@inproceedings{tian-etal-2026-stamp,
    title = "{STAMP}: Selective Task-Aware Mechanism for Text Privacy",
    author = "Tian, Fengwei  and
      Bhattacharjee, Payel  and
      Hanson, Heidi  and
      Rubin, Geoffrey D  and
      Lo, Joseph Y.  and
      Tandon, Ravi",
    editor = "Demberg, Vera  and
      Inui, Kentaro  and
      Marquez, Llu{\'i}s",
    booktitle = "Proceedings of the 19th Conference of the {E}uropean Chapter of the {A}ssociation for {C}omputational {L}inguistics (Volume 1: Long Papers)",
    month = mar,
    year = "2026",
    address = "Rabat, Morocco",
    publisher = "Association for Computational Linguistics",
    url = "https://preview.aclanthology.org/ingest-eacl/2026.eacl-long.61/",
    pages = "1319--1333",
    ISBN = "979-8-89176-380-7",
    abstract = "We present STAMP (Selective Task-Aware Mechanism for Text Privacy), a new framework for task-aware text privatization that achieves an improved privacy{--}utility trade-off. STAMP selectively allocates privacy budgets across tokens by jointly considering (i) each token{'}s importance to the downstream task (as measured via a task- or query-specific representation), and (ii) its privacy sensitivity (e.g., names, dates, identifiers). This token-level partitioning enables fine-grained, group-wise control over the level of noise applied to different parts of the input, balancing privacy protection with task relevance. To privatize individual token embeddings, we introduce the polar mechanism, which perturbs only the direction of embeddings on the unit sphere while preserving their magnitude. Decoding is performed via cosine nearest-neighbor search, aligning the perturbation geometry with the decoding geometry. Unlike isotropic noise mechanisms, the polar mechanism maintains semantic neighborhoods in the embedding space and better preserves downstream utility. Experimental evaluations on SQuAD, Yelp, and AG News datasets demonstrate that STAMP, when combined with the normalized polar mechanism, consistently achieves superior privacy{--}utility trade-offs across varying per-token privacy budgets."
}