U.S. patent application number 14/305400 was filed with the patent office on 2014-10-02 for method and apparatus for secure measurement certification.
The applicant listed for this patent is Certified Measurement, LLC. Invention is credited to James A. Jorasch, Bruce Schneier, Jay S. Walker.
Application Number | 20140298044 14/305400 |
Document ID | / |
Family ID | 41415848 |
Filed Date | 2014-10-02 |
United States Patent
Application |
20140298044 |
Kind Code |
A1 |
Walker; Jay S. ; et
al. |
October 2, 2014 |
METHOD AND APPARATUS FOR SECURE MEASUREMENT CERTIFICATION
Abstract
The invention relates to methods and apparatuses for acquiring a
physical measurement, and for creating a cryptographic
certification of that measurement, such that its value and time can
be verified by a party that was not necessarily present at the
measurement. The certified measurement may also include
corroborative information for associating the actual physical
measurement process with the certified measurement. Such
corroborative information may reflect the internal or external
state of the measurement certification device, as well as witness
identifiers of any persons that may have been present at the
measurement acquisition and certification. The certification may
include a signal receiver to receive timing signals from a
satellite or other external source. The external timing signals may
be used to generate the time included in the certified measurement,
or could be used to determine the location of the measurement
certification device for inclusion in the certified
measurement.
Inventors: |
Walker; Jay S.; (Ridgefield,
CT) ; Schneier; Bruce; (Minneapolis, MN) ;
Jorasch; James A.; (New York, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Certified Measurement, LLC |
Stamford |
CT |
US |
|
|
Family ID: |
41415848 |
Appl. No.: |
14/305400 |
Filed: |
June 16, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13748945 |
Jan 24, 2013 |
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14305400 |
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12491114 |
Jun 24, 2009 |
8549310 |
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13748945 |
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11255240 |
Oct 20, 2005 |
8092224 |
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12491114 |
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10835422 |
Apr 29, 2004 |
7553234 |
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11255240 |
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09165089 |
Oct 1, 1998 |
6751730 |
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10835422 |
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08628920 |
Apr 8, 1996 |
5828751 |
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09165089 |
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Current U.S.
Class: |
713/194 |
Current CPC
Class: |
G06F 2221/2101 20130101;
H04L 2209/805 20130101; G06F 21/725 20130101; H04L 9/3263 20130101;
H04L 9/3297 20130101; G06F 21/86 20130101; H04L 2209/30 20130101;
H04L 9/3218 20130101; H04L 2209/38 20130101; H04L 63/0861
20130101 |
Class at
Publication: |
713/194 |
International
Class: |
G06F 21/86 20060101
G06F021/86 |
Claims
1. A method comprising: receiving a certifiable measurement
generated by a first cryptographic operation performed on at least
a portion of an augmented measurement, wherein the augmented
measurement is based at least in part on a physical measurement and
a time, and wherein the certifiable measurement is generated in a
tamper-resistant environment; performing, by a computing device
comprising a computer processor, a second cryptographic operation
on at least a portion of the received certifiable measurement to
generate at least one of the physical measurement and the time; and
storing at least one of the physical measurement and the time.
2. The method of claim 1, wherein at least a portion of the second
cryptographic operation comprises decryption with a decryption
key.
3. The method of claim 2, wherein the decryption key belongs to an
asymmetric cryptographic protocol.
4. The method of claim 2, wherein the decryption key belongs to a
symmetric cryptographic protocol.
5. The method of claim 1, wherein the time is representative of an
external timing signal.
6. The method of claim 1, wherein the accuracy of the time is
maintained using an external timing signal.
7. The method of claim 1, wherein receiving a certifiable
measurement comprises receiving a certifiable measurement according
to a predetermined schedule.
8. The method of claim 1, further comprising: transmitting a
request for a certifiable measurement, wherein receiving a
certifiable measurement comprises receiving a certifiable
measurement in response to the request.
9. The method of claim 8, wherein transmitting a request for a
certifiable measurement comprises transmitting a request for a
certifiable measurement according to a predetermined schedule.
10. The method of claim 8, wherein the request is encrypted using
an encryption key.
11. The method of claim 10, wherein the encryption key belongs to
an asymmetric cryptographic protocol.
12. The method of claim 10, wherein the encryption key belongs to a
symmetric cryptographic protocol.
13. The method of claim 1, wherein the certifiable measurement
further includes a corroborative datum indicative of an operational
condition.
14. The method of claim 1, wherein the time is based at least in
part on a signal from a global positioning system (GPS).
15. The method of claim 1, wherein the physical measurement
comprises GPS location information.
16. A method comprising: receiving a certifiable measurement
generated by a first cryptographic operation performed on at least
a portion of an augmented measurement, wherein the augmented
measurement is based at least in part on a first physical
measurement, a second physical measurement and a time, and wherein
the certifiable measurement is generated in a tamper-resistant
environment; performing, by a computing device comprising a
computer processor, a second cryptographic operation on at least a
portion of the received certifiable measurement to determine at
least one of the first physical measurement, the second physical
measurement and the time; and storing at least one of the first
physical measurement, the second physical measurement and the
time.
17. The method of claim 16, wherein at least a portion of the
second cryptographic operation comprises decryption with a
decryption key.
18. The method of claim 17, wherein the decryption key belongs to
an asymmetric cryptographic protocol.
19. The method of claim 17, wherein the decryption key belongs to a
symmetric cryptographic protocol.
20. The method of claim 16, wherein the time is representative of
an external timing signal.
21. The method of claim 16, wherein the accuracy of the time is
maintained using an external timing signal.
22. The method of claim 16, wherein receiving a certifiable
measurement comprises receiving a certifiable measurement according
to a predetermined schedule.
23. The method of claim 16, further comprising: transmitting a
request for a certifiable measurement, wherein receiving a
certifiable measurement comprises receiving a certifiable
measurement in response to the request.
24. The method of claim 23, wherein transmitting a request for a
certifiable measurement comprises transmitting a request for a
certifiable measurement according to a predetermined schedule.
25. The method of claim 23, wherein the request is encrypted using
an encryption key.
26. The method of claim 25, wherein the encryption key belongs to
an asymmetric cryptographic protocol.
27. The method of claim 25, wherein the encryption key belongs to a
symmetric cryptographic protocol.
28. The method of claim 16, wherein the certifiable measurement
further includes a corroborative datum indicative of an operational
condition.
29. The method of claim 16, wherein the time is based at least in
part on a signal from a global positioning system (GPS).
30. The method of claim 16, wherein the physical measurement
comprises GPS location information.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/748,945 filed Jan. 24, 2013 and entitled
METHOD AND APPARATUS FOR SECURE MEASUREMENT CERTIFICATION; which is
a continuation of U.S. patent application Ser. No. 12/491,114 filed
Jun. 24, 2009 and entitled METHOD AND APPARATUS FOR SECURE
MEASUREMENT CERTIFICATION; which is a continuation of U.S. patent
application Ser. No. 11/255,240 filed Oct. 20, 2005 and issued as
U.S. Pat. No. 8,092,224 on Jan. 10, 2012 and entitled SYSTEMS AND
METHODS FOR IMPROVED HEALTH CARE COMPLIANCE; which is a
continuation-in-part of U.S. patent application Ser. No. 10/835,422
filed Apr. 29, 2004 and issued as U.S. Pat. No. 7,553,234 and
entitled METHOD AND APPARATUS FOR OUTPUTTING A RESULT OF A GAME VIA
A CONTAINER; which is a continuation-in-part of U.S. patent
application Ser. No. 09/165,089 filed Oct. 1, 1998 and issued as
U.S. Pat. No. 6,751,730 on Jun. 15, 2004 and entitled METHOD AND
APPARATUS FOR DOCUMENTING CAP REMOVAL DATA; which is a
continuation-in part of U.S. patent application Ser. No. 08/628,920
filed Apr. 8, 1996 and issued as U.S. Pat. No. 5,828,751 on Oct.
27, 1998 and entitled METHOD AND APPARATUS FOR SECURE MEASUREMENT
CERTIFICATION.
[0002] Each of the above-referenced applications are incorporated
by reference herein in their entirety
BACKGROUND OF THE INVENTION
[0003] 1. Field Of the Invention
[0004] The present invention relates generally to methods and
apparatuses for acquiring and certifying physical measurements.
More particularly, the invention relates to acquiring and
cryptographically certifying a measurement representative of a
physical parameter, such that the measurement can be verified at a
later time.
[0005] 2. Background
[0006] The use of sensors to acquire physical measurements is a
pervasive and ever-expanding aspect of the electronic age. The
widespread availability of low-cost, highly accurate sensor
technology enables detailed measurements of physical parameters of
concern to a wide variety of commercial and military applications.
For example, the National Weather Service has developed the
Automated Surface Observing System (ASOS) which is a cluster of
sensor instruments that produce weather data. Each ASOS system is
made up of eight sensors that stand in a row about 50 feet long,
typically in an open field. The sensors, linked to an on-site
computer, measure rainfall, wind speed and direction, temperature
and dew point, air pressure, precipitation, visibility (fog and
haze), cloud height, and freezing rain. Another example is
Conductus Technologies Extremely Low Frequency Antenna, which is a
superconductor-based magnetic field sensor capable of measuring
extremely small magnetic signals from distant sources. The system
is designed for applications in mineral resource detection,
experimental studies of seismic activities, and submarine
communications. Yet another example is the Urban Gunshot Location
System, which uses sound sensors to pinpoint the location of
gunshots in a city. The sensors are mounted twenty to thirty feet
above the ground, attached to poles or buildings. Data from the
sensors are transmitted to a central computer which triangulates
the location of the sound source to within 25 feet. The central
computer then provides the location information to nearby police
officers who can investigate the scene.
[0007] As shown by these applications, physical measurements are
being acquired and used to guide activities having significant
economic or safety implications, e.g., predicting the weather,
prospecting/developing mineral resources, predicting earthquakes,
securing military communications, or monitoring criminal activity.
In these and many other instances where a physical measurement is
to be communicated to a temporally or spatially distant recipient,
the recipient would like to be assured of when the measurement was
taken, as well as one or more of: what was measured, where the
measurement was made, and who was present during the
measurement.
[0008] For example, one application involves remote monitoring of
pollution levels at a factory for round-the-clock clean air
compliance verification. There, the certified measurement would
include the pollution measurement and its time of acquisition.
Another application might be the logging of access requests to a
secure location. There, the certified measurement would include an
individual's biometric identifier and his time of entry onto the
premises. Yet another application might be a device to ensure house
arrest. There, the certified measurement might include an
individual's biometric identifier and his location. An example of
an application requiring all four elements (when, what, where, and
who) is the U.S. Army's Intelligence and Electronic Warfare Common
Sensor System, in which land combat elements are sent into the
field with intelligence-gathering sensors and subsystems. These
sensors will provide tactical commanders with tools to
electronically map the entire battlefield in order to identify,
locate, and determine the intentions of enemy forces. In this case,
it is crucial that the certified measurement accurately represent
when the battlefield data were acquired, what was actually
measured, where the measurement was taken, and who took the
measurement, i.e., that the measurement was taken by a friendly
soldier rather than an enemy who had captured or otherwise spoofed
the measurement process. In general, the cryptographic
certification may require elements of authenticity (measurement
origin), integrity (non-modification subsequent to acquisition),
and corroboration (assurance of the measurement process).
[0009] There is known a technique for using a cryptographic
protocol to verify inaccessible foreign countries compliance with
nuclear test ban treaties. Simmons (1981) discloses the insertion
of a seismic signal sensor, along with a public key cryptographic
system, into a borehole for timestamping and encrypting
measurements of seismic vibrations indicative of nuclear weapons
testing. This system was designed to operate under two important
constraints: 1) that the measurements be fully accessible to the
Russian hosts, to ensure them that no unauthorized measurements
were being taken, and 2) that the measurements be transmitted to
the US in spite of lack of local access to the monitoring
equipment. The first constraint compels using public key
cryptography and giving the Russians the public key so they could
decrypt measurements encrypted with the corresponding private key.
Thus, the Russians could monitor the transmitted measurements but
not impersonate them. The second constraint requires transmitting
the measurements rather than storing them locally for later
retrieval. These requirements are unnecessarily limiting for
certain commercial applications of physical event monitoring. For
example, in low-cost applications, or where the receiver has
limited computational capabilities, it may be impractical to use
public key cryptography because it is too computationally
intensive. Instead, a simple hash (if integrity alone is required)
or symmetric key encryption (if authenticity alone is required), or
a combination thereof, might be appropriate. Neither of these
techniques is possible with the Simmons system because of the
possibility of fraud. Still other applications might require only
local acquisition or storage of the certified measurement rather
than transmission--which would result in significant cost and or
device complexity reductions upon elimination of the transmitter
and receiver. The Simmons system does not allow this possibility
because of the lack of US access to Russian soil and the need to
allow Russian monitoring as a precondition of measurement
acquisition. Finally, the Simmons system does not describe
techniques for assuring where the sensor was at the time of
measurement (suppose the sensor and its surrounding soil were
surreptitiously excavated between measurement transmissions and
moved away from the nuclear test site). Furthermore, there is no
provision for certifying who was present during measurement (a
presumably unmanned site) or to otherwise independently corroborate
the measurement to a remote recipient.
[0010] There are also known various devices for cryptographically
certifying the authenticity and integrity of electronic documents.
Examples of such devices may be seen in several U.S. Pat. Nos.
(5,189,700; 5,157,726; 5,136,647; 5,136,646; 5,022,080; 5,001,752;
and 4,786,940) disclosing devices that input a digital data stream,
crytographically certify the digital data, and output a digital
data stream. In addition, certain of these devices optionally add
time from a secure internal clock to the digital data stream.
[0011] Many of the aforementioned devices are directed at
applications whose primary goal is digital data certification,
rather than physical measurement certification. The devices can
assure the authenticity and/or integrity of digital data presented
to the device only as of the time of presentation of the data to
the device. However, they can not assure: 1) when the digital data
were originally acquired prior to presentation to the device, 2)
what the digital data actually represent, 3) where the data were
acquired prior to presentation to the device, or 4) who was present
at the time of measurement. For example, such devices would be
unable to certify: 1) that a digital signal representative of a
physical measurement was not acquired at an earlier time and
subsequently provided to the measurement certification device, 2)
that the purported physical measurement really is a physical
measurement (rather than a man-made signal), 3) that the physical
measurement came from where it was supposed to, rather than from an
alternate location, and 4) who made or witnessed the physical
measurement.
[0012] In a variation of digital data certification, cryptographic
techniques have been used to certify an image recorded by a digital
camera. In one known example of this technology, Aquila
Technologies (1996) discloses a digital image authentication system
that is analogous to, and shares the same drawbacks of, the
aforementioned digital data certification technologies--a lack of
assurance as to the physical measurement itself. At best, a camera
can only be said to certify an image rather than a physical
measurement. Even if an image is taken of a sensor purportedly
displaying the result of a physical measurement, there is no
guarantee of the physical measurement itself. For example, a
timestamped photograph of a thermometer reading is meaningless
because one is not assured of when the reading was taken (suppose
the camera takes a picture of a picture of an earlier reading),
what is being read (maybe the thermometer has just come out of an
ice bath), where the measurement was taken, or who witnessed the
measurement.
[0013] Thus, there exists a need for a device and method for
acquiring and certifying a physical measurement, using a wide
variety of cryptographic protocols, such that the value and time of
measurement can be verified by a party that was not necessarily
present at the time the measurement was taken. There further exists
a need for a device and method which assures where the measurement
was acquired. Finally, the there exists a need for a device and
method which can accommodate independent corroborative evidence of
the measurement or certification event.
SUMMARY OF THE INVENTION
[0014] An object of the present invention is to provide an
apparatus and method for acquiring and certifying a physical
measurement, using a wide variety of cryptographic protocols, in a
manner that the physical measurement and its time of acquisition
can be verified by a later recipient of the certified measurement.
Another object of the invention is to provide an apparatus and
method for certifying where a physical measurement was acquired.
Yet another object of the invention to provide an apparatus and
method for reliably associating the actual physical measurement
with the certified measurement. As will be appreciated by those
skilled in the art, terms such as certified measurement, certified
message, certification, and other equivalents may all be used to
denote the output of the measurement certification device.
[0015] In connection with the foregoing, in one embodiment of the
invention, a measurement certification device encloses a sensor for
providing a measurement representative of a physical parameter, a
battery-powered clock, a cryptographic processor, and a memory
within a tamper-resistant environment. The cryptographic processor
performs a cryptographic operation on the physical measurement and
a representation of time to produce a cryptographically assured,
timestamped, certified measurement. As used herein, the term otimeo
shall be understood to include time, date, day-of-week and any
other chronographic measure. In many cases, such measures are
effectively synonymous; for example, many computer clocks record
time as the number of seconds elapsed since Jan. 1, 1900, which is
easily converted to date and day-of-week formats.
[0016] The physical parameter could be any physical quantity
measurable by a sensor and representable in digital form, including
location data, biometric data, temperature, humidity, light levels,
noise levels, precipitation, pressure, momentum, odor, air
pollution, car exhaust, water purity, weight, orientation, acidity,
proximity, opacity, radioactivity, viscosity, chemical content, and
any other physical parameter whose value and time of measurement is
to be certified to a recipient for later verification.
[0017] The degree of cryptographic processing depends on the degree
of security that is desired. For example, where the primary concern
is integrity, a simple one-way algorithm, e.g. a hash, message
authenticity code (MAC), or cyclic redundancy check (CRC), might be
adequate. Where the measurement certification device is used to
certify a sequence of measurements on a frequent basis, a chain of
hashes--where each certified measurement also includes
representations of one or more previous measurements--provides an
additional degree of measurement integrity. In other cases, the
measurement certification device might sign the time with a
device-specific private key, to provide authenticity in addition to
integrity. Even greater assurance can be provided by adding unique
device IDs, challenge-response protocols, digital certificates,
combinations of symmetric and asymmetric (public key) encryption,
and many other cryptographic techniques, in patterns appropriate to
the particular application at hand.
[0018] In another embodiment of the invention, the measurement
certification device need not generate its own time internally.
Rather, the measurement certification device may include a receiver
to obtain time from the timing signals provided by one or more
Global Positioning System (GPS) satellites, or from radio signals
from the US Naval Observatory atomic clock or any other reliable
external source. Externally originating time is especially
advantageous for deterring hacking of an internal clock. The
receiver could either replace or supplement the clock. In addition,
the clock could be used to double-check the received time (or
vice-versa) by comparing the externally originating time against
the internal clock time. The received time would be deemed accurate
if the two times agreed to within the cumulative inaccuracies of
the received signal (external time source inaccuracy plus any
uncorrected transmission delay) and the internal clock. Finally,
the cryptoprocessor could be programmed to receive the signal
encrypted in the time transmitters private key, or in the receivers
public key, as an extra measure of assurance that an impostor has
not substituted an incorrect time for that of the broadcast
source.
[0019] Certain of the external timing signals (e.g., GPS) may also
be used to determine location information, which can be
incorporated into the certified measurement as the primary physical
parameter. In such a case, the external signal receiver itself
would serve as the physical measurement sensor. Alternatively, the
device could include a physical measurement sensor distinct from
the external signal receiver. In that case, the sensor would
provide the physical measurement, and the external signal receiver
would provide either time and/or location information for inclusion
with the certified physical measurement. Location certification
finds application in devices to limit vehicle operation to a
prescribed area, verify routes traveled, enforce house arrest, and
numerous other monitoring and signaling applications.
[0020] The certified measurement may be outputted in a variety of
formats, for example, as a physical stamp or an electromagnetic
signal. In the former case, the device could include handheld
printers, facsimile machines, computer printers, copiers, or any
other document production device. In the latter case, the signal
could be: 1) recorded to magnetic, optical, or semiconductor media,
2) sent to a display for viewing. Finally, instead of a local
output device, the certified measurement could be transmitted (over
wireless or physical networks) to a remote site for printing,
recording or display thereat.
[0021] Furthermore, the certified measurement may be outputted at a
variety of frequencies, for example: 1) at predetermined times, 2)
upon request of either the user or the recipient, 3) upon
presentation of a request encrypted in a public key corresponding
to the private key of the measurement certification device, 4) upon
production of data by the output device, or 5) under control of a
broadcast signal. Requests for measurement certification would be
received by an input device which generates a certified measurement
request to direct the cryptographic processor to form the certified
measurement. The input device need not be a separate element, but
could comprise the sensor, the external signal receiver, or any
other device capable of detecting a triggering event to order the
certified measurement request.
[0022] As one specific example of the many possible output formats
and frequencies, a transmitter could be included in the measurement
certification device for transmitting a location measurement to a
remote receiver on a periodic basis. Conversely, if the measurement
is transmitted in response to an abnormal event detected by a
sensor, the certified measurement could serve as an automated
distress signal. For certain applications, the measurement
certification device could even be connected to an automatic
disconnect or dead mans switch to automatically disable dangerous
equipment until assistance arrives.
[0023] In general, a recipient of the certified measurement can
determine its authenticity and/or integrity by performing
cryptographic operations on the cleartext and/or ciphertext parts
of the certified measurement. For example, in the case of a hashed
measurement, the recipient can verify the measurement by
recomputing the hash and comparing it with the received hash (the
ciphertext part of the certified measurement). The hash could even
be a keyed operation to provide greater security. Or, if the
measurement was encrypted with the device private key, the
recipient can use the corresponding device public key to decrypt
and verify the measurement. The public key could either be obtained
from a public database or distributed using digital certificates
within the certified measurement. Alternatively, instead of
public/private key pairs, the measurement certification device
could use a symmetric key--either alone or in combination with
public key cryptography.
[0024] The measurement may include additional features to increase
confidence therein. For example, the measurement could include a
unique device ID to identify itself to a measurement recipient.
Furthermore, the measurement certification device could prevent
re-use of a previous measurement by using a challenge-response
protocol in which the requestor transmits a random number to the
device for inclusion in the measurement. Alternatively, the device
could include a random number generator for local generation of the
random number. Those skilled in the art will appreciate that the
challenge can use any datum whose value is unpredictable by the
recipient; random numbers happen to be a particularly convenient
choice.
[0025] Finally, the device may include a signal generator for
providing a corroborative datum, indicative of an operational
condition of the device, to be included in the certified
measurement. The corroborative datum could be any quantity that
independently attests to the acquisition of the physical
measurement. For example, the device could include an internal
state detector providing a normal operation signal as long as the
devices security measures were intact and functional. Conversely,
an external state detector could provide a normal operation signal
indicating that the device was being operated within a prescribed
range of environmental conditions. Alternatively, the external
state detector could be a secondary sensor providing a measurement
corroborative of the primary sensor measurement being certified
(e.g., a temperature detector in addition to a smoke detector for a
certified fire alarm application). Still other possibilities
include human witnessing of the physical measurement, either
through keypads or memory readers for witnesses to input their
witness identifiers. Alternatively, biometric measures could be
used for positive witness identification.
[0026] The features and advantages of the present invention will be
more readily understood and apparent from the following detailed
description of the invention, which should be read in conjunction
with the accompanying drawings, and from the claims which are
appended at the end of the detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 illustrates the basic components of a device for
secure certification of a physical measurement.
[0028] FIGS. 2A,B illustrate bottom and end views, respectively, of
a device for printing the certified measurement on paper
documents.
DETAILED DESCRIPTION OF THE INVENTION
[0029] Devices and methods are disclosed for acquiring and
certifying a physical measurement which may be verified by a party
that was not necessarily present during the measurement. For
example, the measurement could be used for remote monitoring,
access control, or event detection.
[0030] In this disclosure, certain ancillary elements used in
conjunction with the measurement certification device are well
understood to those skilled in the art and are not shown in order
not to obscure the present invention. For example, the design and
construction of clocks, computer memories, and software or hardware
cryptographic algorithms, are well known to those skilled in the
art and will not be described in detail herein.
Measurement Certification Device and Operation
[0031] Referring now to FIG. 1, there is shown one embodiment of a
measurement certification device including a sensor 8, a
cryptoprocessor 10, a clock 20, random access memory (RAM) 30,
nonvolatile memory 40 and output device 100. The cryptoprocessor 10
can be a general purpose processor (e.g., an Intel CPU) receiving
instructions from RAM 30 or memory 40, or it can be a special
purpose processor optimized for performing cryptographic operations
(e.g., a National Semiconductor iPower SPU). That is, the
cryptoprocessor may comprise any hardware or software engine
capable of performing cryptographic operations on a given quantity.
As described in greater detail below, such operations may include
both keyless and keyed operations, as well as various combinations
thereof. The cryptoprocessor 10 and clock 20 are powered by
external power source 50, with standby battery 60 to ensure
operability during replacement or absence of external power source
50. Thus, external power source 50 could be a user-replaceable
battery or an AC power source. Alternatively, the device could be
powered by internal battery 60 alone (in which case the device
stops functioning at battery death) or external power source 50
alone (necessitating resetting the clock from a trusted external
time source--e.g., the GPS satellite signals discussed later--upon
powerup).
[0032] The cryptoprocessor 10, clock 20, RAM 30, memory 40 and the
control signals for output device 100 are contained within secure
perimeter 70, making these components resistant to tampering. The
sensor 8 is also contained within the secure perimeter 70, to the
maximum extent possible consistent with being able to detect the
physical parameter being measured--which will vary with the
application at hand. At a minimum, this would require that
electronic communications between the sensor and other components
of the measurement certification device be within the secure
perimeter, to prevent fraudulent insertion of a signal masquerading
as the measured quantity. Secure perimeter 70 may include physical,
electronic, or a combination of physical and electronic features to
resist tampering. For example, physical features could include
encapsulation, electronic features could include a silicon
firewall, and combination features could include self-zeroizing, or
otherwise volatile, RAM 30 or memory 40 which electrically modifies
its contents upon detection of tampering. Such tampering might
include physically stressing the device, attempting to change the
clock rate by replacing external power source 50 with a battery
outside allowable current or voltage ranges, or attempting to
change the clock rate by replacing external power source 50 with an
AC power source operating outside an allowable frequency range.
Alternatively, secure perimeter 70 could be merely tamper-evident.
In that case, the process of measurement verification should
include checking the measurement certification device for evidence
of tampering. As will be appreciated by those skilled in the art, a
great variety of tamper-resistant/tamper-evident techniques can be
deployed, and will not be enumerated in detail herein. Therefore,
as a matter of convenience, terms such as otamper resistanto or
osecureo shall be understood to refer to any of the aforementioned
or other security measures throughout this discussion.
[0033] In the simplest embodiment of the invention, the measurement
certification device takes a physical measurement using sensor 8,
of any physical parameter or event--e.g., location information,
temperature, humidity, light levels, noise levels, precipitation,
pressure, momentum, odor, air pollution, car exhaust, water purity,
weight, orientation, acidity, proximity, opacity, radioactivity,
viscosity, chemical content--whose value and/or time of measurement
is to be provided to a recipient for later verification. This
measurement is added to a time from clock 20, creating an augmented
measurement comprising the cleartext time plus the physical
measurement. Cryptoprocessor 10 then creates a certified
measurement comprising the (cleartext) augmented measurement and a
(ciphertext) one-way function representative of at least a portion
of the augmented measurement, and outputs the certified measurement
at output device 100. As used herein, a one-way function is one
that outputs a unique representation of an input such that a given
output is likely only to have come from its corresponding input,
and such that the input can not be readily deduced from the output.
Thus, the term one-way function includes hashes, message
authenticity codes (MACs--keyed one-way functions), cyclic
redundancy checks (CRCs), and other techniques well known to those
skilled in the art. See, for example, Bruce Schneier, Applied
Cryptography, Wiley, 1996. As a matter of convenience, the term
hash will be understood to represent any of the aforementioned or
other one-way functions throughout this discussion. Typically, the
hash would be performed by cryptoprocessor 10 using a hardwired
hashing algorithm or one stored in RAM 30 or memory 40. The hash
may either be a keyed or keyless operation.
[0034] Furthermore, a unique device identification number, stored
in RAM 30 or memory 40, can be added to the hash to provide
assurance of authenticity. A recipient wishing to verify the time
would read the cleartext part of the certified measurement (e.g.,
the physical measurement, time, and device ID) and the ciphertext
part of the measurement (e.g., a hash of a portion of the cleartext
part), then perform an identical hashing algorithm on the
appropriate portion of cleartext part to recompute the hash. If the
received and recomputed hashes agree, the recipient is assured that
the measurement came from the measurement certification device and
had not been altered subsequent to certification.
[0035] Where the measurement certification device is used to
certify a sequence of measurements, a chain of hashes--where each
certified measurement also includes representations of one or more
previous certified measurements--provides an additional degree of
assurance. For example, RAM 30 or memory 40 could store a hash of
the last three certified measurements to be incorporated into the
current certified measurement as shown in the following example.
Imagine that certification is performed once monthly, with the
latest four dates being: 11/19, 12/15, 1/13, and 2/24. The hash for
the last measurement could be Hash.sub.--2/24=Hash(oMeasurement of
2/24o)+Hash.sub.--11/19+Hash.sub.--12/15+Hash.sub.--1/13, with the
hashes for the November, December and January dates relating to
their respective previous three months in a similar fashion. The
chained hashes discourage fraudulent modification of a measurement
as described below.
[0036] Suppose a forger discovers the device private key and uses
it to change both the cleartext and hashed parts of the 11/19
certified measurement. A suspicious party could challenge the 11/19
certified measurement by using it to recompute the subsequent three
certified measurements, and comparing them with their known values.
If the known and recomputed certified measurements disagree, the
11/19 measurement is demonstrated to have been altered. When
tampering is generally suspected but no specific certified
measurement is in question, an altered certified measurement can be
determined by recomputing the most recent certified measurement and
continuing backwards until three successive incorrect certified
measurements are found. Of course, the forger could theoretically
change all the certified measurements in the chained hash, but this
would require more effort than changing just the desired one, and
would increase the chances of detection.
[0037] Still greater assurance of integrity and authenticity can be
obtained by encrypting part or all of the measurement in
cryptoprocessor 10 using a key stored in memory 40. For example,
instead of hashing, the physical measurement and/or time might be
encrypted with a device-specific private key if authenticity is
required, with a recipient-specific public key if confidentiality
is desired, or with both.
[0038] Certain well-known enhancements to public key cryptography
could also be used to provide greater assurance. For example, the
measurement could include digital certificates for public key
distribution to a party that does not know the device public key
needed to verify a measurement encrypted with the device private
key. In a digital certificate, the device public key is encrypted
(and vouched for) by the private key of a trusted certifier (e.g.,
a well known manufacturer of the measurement certification device)
whose public key is known to the recipient. The recipient uses the
certifiers public key to decrypt the device public key, then uses
the device public key to verify the measurement. Alternatively, the
recipient could simply obtain the device public key from a publicly
accessible database, eliminating the need for digital
certificates.
[0039] To this point, asymmetric (public key) encryption has been
discussed in the context of the various cryptographic operations.
However, symmetric key (e.g., DES) key encryption is also possible,
either as a replacement for, or adjunct to (e.g., a symmetric
session key transmitted using public key cryptography) public key
cryptography.
[0040] Another commonly used cryptographic technique, the so-called
challenge-response protocol (CRP), may be used to ensure to a
recipient that a measurement is current, i.e., not a copy of a
previously used measurement. In the CRP, a measurement requestor
challenges the measurement certification device by transmitting a
datum to the measurement certification device, and checking for the
same datum in the received response. Thus, reused certified
measurements are prevented (or at least detectable) because a
reused certified measurement would contain a datum corresponding to
a previous request/reply pair, rather than the current datum. Those
skilled in the art will appreciate that the challenge can use any
datum whose value is unpredictable by the recipient; random numbers
happen to be a particularly convenient choice. Alternatively, the
measurement certification device could include a random number
generator 18 to generate random numbers internally. In this
somewhat weaker version of the CRP, the recipient would not
necessarily know that the certified measurement was unique, but
only that he had not been sent a copy of a certified measurement he
himself had previously received.
[0041] Finally, the chaining disclosed above, with respect to
hashing, could also be implemented using encryption, wherein a
finite number of previous measurements would be incorporated into
the encrypted certified measurement.
[0042] Although certain exemplary cryptographic operations
(hashing, asymmetric encryption, symmetric encryption, chaining,
digital certificates, and challenge-response protocols) have been
disclosed for use singly or in specified combinations, those
skilled in the art will appreciate that many other combinations of
these basic operations may be used, depending on the needs of the
specific application.
[0043] The measurement can be acquired and certified upon receipt
of a certification request at input device 12. Input device 12
might be a simple I/O port for receiving an external electronic
request, or could include a push-button or other mechanical device
to generate the certification request. In the case of an electronic
request, the cryptoprocessor 10 might only accept a request
encrypted with a public, private, or symmetric key, and the
cryptoprocessor 10 would then verify the request prior to providing
the requested certified measurement. The external electronic
certification request could be generated by a remote location which
broadcasts or otherwise transmits the certification request to the
measurement certification device.
[0044] Alternatively, the certification request could be internally
generated under control of the cryptoprocessor 10, according to a
predetermined schedule, having either regular or irregular
intervals, loaded in RAM 30 or memory 40. Certification in response
to a predetermined schedule, rather than requestor control, would
be useful in applications such as remote monitoring. The schedule
could either be factory loaded (and unalterable) or loadable
through input device 12. In the latter case, a request to load the
schedule would preferably be encrypted in the device public key, as
described above with respect to requestor certification. As yet
another alternative, certification could be dynamically controlled
using an algorithm in which a future certification is set in
response to one or more previous certifications. For example, in
certain monitoring applications (discussed in more detail below), a
normally infrequent certification schedule could be accelerated in
response to detection of targeted events.
[0045] The certified measurement is outputted through output device
100. In a particularly simple embodiment of the invention, the
output device 100 might be a printer for recording the certified
measurement onto a piece of paper. FIGS. 2A and 2B illustrate
bottom and end views, respectively, of an exemplary printwheel
device 100. Printwheel device 100 rotates rubber-stamp wheels 110
using geared motors 120 under control of an electrical control
signal at input port 130. The wheels 110 have teeth 140 around
their circumference to print an alphanumeric code when a selected
sequence of teeth 140 is in contact with substrate 150. The teeth
140 receive ink from an ink supply 160. As mentioned previously,
the certified measurement would typically include some
cryptographic function of the physical measurement and/or time,
such as a hash or encrypted code, which one could use to verify the
integrity and/or authenticity of the physical measurement and/or
time. If used as a stand-alone device, the certification command
could be given via a push button or could be generated
automatically by pushing down on a spring-loaded housing enclosing
printwheel device 100, much like currently available hand-held
devices for document stamping. This is particularly useful for
mobile data acquisition applications where the entire measurement
certification device, including the output device 100, is designed
for handheld measurement and certification--for example, a
pollution inspectors emissions probe. Access to the measurement
certification device could optionally be controlled by requiring an
authorized password (e.g., via an alphanumeric keypad) before
certification will occur.
[0046] Regardless of the configuration of the device, signal flows
between the cryptoprocessor and the output device could be secured
to provide additional assurance.
[0047] As will be discussed in greater detail below, the certified
measurement may be outputted via a variety of alternative output
devices and media. Whether the certified measurement is printed on
a physical document for public display, recorded on media for
confidential logging, or displayed once for human reading, its
fundamental purpose is for verification by a party who was not
present to witness the measurement and certification. Thus, there
exists a need for two additional mechanisms: 1) one for
verification of the certified measurement, and 2) another for
reliably associating the actual physical measurement in question
with the certified measurement. These mechanisms are discussed
below in the sections entitled Certified Measurement Verification
and Fraud Deterrence, respectively.
Certified Measurement Verification
[0048] In cases where the certified measurement uses hashing, the
recipient need only read the cleartext part (physical measurement
and/or time) and recompute the hash to verify the ciphertext part.
If the received and recomputed hashes agree, the measurement has
not been changed.
[0049] In cases where the measurement is encrypted in the
corresponding device private key, the recipient can then simply
decrypt the measurement and perform any other cryptographic
operations needed to verify the measurement. The recipient would
read the certified measurement from the output medium (paper,
recording medium, or display), determine the device from the
cleartext part of the certified measurement, look up the
corresponding public key from a public database, and decrypt the
encrypted measurement using the public key. Alternatively, as
suggested earlier, digital certificates could be used to distribute
the device public key to a certified measurement recipient.
[0050] In certain situations, the above procedures are not
possible--for example: 1) when public key cryptography is not used,
2) when it is desired to keep the cryptographic algorithms
confidential from the recipient, or 3) when the recipient lacks the
capability to perform cryptographic verifications. In such cases,
the verification can be implemented by a public database located on
a central computer accessible via a free or toll-based telephone
line. A caller would use his touch-tone keypad to enter the ID
number of the measurement certification device and the cleartext
and/or ciphertext parts of the certified measurement to be
verified. The central computer would use the ID number to look up
the database record for that particular device, retrieve its
cryptographic key, and use the cryptographic key to perform the
appropriate cryptographic operation (recomputed hash, decryption,
etc.) and provide a confirmation to the caller.
[0051] In general, the recipient will verify the certified
measurement by performing some combination of hashing and
decryption appropriate to the particular combination of
cryptographic operations used to create the certified
measurement.
Fraud Deterrence
[0052] There are a number of ways in which a fraudulent user may
attempt to alter or manipulate a certified measurement. To help
illustrate these attacks, consider an exemplary measurement device
used to ensure compliance with pollution control laws. The device
tracks carbon monoxide levels at a manufacturing facility and
prints the resulting certified measurements to a paper substrate
which acts as a log of entries.
[0053] One method of attack would be to simply remove an
incriminating certified measurement from the log. This would entail
erasing the certified measurement or perhaps cutting out a portion
of the log. Such an action, however, would be detectable if
cryptographic chaining were used as described previously. Since
each certified measurement can contain a record of a number of
prior measurements, deleting one undetectably is impossible without
altering all the other measurements.
[0054] Instead of deleting a certified measurement, the user could
try to replace the measurement with a measurement obtained from
another device. The user could find a pollution control device from
another location that had lower carbon monoxide levels and use one
of its certified measurements as a replacement for the original
measurement. This replacement, however, would be easily detected
for a number of reasons. The device ID would be incorrect, and any
GPS information incorporated into the certified measurement would
reveal the wrong location.
[0055] The fraudulent user might also attempt to directly alter the
plaintext portion of the certified measurement, perhaps changing
the carbon monoxide level from thirty parts per billion to three
parts per billion. When the measurement was cryptographically
certified, however, the plaintext portion would not match the
ciphertext portion, revealing the fraud. Attempting to modify the
ciphertext portion to match the change in the plaintext portion
would require knowledge of the private key or hash algorithms of
the measurement device.
[0056] Even if the attacker managed to obtain the private key of
the measurement device, undetected alteration of certified
measurements would be difficult. As described above, chaining
techniques would require the attacker to alter all certified
measurements from that device. The use of challenge/response
protocols would make the alteration even more difficult.
[0057] Another defensive tactic involves the use of a secure audit
trail. As the measurement device writes certified measurements to
the paper log, the values could be contemporaneously stored
electronically in non-volatile memory within the secure perimeter.
This log might be available for download to disk upon presentation
of a password or cryptographic key to the measurement device.
[0058] Broadcasting the certified measurements is another effective
method of preventing fraud. A user would have to change all copies
of the certified measurement to conceal the fraud.
[0059] Although the above defensive methods provide a considerable
barrier to fraud, there are also physical techniques that may be
used in combination with the above to provide even greater levels
of security. When certified measurements are applied to a paper
substrate, delayed-visibility inks that are initially invisible but
develop slowly over time in response to aging or light exposure can
be used. The fraudulent user might be required to submit the log of
certified measurements to a government agency every two months. If
the ink were not visible until three months had passed, the user
would be unable to read the certified measurement and thus unable
to make alterations. Another defensive technique is to print the
certified measurement in such a way that each measurement overlaps
at least one other measurement, making it harder to alter one
certified measurement without affecting another. Such uncopyable
inks or patterns would be especially useful where the document
containing the certified measurement is to be transmitted via an
unsecured courier.
[0060] All of the above attacks and countermeasures have been
described in the context of a pollution measuring device, but are
in fact independent of the actual measurement technology. Thus,
those skilled in the art will appreciate that such countermeasures
are equally applicable to any measurement device that outputs the
certified measurement in a similar fashion.
[0061] Another type of physical fraud involves modifying the
measurement input rather than the certified measurement output.
That is, a dishonest user might physically tamper with the
measurement process, for example, by blowing cold air over a
temperature sensor, shining light on an optical sensor, or
shielding a pressure sensor. More generally, such fraud might take
the form of staging or otherwise modifying the physical parameter
or event being measured. One technique for reliably associating the
actual physical measurement in question with the certified
measurement involves incorporating corroborative information about
the physical measurement process into the certified
measurement.
[0062] Corroborative data might be provided by state detectors that
produce a digital signal indicative of normal (or abnormal)
operation of the device, for inclusion into the certified
measurement. Such detectors may reflect either the internal or
external state of the measurement certification device. An internal
state detector might provide a normal operation signal as long as
the measurement certification device's security measures remained
intact and operational. An external state detector might provide a
normal operation signal as long as the device was being operated
within a prescribed range of environmental conditions.
Alternatively, the external state detector could be a secondary
sensor providing a measurement corroborative of the primary sensor
measurement being certified. Such secondary sensor measurements are
especially appropriate where the physical event being measured is
characterized by two or more correlated measurements. For example,
a fire monitor could use both smoke and temperature measurements,
while an explosion monitor could use pressure and noise
measurements. Those skilled in the art of sensing will appreciate
that these and many other applications of internal or external
state detection could be used, depending on the particular
application at hand.
[0063] State detectors provide an automated or mechanistic measure
of the operational state of the measurement certification device.
Alternatively, a human witness could enter his unique witness
identifier into the measurement certification device as an
attestation of the propriety of the measurement process. In a
simple form of witness identifier, each witness to the event enters
a unique private identifier (such as his private key or personal ID
number) into the measurement certification device after the
measurement is taken, but before the certified measurement is
computed. The private identifier is then incorporated into the
cleartext and/or ciphertext portion of the certified measurement.
The private identifier could be entered manually via a keypad, or
automatically via touch memory buttons (described in more detail
below), PCMCIA cards, or other portable personal access tokens.
[0064] If greater levels of security are required, a
challenge-response protocol can be used to verify that none of the
event witnesses has stolen another person's private identifier.
After entering his private identifier, a witness would be
challenged by the measurement certification device to enter an
additional piece of information, such as his mother's maiden name.
The response would be compared against its expected value stored in
a database in the memory of the measurement certification device
when the private identifier was first registered with the device.
Incorrect responses would invalidate the previously entered private
identifier.
[0065] In the above embodiments, users must be careful when
entering private identifiers to ensure that they are not stolen by
other users of the measurement certification device. To make this
process more secure, tokens such as the touch memory buttons
manufactured by Dallas Semiconductor can be used. Each measurement
certification device user would have his private identifier stored
in a touch memory button which consists of a computer chip housed
within a small button shaped stainless steel case. The case may be
ring-shaped and worn around a user's finger. The chip contains up
to 64 kb of RAM or EPROM, sufficient to store a plurality of
cryptographic keys. The device transmits data bidirectionally at
16.3 kb per second when placed into contact with a reader device,
which would reside within the measurement certification device. The
user touches the button device to the reader each time that he
wants his private identifier incorporated into the certified
measurement. Each chip contains a unique serial number that is
laser-etched into the chip at the time of manufacture. The DS1427
configuration includes a tamper-resistant real-time clock that may
be utilized as a supplementary audit trail to that in the
measurement certification device, so that authenticatable
information would also be stored in the user's touch memory button
in addition to being incorporated into the certified
measurement.
[0066] Still greater levels of security can be obtained if
biometric readers are built into the measurement certification
device for incorporating biometric data (e.g., fingerprint,
voiceprint, retinal pattern or any other unique physiological
parameter) into the certified measurement. Biometric readers could
also be used to authenticate the private identifiers that are
entered by all witnesses.
[0067] Finally, instead of or in addition to human identifiers, the
corroborative data could originate from other devices. For example,
a second measurement device could take an independent measurement
of the physical parameter in question, and provide that measurement
to the primary measurement device for inclusion in the primary
measurement devices certified measurement. The corroborative
measurement could either be in cleartext or cryptographic form.
Those skilled in the art will appreciate that the cryptographic
form could include any combination of hashing, encryption, digital
certificates, challenge-response protocols, and other cryptographic
techniques disclosed herein with respect to the primary measurement
certification device. Alternatively, the second measurement device
could send only a corroborative data identifier to the primary
measurement device, but retain (or otherwise escrow) the
corroborative measurement in a safe location.
Alternative Time Sources
[0068] It was mentioned previously that the time is generated via
an internal clock 20. In another embodiment of the invention, the
measurement certification device could obtain time from an external
source via signal receiver 24 disposed inside the secure perimeter
70. The signal receiver 24 could receive time signals from ground
stations (e.g., the US Naval Observatory atomic clock), from
orbiting satellites, or from any other trusted external time
source. External time signals are especially advantageous for
deterring hacking of an internal clock.
[0069] In the satellite example, the measurement certification
device could receive timing signals from the American Global
Positioning System (GPS), for which sensors (receivers) are widely
available on the commercial market. Alternatively, the receiver
could receive signals from the Russian Glonass system. Although GPS
is primarily used for location finding, those skilled in the art
will appreciate that the same timing signals can also be used as an
accurate time source. Consequently, the signal receiver 24 may be
as an alternative time generator to clock 20 These basic operating
principles of satellite ranging systems are well known (e.g.,
Herring, The Global Positioning System, Scientific American,
February 1996, pp. 44-50; and How Does GPS Work?, Janes Intl.
Defense Review, Dec. 31, 1994, p. 147) but will be briefly
summarized below to illustrate the dual location- and
time-determining capabilities of GPS.
[0070] Any signal sent from a satellite to a terrestrial receiver
is delayed by an amount proportional to the distance from the
satellite to the receiver. Therefore, the difference between a
clock signal sent from a satellite and a receivers local clock
(typically a few hundredths of a second) will determine the
distance from the satellite to the receiver. Knowing this distance
establishes that the receiver is located somewhere on the surface
of a sphere, of radius equal to the determined distance, centered
about the satellite. However, the receivers exact location--a
particular point on the surface of that sphere--remains
undetermined. By receiving signals from several orbiting
satellites, the receivers exact three-dimensional location on the
surface of the earth can be determined as the point of intersection
of all their locating spheres.
[0071] In practice, the receiver clock is cheaper, and therefore
less accurate, than the satellites highly accurate atomic clocks.
This means that all of the locating spheres will be slightly
smaller or larger than their true values, depending on whether the
receiver clock runs slow or fast, respectively. Consequently, the
location spheres may not intersect at a single point. This
difficulty is overcome by adjusting the receiver clock by an
arbitrary amount, which in turn changes each of the location radii
by the same amount, and to check for a single point of intersection
of the locating spheres. If not, the receiver clock is readjusted,
in an iterative process, until a single point of intersection is
found. That is, the inaccurate receiver clock provides a good
initial guess regarding the point of intersection, and the fact
that the locating spheres must intersect at a single point
corresponding to the receivers terrestrial location is used to
improve the initial guess. Taken to its extreme, such iteration
could be performed without requiring a receiver clock at all--this
would simply require more iterations than if the receiver clock had
been available to provide an initial guess.
[0072] The end result of the iteration process is a determination
of both the exact location of the receiver and the correct time.
This time can then be used as part of the certification process. Of
course, if high time accuracy is not required (the received GPS
time is only off by a few hundredths of a second), the measurement
certification device could simply accept the received satellite
clock signal (or an average of several such signals) as an
approximation to the correct time without performing the iterative
process described above.
[0073] Finally, as is currently done for certain military
applications, the received time signals could be encrypted in the
time transmitters private key, or in the receivers public key, as
an extra measure of assurance that an impostor has not substituted
an incorrect time for that of the broadcast source. In the latter
example, the broadcasted time signal may be thought of as
narrowcasted because only a specific recipient can decrypt the
time. In such applications, the cryptoprocessor 10, RAM 30 and
memory 40 may be used to perform the necessary decrypting (or other
decoding). It will be advantageous to dispose the receiver within
the secure perimeter to prevent insertion of fraudulent signals.
Alternatively, an encrypted time could be certified without prior
decryption, with this step to be performed by the recipient during
subsequent verification.
[0074] As the foregoing illustrates, the signal receiver 24 could
either supplement or replace the clock 20. In certain embodiments,
the clock 20 could be used to double-check the received time (or
vice-versa) by comparing the received time against the internal
clock time--which could have been set at the factory or by a
previous radio broadcast. The received time would be deemed
accurate provided the two times agreed to within the cumulative
inaccuracies of the received signal (external time source
inaccuracy plus any uncorrected transmission delay) and the
internal clock 20. Such double-checking might be especially useful
where the GPS signals are broadcast in slightly degraded form
(e.g., the Standard Positioning mode used in many commercial
applications).
Authenticated Location
[0075] In certain cases, it will be desired to certify both the
time and geographical location at which the physical measurement
was taken. As discussed above with respect to external time, the
GPS signal receiver 24 is also ideally suited to provide the
necessary location signals. Such signals would be incorporated into
the certified measurement, along with the physical measurement and
time, in cleartext and/or cryptographic form. Even if no separate
physical measurement is made, the location per se--itself a
physical parameter--would be considered the physical measurement to
be certified.
Alternative Output Devices
[0076] It was mentioned previously that the certified measurement
could be printed to paper using a simple printwheel mechanism, but
more sophisticated printers can also be used at the output device.
For example, the printer could include traditional dot- or
character-based computer printers (e.g., laser, bubble, inkjet,
daisywheel, or line printers) as well as facsimile machines,
photocopiers, or even barcode printers. Each of these devices could
route a certification request through input 12, either
automatically upon document printing or manually upon operator
request (e.g., a "certify" button to be used manually after
printing a page). Furthermore, manual or automatic operation could
be selectable via an on/off toggle.
[0077] Still other output devices are possible, especially when the
certified measurement is not required to be directly printed on a
paper substrate. For example, the output device could be printed on
a special, difficult-to-forge label to be applied to the surface of
a paper document or other substrate. Furthermore, the certified
measurement has been described previously as a human-readable
alphanumeric code, but this is not necessary. Any machine-readable,
optically detectable code would serve equally well, and might be
preferred to deter casual snooping. For example, the certified
measurement could be a fine mesh of dots covering the paper
substrate. The dots could be laid down using any arbitrary
machine-readable coding scheme. For example, the distance between
individual dots could represent the digits of the ciphertext part
of the certified measurement. Such an embodiment is most
practically performed by a measurement certification device
connected to a printer or fax machine which is easily capable of
setting down such a fine mesh of dots.
[0078] Machine-readable, optically-detectable codes are also
appropriate when the output device is a recorder used for writing
the certified measurement to a non-paper medium. Certain of these
media have an added advantage of being write-only, which can
provide extra assurance against measurement modification. For
example, an electromagnetic write head could write to magnetic
media (e.g., diskette or tape), a laser could write to optical
media (e.g., CD-ROM or magneto-optical disk), or an electric charge
could be applied to semiconductor media (e.g., a DRAM or PROM).
[0079] As yet another alternative, the certified measurement need
not be written to a permanent or semi-permanent media, but could be
displayed for transient viewing on an electronic or other display
in human- or machine-readable form. This would be useful, for
example, in a monitoring process whereby the measurement is
indicative of the existence and normal operation of the monitored
device.
[0080] Finally, the output device 100 in FIG. 1 could be a
transmitter for transmitting the measurement to a remote location.
The transmitter would be triggered under control of the measurement
output methodology or the intended use of the measurement
certification device. For example, as described previously,
certified measurements could be transmitted at predetermined
intervals under the control of the cryptoprocessor. Alternatively,
the transmitter could contain logic to accumulate the certified
measurements and only transmit them upon external request. Or, the
transmitter could itself initiate the certified measurement in
response to a received external request, e.g., the transmitter
could be combined with the input device 12 in the form of a
transponder. Finally, in certain applications, the certified
measurement could be escrowed rather than transmitted, so that an
authorized party could trace the location without necessarily
broadcasting the information. The escrow could either be internal
or external.
Certification Requests
[0081] It was mentioned previously that the measurement
certification device could operate in response to an external
request received at the input device 12. Although such an external
request will often be a request from a measurement recipient, it
could also be generated automatically upon detection of an event
external to the measurement certification device. Such an event
could be any normal or abnormal occurrence that is to be
transmitted to the recipient of the signal. Thus, input device 12
need not be a separate device, but could be integrated with sensor
8.
[0082] For example, where the measurement certification device is
used for mobile applications, normal events might include entering
an automated toll road or a police car passing a prescribed
checkpoint. Conversely, abnormal events might include a rental car
leaving an authorized operating area or detection of air bag
inflation in the event of an accident. In the latter example, the
combination of certification, satellite triangulation for location,
other sensors to detect a triggering event, and a transmitter leads
to an automated distress call system for summoning assistance in
the event of an emergency. Such a system would have natural
applications in mobile applications (e.g., cars) where the vehicle
location must be transmitted to the rescuer. For example, the GPS
receiver could be linked to a transmitter for broadcasting the cars
location upon receipt of an authorized request at an airbag sensor.
Considered together, the GPS receiver, transmitter, and airbag
sensor could be regarded as a transponder. The actual transmitters,
receivers, and sensors needed for such location transmitters will
not be discussed in detail, as those skilled in the art will
appreciate that all the necessary components are widely
commercially available. For example, the Lojak car anti-theft
system uses such components--but without certification or
cryptographic assurance--to transmit a stolen cars location upon
request of a radio signal. Location transmitters would also be
useful for non-mobile applications where the location data, in
conjunction with the device ID, would serve to deter false or prank
distress calls. Such a transmitter could take many forms, ranging
from a dedicated, single-purpose module located within the secure
perimeter to a cellular phone or other external, multi-purpose
telecommunications device. As yet another example, the transmitter
could be augmented with an automatic cut-off switch triggered upon
the abnormal event to form a so-called dead mans switch to disable
potentially dangerous equipment until assistance arrives.
[0083] Still other applications of certified location include a
device to enforce house arrest, a secure gambling device that only
worked within a certain state or country, a radio that changed its
presets in different geographical locations, a mobile vending
machine that collected sales taxes according to the state it was
in, a car that stopped working if taken across the border, and a
smart bomb that would not explode over friendly territory.
[0084] The above examples illustrate several of many possible
mobile uses of measurement certification devices in connection with
location certification. Of course, the physical parameter being
measured need not be restricted to location, but could include any
physical quantity capable of being transduced into a digital signal
by a secure sensor. Location certification simply happens to be a
natural application of mobile measurement certification
devices.
[0085] Conversely, a stationary measurement certification device
could be used to track a mobile physical event. For example, an
array of smog sensing devices could be used to track pollutant
dispersion for air quality studies. These and many other different
combinations of measurement certification and location
certification will be known to those skilled in the art.
[0086] For purposes of illustration only, and not to limit
generality, the present invention has been explained with reference
to various examples of time sources, cryptographic operations,
output devices, and sensors. However, one skilled in the art will
appreciate that the invention is not limited to the particular
illustrated embodiments or applications, but includes many others
that operate in accordance with the principles disclosed
herein.
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