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Communication Cost Reduction for Subgraph Counting under Local Differential Privacy via Hash Functions

Created by
  • Haebom

Author

Quentin Hillebrand, Vorapong Suppakitpaisarn, Tetsuo Shibuya

Outline

This paper proposes a method to reduce communication costs by using hash functions in the process of counting the number of subgraphs under edge-local differential privacy. Existing graph statistics computation algorithms based on edge-local differential privacy have high communication costs, making them difficult to apply to large-scale graphs. In this paper, we introduce linear congruence hashing to solve this problem. Using a sampling rate $s$ can reduce the communication cost by $s^2$, but the variance of the published graph statistics increases by $s$. Experimental results show that the $\ell_2$-error for the triangle count is reduced by up to 1000 times compared to the existing state-of-the-art algorithms with the same communication cost.

Takeaways, Limitations

Takeaways:
We present a novel method for efficiently counting the number of subgraphs in a large graph under edge-local differential privacy.
We experimentally demonstrate that linear joint hashing can dramatically reduce communication costs.
Compared to existing algorithms, the $\ell_2$-error can be significantly reduced.
Limitations:
As the sampling rate increases, the variance of the published graph statistics increases.
The effectiveness of the proposed method may depend on the specific hash function and sampling strategy.
The experiments are limited to the number of triangles, and generalizability to other types of subgraphs requires further study.
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