Selective denial of encrypted high precision data by indirect keying

• US 5,982,897 A
• Filed: 06/10/1998
• Issued: 11/09/1999
• Est. Priority Date: 04/26/1995
• Status: Expired due to Term

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: ITT Corporation (ITT, Inc.)
• Inventors: Clark, James Monroe
• Primary Examiner(s): Hayes, Gail O.
• Assistant Examiner(s): SAYADIAN, HRAYR
• Application Number:
  US09/095,623
• Time in Patent Office: 517 Days
• Field of Search: 380/21, 380/9, 342/357, 342/354
• US Class Current: 380/258
• CPC Class Codes: G01S 19/015 Arrangements for jamming, spoofing or other methods of denial of service of such systems
• CPC Class Codes: G01S 19/02 Details of the space or ground control segments
• CPC Class Codes: H04B 7/18593 Arrangements for preventing unauthorised access or for providing user protection arrangements for secret or secure communication H04L9/00

Abstract

High precision transmitted navigational data as encrypted data transmitted by global positioning (GPS) satellites is made unavailable in regions designated as hostile and during desired intervals, while allowing the data to be available outside the hostile region. All satellites in the GPS constellation transmit the high precision navigational data in encrypted form. However, only the satellites that are not visible to the hostile region transmit the periodic key necessary to decrypt the data. The periodic key changes after a predetermined time interval. During a given time interval the same key value is used by all satellites for encryption of the high precision navigational data. A receiver can obtain the current periodic key from any visible satellite which is transmitting the periodic key. This key is then used to decrypt the high precision navigational data from that satellite and all other visible satellites. As a result, users in the hostile region are denied access to the high precision navigational data because they are unable to obtain the periodic key necessary to decrypt the data.

Claims

1. A system for selectively retarding decryption access to encrypted high precision navigational data by selectively transmitting by satellite in a global positioning system an encryption key when access to said data is permitted and suppressing transmission of said key when decryption access to said data is to be retarded, comprising:

transmitting means operative to transmit said encrypted data and said key,

means coupled to said transmitting means for selectively suppressing the transmission of said key during a desired interval while continuing to transmit said encrypted high precision navigational data, and,

receiving means capable of receiving said encrypted data and said key and including means for decrypting said data strictly according to receipt of said key, wherein when said key is suppressed during said interval said receiving means cannot decrypt said data.

2. The system according to claim 1 wherein said transmitting means includes an orbiting satellite having a transmitter for transmitting encrypted navigational data to the ground and for transmitting said key, said satellite transmitter including means for suppressing transmission of said key according to the position of said satellite will respect to a designated ground area, whereby said decrypting means located within said designated ground area is retarded from decrypting said data due to said key suppression.

3. The system according to claim 2 wherein said satellite is a Global Positioning Satellite (GPS).

4. A method of selectively retarding access to encrypted high precision navigational data transmitted by the satellite transmitters employed in a global positioning system, comprising the steps of:

providing an encryption key which is transmitted with said high precision encrypted data from said satellites,

receiving said transmitted encrypted data and said key,

decoding said received encrypted data solely according to said received key, and,

suppressing the transmission of said key while transmitting said encrypted high precision data at desired times, whereby during the suppression of said key said decoding of said received encrypted data is retarded.

5. The method according to claim 4 further including the step of:

designating certain transmission areas as hostile areas, and

suppressing the transmission of said key when said satellite transmitter transmits to said hostile area.

6. The method according to claim 5 further comprising the step of:

changing said key during predetermined time intervals.

7. The method according to claim 6 further comprising the step of:

transmitting a control signal from the ground to selected satellites,

receiving said transmitted control signal at said satellites,

and, suppressing the transmission of said encryption key according to said received control signal.

8. A global positioning system including a plurality of orbiting and moving satellites each capable of transmitting to the ground, high precision navigational data which data is encrypted according to encryption format, wherein a receiver located at the ground and capable of receiving said data and decrypting said data in response to an encryption key, the combination therewith of an apparatus for selectively retarding access to said encrypted data at said ground, comprising:

encryption means located in said satellites for defining said encryption format by means of said encryption key including means for selectively transmitting said key with said encrypted data, and,

control means coupled to said encryption means for suppressing the transmission of said key while continuing to transmit said high precision navigational data during predetermined intervals according to a position of at least one of said satellite transmitters relative to a predetermined region, wherein said receiver located at the ground within said region is retarded from decrypting said data during the suppression of said key.

9. The GPS system according to claim 8 wherein said control means operates to suppress said key transmission for ground regions designated as hostile areas.

10. The GPS system according to claim 8 wherein said encryption means includes means for periodically changing said key according to a predetermined encryption format.

11. In a global positioning system having a plurality of orbiting and moving satellites each including a transmitter for transmitting to the ground, encrypted high precision navigational data which is encrypted according to an encryption format, defined by a transmitted encryption key, and a receiver located at the ground for receiving both the transmitted high precision data and said key, said receiver comprising:

a memory for storing on enrollment key indicative of an authorized high precision data user, for controlling the decrypting of said data; and

,

means responsive to the receipt of said encryption key and said high precision data user, for decrypting said data according to said encryption key as controlled by said enrollment key, wherein said satellites include means for selectively suppressing the transmission of said encryption key while transmitting said encrypted high precision navigational data during predetermined intervals to retard said receiver from decrypting said data during intervals of key suppression, wherein said predetermined intervals are selected according to predetermined ground areas designated as hostile areas.

12. The GPS System receiver according to claim 11 further including means for storing the decoded encryption key in said memory.

13. A method for providing selective access to navigational data comprising the steps of:

continuously transmitting high precision navigational data from each of a plurality of transmitters, said navigational data being encrypted in response to a periodic varying key;

selectively transmitting said periodic key from a subset of transmitters of said plurality of transmitters only during predetermined intervals;

receiving said encrypted data from a predetermined number of transmitters;

receiving said periodic key from at least one of said transmitters;

decrypting each of said received encrypted data in response to said received periodic key only during said predetermined intervals.

14. The method as recited in claim 13, further comprising the step of selecting a denial region wherein said subset of transmitters do not transmit said periodic key within said denial region.

15. The method as recited in claim 13, further comprising the steps of:

encrypting said periodic key in response to an enrollment key before transmitting said periodic key;

decrypting said periodic key after receiving in response to said enrollment key.

16. The method as recited in claim 13, further comprising the step of generating said periodic key in response to a master key.

17. The method as recited in claim 13, further comprising the step of selectively enabling the step of encrypting.

18. The method as recited in claim 13, wherein said periodic key changes as a function of time.

19. The method as recited in claim 13, further comprising the step of storing the received periodic key for use when the periodic key is not received from at least one of the subset of transmitters.

20. The method as recited in claim 13, wherein the step of transmitting said periodic key occurs at least twice as often as the step of selecting the periodic key.

21. A method for selectively providing high precision navigational signals adapted to enable users to determine respectively associated geographical positions, sad method comprising the steps of:

providing a plurality of transmitters;

defining a select geographical region;

selecting first and second groups from said plurality of transmitters upon said defined select geographical region;

transmitting from each of said first group of transmitters encrypted high precision navigational data, while suppressing transmission, in each of said first group of transmitters, of a cryptographic key adapted to enable decryption of said encrypted navigational data; and

,

transmitting from each of said second group of transmitters said encrypted navigational data and said cryptographic key.

22. A method for selectively providing signals adapted to enable users to determine respectively associated geographical positions, said method comprising the steps of:

defining a plurality of geographical regions;

continuously transmitting high precision navigational data into each of said plurality of geographic regions;

suppressing transmission of a cryptographic key adapted to enable decryption of said encrypted navigational data into at least one select geographical region selected from said plurality of geographical regions; and

,

transmitting said cryptographic key into each of said plurality of geographical regions which is not said at least one select geographical region.

23. The method of claim 22, further comprising the step of transmitting encrypted navigational data into each of said plurality of geographical regions.

24. A method for selectively providing signals adapted to enable users to determine respectively associated geographical positions, said method comprising the steps of:

providing a plurality of transmitters; and

,

providing selection means for individually operating each of said transmitters in a first mode and a second mode, wherein;

said first mode comprises the step of;

transmitting from each of said plurality of transmitters navigational data intended to be received by each of a plurality of receivers and enable each of said plurality of receivers to accurately identify its respective geographical location; and

,

said second mode comprises the steps of;

defining a plurality of geographical regions;

transmitting encrypted high precision navigational data into each of said plurality of geographic regions;

suppressing transmission of a cryptographic key adapted to enable decryption of said encrypted navigational data into at least one select geographical region selected from said plurality of geographical regions; and

,

transmitting said cryptographic key into each of said plurality of geographical regions which is not said at least one select geographical region.