Visible to the public Biblio

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2021-02-22
Li, M., Zhang, Y., Sun, Y., Wang, W., Tsang, I. W., Lin, X..  2020.  I/O Efficient Approximate Nearest Neighbour Search based on Learned Functions. 2020 IEEE 36th International Conference on Data Engineering (ICDE). :289–300.
Approximate nearest neighbour search (ANNS) in high dimensional space is a fundamental problem in many applications, such as multimedia database, computer vision and information retrieval. Among many solutions, data-sensitive hashing-based methods are effective to this problem, yet few of them are designed for external storage scenarios and hence do not optimized for I/O efficiency during the query processing. In this paper, we introduce a novel data-sensitive indexing and query processing framework for ANNS with an emphasis on optimizing the I/O efficiency, especially, the sequential I/Os. The proposed index consists of several lists of point IDs, ordered by values that are obtained by learned hashing (i.e., mapping) functions on each corresponding data point. The functions are learned from the data and approximately preserve the order in the high-dimensional space. We consider two instantiations of the functions (linear and non-linear), both learned from the data with novel objective functions. We also develop an I/O efficient ANNS framework based on the index. Comprehensive experiments on six benchmark datasets show that our proposed methods with learned index structure perform much better than the state-of-the-art external memory-based ANNS methods in terms of I/O efficiency and accuracy.
Chen, T., Lin, T., Hong, Y.- P..  2020.  Gait Phase Segmentation Using Weighted Dynamic Time Warping and K-Nearest Neighbors Graph Embedding. ICASSP 2020 - 2020 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP). :1180–1184.
Gait phase segmentation is the process of identifying the start and end of different phases within a gait cycle. It is essential to many medical applications, such as disease diagnosis or rehabilitation. This work utilizes inertial measurement units (IMUs) mounted on the individual's foot to gather gait information and develops a gait phase segmentation method based on the collected signals. The proposed method utilizes a weighted dynamic time warping (DTW) algorithm to measure the distance between two different gait signals, and a k-nearest neighbors (kNN) algorithm to obtain the gait phase estimates. To reduce the complexity of the DTW-based kNN search, we propose a neural network-based graph embedding scheme that is able to map the IMU signals associated with each gait cycle into a distance-preserving low-dimensional representation while also producing a prediction on the k nearest neighbors of the test signal. Experiments are conducted on self-collected IMU gait signals to demonstrate the effectiveness of the proposed scheme.
Bashyam, K. G. Renga, Vadhiyar, S..  2020.  Fast Scalable Approximate Nearest Neighbor Search for High-dimensional Data. 2020 IEEE International Conference on Cluster Computing (CLUSTER). :294–302.
K-Nearest Neighbor (k-NN) search is one of the most commonly used approaches for similarity search. It finds extensive applications in machine learning and data mining. This era of big data warrants efficiently scaling k-NN search algorithms for billion-scale datasets with high dimensionality. In this paper, we propose a solution towards this end where we use vantage point trees for partitioning the dataset across multiple processes and exploit an existing graph-based sequential approximate k-NN search algorithm called HNSW (Hierarchical Navigable Small World) for searching locally within a process. Our hybrid MPI-OpenMP solution employs techniques including exploiting MPI one-sided communication for reducing communication times and partition replication for better load balancing across processes. We demonstrate computation of k-NN for 10,000 queries in the order of seconds using our approach on 8000 cores on a dataset with billion points in an 128-dimensional space. We also show 10X speedup over a completely k-d tree-based solution for the same dataset, thus demonstrating better suitability of our solution for high dimensional datasets. Our solution shows almost linear strong scaling.
Fang, S., Kennedy, S., Wang, C., Wang, B., Pei, Q., Liu, X..  2020.  Sparser: Secure Nearest Neighbor Search with Space-filling Curves. IEEE INFOCOM 2020 - IEEE Conference on Computer Communications Workshops (INFOCOM WKSHPS). :370–375.
Nearest neighbor search, a classic way of identifying similar data, can be applied to various areas, including database, machine learning, natural language processing, software engineering, etc. Secure nearest neighbor search aims to find nearest neighbors to a given query point over encrypted data without accessing data in plaintext. It provides privacy protection to datasets when nearest neighbor queries need to be operated by an untrusted party (e.g., a public server). While different solutions have been proposed to support nearest neighbor queries on encrypted data, these existing solutions still encounter critical drawbacks either in efficiency or privacy. In light of the limitations in the current literature, we propose a novel approximate nearest neighbor search solution, referred to as Sparser, by leveraging a combination of space-filling curves, perturbation, and Order-Preserving Encryption. The advantages of Sparser are twofold, strengthening privacy and improving efficiency. Specifically, Sparser pre-processes plaintext data with space-filling curves and perturbation, such that data is sparse, which mitigates leakage abuse attacks and renders stronger privacy. In addition to privacy enhancement, Sparser can efficiently find approximate nearest neighbors over encrypted data with logarithmic time. Through extensive experiments over real-world datasets, we demonstrate that Sparser can achieve strong privacy protection under leakage abuse attacks and minimize search time.
Han, Z., Wang, F., Li, Z..  2020.  Research on Nearest Neighbor Data Association Algorithm Based on Target “Dynamic” Monitoring Model. 2020 IEEE 4th Information Technology, Networking, Electronic and Automation Control Conference (ITNEC). 1:665–668.
In order to solve the problem that the Nearest Neighbor Data Association (NNDA) algorithm cannot detect the “dynamic” change of the target, this paper proposes the nearest neighbor data association algorithm based on the Targets “Dynamic” Monitoring Model (TDMM). Firstly, the gate searching and updating of targets are completed based on TDMM, then the NNDA algorithm is utilized to achieve the data association of targets to realize track updating. Finally, the NNDA algorithm based on TDMM is realized by simulation. The experimental results show that the algorithm proposed can achieve “dynamic” monitoring in multi-target data association, and have more obvious advantages than Multiple Hypothesis Tracking (MHT) in timeliness and association performance.
Haile, J., Havens, S..  2020.  Identifying Ubiquitious Third-Party Libraries in Compiled Executables Using Annotated and Translated Disassembled Code with Supervised Machine Learning. 2020 IEEE Security and Privacy Workshops (SPW). :157–162.
The size and complexity of the software ecosystem is a major challenge for vendors, asset owners and cybersecurity professionals who need to understand the security posture of these systems. Annotated and Translated Disassembled Code is a graph based datastore designed to organize firmware and software analysis data across builds, packages and systems, providing a highly scalable platform enabling automated binary software analysis tasks including corpora construction and storage for machine learning. This paper describes an approach for the identification of ubiquitous third-party libraries in firmware and software using Annotated and Translated Disassembled Code and supervised machine learning. Annotated and Translated Disassembled Code provide matched libraries, function names and addresses of previously unidentified code in software as it is being automatically analyzed. This data can be ingested by other software analysis tools to improve accuracy and save time. Defenders can add the identified libraries to their vulnerability searches and add effective detection and mitigation into their operating environment.
Lei, X., Tu, G.-H., Liu, A. X., Xie, T..  2020.  Fast and Secure kNN Query Processing in Cloud Computing. 2020 IEEE Conference on Communications and Network Security (CNS). :1–9.
Advances in sensing and tracking technology lead to the proliferation of location-based services. Location service providers (LSPs) often resort to commercial public clouds to store the tremendous geospatial data and process location-based queries from data users. To protect the privacy of LSP's geospatial data and data user's query location against the untrusted cloud, they are required to be encrypted before sending to the cloud. Nevertheless, it is not easy to design a fast and secure location-based query processing scheme over the encrypted data. In this paper, we propose a Fast and Secure kNN (FSkNN) scheme to support secure k nearest neighbor (k NN) search in cloud computing. We reveal the inherent connection between an Sk NN protocol and a secure range query protocol and further describe how to construct FSkNN based on a secure range query protocol. FSkNN leverages a customized accuracy-assured strategy to ensure the result accuracy and adopts a data structure named random Bloom filter (RBF) to build a secure index for efficiently searching. We formally prove the security of FSkNN under the random oracle model. Our evaluation results show that FSkNN is highly practical.
Kornaropoulos, E. M., Papamanthou, C., Tamassia, R..  2020.  The State of the Uniform: Attacks on Encrypted Databases Beyond the Uniform Query Distribution. 2020 IEEE Symposium on Security and Privacy (SP). :1223–1240.
Recent foundational work on leakage-abuse attacks on encrypted databases has broadened our understanding of what an adversary can accomplish with a standard leakage profile. Nevertheless, all known value reconstruction attacks succeed under strong assumptions that may not hold in the real world. The most prevalent assumption is that queries are issued uniformly at random by the client. We present the first value reconstruction attacks that succeed without any knowledge about the query or data distribution. Our approach uses the search-pattern leakage, which exists in all known structured encryption schemes but has not been fully exploited so far. At the core of our method lies a support size estimator, a technique that utilizes the repetition of search tokens with the same response to estimate distances between encrypted values without any assumptions about the underlying distribution. We develop distribution-agnostic reconstruction attacks for both range queries and k-nearest-neighbor (k-NN) queries based on information extracted from the search-pattern leakage. Our new range attack follows a different algorithmic approach than state-of-the-art attacks, which are fine-tuned to succeed under the uniformly distributed queries. Instead, we reconstruct plaintext values under a variety of skewed query distributions and even outperform the accuracy of previous approaches under the uniform query distribution. Our new k-NN attack succeeds with far fewer samples than previous attacks and scales to much larger values of k. We demonstrate the effectiveness of our attacks by experimentally testing them on a wide range of query distributions and database densities, both unknown to the adversary.
Oliver, J., Ali, M., Hagen, J..  2020.  HAC-T and Fast Search for Similarity in Security. 2020 International Conference on Omni-layer Intelligent Systems (COINS). :1–7.
Similarity digests have gained popularity for many security applications like blacklisting/whitelisting, and finding similar variants of malware. TLSH has been shown to be particularly good at hunting similar malware, and is resistant to evasion as compared to other similarity digests like ssdeep and sdhash. Searching and clustering are fundamental tools which help the security analysts and security operations center (SOC) operators in hunting and analyzing malware. Current approaches which aim to cluster malware are not scalable enough to keep up with the vast amount of malware and goodware available in the wild. In this paper, we present techniques which allow for fast search and clustering of TLSH hash digests which can aid analysts to inspect large amounts of malware/goodware. Our approach builds on fast nearest neighbor search techniques to build a tree-based index which performs fast search based on TLSH hash digests. The tree-based index is used in our threshold based Hierarchical Agglomerative Clustering (HAC-T) algorithm which is able to cluster digests in a scalable manner. Our clustering technique can cluster digests in O (n logn) time on average. We performed an empirical evaluation by comparing our approach with many standard and recent clustering techniques. We demonstrate that our approach is much more scalable and still is able to produce good cluster quality. We measured cluster quality using purity on 10 million samples obtained from VirusTotal. We obtained a high purity score in the range from 0.97 to 0.98 using labels from five major anti-virus vendors (Kaspersky, Microsoft, Symantec, Sophos, and McAfee) which demonstrates the effectiveness of the proposed method.
2021-01-25
Arthy, R., Daniel, E., Maran, T. G., Praveen, M..  2020.  A Hybrid Secure Keyword Search Scheme in Encrypted Graph for Social Media Database. 2020 Fourth International Conference on Computing Methodologies and Communication (ICCMC). :1000–1004.

Privacy preservation is a challenging task with the huge amount of data that are available in social media. The data those are stored in the distributed environment or in cloud environment need to ensure confidentiality to data. In addition, representing the voluminous data is graph will be convenient to perform keyword search. The proposed work initially reads the data corresponding to social media and converts that into a graph. In order to prevent the data from the active attacks Advanced Encryption Standard algorithm is used to perform graph encryption. Later, search operation is done using two algorithms: kNK keyword search algorithm and top k nearest keyword search algorithm. The first scheme is used to fetch all the data corresponding to the keyword. The second scheme is used to fetch the nearest neighbor. This scheme increases the efficiency of the search process. Here shortest path algorithm is used to find the minimum distance. Now, based on the minimum value the results are produced. The proposed algorithm shows high performance for graph generation and searching and moderate performance for graph encryption.

2020-06-12
[Anonymous].  2018.  Discrete Locally-Linear Preserving Hashing. {2018 25th IEEE International Conference on Image Processing (ICIP). :490—494.

Recently, hashing has attracted considerable attention for nearest neighbor search due to its fast query speed and low storage cost. However, existing unsupervised hashing algorithms have two problems in common. Firstly, the widely utilized anchor graph construction algorithm has inherent limitations in local weight estimation. Secondly, the locally linear structure in the original feature space is seldom taken into account for binary encoding. Therefore, in this paper, we propose a novel unsupervised hashing method, dubbed “discrete locally-linear preserving hashing”, which effectively calculates the adjacent matrix while preserving the locally linear structure in the obtained hash space. Specifically, a novel local anchor embedding algorithm is adopted to construct the approximate adjacent matrix. After that, we directly minimize the reconstruction error with the discrete constrain to learn the binary codes. Experimental results on two typical image datasets indicate that the proposed method significantly outperforms the state-of-the-art unsupervised methods.

Al Kobaisi, Ali, Wocjan, Pawel.  2018.  Supervised Max Hashing for Similarity Image Retrieval. 2018 17th IEEE International Conference on Machine Learning and Applications (ICMLA). :359—365.

The storage efficiency of hash codes and their application in the fast approximate nearest neighbor search, along with the explosion in the size of available labeled image datasets caused an intensive interest in developing learning based hash algorithms recently. In this paper, we present a learning based hash algorithm that utilize ordinal information of feature vectors. We have proposed a novel mathematically differentiable approximation of argmax function for this hash algorithm. It has enabled seamless integration of hash function with deep neural network architecture which can exploit the rich feature vectors generated by convolutional neural networks. We have also proposed a loss function for the case that the hash code is not binary and its entries are digits of arbitrary k-ary base. The resultant model comprised of feature vector generation and hashing layer is amenable to end-to-end training using gradient descent methods. In contrast to the majority of current hashing algorithms that are either not learning based or use hand-crafted feature vectors as input, simultaneous training of the components of our system results in better optimization. Extensive evaluations on NUS-WIDE, CIFAR-10 and MIRFlickr benchmarks show that the proposed algorithm outperforms state-of-art and classical data agnostic, unsupervised and supervised hashing methods by 2.6% to 19.8% mean average precision under various settings.

2020-06-08
Fang, Bo, Hua, Zhongyun, Huang, Hejiao.  2019.  Locality-Sensitive Hashing Scheme Based on Heap Sort of Hash Bucket. 2019 14th International Conference on Computer Science Education (ICCSE). :5–10.
Nearest neighbor search (NNS) is one of the current popular research directions, which widely used in machine learning, pattern recognition, image detection and so on. In the low dimension data, based on tree search method can get good results. But when the data dimension goes up, that will produce a curse of dimensional. The proposed Locality-Sensitive Hashing algorithm (LSH) greatly improves the efficiency of nearest neighbor query for high dimensional data. But the algorithm relies on the building a large number of hash table, which makes the space complexity very high. C2LSH based on dynamic collision improves the disadvantage of LSH, but its disadvantage is that it needs to detect the collision times of a large number of data points which Increased query time. Therefore, Based on LSH algorithm, later researchers put forward many improved algorithms, but still not ideal.In this paper, we put forward Locality-Sensitive Hashing Scheme Based on Heap Sort of Hash Bucket (HSLSH) algorithm aiming at the shortcomings of LSH and C2LSH. Its main idea is to take advantage of the efficiency of heapsort in massive data sorting to improve the efficiency of nearest neighbor query. It only needs to rely on a small number of hash functions can not only overcome the shortcoming of LSH need to build a large number of hash table, and avoids defects of C2LSH. Experiments show that our algorithm is more than 20% better than C2LSH in query accuracy and 40% percent lower in query time.
2020-05-22
Sheth, Utsav, Dutta, Sanghamitra, Chaudhari, Malhar, Jeong, Haewon, Yang, Yaoqing, Kohonen, Jukka, Roos, Teemu, Grover, Pulkit.  2018.  An Application of Storage-Optimal MatDot Codes for Coded Matrix Multiplication: Fast k-Nearest Neighbors Estimation. 2018 IEEE International Conference on Big Data (Big Data). :1113—1120.
We propose a novel application of coded computing to the problem of the nearest neighbor estimation using MatDot Codes (Fahim et al., Allerton'17) that are known to be optimal for matrix multiplication in terms of recovery threshold under storage constraints. In approximate nearest neighbor algorithms, it is common to construct efficient in-memory indexes to improve query response time. One such strategy is Multiple Random Projection Trees (MRPT), which reduces the set of candidate points over which Euclidean distance calculations are performed. However, this may result in a high memory footprint and possibly paging penalties for large or high-dimensional data. Here we propose two techniques to parallelize MRPT that exploit data and model parallelism respectively by dividing both the data storage and the computation efforts among different nodes in a distributed computing cluster. This is especially critical when a single compute node cannot hold the complete dataset in memory. We also propose a novel coded computation strategy based on MatDot codes for the model-parallel architecture that, in a straggler-prone environment, achieves the storage-optimal recovery threshold, i.e., the number of nodes that are required to serve a query. We experimentally demonstrate that, in the absence of straggling, our distributed approaches require less query time than execution on a single processing node, providing near-linear speedups with respect to the number of worker nodes. Our experiments on real systems with simulated straggling, we also show that in a straggler-prone environment, our strategy achieves a faster query execution than the uncoded strategy.
Despotovski, Filip, Gusev, Marjan, Zdraveski, Vladimir.  2018.  Parallel Implementation of K-Nearest-Neighbors for Face Recognition. 2018 26th Telecommunications Forum (℡FOR). :1—4.
Face recognition is a fast-expanding field of research. Countless classification algorithms have found use in face recognition, with more still being developed, searching for better performance and accuracy. For high-dimensional data such as images, the K-Nearest-Neighbours classifier is a tempting choice. However, it is very computationally-intensive, as it has to perform calculations on all items in the stored dataset for each classification it makes. Fortunately, there is a way to speed up the process by performing some of the calculations in parallel. We propose a parallel CUDA implementation of the KNN classifier and then compare it to a serial implementation to demonstrate its performance superiority.
Varricchio, Valerio, Frazzoli, Emilio.  2018.  Asymptotically Optimal Pruning for Nonholonomic Nearest-Neighbor Search. 2018 IEEE Conference on Decision and Control (CDC). :4459—4466.
Nearest-Neighbor Search (NNS) arises as a key component of sampling-based motion planning algorithms and it is known as their asymptotic computational bottleneck. Algorithms for exact Nearest-Neighbor Search rely on explicit distance comparisons to different extents. However, in motion planning, evaluating distances is generally a computationally demanding task, since the metric is induced by the minimum cost of steering a dynamical system between states. In the presence of driftless nonholonomic constraints, we propose efficient pruning techniques for the k-d tree algorithm that drastically reduce the number of distance evaluations performed during a query. These techniques exploit computationally convenient lower and upper bounds to the geodesic distance of the corresponding sub-Riemannian geometry. Based on asymptotic properties of the reachable sets, we show that the proposed pruning techniques are optimal, modulo a constant factor, and we provide experimental results with the Reeds-Shepp vehicle model.
Yan, Donghui, Wang, Yingjie, Wang, Jin, Wang, Honggang, Li, Zhenpeng.  2018.  K-nearest Neighbor Search by Random Projection Forests. 2018 IEEE International Conference on Big Data (Big Data). :4775—4781.
K-nearest neighbor (kNN) search has wide applications in many areas, including data mining, machine learning, statistics and many applied domains. Inspired by the success of ensemble methods and the flexibility of tree-based methodology, we propose random projection forests, rpForests, for kNN search. rpForests finds kNNs by aggregating results from an ensemble of random projection trees with each constructed recursively through a series of carefully chosen random projections. rpForests achieves a remarkable accuracy in terms of fast decay in the missing rate of kNNs and that of discrepancy in the kNN distances. rpForests has a very low computational complexity. The ensemble nature of rpForests makes it easily run in parallel on multicore or clustered computers; the running time is expected to be nearly inversely proportional to the number of cores or machines. We give theoretical insights by showing the exponential decay of the probability that neighboring points would be separated by ensemble random projection trees when the ensemble size increases. Our theory can be used to refine the choice of random projections in the growth of trees, and experiments show that the effect is remarkable.
Kang, Hyunjoong, Hong, Sanghyun, Lee, Kookjin, Park, Noseong, Kwon, Soonhyun.  2018.  On Integrating Knowledge Graph Embedding into SPARQL Query Processing. 2018 IEEE International Conference on Web Services (ICWS). :371—374.
SPARQL is a standard query language for knowledge graphs (KGs). However, it is hard to find correct answer if KGs are incomplete or incorrect. Knowledge graph embedding (KGE) enables answering queries on such KGs by inferring unknown knowledge and removing incorrect knowledge. Hence, our long-term goal in this line of research is to propose a new framework that integrates KGE and SPARQL, which opens various research problems to be addressed. In this paper, we solve one of the most critical problems, that is, optimizing the performance of nearest neighbor (NN) search. In our evaluations, we demonstrate that the search time of state-of-the-art NN search algorithms is improved by 40% without sacrificing answer accuracy.
Chen, Yalin, Li, Zhiyang, Shi, Jia, Liu, Zhaobin, Qu, Wenyu.  2018.  Stacked K-Means Hashing Quantization for Nearest Neighbor Search. 2018 IEEE Fourth International Conference on Multimedia Big Data (BigMM). :1—4.
Nowadays, with such a huge amount of information available online, one key challenge is how to retrieve target data efficiently. A recent state-of-art solution, k-means hashing (KMH), codes data via a string of binary code obtained by iterative k-means clustering and binary code optimizing. To deal with high dimensional data, KMH divides the space into low-dimensional subspaces, places a hypercube in each subspace and finds its proper location by the mentioned optimizing process. However, the complexity of the optimization increases rapidly when the dimension of the hypercube increases. To address this issue, we propose an improved hashing method stacked k-means hashing (SKMH). The main idea is to increase the approximation by a coarse-to-fine multi-layer lower-dimensional cubes. With these kinds of lower-dimensional cubes, SKMH can achieve a similar approximation ability via a less optimizing time, compared with KMH method using higher-dimensional cubes. Extensive experiments have been conducted on two public databases, demonstrating the performance of our method by some common metrics in fast nearest neighbor search.
Ito, Toshitaka, Itotani, Yuri, Wakabayashi, Shin'ichi, Nagayama, Shinobu, Inagi, Masato.  2018.  A Nearest Neighbor Search Engine Using Distance-Based Hashing. 2018 International Conference on Field-Programmable Technology (FPT). :150—157.
This paper proposes an FPGA-based nearest neighbor search engine for high-dimensional data, in which nearest neighbor search is performed based on distance-based hashing. The proposed hardware search engine implements a nearest neighbor search algorithm based on an extension of flexible distance-based hashing (FDH, for short), which finds an exact solution with high probability. The proposed engine is a parallel processing and pipelined circuit so that search results can be obtained in a short execution time. Experimental results show the effectiveness and efficiency of the proposed engine.
Wang, Xi, Yao, Jun, Ji, Hongxia, Zhang, Ze, Li, Chen, Ma, Beizhi.  2018.  A Local Integral Hash Nearest Neighbor Algorithm. 2018 3rd International Conference on Mechanical, Control and Computer Engineering (ICMCCE). :544—548.

Nearest neighbor search algorithm plays a very important role in computer image algorithm. When the search data is large, we need to use fast search algorithm. The current fast retrieval algorithms are tree based algorithms. The efficiency of the tree algorithm decreases sharply with the increase of the data dimension. In this paper, a local integral hash nearest neighbor algorithm of the spatial space is proposed to construct the tree structure by changing the way of the node of the access tree. It is able to express data distribution characteristics. After experimental testing, this paper achieves more efficient performance in high dimensional data.

Vijay, Savinu T., Pournami, P. N..  2018.  Feature Based Image Registration using Heuristic Nearest Neighbour Search. 2018 22nd International Computer Science and Engineering Conference (ICSEC). :1—3.
Image registration is the process of aligning images of the same scene taken at different instances, from different viewpoints or by heterogeneous sensors. This can be achieved either by area based or by feature based image matching techniques. Feature based image registration focuses on detecting relevant features from the input images and attaching descriptors to these features. Matching visual descriptions of two images is a major task in image registration. This feature matching is currently done using Exhaustive Search (or Brute-Force) and Nearest Neighbour Search. The traditional method used for nearest neighbour search is by representing the data as k-d trees. This nearest neighbour search can also be performed using combinatorial optimization algorithms such as Simulated Annealing. This work proposes a method to perform image feature matching by nearest neighbour search done based on Threshold Accepting, a faster version of Simulated Annealing.The experiments performed suggest that the proposed algorithm can produce better results within a minimum number of iterations than many existing algorithms.
Song, Fuyuan, Qin, Zheng, Liu, Qin, Liang, Jinwen, Ou, Lu.  2019.  Efficient and Secure k-Nearest Neighbor Search Over Encrypted Data in Public Cloud. ICC 2019 - 2019 IEEE International Conference on Communications (ICC). :1—6.
Cloud computing has become an important and popular infrastructure for data storage and sharing. Typically, data owners outsource their massive data to a public cloud that will provide search services to authorized data users. With privacy concerns, the valuable outsourced data cannot be exposed directly, and should be encrypted before outsourcing to the public cloud. In this paper, we focus on k-Nearest Neighbor (k-NN) search over encrypted data. We propose efficient and secure k-NN search schemes based on matrix similarity to achieve efficient and secure query services in public cloud. In our basic scheme, we construct the traces of two diagonal multiplication matrices to denote the Euclidean distance of two data points, and perform secure k-NN search by comparing traces of corresponding similar matrices. In our enhanced scheme, we strengthen the security property by decomposing matrices based on our basic scheme. Security analysis shows that our schemes protect the data privacy and query privacy under attacking with different levels of background knowledge. Experimental evaluations show that both schemes are efficient in terms of computation complexity as well as computational cost.
Dubey, Abhimanyu, Maaten, Laurens van der, Yalniz, Zeki, Li, Yixuan, Mahajan, Dhruv.  2019.  Defense Against Adversarial Images Using Web-Scale Nearest-Neighbor Search. 2019 IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR). :8759—8768.
A plethora of recent work has shown that convolutional networks are not robust to adversarial images: images that are created by perturbing a sample from the data distribution as to maximize the loss on the perturbed example. In this work, we hypothesize that adversarial perturbations move the image away from the image manifold in the sense that there exists no physical process that could have produced the adversarial image. This hypothesis suggests that a successful defense mechanism against adversarial images should aim to project the images back onto the image manifold. We study such defense mechanisms, which approximate the projection onto the unknown image manifold by a nearest-neighbor search against a web-scale image database containing tens of billions of images. Empirical evaluations of this defense strategy on ImageNet suggest that it very effective in attack settings in which the adversary does not have access to the image database. We also propose two novel attack methods to break nearest-neighbor defense settings and show conditions under which nearest-neighbor defense fails. We perform a series of ablation experiments, which suggest that there is a trade-off between robustness and accuracy between as we use features from deeper in the network, that a large index size (hundreds of millions) is crucial to get good performance, and that careful construction of database is crucial for robustness against nearest-neighbor attacks.
Markchit, Sarawut, Chiu, Chih-Yi.  2019.  Hash Code Indexing in Cross-Modal Retrieval. 2019 International Conference on Content-Based Multimedia Indexing (CBMI). :1—4.

Cross-modal hashing, which searches nearest neighbors across different modalities in the Hamming space, has become a popular technique to overcome the storage and computation barrier in multimedia retrieval recently. Although dozens of cross-modal hashing algorithms are proposed to yield compact binary code representation, applying exhaustive search in a large-scale dataset is impractical for the real-time purpose, and the Hamming distance computation suffers inaccurate results. In this paper, we propose a novel index scheme over binary hash codes in cross-modal retrieval. The proposed indexing scheme exploits a few binary bits of the hash code as the index code. Based on the index code representation, we construct an inverted index structure to accelerate the retrieval efficiency and train a neural network to improve the indexing accuracy. Experiments are performed on two benchmark datasets for retrieval across image and text modalities, where hash codes are generated by three cross-modal hashing methods. Results show the proposed method effectively boosts the performance over the benchmark datasets and hash methods.