Vision Transformers (ViTs) are vulnerable to adversarial patch attacks, posing serious challenges to their deployment in security-critical applications. Existing defense strategies improve robustness but at the cost of significant computational overhead, limiting their practicality. To address this, we propose STEM, a lightweight and parallelizable token pruning defense mechanism that enhances robustness while reducing inference cost. STEM integrates two components: Block-wise Selective Fusion (BSF), which fuses redundant tokens and flags suspicious ones, and Identify-Prune (IP), which identifies and prunes adversarial tokens based on multi-head attention statistics.To support STEM efficiently in hardware, we further design STEMA, a scalable accelerator featuring a dedicated Security Core operating in parallel with the ViT backbone. STEMA includes specialized engines for token fusion, top-k selection, and metadata management, occupying only 5% of chip area.Experimental results show that STEM achieves state-of-the-art (SOTA) defense performance and demonstrates excellent efficiency. Specifically, STEM improves robustness by up to 4.7× compared to token pruning methods and achieves 46.8×–105.8× runtime improvements over defense baselines. STEMA further delivers up to 71× speedups and 397× energy efficiency improvements, demonstrating its suitability for secure and efficient ViT deployment, especially in edge environments.

Abstract Previous work on privacy-aware ranking has addressed the minimization of information leakage when scoring top k documents, and has not studied on how to retrieve these top documents and their features for ranking. This paper proposes a privacy-aware document retrieval scheme with a two-level inverted index structure. In this scheme, posting records are grouped with bucket tags and runtime query processing produces query-specific tags in order to gather encoded features of matched documents with a privacy protection during index traversal. To thwart leakage-abuse attacks, our design minimizes the chance that a server processes unauthorized queries or identifies document sharing across posting lists through index inspection or across-query association. This paper presents the evaluation and analytic results of the proposed scheme to demonstrate the tradeoffs in its design considerations for privacy, efficiency, and relevance.

Recently transformer-based ranking models have been shown to deliver high relevance for document search and the relevance-efficiency tradeoff becomes important for fast query response times. This paper presents BECR (BERT-based Composite Re-Ranking), a lightweight composite re-ranking scheme that combines deep contextual token interactions and traditional lexical term-matching features. BECR conducts query decomposition and composes a query representation using pre-computable token embeddings based on uni-grams and skip-n-grams, to seek a tradeoff of inference efficiency and relevance. Thus it does not perform expensive transformer computations during online inference, and does not require the use of GPU. This paper describes an evaluation of relevance and efficiency of BECR with several TREC datasets.

BlockMax WAND (BMW) and its variants can effectively prune low-scoring documents for fast top-k disjunctive query processing. This paper studies a boosting approach that further accelerates document retrieval by executing BMW, or one of its variants, on a sequence of posting windows with an order prioritized to tighten the threshold bound earlier. This optimization could add benefits to safely eliminate more operations involved in posting block visitation and document score evaluation. This paper evaluates such index navigation for BMW and two of its variants.

This paper studies privacy-aware inverted index design and document retrieval for multi-keyword document search in a trusted hardware execution environment such as Intel SGX. The previous work uses time-consuming oblivious computing techniques to avoid the leakage of memory access patterns for privacy preservations in such an environment. This paper proposes an efficiency-enhanced design that obfuscates the inverted index structure with posting bucketing and document ID masking, which aims to hide document-term association and avoid the access pattern leakage. This paper describes privacy-aware oblivious document retrieval during online query processing based on such an index. Both privacy and efficiency analyses are provided, followed by evaluation results comparing proposed designs with multiple baselines.

The recent work on neural ranking has achieved solid relevance improvement, by exploring similarities between documents and queries using word embeddings. It is an open problem how to leverage such an advancement for privacy-aware ranking, which is important for top K document search on the cloud. Since neural ranking adds more complexity in score computation, it is difficult to prevent the server from discovering embedding-based semantic features and inferring privacy-sensitive information. This paper analyzes the critical leakages in interaction-based neural ranking and studies countermeasures to mitigate such a leakage. It proposes a privacy-aware neural ranking scheme that integrates tree ensembles with kernel value obfuscation and a soft match map based on adaptively-clustered term closures. The paper also presents an evaluation with two TREC datasets on the relevance of the proposed techniques and the trade-offs for privacy and storage efficiency.

Interaction-based neural ranking has been shown to be effective for document search using distributed word representations. However the time or space required is very expensive for online query processing with neural ranking. This paper investigates fast approximation of three interaction-based neural ranking algorithms using Locality Sensitive Hashing (LSH). It accelerates query-document interaction computation by using a runtime cache with precomputed term vectors, and speeds up kernel calculation by taking advantages of limited integer similarity values. This paper presents the design choices with cost analysis, and an evaluation that assesses efficiency benefits and relevance tradeoffs for the tested datasets.

Tree-based ensembles are widely used for document ranking but supporting such a method efficiently under a privacy-preserving constraint on the cloud is an open research problem. The main challenge is that letting the cloud server perform ranking computation may unsafely reveal privacy-sensitive information. To address privacy with tree-based server-side ranking, this paper proposes to reduce the learning-to-rank model dependence on composite features as a trade-off, and develops comparison-preserving mapping to hide feature values and tree thresholds. To justify the above approach, the presented analysis shows that a decision tree with simplifiable composite features can be transformed into another tree using raw features without increasing the training accuracy loss. This paper analyzes the privacy properties of the proposed scheme, and compares the relevance of gradient boosting regression trees, LambdaMART, and random forests using raw features for several test data sets under the privacy consideration, and assesses the competitiveness of a hybrid model based on these algorithms.

This paper proposes a private ranking scheme with linear additive scoring for efficient top K keyword search on modest-sized cloud datasets. This scheme strikes for tradeoffs between privacy and efficiency by proposing single-round client-server collaboration with server-side partial ranking based on blinded feature weights with random masks. Client-side preprocessing includes query decomposition with chunked postings to facilitate earlier range intersection and fast access of server-side key-value stores. Server-side query processing deals with feature vector sparsity through optional feature matching and enables result filtering with query-dependent chunk-wide random masks for queries that yield too many matched documents. This paper provides details on indexing and run-time conjunctive query processing and presents an evaluation that assesses the accuracy, efficiency, and privacy tradeoffs of this scheme through five datasets with various sizes.

Via analyzing the characteristics of life sign, a novel method is proposed to detect multiple trapped victims by ultra-wideband radar in this letter. The signal-to-noise and clutter ratio (SNCR) is greatly improved. The non-static clutter can be removed effectively. The number, range position and respiratory frequency of life signs can be detected automatically and accurately in low SNCR environment. By using experiment and numerical simulation, the good performance of the new method is proved.