We study differential privacy (DP) in a multi-party setting where each party only trusts a (known) subset of the other parties with its data. Specifically, given a trust graph where vertices correspond to parties and neighbors are mutually trusting, we give a DP algorithm for aggregation with a much better privacy-utility trade-off than in the well-studied local model of DP (where each party trusts no other party). We further study a robust variant where each party trusts all but an unknown subset of at most t of its neighbors (where t is a given parameter), and give an algorithm for this setting. We complement our algorithms with lower bounds, and discuss implications of our work to other tasks in private learning and analytics.
@InProceedings{ghazi_et_al:LIPIcs.ITCS.2025.53, author = {Ghazi, Badih and Kumar, Ravi and Manurangsi, Pasin and Wang, Serena}, title = {{Differential Privacy on Trust Graphs}}, booktitle = {16th Innovations in Theoretical Computer Science Conference (ITCS 2025)}, pages = {53:1--53:23}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-361-4}, ISSN = {1868-8969}, year = {2025}, volume = {325}, editor = {Meka, Raghu}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITCS.2025.53}, URN = {urn:nbn:de:0030-drops-226816}, doi = {10.4230/LIPIcs.ITCS.2025.53}, annote = {Keywords: Differential privacy, trust graphs, minimum dominating set, packing number} }
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