Shattering the Glass Maze

Template protection plays a crucial role in protecting the privacy of biometric data, by providing irreversibility and unlinkability. The Glass Maze, as presented by Trugenberger at BIOSIG 2011, is a fingerprint key binding mechanism that is claimed to provide template protection. With the correct fingerprint, the key that is entangled with the fingerprint data can be retrieved. The template protection of the Glass Maze is based on the convergence properties of a Hopfield model, a neural network. We however show how to revert the Glass Maze to recover the key, without requiring a correct fingerprint. This completely breaks the irreversibility property, and hence also unlinkability.