D.C.
- I believe that the effectiveness of "liveness"
detection in a given fingerprint scanning device is mostly a
matter of probability. It involves associating the
relationship between the fingerprint captured and the object
(finger), such that the probability of the two being
discrete objects statistically approaches zero. I doubt you
would need to go through all of the mathematical gyrations
with Optel's new technical approach, since it in and of
itself eliminates the possibility for the two objects to be
discrete. Optel proposed approach detects and scans the
object when it comes into contact with the scanning surface.
It emits acoustic waves that may be varied within a specific
frequency range, then it receives the return, or waves
reflected back to the receiver within a specific frequency
range (based on the emitted frequency, object
characteristics and surface scattering dynamics). The
received waves are then analyzed and processed to
reconstruct the fingerprint image. Any acoustic waves
received that are inconsistent with those of live tissue are
discarded.
W.B. - True, but for purposes of
clarification, you should note the following:
Acoustic waves are mechanical waves, and their behavior
depends on mechanical properties of materials. If the
velocities of two kinds of acoustic waves: longitudinal and
shear are known, all so-called Lamé constants (that
describes mechanical properties of material) can be
calculated. The situation is much more complicated (but
better from the point of view of finger recognition), if we
have to do this with a finger lying on the sensor plate. A
person's finger has a very complicated structure: the outer,
or dead layer of the finger's skin is made from a very hard
material, called keratin. Keratin is elastic due to its
structure, but has mechanical properties very different from
the properties of water. Yet, it is connected to thicker
layer of material (live skin tissue) that has properties
similar to water. The finger's inner structure is very
complicated, containing muscles, blood vessels, bone, etc.
It should be noted that the optical and electrical features
of finger are not very special and can be copied with other
materials. (Note: I have discussed this with others, who
have conducted studies on this subject). In contrast, the
mechanical parameters are not easy to copy, if at all, and
the associated behaviors of this structure are probably
impossible to accurately reproduce.
Using our existing prototypes, we have determined that
material (and probably structure) differences are causing
strong difference (variance) in the amplitude of the
acoustic signal scattered from the skin lying on the solid
state surface, when compared to other artifacts. Furthermore,
it was also noted that there were significant differences in
the "character" of the signal (this can be shown
in FFT, among others). It is easy to assume that these two
points are true, because mechanical properties of skin are
very different from mechanical properties of artificial
finger. However, the situation is much more complicated,
since we have no theoretical description for a phenomena
that I am calling "contact scattering". Moreover,
we do not know which parameters are causing what; the
object's material or its structure. Indeed, we were very
surprised at the results of the initial testing with shear
waves used in the prototypes of the solid-state device.
From my point of view, we are only scratching the surface of
a large range of possibilities that might become available
through phenomena such as contact scattering. This will
become clearer and many questions answered as our research
continues. Even so, the knowledge we have acquired through
our research to date has enabled us to propose a unique and
powerful new technical approach to fingerprint scanning and
recognition that far exceeds the capabilities of existing
conventional technologies. The concepts and technologies for
this new device are proven. Now, it is just a matter of
design and implementation to develop a device in the optimal
configuration. I think, that it will certainly be possible
to create such device quicker, than to determine all the
answers and explanations from a theoretical perspective. And,
this explanation was limited to only those issues concerning
the "material and its structure" recognition.
D.C. - Optel's ability to determine
the "living" state of the object being scanned
effectively rules out a cost-effective approach for using a
gel appliqué, as it must not only match the fingerprint,
but 'live' tissue acoustic characteristics as well. This is
especially true when you consider that the latter is the
result of technology and developments that are proprietary
to Optel's new technical approach and, therefore, will be
virtually impossible to acquire without costly research or
other less ethical means (which should also be a costly
proposition). To augment the inherent 'live' tissue test in
analyzing the returns from acoustic emissions, Optel's new
approach also has the ability to check for pulse, which it
can match with volumetric changes in the blood vessels that
it scans within the subject's finger.
Finally, and this is something that has only briefly been
mentioned within the last week or so, Optel should also have
the ability to check for biometric changes that are
typically associated with an individual's stress level.
Therefore, in select mid- to high-security applications,
Optel's design might also provide an indicator of subject
duress by comparing selected biometric data captured during
the subject's initial enrollment and subsequent entries with
the current data. This can easily be used as a flag to
notify security of a potential problem.
W.B.: This is also correct. The
ensuing paragraphs provide a more detailed explanation of
our position:
Signal scattered from finger contains information coming not
only from the contact area of finger and sensor surface of
the solid-state device, but also from structures lying
deeper in the finger, which will be delayed. Moreover, it
also contains data about the changes in time, which is
exclusive to our application of ultrasound as a scanning
medium.
In our experiments we demonstrated that changes in time
caused by blood flow (pulse) could be used for detection of
living fingers, even in the primitive versions of our
software. At this point, this functionality is working well,
allowing the detection of artificial fingerprints on a thin
layer of gel applied to a real finger. Yet, even here, I am
sure that we have just scratched the surface of what might
prove to be a wide range of possibilities that can be
detected and applied here:
In earlier testing, we detected something that could only be
described as "global" changes in the signal and
were not able to detect fine changes. As our technology,
design and testing evolves, it will allow us to detect and
describe how blood is flowing through the vessels of the
finger. We also note that blood must flow in the form of
three-dimensional waves that have a shape, which is surely a
characteristic that has a high probability of being unique
to each person, much like retinal scans or large vein scans
of the hand. Furthermore, it appears to be a very realistic
to believe that we will also be able to be detect and
analyze emotional (behavioral) and/or other physiological
changes that impact the "character of blood flow"
of a given subject. Examples of these include, but are not
limited to, changes caused by stress/duress (behavioral) and
illness (physiological).
We also know that acoustic signals reflected from the finger
also contain information coming from the inside of the
finger, depending on the time it is received and the nature
of the received wave. However, since we still have a great
deal of research to do in this area, we can only speculate
on the possibilities offered by this particular capability.
For example, we believe it is possible to capture and
analyze information received from the finger's internal
structure and, assuming this is true, it should then be
possible to reconstruct images of that structure. However,
we have just begun research in this area, so we still have
many more questions than answers regarding its operation and
potential.
Yet, to truly replicate a person's finger in order to create
a viable 'fake', somebody must have definite answers to
these questions and more. Furthermore, the must have the
capability to construct the artificial finger replicating
many of the features in the subjects' fingers in a cost
effective manner. So, this process would need to be created
on a production scale, since a single reproduction of a
subject's finger would almost certainly be cost preclusive.
Fortunately, even current state of the art technology will
not even come close to considering such a construction, or
re-construction, as the case may be.
Some might propose that cloning technology might allow for
the replication of a real subject's finger, and that this
could be done on a scale that might make it cost-effective.
Yet, even a cloned copy of a real finger would contain
internal and external variations in structure that could be
detected to prevent fraud. Furthermore, for such an approach
to be feasible, it would be necessary to cause the blood
flow in the 'replicated' finger to be exactly as in the real
one. In truth, there are probably even more points that must
be considered in order to realize the possibility of finger
replicas, as we have described above, which only serves to
further compound the problem. Such a possibility does not
appear to be a realistic goal for the foreseeable future…
especially at the level of exactitude that would be required.
While we will concede that that our approach and resultant
capabilities may seem a bit "esoteric" now, it is
only because very few considered such a possibility as a
viable alternative for a biometrics application. As a result,
very few have conducted research in this or a related area.
Yet, biometrics are only one of the technical applications
for the results of our research. We have many possibilities
to consider in terms of technical applications from a
medical perspective, just as we have from a physical
perspective in applications such as non-destructive testing.
Given the findings of our research to date, such
applications appear to be within the realm of possibilities,
with great potential for new gains in efficiency and
cost-effectiveness. After all, we have just scratched the
surface in terms of the potential for discoveries in this
new area.
Additional comments: It is important to note that
even people with very poor fingerprints that cannot be
detected, resolved, and/or captured with any existing
conventional fingerprint scanner, are viable candidates for
using our proposed fingerprint scanning approach. These
users are capable of generating sufficient unique scattering
of sound waves to allow for the capture and reconstruction
of a resolvable fingerprint image. To date, we have
concentrated our discussions on fingerprint recognition
using a conventional imaging approach. However, future
discussions will focus on an innovative new imaging approach
based, in part, on the application of holographic technology.
Finally, it is also important to note that all of the
capabilities and features discussed in Optel's approach to
"liveness" detection, above, are inherent to
ultrasound. As such, they do not require the addition of any
new elements or components, other than that which is in the
actual device. Modifications, should they be necessary,
would be limited to software changes for additional signal
analyses. In certain cases, it might also be necessary to
improve the amplifiers and filters to enhance its ability to
receive weaker signals, such as those from internal
structures of the finger. In the solid-state version of the
device this should be very easy to do. We are also
considering the development of a more suitable device
configuration that will allow for "comfortable"
detection of all finger features. Such devices might no
longer be called "fingerprint" readers, but more
aptly called "finger" or "hand" readers.
