Note: Descriptions are shown in the official language in which they were submitted.
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Doc. No. 12_20 ; ~ ~ ' ~ - ;
Biometric Security Encryption System
Field of the Invention
This invention relates generally to identification of individuals and more
particularly relates to a method of selecting a biorxetric template for
identification of
individuals.
Background of the Invention
Computer security is fast becoming an important issue. With the proliferation
of computers and computer networks into all aspects of business and daily life
-
financial, medical, education, government, and communications - the concern
over
secure file access is growing. A common method of providing security is using
l5 passwords. Password protection and/or combination type locks are employed
for
computer network security, automatic teller machines, telephone banking,
calling
cards, telephone answering services, houses, and safes. These systems
generally
require the knowledge of an entry code that has been selected by a user or has
been
preset.
Preset codes are often forgotten as users have no reliable method of
remembering them. Writing down the codes and storing them in close proximity
to
the access control device (i.e. The combination lock) results in a secure
access control
system with a very insecure code. Alternatively, the nuisance of trying
several code
variations renders the access control system more of a problem than a
solution.
Password systems are known to suffer from other disadvantages. Usually,
passwords
are specified by a user. Most users, being unsophisticated users of security
systems,
choose passwords which are relatively insecure. As such, many password systems
are
easily accessed through a simple trial and error process.
A security access system that provides substantially secure access and does
not
require a password or access code is a biometric identification system. A
biometric
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identification system accepts unique biometric information from a user and
identifies
the user by matching the information against information belonging to
registered users
of the system.
Biometric information is defined in the art as a unique, measurable
characteristic or
trait of a human being for automatically recognizing or verifying identity.
Such a
definition can be found, for example, in " Biometrics Explained"
by Gary Roethenbaugh, Industry Analyst of ICSA, Va. People in the art
distinguish
between physical biometrics such as eye (iris, and retina), face, fingerprint,
hand and
voice and behavioral biometrics such as signature and typing rhythm.
One such physical biometric identification system is a fingerprint recognition
system.
In a fingerprint input transducer or sensor, the finger under investigation is
usually pressed against a flat surface, such as a side of a glass plate; the
ridge and
valley pattern of the finger tip is sensed by a sensing means such as an
interrogating
light beam.
Various optical devices are known which employ prisms upon which a finger
whose
print is to be identified is placed. The prism has a first surface upon which
a finger is
2o placed, a second surface disposed at an acute angle to the first surface
through which the
fingerprint is viewed and a third illumination surface through which light is
directed into
the prism. In some cases, the illumination surface is at an acute angle to the
first surface,
as seen for example, in US Patents 5,187,482 and 5,187,748. In other cases,
the
illumination surface is parallel to the first surface, as seen for example, in
US Patents
5,109,427 and 5,233,404. Fingerprint identification devices of this nature are
generally
used to control the building-access or information-access of individuals to
buildings,
rooms, and devices such as computer terminals.
United States patent number 4,353,056 in the name of Tsikos issued October 5,
3o 1982, discloses an alternative kind of fingerprint sensor that uses a
capacitive sensing
approach. The described sensor has a two dimensional, row and column, array of
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capacitors, each comprising a pair of spaced electrodes, carried in a sensing
member and
covered by an insulating film. The sensors rely upon deformation to the
sensing member
caused by a finger being placed thereon so as to vary locally the spacing
between
capacitor electrodes, according to the ridge/trough pattern of the
fingerprint, and hence,
the capacitance of the capacitors. In one arrangement. the capacitors of each
column are
connected in series with the columns of capacitor s connected in parallel and
a voltage is
applied across the columns. In another arrangement, a voltage is applied to
each
individual capacitor in the array. Sensing in the respective two arrangements
is
accomplished by detecting the change of voltage distribution in the series
connected
capacitors or by measuring the voltage values of the individual capacitances
resulting
from local deformation. To achieve this, an individual connection is required
from the
detection circuit to each capacitor.
Before the advent of computers and imaging devices, research was conducted
into fingerprint characterisation and identification. Today, much of the
research focus in
biometrics has been directed toward improving the input transducer and the
quality of
the biometric input data. A second important issue to be addressed is the
identification
process itself and more particularly, the registration process.
A common method of registering users for a biometric identification system is
to
2p capture biometric input information, characterise it, and store it as a
template. The same
user then provides biometric input information to the system for
identification. This is
repeated several times and if identification is successful, the user and their
biometric
template are registered. Further, the system requires an experienced operator
to accept or
reject instances of biometric information intended as templates.
Another common method of registering users is used in signature verification
systems as
disclosed, for example, in "Reference Design Procedure for Signature
Verification" by
C. N. Liu in IBM Technical Bulletin, vol. 21, no. 1, June 1978, page 426-427.
Upon
registration an individual is required to sign n times for the verification
system. Each
3p signature is compared with the other n-1 signatures and a threshold value
is calculated.
The signature satisfying a predetermined threshold value is then selected as a
template.
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This method is considered necessary in the art because the signature is a
behavioral
biometric identifying an individual and chznges considerably under different
circumstances such as using different writing tools, writing on different
surfaces. The
signature is also affected by the physiological and psychological condition of
the signing
individual.
A further method of registering users for a biometric identification system is
to
capture a plurality of instances of biometric input informaticn from a same
user and to
characterise each instance. A composite biometric template is then constructed
in
1 o dependence upon the plurality of instances provided. Such a system is
complicated and
it requires an experienced operator to accept or reject instances of biometric
information
intended for template construction.
Object of the Invention
It is an object of this invention to provide a means of selecting a physical
biometric template or physical biometric information from which to derive a
template.
It is an object of the invention to provide a method of training users to more
effectively use biometric identification systems.
Summary of the Invention
In accordance with the invention there is provided a method of selecting a
physical biometric template for use in registering biometric information from
a source
comprising the steps of:
providing a plurality of different instances of same physical biometric
information
from the source to a processor;
using the processor, comparing the different instances of biometric
information with
other instances of the same physical biometric information from the different
3o instances, and determining a registration value corresponding to
similarities or
differences between each of the plurality of different instances and the other
instances,
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Doc. No. l2-20 -
selecting as the biometric template an instance from the plurality of
different instances
of the same biometric information for which the registration value is within
predetermined limits.
The advantages of a system in accordance with this invention are numerous.
For example, registration of authorized users requires little time and
expense. The
chance of deriving a biometric template from poor biometric information is
greatly
reduced.
Brief Description of the Drawings
An exemplary embodiment of the invention will now be described in conjunction
with
the attached drawings, in which:
Fig. 1 a is a representation of a fingerprint image captured by an optical
fingerprint
~ 5 imaging means;
Fig. 1 b is a representation of another instance of a fingerprint image
captured by an
optical fingerprint imaging means imaging the same fingertip as that of Fig. 1
a;
Fig. 1 c is a representation of another instance of a fingerprint image
captured by an
optical fingerprint imaging means imaging the same fingertip as that of Fig. 1
a;
2o Fig. 2 is a flow diagram of a method of selecting a biometric template
requiring 3
different biometric data sets in accordance with the invention;
Fig. 3 is a flow diagram of a further method of selecting a biometric template
requiring n biometric data sets;
Fig. 4 is a flow diagram of a method of training users of a biometric input
system
25 according to the invention;
Fig. 5 is a flow diagram of a method reducing false acceptance (incorrect
registration)
of users of a biometric identification system according to the invention;
Fig. 6 is a flow diagram of a method of identifying the source of biometric
input
information in a system employing the method shown in the flow diagram of Fig.
5;
3o and
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Fig. J is a chart showing results from registrations using each of the
fingerprint
images of Figs. 1 a, 1 b, and 1 c as templates and the others as biometric
input
information.
Detailed Description
The invention will be described with respect to finger print registration. The
method of this invention is useful in other biometric template selection
processes as
well.
to
Referring to Figs. 1 a, 1 b, and 1 c, a fingerprint is shown. A fingerprint is
substantially unique and is identifiable by a series of criteria. These
criteria include
core size, core type, location of minutia, ridge spacing, ridge type, etc.
Each feature
can be located and stored for later registration of unknown prints.
Unfortunately,
t 5 accurately mapping out all features and determining registration based on
partial
prints and skewed prints is very time consuming; and, it is beneficial to
minimize the
time required to register a print. Therefore, not all features are analyzed to
register
each print.
zo A comparison of the fingerprint of Fig. 1 a, Fig. 1 b, and Fig. 1 c will
show them
to have a same source; however, a comparison of the images directly is
difficult as
they are each different. Each time a person places a finger tip onto a
fingerprint
scanner, a slightly different image is captured. From one instance to another
a
fingerprint may be shifted, skewed, cover different parts of the finger tip or
be applied
25 with different pressure. Since each captured image is substantially unique,
it is likely
that some images form better templates for registration than others. A method
of
selecting those fingerprints that form better templates is herein disclosed.
Referring to Fig. 2 a flow chart of a method according to the present
invention
3o is shown. Three instances of biometric information in the form of finger
prints are
captured. As shown in the flow diagram, each instance is captured
individually.
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Doc. No. 12_20 ;
Preferably all instances are captured in such a way as to simulate normal use.
For
example, when using a fingerprint sensor for unlocking a door, a person steps
up to
the door and presses their finger tip against the sensor. The person then
steps away
from the door and approaches the door from a second different angle. In this
way, the
linaerprints imaged by the sensor will better reflect a variety of possible
fingerprints
from a same user during normal operation and each captured image is
independent,
excepting the relation to a known fingertip.
Preferably, an operator ensures that each image is a "good fingerprint" prior
to
storing the image for characterization. Operator skill is not required when
using the
1 o method of this invention, but may result in an improved template.
Each fingerprint is then characterized. Fingerprint characterization is well
known and can involve many aspects of fingerprint analysis. The analysis of
fingerprints is discussed in the following references which are hereby
incorporated by
reference:
Xiao Qinghan and Bian Zhaoqi,: An approach to Fingerprint Identification By
Using
the Attributes of Feature Lines of Fingerprint," IEEE Pattern Recognition, pp
663,
1986
C.B. Shelman, " Fingerprint Classification - Theory and Application," Proc. 76
2o Carnahan Conference on Electronic Crime Countermeasures, 1976.
Feri Pernus, Stanko Kovacic, and Ludvik Gyergyek, "Minutaie Based Fingerprint
Registration," IEEE Pattern Recognition, pp 1380, 1980.
J.A. Ratkovic, F.W. Blackwell, and H.H. Bailey, "Concepts for a Next
Generation
Automated Fingerprint System," Proc. 78 Carnahan Conference on Electronic
Crime
Countermeasures, 1978.
K. Millard, " An approach to the Automatic Retrieval of Latent Fingerprints,"
Proc.
75 Carnahan Conference on Electronic Crime Countermeasures, 1975.
Moayer and K.S. Fu, "A Syntactic Approach to Fingerprint Pattern Recognition,"
Memo Np. 73-18, Purdue University, School of Electrical Engineering, 1973.
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Doc. No. l2_2p ;
Wegstein, An Automated Fingerprint Identification System, NBS special
publication,
U.S. Department of Commerce/National Bureau of Standards, ISSN 0083-1883; no.
X00-89, 1982.
Woenssens, Arldre A., Fingerprint Techniques, Chilton Book Co., 1971.
Wegstein and J.F. Rafferty, The LY39 Latent Fingerprint Llatcher, NBS special
publication, U.S. Department of Commerce/National Bureau of StandaYds; no. ~00-
36, 1978.
Using the method of the present invention, a same characterization method is
1 o employed in characterizing each fingerprint. This allows for comparisons
between .
characterized images. Alternatively, a series of characterizations are
performed on
each fingerprint to determine a best fingerprint from which to select the
template and
a best characterization for the template. Use of multiple characterizations
increases the
overhead required to characterize a fingerprint during normal use. It will be
apparent
to those of skill in the art that when multiple characterizations are
employed, only
similarly characterized fingerprints are compared. The remainder of this
description
assumes the use of only one form of characterization.
Each characterized image is selected, one at a time, and all other
characterized images
are registered against the selected characterized image. The selected
characterized
2p image acts as a template and the remaining characterized images act as user
input
biometric information. This results in six registrations. For each
characterized image
(serving as a template) a score is achieved. The score is based on the
correlation
between the characterized image (as template) and the other characterized
images. The
six registrations produce six different scores,two for each characterized
image, which
are compared. Alternatively, the scores for each characterized image, as
template are
added or averaged. The characterized image with the most desirable scores) is
selected to be the template. The scores) is(are) then compared to a threshold
value to
determine suitability. When suitable, the image and the characterized image
are stored
and form the biometric information registration template. Alternatively, only
the
3p characterized image is stored. When the scores are not suitable, the
characterized
images are discarded and the method is followed again. Alternatively, only
some
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Doc. No. 12-20
characterized images are discarded and others are stored; the method is
reapplied
.capturing only as many new images as are necessary in order to select a
template.
In an alternative embodiment shown in Fig. 3, n instances of biometric
information in the form of fingerprints are captured. Preferably, the captured
images
_ are independent as described above. Each image is characterized to produce a
characterized image. At least some of the characterized images are selected.
Against
each of the characterized images selected, some other characterized images are
registered. Should all characterized images be selected and compared against
all other
1 o images, the number of resulting comparisons is (n) (n-1 ). For each
registration, a
resulting score is associated with the selected characterized image. The
scores
associated with each selected characterized image are compared and a
characterized
image with a most desirable set of scores is identified. The scores of the
identified
characterized image are verified against a threshold value to ensure that the
identified
characterized image is acceptable and the identified characterized image and
the
associated image are stored as a template. Alternatively, only the identified
characterized image is stored as a template.
Alternatively, n instances of biometric information in the form of
fingerprints
2o are captured as shown in Fig. 3 and m further instances of biometric
information in
the form of fingerprints are provided. Preferably, the further images are
selected to
ensure a selected biometric template is unlikely to result in false
registrations. The
selection of the m instances is based on false authorizations that have
occurred with
some templates. Alternatively, the selection of the m instances is based on
the
characterization of the n images. Alternatively, the selection of the m
instances is
based on a random selection. Against each of the characterized images from the
n
instances, some other characterized images are registered as are characterized
images
from the m instances. For each registration, a resulting score is associated
with the
selected characterized image. Scores indicative of similarities are desirable
for
registrations with characterized images from the n instances. Scores
indicative of
differences are desirable for characterized images from the m instances. The
scores
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associated with each selected characterized image are compared and a
characterized
image with a most desirable set of stores is identified. Desirability of a set
of scores is
dependent on a predetermined level of security and on an application in which
biometric identification is being used. The scores of the identified
characterized image
are verified against a threshold value to ensure that the identified
characterized image
is an acceptable template. Preferably, the template results in no
authorization of
instances from the m instances.
Preferably, the same characterized images are registered against each
template.
1 o Further preferably, the scores are added or averaged.
Alternatively, the characterized image is modified prior to storing same. The
modifications include removing features that failed to match similar features
in at
least some of the other characterized images. In this way, false features are
reduced
and improved registration results.
Most biometric identification systems work most effectively when users
provide similar biometric input information each time they access a system.
False
rejections often result from inexperienced users of a biometric input device
and more
2o specifically from poor presentation of biometric information.
Referring to Fig. 4, a further use of a method according to this invention is
automated
training of users of biometric identification systems. A user provides a
plurality of
biometric input samples to a system. The system selects a sample as a template
according to the present invention and reports on the resulting selected
template and
the resulting score(s). A first sample is discarded and replaced by a new
sample. This
is repeated for several trials until the template and the scores) are
substantially
similar between trials. Given that the score exceeds a predetermined
threshold, it is
likely that the user is providing biometric input information to the system
that is
useable for user identification.
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Doc. No. t 2-20
In using biometric information in the form of fingerprint images for user
identification, false registration is a great concern. Often, false
registration is a
function of the biometric information and not an "error" on the part of an
identification system. Two different users may share many common features in
their
biometric information, and therefore, each may register as the other. In
selecting
templates, it would be advantageous to reduce false registration as mach as
possible.
Referring to Fig. 5, a method of using a method according to the present
invention for
reducing false registration is presented. Templates are selected according to
a known
method of selecting same. A plurality of images are captured for each
individual
t 0 having a template. The images are each characterized and their
characterizations are
stored. Each image is registered against every template to identify potential
false
registrations. For large systems, such a task is very time consuming and would
be best
executed as a background task. When a possible false registration is
identified, a
further template is selected (from the images and characterized images) to
distinguish
t 5 between correct and false registration. The further template is stored
with the original
~mplate in a hierarchical fashion. The task executes until all images have
been
registered against all templates.
Referring to Fig. 6, a flow diagram of a method of identifying a user in
20 dependence upon biometric input information is shown for a system employing
a
method of reducing false registration as described with reference to Fig. 5. A
user
provides biometric information in the form of a fingerprint image. The image
is
characterized. The characterized image is compared against templates to locate
user
information. When a registration occurs (a template is sufficiently similar to
the
25 biometric information provided) the system verifies that false registration
is unlikely.
When false registration is unlikely, registration is complete. When it is
likely, the
biometric information provided is compared to templates corresponding to each
potential false registration associated with the registered template. When no
further
registration occurs, the registration process is complete.
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When a further registration occurs, the registration process selects at least
another template against which to verify the provided biometric information.
This at
least another template is stored associated with the templates against which
registration has occurred. Selecting and storing the further template is
described above
with reference to Fig. ~. The further template improves the probability of
distinguishing between each of the two potential false registrations
identified.
Referring to Fig. 7, correlation results are shown for the finger prints of
Fig.
1 a, Fig. 1 b, and Fig. 1 c. The results indicate that registering a
fingerprint on a second
1 o fingerprint is not commutative. As such, the number of registrations
required to select
a template can not be reduced by registering each pair only one time.
Alternatively, the method is employed with retinal scanned biometric
information. Further alternatively, the method is employed with palm prints.
Further
alternatively, the method is employed with non image biometric rata such as
voice
prints.
Numerous other embodiments may be envisaged without departing from the spirit
and
scope of the invention.
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