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System for proximity determination

  • US 8,051,292 B2
  • Filed: 05/11/2005
  • Issued: 11/01/2011
  • Est. Priority Date: 06/28/2004
  • Status: Active Grant
First Claim
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1. A method for determining proximity between a first device and a second device, the method comprising:

  • providing a first device storing a first device private key, the first device having an associated secure first device certificate storing secured information, the secured information comprising;

    a first device public key corresponding to the first device private key;

    providing a second device storing a second device private key, the second device having an associated secure second device certificate storing secured information, the secured information comprising;

    a second device public key corresponding to the second device private key; and

    a second device processing delay;

    providing a copy of the second device certificate to the first device;

    establishing a secure authenticated channel between the first device and the second device;

    sending a first proximity challenge from the first device to the second device, the proximity challenge including a numeric challenge value;

    receiving the first proximity challenge at the second device, processing the proximity challenge at the second device to produce a response to the first proximity challenge, and sending the response to the first proximity challenge from the second device to the first device;

    receiving the response to the first proximity challenge at the first device; and

    performing the following at the first device;

    verifying, at the first device, that the response to the first proximity challenge is legitimate;

    determining a gross time between sending the first proximity challenge and receiving the response to the first proximity challenge;

    subtracting the second device processing delay from the gross time to produce a first net response time; and

    comparing the first net response time to a first threshold and determining whether the first device and the second device are in proximity based on a result of the comparing.

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