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.
