Privacy, Secrecy, and Storage with Multiple Noisy Measurements of Identifiers
This work addresses privacy and security in communication systems, but it is incremental as it extends a classic model with noisy measurements.
The paper tackles the problem of key agreement with noisy identifier measurements, deriving the key-leakage-storage region and applying it to binary symmetric channels to quantify improvements with multiple measurements and reduced privacy leakage compared to noise-free cases.
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.