed generic construction, a quantum-resistant private IPE can be obtained.

Privacy-Preserving Location-Based Services Query Scheme Against Quantum Attacks

Location-based service (LBS) provides more and more conveniences to people. However, it also brings potential threats of offending users’ privacy. How to protect users’ privacy in LBS schemes has aroused increasing research interests in recent years. Most of the existing privacy-preserving LBS schemes are based on the hardness of traditional number-theoretic problems such as the integer factorization or the discrete logarithm problems. However, with the development of large scale quantum computers, these traditional problems can be easily solved by Shor's algorithms, hence the security of these LBS schemes is greatly threatened. In this paper, we solve this problem by constructing a privacy-preserving LBS scheme against quantum attacks from an LWE-based key-homomorphic pseudorandom functions (PRF). In our scheme, due to the key-homomorphic property of the PRF, an LBS user only has to compute one PRF value of the target location and the remaining computation is outsourced to a cloud server, which releases the user from heavy computation burden. In addition, by dividing the key encrypting LBS data into two parts and assigning the two parts to the cloud sever and each user respectively, our scheme avoids the threats of key abuse and information leaking of LBS data. Moreover, we use this PRF to realize an authenticated protocol, which protects the communications between the LBS users and the cloud server. We stress that the security of our scheme is based only on the security of the LWE-based key-homomorphic PRF, hence our scheme is the first LBS scheme secure against quantum attacks.

Multi-client Cloud-based Symmetric Searchable Encryption

We propose a multi-client Symmetric Searchable Encryption (SSE) scheme based on the single-user protocol [3] . The scheme allows any user to generate a search query by interacting with any $\theta -1$ θ - 1 ( $\theta$ θ is a threshold parameter) ‘helping’ users. It preserves the privacy of a database content against the server assuming a leakage of up to $\theta -1$ θ - 1 users’ keys to the server while hiding the query from the $\theta -1$ θ - 1 ‘helping users’. To achieve the query privacy, we design a new distributed key-homomorphic pseudorandom function (PRF) that hides the PRF input (search keyword) from the ‘helping’ users. We present a concrete construction of our randomizable distributed PRF. By distributing the utilized keys among the users, the need for a constant online presence of the data owner to provide services to the users is eliminated, while providing resilience against a user key exposure. We extended our scheme to support user revocation in two different scenarios. In addition, we give a solution for fast update of the encryption key with the overhead significantly smaller than the re-encryption and re-uploading the database. Moreover, our scheme is secure against passive and active collusion between the server and a subset of users.

Secure and efficient proxy re-encryption scheme based on key-homomorphic constrained PRFs in cloud computing

With the rapid development of cloud computing, its security and privacy are of great concern. Since the cloud service provider is not completely trustworthy, the security of the outsourced files has become serious issues. Identity-based proxy re-encryption (IBPRE) schemes have been proposed to achieve feasible access control of encrypted data under the condition of guaranteeing the confidentiality of data, which can transfer the original ciphertexts to the re-encrypted ciphertexts for a designated decryptor. However, most of the existing IBPRE schemes either do not support revocation or computational complexity is too high. In this paper, we combine the properties of constrained pseudorandom functions (PRFs) and key homomorphic PRFs to construct a secure and efficient proxy re-encryption scheme for cloud computing. In our proposed scheme, the data owner authenticates the requesters and distributes the decryption keys by using an identity-based key exchange method. Meanwhile, a proxy re-encryption scheme is used to achieve data sharing and ciphertext update. We present the security proof of our scheme. In addition, compared with other existing schemes, our scheme has low computational complexity and communication cost.

Updatable encryption in distributed storage systems using key-homomorphic pseudorandom functions

Distributed storage systems DSSs store linear combinations of data across different nodes such that, data lost due to node failures can be restored from surviving nodes. We address key rotation in DSSs: assume that a user wants to remotely change the encryption key of a file stored in a DSS by safely delegating the re-encryption process to the storage network. A problem arises because the data to be re-encrypted is not directly stored in the system only linear combinations are stored. We propose a solution in which a key-homomorphic pseudorandom function KH-PRF is used in counter-mode encryption to make this delegation possible. Our solution requires the homomorphism to be applied several times. Previous constructions of KH-PRFs add noise to their functions which limits the number of times that the homomorphism can be applied. In this paper, we propose the first 'noiseless' key-homomorphic PRFs.