Privacy, Secrecy, and Storage with Multiple Noisy Measurements of Identifiers

TL;DR

This paper derives the key-leakage-storage region for a model where the encoder observes noisy, hidden identifiers and performs multiple measurements, analyzing how these factors affect privacy and reliability in key agreement.

Contribution

It extends the classic key agreement model by incorporating noisy, hidden observations and multiple measurements, providing a detailed analysis of their impact on privacy and storage.

Findings

The key-leakage-storage region is explicitly characterized for the generalized model.

Increasing measurements improves the key-leakage-storage trade-off.

Mis-modeling the source as visible can lead to significant secrecy leakage.

Abstract

The key-leakage-storage region is derived for a generalization of a classic two-terminal key agreement model. The additions to the model are that the encoder observes a hidden, or noisy, version of the identifier, and that the encoder and decoder can perform multiple measurements. To illustrate the behavior of the region, the theory is applied to binary identifiers and noise modeled via binary symmetric channels. In particular, the key-leakage-storage region is simplified by applying Mrs. Gerber's lemma twice in different directions to a Markov chain. The growth in the region as the number of measurements increases is quantified. The amount by which the privacy-leakage rate reduces for a hidden identifier as compared to a noise-free (visible) identifier at the encoder is also given. If the encoder incorrectly models the source as visible, it is shown that substantial secrecy leakage may occur and the reliability of the reconstructed key might decrease.