  Biometric matching involves storing and processing sensitive user
information. Maintaining the privacy of this data is thus a major challenge,
and homomorphic encryption offers a possible solution. We propose a
privacy-preserving biometrics-based authentication protocol based on fully
homomorphic encryption, where the biometric sample for a user is gathered by a
local device but matched against a biometric template by a remote server
operating solely on encrypted data. The design ensures that 1) the user's
sensitive biometric data remains private, and 2) the user and client device are
securely authenticated to the server. A proof-of-concept implementation
building on the TFHE library is also presented, which includes the underlying
basic operations needed to execute the biometric matching. Performance results
from the implementation show how complex it is to make FHE practical in this
context, but it appears that, with implementation optimisations and
improvements, the protocol could be used for real-world applications.
