Dongmei Liu

Deep hashing algorithms have demonstrated considerable success in recent years, particularly in cross-modal retrieval tasks. Although hash-based cross-modal retrieval methods have demonstrated considerable efficacy, the vulnerability of deep networks to adversarial examples represents a significant challenge for the hash retrieval. In the absence of target semantics, previous non-targeted attack methods attempt to attack depth models by adding disturbance to the input data, yielding some positive outcomes. Nevertheless, they still lack specific instancelevel hash codes and fail to consider the diversity and semantic association of different modalities, which is insufficient to meet the attacker's expectations. In response, we present a novel Primary code Guided Targeted Attack (PGTA) against crossmodal hashing retrieval. Specifically, we integrate cross-modal instances and labels to obtain well-fused target semantics, thereby enhancing cross-modal interaction. Secondly, the primary code is designed to generate discriminable information with fine-grained semantics for target labels. Benign samples and target semantics collectively generate adversarial examples under the guidance of primary codes, thereby enhancing the efficacy of targeted attacks. Extensive experiments demonstrate that our PGTA outperforms the most advanced methods on three datasets, achieving stateof-the-art targeted attack performance.