Cryptographic key exchange over an electrostatic channel

Patent metadata

Field	Value
Publication number	US-2016014598-A1
Application number	US-201414330981-A
Country	US
Kind code	A1
Filing date	Jul 14, 2014
Priority date	Jul 14, 2014
Publication date	Jan 14, 2016
Grant date	—

Abstract

Various embodiments relating to exchanging a cryptographic key between a display device and an input device via electrostatic communication are disclosed. In one embodiment, an interactive communication device includes one or more electrodes and a radio transceiver. The one or more electrodes may be excited to capacitively couple with one or more electrodes of a proximate communication device so as to capacitively send a cryptographic key from the interactive communication device to the proximate communication device. The radio transceiver may be configured to communicate with a radio transceiver of the proximate communication device via a radio channel. The interactive communication device may be configured to subsequently exchange encrypted communications with the proximate communication device over the radio channel. The encrypted communications may be encrypted using the cryptographic key.

First claim

1 . An interactive display device comprising:
a touch sensor including an electrode matrix having row electrodes and column electrodes, where the interactive display device is configured to excite one or more electrodes of the electrode matrix to form a capacitive coupling to capacitively send a cryptographic key via an electrostatic channel; and a radio transceiver configured to communicate via a radio channel, where the interactive communication device is configured to subsequently exchange encrypted communications over the radio channel, the encrypted communications being encrypted using the cryptographic key.

2 . The interactive display device of claim 1 , where the cryptographic key is a symmetric key.

3 . The interactive display device of claim 2 , where a new version of the symmetric key is randomly generated each time a trigger event occurs.

4 . The interactive display device of claim 1 ,
where the one or more electrodes of the electrode matrix capacitively couple with an electrode tip of an input device; and where capacitive coupling between the electrode tip and the one or more electrodes of the electrode matrix is used to determine a position of the electrode tip relative to the electrode matrix.

5 . The interactive display device of claim 4 , where the cryptographic key is sent by exciting a subset of the one or more electrodes of the electrode matrix, the subset being selected based on the position of the electrode tip relative to the electrode matrix.

6 . The interactive display device of claim 4 , where the cryptographic key is sent during designated time slots of a frame during which position information is sent via capacitive coupling between the electrode tip and the electrode matrix.

7 . The interactive display device of claim 1 , where the cryptographic key is an asymmetric key.

8 . An input device configured to interact with an interactive display device, the input device comprising:
an electrode tip configured to be excited to form a capacitive coupling to capacitively send a cryptographic key via an electrostatic channel; and a radio transceiver configured to communicate via a radio channel, where the input device is configured to subsequently exchange encrypted communications over the radio channel, the encrypted communications being encrypted using the cryptographic key.

9 . The input device of claim 8 , where the cryptographic key is a symmetric key.

10 . The input device of claim 9 , where a new version of the symmetric key is randomly generated each time a trigger event occurs.

11 . The input device of claim 8 , where the encrypted communications include an upgraded version of firmware for the input device.

12 . The input device of claim 8 ,
where the electrode tip capacitively couples with one or more electrodes of an electrode matrix included in a touch sensor of an interactive display; and where capacitive coupling between the electrode tip and the one or more electrodes of the electrode matrix is used to determine a position of the electrode tip relative to the electrode matrix.

13 . The input device of claim 12 , where the interactive display is configured to randomly excite one or more electrodes of the electrode matrix while the input device is sending the cryptographic key to the interactive display.

14 . The input device of claim 13 , where the interactive display is configured to sense a capacitive signal from the touch sensor and extract the cryptographic key from the capacitive signal by subtracting noise generated by random excitation of the one or more electrodes of the electrode matrix from the capacitive signal.

15 . The input device of claim 11 , where the cryptographic key is sent during designated time slots of a frame during which position information is sent via capacitive coupling between the electrode tip and the electrode matrix.

16 . The input device of claim 11 , where the electrode tip capacitively couples with one or more electrodes of a display of a tablet computing device; and
where capacitive coupling between the electrode tip and the one or more electrodes of the display is used to determine a position of the electrode tip relative to the one or more electrodes of the display.

17 . A method for transmitting information between a first communication device and a second communication device, the method comprising:
sending a symmetric cryptographic key from the first communication device to the second communication device via capacitive coupling of one or more electrodes of the first communication device and one or more electrodes of the second communication device; and subsequently exchanging encrypted communications with the second communication device over a radio channel formed between a first radio transceiver of the first communication device and a second radio transceiver of the second communication device, the encrypted communications being encrypted using the symmetric cryptographic key.

18 . The method of claim 17 ,
where the first communication device is an input device; where the one or more electrodes of the input device includes an electrode tip; where the second communication device is an interactive display; where the one or more electrodes of the interactive display are part of a touch sensor of the interactive display and include an electrode matrix having row electrodes and column electrodes; and where capacitive coupling between the electrode tip and the electrode matrix is used to determine a position of the electrode tip relative to the electrode matrix.

19 . The method of claim 18 , where the interactive display is configured to randomly excite one or more electrodes of the electrode matrix while the input device is sending the symmetric cryptographic key to the interactive display.

20 . The method of claim 19 , where the interactive display is configured to sense a capacitive signal from the touch sensor and extract the cryptographic key from the capacitive signal by subtracting noise generated by random excitation of the one or more electrodes of the electrode matrix from the capacitive signal.

Assignees

• Microsoft Corp

Inventors

• Westhues Jonathan

Classifications

• H04W12/04 Primary

  Key management, e.g. using generic bootstrapping architecture [GBA] · CPC title

• H04L9/08

  Key distribution {or management, e.g. generation, sharing or updating, of cryptographic keys or passwords (network architectures or network communication protocols for supporting key management in a packet data network H04L63/06)} · CPC title

• G06F3/0412 Primary

  Digitisers structurally integrated in a display · CPC title

• G06F3/03545 Primary

  Pens or stylus · CPC title

• G06F3/044

  by capacitive means · CPC title