  Cancelable biometric schemes aim at generating secure biometric templates by
combining user specific tokens, such as password, stored secret or salt, along
with biometric data. This type of transformation is constructed as a
composition of a biometric transformation with a feature extraction algorithm.
The security requirements of cancelable biometric schemes concern the
irreversibility, unlinkability and revocability of templates, without losing in
accuracy of comparison. While several schemes were recently attacked regarding
these requirements, full reversibility of such a composition in order to
produce colliding biometric characteristics, and specifically presentation
attacks, were never demonstrated to the best of our knowledge. In this paper,
we formalize these attacks for a traditional cancelable scheme with the help of
integer linear programming (ILP) and quadratically constrained quadratic
programming (QCQP). Solving these optimization problems allows an adversary to
slightly alter its fingerprint image in order to impersonate any individual.
Moreover, in an even more severe scenario, it is possible to simultaneously
impersonate several individuals.
