Differential privacy and sublinear algorithms are both rapidly emerging algorithmic themes in times of big data analysis. Although recent works have shown the existence of differentially private sublinear algorithms for many problems including graph parameter estimation and clustering, little is known regarding hardness results on these algorithms. In this paper, we initiate the study of lower bounds for problems that aim for both differentially-private and sublinear-time algorithms. Our main result is the incompatibility of both the desiderata in the general case. In particular, we prove that a simple problem based on one-way marginals yields both a differentially-private algorithm, as well as a sublinear-time algorithm, but does not admit a "strictly" sublinear-time algorithm that is also differentially private.
@InProceedings{blocki_et_al:LIPIcs.ITCS.2025.19, author = {Blocki, Jeremiah and Fichtenberger, Hendrik and Grigorescu, Elena and Mukherjee, Tamalika}, title = {{Differential Privacy and Sublinear Time Are Incompatible Sometimes}}, booktitle = {16th Innovations in Theoretical Computer Science Conference (ITCS 2025)}, pages = {19:1--19:18}, 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.2025.19}, URN = {urn:nbn:de:0030-drops-226473}, doi = {10.4230/LIPIcs.ITCS.2025.19}, annote = {Keywords: differential privacy, sublinear algorithms, sublinear-time algorithms, one-way marginals, lower bounds} }
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