Method of detecting a redirection or relaying of a contactless data transmission using at least two sequentially driven transmitting antennas

• US 20030119453A1
• Filed: 12/04/2002
• Published: 06/26/2003
• Est. Priority Date: 12/05/2001
• Status: Active Grant

• Current Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Original Assignee: Atmel Germany GmbH (Microchip Technology Incorporated)
• Inventors: Blatz, Werner, Moser, Helmut
• Granted Patent: US 6,970,679 B2
• Time in Patent Office: Days
• US Class Current: 455/73
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• CPC Class Codes: G07C 2009/00555 comprising means to detect or avoid relay attacks
• CPC Class Codes: G07C 2009/00793 by Hertzian waves
• CPC Class Codes: G07C 9/00309 operated with bidirectional data transmission between data carrier and locks

Abstract

A method detects relaying of a contactless data communication by a radio amplifier for intercepting and manipulating the communication to achieve an unauthorized authentication. The method involves transmitting an electromagnetic field successively from at least two spatially separated antennas of a transmitting unit, receiving the transmitted fields in a receiving unit, determining field strength vectors of the received fields allocated to each antenna, and comparing actual values of the vectors with prescribed nominal values stored in a nominal value field that maps the true field strength distribution in multi-dimensional space around the transmitting unit. The actual field strength magnitude and the reception angle between the transmitting antennas can be determined from the vectors and compared with stored nominal values in this manner. When the determined actual values match prescribed nominal values of the nominal value field, the occurrence of a relaying of the signal can be reliably excluded.

Claims

1. A method of detecting a relaying of a contactless electromagnetic data transmission, comprising the steps:

a) transmitting a first electromagnetic field from a first transmitting antenna of a first unit having at least a transmitting capability;

b) sequentially after said step a), transmitting a second electromagnetic field from a second transmitting antenna of said first unit, wherein said first and second transmitting antennas are spatially separated from each other;

c) sequentially receiving said first electromagnetic field and said second electromagnetic field with a second unit having at least a receiving capability;

d) determining a first actual field strength value of a field strength of said first electromagnetic field and a second actual field strength value of a field strength of said second electromagnetic field as respectively received by said second unit;

e) comparing said first and second actual field strength values respectively with prescribed first and second nominal field strength values of a nominal value field; and

f) detecting that a relaying of at least one of said first and second electromagnetic fields has occurred if said comparing determines that said first and second actual field strength values unacceptably deviate from said prescribed first and second nominal field strength values of said nominal value field.

2. The method according to claim 1, wherein said first and second electromagnetic fields as transmitted respectively by said first and second transmitting antennas both have the same amplitude.

3. The method according to claim 1, wherein said first and second electromagnetic fields as transmitted respectively by said first and second transmitting antennas both correspond to the same electromagnetic signal transmitted successively from said first transmitting antenna and then again from said second transmitting antenna.

4. The method according to claim 1, further comprising comparing said first and second actual field strength values with a prescribed maximum value and with a prescribed minimum value, and detecting that a relaying of at least one of said first and second electromagnetic fields has occurred if at least one of said first and second actual field strength values lies above said maximum value or below said minimum value.

5. The method according to claim 1, wherein said comparing of said step e) comprises determining whether said first and second actual field strength values respectively fall within a prescribed acceptable variation range respectively around said first and second nominal field strength values, and if at least one of said first and second actual field strength values falls outside of said prescribed acceptable variation range respectively around said first and second nominal field strength values then it is determined that said first and second actual field strength values unacceptably deviate from said prescribed first and second nominal field strength values.

6. The method according to claim 1, wherein said nominal value field includes a plurality of value sets that each respectively include a respective one of said first nominal field strength values and a respective one of said second nominal field strength values which are prescribed for a respective spatial point in multi-dimensional space around said first unit, and wherein said comparing of said step e) comprises determining whether said first and second actual field strength values respectively match or fall acceptably close to said first and second nominal field strength values of any one of said value sets.

7. The method according to claim 6, further comprising a preliminary step of mapping out a field strength distribution pattern of said first electromagnetic field transmitted by said first transmitting antenna and of said second electromagnetic field transmitted by said second transmitting antenna in said multi-dimensional space around said first unit, by transmitting said first and second electromagnetic fields successively from said first and second transmitting antennas respectively, measuring a respective first true field strength value of said first electromagnetic field and a respective second true field strength value of said second electromagnetic field respectively at each one of plural spatial points in said multi-dimensional space around said first unit, and respectively storing said first and second true field strength values as said first and second nominal field strength values of a respective one of said value sets respectively for each respective one of said spatial points in said multi-dimensional space around said first unit to make up said nominal value field.

8. The method according to claim 6,

wherein each respective one of said value sets respectively further includes a respective nominal reception angle value of an angle between said first and second transmitting antennas with respect to a respective angle vertex at said respective spatial point associated with said respective value set;

wherein said method further comprises determining from said first and second electromagnetic fields received by said second unit an actual reception angle value of a reception angle between said first and second transmitting antennas relative to said second unit, and comparing said actual reception angle value with said nominal reception angle values of said value sets; and

wherein said step f) comprises detecting that a relaying of at least one of said first and second electromagnetic signals has occurred if said first and second actual field strength values do not respectively match or fall acceptably close to said first and second nominal field strength values or said actual reception angle value does not match or fall acceptably close to said respective nominal reception angle value of any single one of said value sets.

9. The method according to claim 1, wherein said step c) comprises respectively receiving three mutually orthogonal field strength components of a first field vector of said first electromagnetic field and of a second field vector of said second electromagnetic field, and said step d) comprises determining said first actual field strength value as an absolute magnitude of said first electromagnetic field from said orthogonal field strength components of said first field vector of said first electromagnetic field and determining said second actual field strength value as an absolute magnitude of said second electromagnetic field from said orthogonal field strength components of said second field vector of said second electromagnetic field.

10. The method according to claim 9, further comprising determining a reception angle between said first and second transmitting antennas relative to said second unit from said field vectors of said first and second electromagnetic fields.

11. The method according to claim 1, further comprising transmitting a third electromagnetic field from a third transmitting antenna of said first unit which is spatially separated from said first and second transmitting antennas sequentially after said step b), receiving said third electromagnetic field with said second unit, determining a third actual field strength value of a field strength of said third electromagnetic field as received by said second unit, comparing said third actual field strength value with prescribed third nominal field strength values of said nominal value field, and detecting that a relaying of at least one of said first, second and third electromagnetic fields has occurred if said comparing determines that at least one of said first, second and third actual field strength values unacceptably deviates respectively from said prescribed first, second and third nominal field strength values of said nominal value field.

12. The method according to claim 1, wherein said second unit comprises three receiving antennas having respective effective axes that are oriented orthogonally relative to each other, and wherein said step c) is carried out by said three receiving antennas.

13. The method according to claim 12, wherein said three receiving antennas comprise an annular ring-shaped antenna extending on a plane and two rod-shaped antennas extending on said plane of said ring-shaped antenna.

14. The method according to claim 1, wherein said first and second actual field strength values are respective absolute magnitude values of a field strength of said first and second electromagnetic fields respectively.

15. The method according to claim 1, further comprising determining a reception angle between said first and second transmitting antennas from said actual field strength values, and comparing said reception angle with a prescribed angle to determine whether a correspondence exists therebetween.

16. The method according to claim 1, further comprising storing results of said comparing of said step e).

17. The method according to claim 1, wherein said actual field strength values are magnetic field strength values of respective magnetic portions of said first and second electromagnetic fields.

18. The method according to claim 1, further comprising carrying out a data transmission by modulating data onto at least one of said first and second electromagnetic signals.

19. The method according to claim 18, wherein said modulating comprises a phase modulation or a frequency modulation.

20. The method according to claim 18, wherein said steps a) to e) are carried out before or at a beginning of said data transmission.

21. The method according to claim 18, wherein said steps d) and e) are carried out repeatedly at intervals while carrying out said data transmission.

22. The method according to claim 1, wherein said step e) is carried out in said second unit.

23. The method according to claim 22, wherein said second unit further has a transmitting capability and said first unit further has a receiving capability, and further comprising transmitting a result of said comparing of said step e) from said second unit to said first unit.

24. The method according to claim 1, wherein said second unit further has a transmitting capability and said first unit further has a receiving capability, and further comprising transmitting said actual field strength values from said second unit to said first unit, and wherein said step e) is carried out in said first unit.