  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.
