Reactivating Fingerprints II
It was also possible to reactivate latent fingerprints by carefully placing a thin-walled water-filled plastic bag onto the sensors surface. The advantage of this technique is that the water spreads more evenly across the sensors surface. When the latent fingerprint was a good quality one few attempts would normally suffice to gain us access to the system. Even when the security mode was set to its maximum (extended mode) we were able to undertake these simple latent image activations at the ID Mouse. The probable reason for this phenomenon being that the capacitators of the capacitive sensor are sensitive to humidity. Damp air that, for instance, condenses on the sensors surface where there are residues of fat causes the relative dielectric constant on the sensors surface to change thus leading to a change in capacitance which the device interprets as a release signal inducing it to undertake a measurement. The ID Mouse can be outfoxed even more easily by dusting the fatty residue of the fingerprint on the sensor with commercially available graphite powder (Ravenol), then stretching an adhesive film over the sensors surface and gently applying pressure on it. Whereas we were only intermittently successful at overcoming the biometrics barrier when using the breathing or the water bag method our success rate with the adhesive film technique when the latent fingerprints were of good quality was almost one hundred percent. According to Siemens, especially designed algorithms of the security software belonging to the package check whether the currently scanned fingerprint in terms of its position and angle coincides within certain predetermined tolerances with the last registered version of the print. This is supposed to prevent the system from being taken in by all attempts based on latent image reactivation or replay.
According to a statement from Munich, the company could not conceive of a reason why their procedure should have failed when we tested it. In future, the statement went on, the company would focus even more on the problem of latent image reactivation.