Method for generating a digital key for secure wireless communication

• US 10,462,655 B2
• Filed: 08/31/2016
• Issued: 10/29/2019
• Est. Priority Date: 09/01/2015
• Status: Active Grant

• Current Assignee: Airbus Defence and Space GmbH (Airbus SE)
• Original Assignee: Airbus Defence and Space GmbH (Airbus SE)
• Inventors: Klaue, Jirka, Heller, Christoph, Kubisch, Martin, Stemmer, Sebastian
• Primary Examiner(s): Pham, Luu T
• Assistant Examiner(s): Cohen, Harvey I
• Application Number:
  US15/253,367
• Publication Number:
  US 20170064547A1
• Time in Patent Office: 1,154 Days
• CPC Class Codes: H04L 2209/24 Key scheduling, i.e. generating round keys or sub-keys for block encryption
• CPC Class Codes: H04L 2209/80 Wireless
• CPC Class Codes: H04L 2209/805 Lightweight hardware, e.g. radio-frequency identification [RFID] or sensor
• CPC Class Codes: H04L 63/0435 wherein the sending and receiving network entities apply symmetric encryption, i.e. same key used for encryption and decryption cryptographic mechanisms or cryptographic arrangements for symmetric key encryption H04L9/06
• CPC Class Codes: H04L 9/0838 Key agreement, i.e. key establishment technique in which a shared key is derived by parties as a function of information contributed by, or associated with, each of these network architectures or network communication protocols for key exchange in a packet data network H04L63/061
• CPC Class Codes: H04L 9/0875 based on channel impulse response [CIR]
• CPC Class Codes: H04W 12/041 Key generation or derivation

Abstract

In a method for generating a digital key in a first communication device and in a second communication device, the first communication device transmits a first electromagnetic signal to the second communication device, which extracts the digital key from the received first electromagnetic signal. The second communication device transmits a second electromagnetic signal to the first communication device, which likewise extracts the digital key from the received second electromagnetic signal. A direct signal component, transmitted on a direct signal path between the first communication device and the second communication device, of the first electromagnetic signal and of the second electromagnetic signal is attenuated.

Claims

1. A method for generating a first digital key in a first communication device and a second digital key in a second communication device, the method comprising:

transmitting a first electromagnetic signal from the first communication device to the second communication device via a reciprocal transmission channel, wherein the first electromagnetic signal is changed by properties of the reciprocal transmission channel;

estimating the reciprocal transmission channel between the first communication device and the second communication device from the first electromagnetic signal received by the second communication device;

determining properties of the estimated reciprocal transmission channel;

generating the second digital key from the properties of the estimated reciprocal transmission channel;

transmitting a second electromagnetic signal from the second communication device to the first communication device via the reciprocal transmission channel, wherein the second electromagnetic signal is changed by properties of the reciprocal transmission channel;

estimating the reciprocal transmission channel between the first communication device and the second communication device from the second electromagnetic signal received by the first communication device;

determining properties of the estimated reciprocal transmission channel; and

generating the first digital key from the properties of the estimated reciprocal transmission channel;

wherein a direct signal component, transmitted on a direct signal path between the first communication device and the second communication device, of the first electromagnetic signal and of the second electromagnetic signal is attenuated;

wherein the transmission channel between the first communication device and the second communication device is reciprocal when a time interval between a transmission of the first electromagnetic signal and transmission of the second electromagnetic signal is less than a coherence time of the transmission channel;

wherein generating the first digital key and the second digital key further comprises;

a quantisation step comprising comparing received electromagnetic signal values with one or more thresholds to determine a bit sequence from which each the digital key is calculated;

or

both the quantisation step and an error correction step;

wherein the properties of the estimated reciprocal transmission channel comprise;

multi-path propagation, free space attenuation, shadowing, diffraction and absorption losses;

utilizing the first digital key to encrypt communication from the first communication device to the second communication device;

utilizing the second digital key to encrypt communication from the second communication device to the first communication device;

wherein attenuation of the direct signal component is brought about by arranging part of a scattering object on the direct signal path; and

wherein the scattering object has a conical or hemispherical or pyramid-shaped portion.

2. The method of claim 1 wherein attenuation of the direct signal component comprises adapting a directional characteristic of an antenna unit of the first or second communication device.

3. The method of claim 1 wherein the first digital key and the second digital key are extracted from a phase or amplitude of the received first and second electromagnetic signal.

4. The method of claim 1 wherein the first and second electromagnetic signal comprise a sequence of at least two different signal values transmitted in succession.

5. The method of claim 1 wherein the first electromagnetic signal is transmitted on at least two different frequencies and the second electromagnetic signal is also transmitted on the at least two different frequencies.

6. The method of claim 1 wherein the direct signal path is a line-of-sight connection between the first communication device and the second communication device.

7. The method of claim 1 wherein the direct signal component is attenuated relative to other signal components which are not transmitted on the direct signal path and are transmitted between the first and second communication device by multi-path propagation.

8. The method of claim 1 wherein signal components which are not transmitted on the direct signal path and are transmitted between the first and second communication device by multi-path communication are amplified.

9. The method of claim 1 wherein the direct signal component is completely suppressed.

10. A communication system comprising:

a first communication device; and

a second communication device,

wherein the first communication device is configured to transmit a first electromagnetic signal from the first communication device to the second communication device via a reciprocal transmission channel, and to generate a first digital key from a received second electromagnetic signal which was transmitted by the second communication device, and

wherein the second communication device is configured to transmit the second electromagnetic signal to the first communication device via the reciprocal transmission channel, and to generate a second digital key from the received first electromagnetic signal,

a direct signal component, transmitted on a direct signal path between the first communication device and the second communication device, of the first electromagnetic signal and of the second electromagnetic signal being attenuated,

wherein the first electromagnetic signal and the second electromagnetic signal are changed by properties of the reciprocal transmission channel,

wherein the first communication device is configured to;

estimate the reciprocal transmission channel between the first communication device and the second communication device from the second electromagnetic signal transmitted by the second communication device;

determine properties of the estimated reciprocal transmission channel; and

generate the first digital key from the properties of the estimated reciprocal transmission channel;

wherein the second communication device is configured to;

estimate the reciprocal transmission channel between the first communication device and the second communication device from the first electromagnetic signal transmitted by the first communication device;

determine properties of the estimated reciprocal transmission channel; and

generate the second digital key from the properties of the estimated reciprocal transmission channel;

wherein the transmission channel between the first communication device and the second communication device is reciprocal when a time interval between a transmission of the first electromagnetic signal and transmission of the second electromagnetic signal is less than a coherence time of the transmission channel;

wherein the first communication device and the second communication device are configured to generate the first digital key and the second digital key, at least in part, by;

a quantisation step comprising comparing received electromagnetic signal values with one or more thresholds to determine a bit sequence from which the digital key is calculated;

or

both the quantisation step and an error correction step

wherein the properties of the estimated reciprocal transmission channel comprise;

multi-path propagation, free space attenuation, shadowing, diffraction and absorption losses;

wherein the first communication device is further configured to utilize the first digital key to encrypt communication from the first communication device to the second communication device;

wherein the second communication device is further configured to utilize the second digital key to encrypt communication from the second communication device to the first communication device;

wherein attenuation of the direct signal component is brought about by arranging part of a scattering object on the direct signal path; and

wherein the scattering object has a conical or hemispherical or pyramid-shaped portion.