Method for providing location certificates

• US 5,659,617 A
• Filed: 09/22/1994
• Issued: 08/19/1997
• Est. Priority Date: 09/22/1994
• Status: Expired due to Term

• Current Assignee: Addison M. Fischer
• Original Assignee: Addison M. Fischer
• Inventors: Fischer, Addison M.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): SAYADIAN, HRAYR
• Application Number:
  US08/310,022
• Time in Patent Office: 1,062 Days
• Field of Search: 380/23, 380/25, 342/357, 342/450-465
• US Class Current: 380/258
• CPC Class Codes: H04L 2209/805 Lightweight hardware, e.g. radio-frequency identification [RFID] or sensor
• CPC Class Codes: H04L 9/3263 involving certificates, e.g. public key certificate [PKC] or attribute certificate [AC]; Public key infrastructure [PKI] arrangements network architectures or network communication protocols for supporting authentication of entities using certificates in a packet data network H04L63/0823
• CPC Class Codes: H04L 9/3271 using challenge-response
• CPC Class Codes: H04L 9/3297 involving time stamps, e.g. generation of time stamps

Abstract

Methods and apparatus for providing location certificates to certify the position or location of an object are disclosed. The position of the object is computed using radio signals and the secure transmission of the computed position is achieved using public key encryption techniques.

Claims

1. A secure method of establishing the location of an object by calculating in-situ the location of the object from received radio signals wherein the radio signals are received from a beacon via a two-way communication between the beacon and a sensor on the object, comprising

computing and transmitting at said sensor a signal including a challenge value and observing a clock associated with said sensor,

recognizing at said beacon the transmitted sensor signal, observing at the beacon a clock associated with the beacon, constructing a response message including the sensor'"'"'s received challenge value, the beacon'"'"'s location, its location certificate and a time stamp, and transmitting the response message to said sensor,

recognizing at said sensor said transmitted response message, observing the sensor clock, and validating the response message, computing the signal transit time and estimating the distance to the beacon, and based on the location of the beacon and the distance, calculating the location of the sensor and thereby the location of the object, and

transmitting in response to a request from a requestor a message comprising the digitally signed calculated location of the object.

2. A method as in claim 1 and including transmitting a certificate for the object in the message comprising the digitally signed calculated location of the object.

3. A method as in claim 1 wherein the clocks associated with the beacon and the sensor are synchronized and including,

calculating the transit time from the time stamp and the observed time for receipt of the response message at the sensor and comparing this time with the computed signal transit time.

4. A method as in claim 1 wherein said object includes a sensor with a accurate clock synchronized with a beacon clock and includes the step of receiving a time stamp from the beacon and comparing it with the sensor clock to authenticate the receipt of location information is from a valid beacon.

5. A method as in claim 1 wherein said beacon and said sensor each include an accurate clock and includes the step of updating the sensor clock in accordance with the time stamp transmitted by the beacon.

6. Apparatus for providing location certificates comprising

a location certification unit for receiving radio signals from two or more beacons,

said location certificate unit including position determination means and secure authorization means,

said secure authorization means including a private key of a private key-public key pair for digitally signing messages sent to a requesting source, a certificate for the public key certifying that the public key is in fact the public key of the secure authorization means, a clock synchronized with clocks in the beacons, means for receiving and processing a time stamp transmitted by a beacon, and means for determining from the time stamp and the clock in the secure authorization means that a received radio signal is from a valid beacon,

said beacons providing radio signals from which said position determination means can compute its position and said secure authorization means can determine that the signals are valid, and

means for sending to said requesting source upon request a digitally signed message including the computed position of said location certificate unit and the certificate for the public key which public key is to be used by the requesting source to verify the signed message.

7. Apparatus as in claim 6 further comprising means for establishing a secure two-way communication link between each beacon and the sensor in the secure authorization means.

8. Apparatus as in claim 6 wherein said location certification unit is a component of a digital signature device.

9. Apparatus as in claim 6 wherein said location certification unit is a component of a satellite signal box.

10. A location certification unit comprising a position determination unit, a secure authorization unit coupled to said position determination unit, a memory within said secure authorization unit, a digital signature key stored in the form of digital data in said memory, said key having an associated public key, a certificate for said public key, said certificate being stored in said memory, a sensor for receiving a message from a beacon that includes the clock time at which the message was transmitted and for processing the message to retrieve the clock time, the sensor including a clock, said position determination unit computing from the retrieved clock time and the time of sensing a received message as indicated by the sensor clock the radial distance the location certification unit is from the beacon thereby determining the location of the location certification unit as being within a geographical area centered on the beacon, and means for communicating to a requestor in response to a request the certified location of said location unit, said certified location comprising the location as determined by said position determining unit signed with said digital signature key and the certificate for said public key.

11. A location certification unit as in claim 10 wherein said memory further stores a personal identification number and a password and said location certification unit is a component of a computer log-on card.

12. A location certification unit as in claim 10 wherein the location certification unit is a component of a digital signature device.

13. A location certification unit as in claim 10 wherein the location certification unit is a component of a satellite signal decoder box.

14. A location certification unit as in claim 10 wherein the message from a beacon includes the digital signature of the clock time at which the message was transmitted, and said sensor has stored therein the public key of the beacon for verifying the clock time using the public key of the beacon.

15. A location certification unit comprising;

a position determination unit for determining the position of the location certification unit from received radio signals,

a secure authorization unit coupled to the position determination unit and comprising a memory, a sensor having a clock for providing clock time, and means for communicating to a requestor in response to a request a message containing the certified position of the location certification unit as determined by the position determination unit,

said memory having stored therein a digital signature key and a certificate for a public key associated with the digital signature key,

said clock providing a clock time for validating a received radio signal, the signal containing the time at which it was transmitted, sensed by the sensor as being from a valid source, and

said certified position of the location certification unit comprising (1) the position of the location certification unit as determined by the position determination unit signed using the digital signature key and (2) the certificate.

16. A location certification unit as in claim 15, said sensor further comprising a processor for processing sensed radio signals to provide the identity of the source of the signal where that information is contained in the signal, and for decrypting a sensed digitally signed radio signal with the public key of the source of the signal to verify the identity of the source and the time at which the signal was transmitted.

17. A location certification unit as in claim 15 wherein time differentials between the time the sensor clock marks a sensed signal and the time at which the signal was sent with respect to a plurality of sources are used to calculate the position of the location certification unit and each time differential is checked with the calculated signal transit time from the calculated position to the known location of the source.

18. A location certification unit as in claim 15 wherein said sensor is capable of receiving and processing signals received from more than one source and said position determining means determines the position of the location certification unit based on the messages from at least two sources.

19. A location certification unit as in claim 18 wherein the sources are beacons, and the location certification unit further comprises a transmitter for sending messages to a beacon that trigger the beacon into transmitting a response message that includes a time stamp, whereby it can be verified that the response message is a current message and not a copied message that is being replayed by comparing the time stamp with the sensor clock time at the time of receipt of the response message.

20. A location certification unit as in claim 18 further comprising a transmitter for sending a message to a beacon that triggers the beacon into transmitting a response message that includes a time stamp, whereby the total time for the sent message to travel to the beacon and the response message from the beacon to be sensed at the sensor, adjusted for by beacon delay and internal location certification unit delay, is divided in half and compared with the difference between the clock time at the time of receipt of the message and the time stamp to verify that the response message is valid.