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Plausible Deniability of Redacted Text

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Computer Security. ESORICS 2024 International Workshops (ESORICS 2024)

Abstract

Providing privacy for natural language text data remains a largely open problem, despite its great practical importance. The current state of the art is manual redaction of sensitive words such as names, addresses etc. In this paper we propose viewing a corpus of text as a probability distribution over sequences of words. A sentence is then one realization from this distribution and redacting words changes the probability distribution. We use the Renyi-divergence divergence as a measure of the distance between two redacted datasets. We show that if enough words are redacted then sensitive redacted text can be made be statistically indistinguishable from non-sensitive redacted text. This can be used to develop efficient redaction strategies, that minimise the amount of redaction while meeting a privacy target.

This work was supported by Science Foundation Ireland grant 16/IA/4610.

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Notes

  1. 1.

    Adding noise to an embedding perturbs it to nearby words, the way in which words are mapped to be close together (or far apart) therefore directly affects the output of the word-level DP sanitisation process.

  2. 2.

    See Appendix https://anonymous.4open.science/r/appendix_repo-F4CC for more details.

  3. 3.

    The choice of embedding will, in general, affect the estimated divergence. This can be mitigated by calculating the divergence for many different embeddings and using the worst-case (i.e. largest) value. However, we found the impact to be relatively minor in practice, see Section-6.3, and SentenceBERT [15] to work well.

  4. 4.

    We select the range to be large enough that \(D_{\alpha }\) no longer increases as we increase \(\alpha \).

  5. 5.

    https://huggingface.co/datasets/medal.

  6. 6.

    Data can be downloaded by following the instructions in the repository https://github.com/xuqiongkai/PATR.

  7. 7.

    https://huggingface.co/datasets/amazon_reviews_multi.

  8. 8.

    https://www.kaggle.com/general/256134.

  9. 9.

    In particular, the DP analysis ignores correlations between the words in a sentence and so may greatly underestimate the information release. The impact of correlations on DP is well known and was first noted by [9].

  10. 10.

    https://anonymous.4open.science/r/appendix_repo-F4CC.

  11. 11.

    Training code can be found at: https://github.com/pytorch/examples/tree/main/word_language_model.

  12. 12.

    And one of the major deficiencies of all approaches tied to a single up front choice of embedding, such as word-level DP approaches.

  13. 13.

    https://www.sbert.net/.

  14. 14.

    The embedding vector of each word in a sentence is calculated, and the mean of these vectors is used as the sentence embedding.

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Correspondence to Vaibhav Gusain .

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Gusain, V., Leith, D. (2025). Plausible Deniability of Redacted Text. In: Garcia-Alfaro, J., et al. Computer Security. ESORICS 2024 International Workshops. ESORICS 2024. Lecture Notes in Computer Science, vol 15263. Springer, Cham. https://doi.org/10.1007/978-3-031-82349-7_4

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  • DOI: https://doi.org/10.1007/978-3-031-82349-7_4

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