Practical and fully secure multi keyword ranked search over encrypted data with lightweight client

Cloud computing offers computing services such as data storage and computing power and relieves its users of the burden of their direct management. While being extremely convenient, therefore immensely popular, cloud computing instigates concerns of privacy of outsourced data, for which conventional encryption is hardly a solution as the data is meant to be accessed, used and processed in an efficient manner. Multi keyword ranked search over encrypted data (MRSE) is a special form of secure searchable encryption (SSE), which lets users to privately find out the most similar documents to a given query using document representation methods such as tf-idf vectors and metrics such as cosine similarity. In this work, we propose a secure MRSE scheme that makes use of both a new secure k-NN algorithm and somewhat homomorphic encryption (SWHE). The scheme provides data, query and search pattern privacy and is amenable to access pattern privacy. We provide a formal security analysis of the secure k-NN algorithm and rely on IND-CPA security of the SWHE scheme to meet the strong privacy claims. The scheme provides speedup of about two orders of magnitude over the privacy-preserving MRSE schemes using only SWHE while its overall performance is comparable to other schemes in the literature with weaker forms of privacy claims. We present implementations results including one from the literature pertaining to response times, storage and bandwidth requirements and show that the scheme facilitates a lightweight client implementation

Zero-Value Filtering for Accelerating Non-Profiled Side-Channel Attack on Incomplete NTT based Implementations of Lattice-based Cryptography

Lattice-based cryptographic schemes such as Crystals-Kyber and Dilithium are post-quantum algorithms selected to be standardized by NIST as they are considered to be secure against quantum computing attacks. The multiplication in polynomial rings is the most time-consuming operation in many lattice-based cryptographic schemes, which is also subject to side-channel attacks. While NTT-based polynomial multiplication is almost a norm in a wide range of implementations, a relatively new method, incomplete-NTT is preferred to accelerate lattice-based cryptography, especially on some computing platforms that feature special instructions. In this paper, we present a novel, efficient and non-profiled power/EM side-channel attack targeting polynomial multiplication based on the incomplete NTT algorithm. We apply the attack on the Crystals-Dilithium signature algorithm and demonstrate that the method accelerates attack run-time when compared to conventional correlation power attacks (CPA). While a conventional CPA tests much larger hypothesis set due to the fact that it needs to predict two coefficients of secret polynomials together, we propose a much faster zero-value filtering attack (ZV-FA), which reduces the size of the hypothesis set by targeting the coefficients individually. We also propose an effective and efficient validation and correction technique to estimate and modify the mis-predicted coefficients. Our experimental results show that we can achieve a speed-up of 128.1× over conventional CPA using a total of 13K traces

Exploiting the Central Reduction in Lattice-Based Cryptography

This paper presents a novel and efficient way of exploiting side-channel leakage of masked implementations of lattice-based cryptography (LBC). The presented attack specifically targets the central reduction technique, which is widely adapted in efficient implementations of LBC. We show that the central reduction leads to a vulnerability by creating a strong dependency between the power consumption and the sign of sensitive intermediate variables. We exploit this dependency by introducing a novel hypothetical power model, the range power model, which can be employed in higher-order multi-query side-channel analysis attacks. We particularly show that our approach is valid for the prime moduli employed by Kyber and Dilithium, the lattice-based post-quantum algorithms selected by NIST, while it generalizes to other primes used in LBC as well. We practically evaluate our introduced approach by performing second-order non-profiled attacks against a masked implementation of Kyber on an Arm Cortex-M4 micro-processor. In our experiments we revealed the full secret key of the aforementioned implementation with only 2100 electro-magnetic (EM) traces without profiling, achieving a more than 14 times reduction in the number of traces compared to classical attacks

FSDS: a practical and fully secure document similarity search over encrypted data with lightweight client

In this paper, we propose a highly accurate, fully secure document similarity search (FSDS) scheme that makes use of both a novel variant of the secure K-NN algorithm and somewhat homomorphic encryption (SWHE). The scheme provides data, query and search pattern privacy and is amenable to access pattern privacy. We provide formal security analyzes of both the original and the new secure K-NN algorithms and show the latter is IND-CPA secure. We also rely on IND-CPA security of the SWHE scheme to meet the strong privacy claims. The scheme provides a speedup of about two orders of magnitude over the schemes using only SWHE while its overall performance is comparable (and faster for certain cases) to other schemes in the literature with weaker forms of privacy claims. We present implementation results including those from the literature pertaining to response times, storage and bandwidth requirements and show that the proposed scheme facilitates a lightweight client implementation

Zero-value filtering for accelerating non-profiled side-channel attack on incomplete NTT-based implementations of lattice-based cryptography

Lattice-based cryptographic schemes such as Crystals-Kyber and Dilithium are post-quantum algorithms selected to be standardized by NIST as they are considered to be secure against quantum computing attacks. The multiplication in polynomial rings is the most time-consuming operation in many lattice-based cryptographic schemes, which is also subject to side-channel attacks. While NTT-based polynomial multiplication is almost a norm in a wide range of implementations, a relatively new method, incomplete NTT is preferred to accelerate lattice-based cryptography, especially on some computing platforms that feature special instructions. In this paper, we present a novel, efficient and non-profiled power/EM side-channel attack targeting polynomial multiplication based on the incomplete NTT algorithm. We apply the attack on the Crystals-Dilithium signature algorithm and Crystals-Kyber KEM. We demonstrate that the method accelerates attack run-time when compared to the existing approaches. While a conventional non-profiled side-channel attack tests a much larger hypothesis set because it needs to predict two coefficients of secret polynomials together, we propose a much faster zero-value filtering attack (ZV-FA), which reduces the size of the hypothesis set by targeting the coefficients individually. We also propose an effective and efficient validation and correction technique employing the inverse NTT to estimate and modify the mispredicted coefficients. Our experimental results show that we can achieve a speed-up of 1915×over brute-force