# US 11,122,425 B2 · Systems and methods for encrypting communication between vehicles

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- Number: US 11,122,425 B2
- Document ID: US11122425B2
- Status: Granted
- Kind: B2
- Application number: 16/510,097
- Filed: 2019-07-12
- Published: 2020-01-16
- Granted: 2021-09-14
- Earliest claimed: 2018-07-13
- Assignees: The Regents of the University of California
- Applicants: The Regents of the University of California
- Inventors: Imam Uz Zaman; Anthony Bahadir Lopez; Mohammad Abdullah Al Faruque; Ozdal Boyraz
- Web page: https://patentgrep.com/patent/US11122425B2

## CPC

- H04L 9/12: Transmitting and receiving encryption devices synchronised or initially set up in a particular manner
- H04W 12/03: Protecting confidentiality, e.g. by encryption
- H04B 10/116: Visible light communication
- H04L 9/0852: {Quantum cryptography (transmission systems employing electromagnetic waves other than radio waves, e.g. light, infrared H04B10/00; wavelength-division multiplex systems H04J14/02; WDM arrangements H04J14/03)}
- H04L 9/0866: {involving user or device identifiers, e.g. serial number, physical or biometrical information, DNA, hand-signature or measurable physical characteristics}
- 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)}
- H04L 63/061: {for key exchange, e.g. in peer-to-peer networks (cryptographic mechanisms or cryptographic arrangements for key agreement H04L9/0838)}
- H04W 4/46: for vehicle-to-vehicle communication [V2V]
- H04W 12/041: Key generation or derivation
- H04L 2209/80: Wireless
- H04L 2209/84: Vehicles
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72)
- H04B: TRANSMISSION

## Abstract

A physical layer secret key generation scheme exploiting randomness of the road surface and driving behavior is described herein. A symmetric key generation scheme can be implemented in any existing V2V visible light communication. By analyzing and simulating numerous samples taken from NGSIM vehicle trajectory data, the natural driving behavior and road surface roughness can be exploited as a source of randomness to generate symmetric cryptographic security keys.

## Claims

### Claim 1

A method of generating a set of at least two identical encryption keys, for encrypting data across a communications channel shared by at least two vehicles, wherein the encryption keys are generated independently by each vehicle, wherein the encryption keys are generated from a stochastic process of the communications channel shared by the vehicles, wherein the stochastic process is observable to all of the vehicles and caused by road conditions and driving behavior, said method comprising:
a. coordinating a common time for the vehicles to begin sampling the stochastic process (101);
b. for all of the vehicles, simultaneously sampling a plural number of sample points of the stochastic process (102), wherein the number of sample points is identical for all of the vehicles, wherein each sample point has a corresponding index;
c. for each vehicle, for each sample in the plurality of samples (103) thus sampled, quantizing the sample point using a quantization rule (104), wherein the quantization rule is the same for all vehicles, wherein the quantized point is a key bit of the encryption key, wherein the quantization rule determines if the key bit is a one “1”, a “0”, or invalid, wherein if the sample point is a “1” or a “0”, it is a valid sample point, wherein the indices corresponding to the valid sample points comprise a plurality of valid indices (105), wherein the key bits of all of the valid sample points together comprise a plurality of key bits (109);
d. for each vehicle, sharing the plurality of valid indices with all other vehicles;
e. for each vehicle, comparing the pluralities of valid indices for all of the other vehicles, selecting only the valid indices shared by all vehicles (107), and determining a plurality of shared valid indices (108) that are common to all of the at least two vehicles, and
f. for each vehicle, selecting the plurality of key bits corresponding to the shared valid index values (110), wherein the plurality of key bits thus selected comprises the encryption key (111),
wherein because the stochastic process is observable to all of the vehicles, and the process used to generate the plurality of key bits is common to all vehicles, the encryption keys thus generated are identical.

### Claim 2 (depends on 1)

The method of claim 1, wherein the communications channel is a vehicle to vehicle visible light communication channel, wherein a pre-defined visible light signal is simultaneously transmitted between the at least two vehicles, wherein the signal is symmetrically affected by road conditions and driving behavior in a manner observable to the vehicles, wherein the stochastic process comprises fluctuations in a signal strength of the visible light signal transmitted between the vehicles.

### Claim 3 (depends on 1)

The method of claim 1, wherein the signal is an RF signal, wherein the stochastic process comprises fluctuations of RF signal strength caused by road conditions and driving behavior.

### Claim 4 (depends on 1)

The method of claim 1, wherein the signal is visible light of headlights from one vehicle to the other, wherein the stochastic process comprises fluctuations of headlight light brightness due to the road conditions and driving behavior.

### Claim 5 (depends on 1)

The method of claim 1, wherein the quantization rule comprises an upper and a lower threshold, wherein the key bit is a 1 if the sample value is greater than the upper threshold, wherein the key bit is a 0 if the sample is below the lower threshold, wherein the sample is invalid otherwise.

### Claim 6 (depends on 5)

The method of claim 5, wherein the threshold values vary depending on the index corresponding to the sample point.

### Claim 7

A system (200) for sending encrypted messages between a first vehicle and a second vehicle, wherein the first vehicle and the second vehicle are symmetrically affected by a stochastic nature of road conditions and driving behavior, wherein a pre-defined probe signal is sent between the first vehicle and the second vehicle which is symmetrically affected by road conditions and driving behavior, wherein received probe signals are used to generate symmetric encryption keys, the system comprising:
a. the first vehicle (201), capable of transmitting a first light signal (210);
b. a first transceiver (202) disposed on the first vehicle (201);
c. a first sensor (203) disposed on the first vehicle (201), capable of sensing a second light signal (211) transmitted by the second vehicle (205);
d. a first processor (204), operatively connected to the first transceiver (202) and the first sensor (203), executing computer readable instructions comprising:
i. instructions for sending messages (209) to the second vehicle via the first transceiver, and for receiving messages from the second vehicle via the first transceiver;
ii. instructions for sending a pre-defined probe signal to the second vehicle;
iii. instructions for receiving the pre-defined probe signal from the second vehicle;
iv. instructions for sampling a fixed number of sample points from the pre-defined probe signal at fixed intervals, producing a first plurality of sample points (212), wherein each sample point has an index value;
v. instructions for quantizing the first plurality of sample points, wherein the quantized sample point is a “1” or a “0”, or invalid, wherein the quantized sample points that are “1” or “0” are valid, wherein the index values of the valid sample points comprise a first plurality of valid index values, wherein the valid quantized sample points comprise a first plurality of key bits corresponding to the first plurality of valid index values,
vi. instructions for transmitting the first plurality of valid index values to the second vehicle (214),
vii. instructions for receiving a second plurality of valid index values from the second vehicle (214),
viii. instructions for comparing the first plurality of valid index values to the second plurality of valid index values, and for determining a plurality of shared valid index values;
ix. instructions for selecting the plurality of key bits corresponding to the plurality of shared valid index values, wherein the plurality of key bits thus selected comprises a first encryption key (215);
x. instructions for encrypting a first message using the first encryption key;
xi. instructions for transmitting the encrypted first message to the second vehicle;
xii. instructions for receiving an encrypted second message from the second vehicle; and
xiii. instructions for decrypting the encrypted second message using the first encryption key;
e. the second vehicle (205), capable of transmitting the second light signal (211);
f. a second transceiver (206), disposed on the second vehicle;
g. a second sensor (207), disposed on the second vehicle, capable of sensing the first light signal (210) of the first vehicle;
h. the second processor (208), operatively connected to the second transceiver and the second sensor, capable of executing computer readable instructions comprising:
i. instructions for sending messages (209) to the first vehicle via the transceiver, and receiving messages from the second vehicle via the transceiver;
ii. instructions for sending the pre-defined probe signal to the first vehicle;
iii. instructions for receiving the pre-defined probe signal from the first vehicle;
iv. instructions for sampling a fixed number of sample points from the received probe signal at fixed intervals, producing a second plurality of sample points (213), wherein each sample point has an index value;
v. instructions for quantizing the second plurality of sample points, wherein the quantized sample point is a “1” or a “0”, or invalid, wherein the quantized sample points that are “1” or “0” are valid, wherein the index values of the valid sample points comprise a second plurality of valid index values, wherein the valid quantized sample points comprise a second plurality of key bits corresponding to the second plurality of valid index values,
vi. instructions for transmitting the second plurality of valid index values to the first vehicle (214),
vii. instructions for receiving a first plurality of valid index values from the first vehicle,
viii. instructions for comparing the first plurality of valid index values to the second plurality of valid index values, and for producing a plurality of shared valid index values;
ix. instructions for selecting the plurality of key bits corresponding to the shared valid index values, wherein the plurality of key bits thus selected is a second encryption key (216);
x. instructions for encrypting a second message using the second encryption key;
xi. instructions for transmitting the encrypted second message to the first vehicle
xii. instructions for receiving the encrypted first message from the first vehicle
xiii. instructions for decrypting the encrypted first message using the second encryption key;
wherein the instructions for quantizing the sample points are the same for both vehicles, wherein the same number of sample points is sampled by both vehicles, wherein consequently the encryption keys generated are identical, wherein as a result the first vehicle is able to correctly decrypt the encrypted second message from the second vehicle, and the second vehicle is able to correctly decrypt the encrypted first message from the first vehicle.

### Claim 8 (depends on 7)

The system (200) of claim 7, wherein the quantization rule comprises an upper and a lower threshold, wherein the key bit is a 1 if the sample value is greater than the upper threshold, wherein the key bit is a 0 if the sample is below the lower threshold, wherein the sample is invalid otherwise.

### Claim 9 (depends on 8)

The system (200) of claim 8, wherein the threshold values vary depending on the sample index value corresponding to the sample point.

### Claim 10

A system (200) for sending encrypted messages between a first vehicle and a second vehicle that are symmetrically affected by a stochastic process, wherein the stochastic process is observable to the first vehicle and the second vehicle and caused by road conditions and driving behavior, said system comprising:
a. the first vehicle (201) capable of transmitting a signal (210);
b. a first transceiver (202) disposed on the first vehicle (201);
c. a first sensor (203) disposed on the first vehicle (201), capable of sensing a signal (211) transmitted by the second vehicle (205);
d. a first processor (204) operatively connected to the first transceiver (202) and the first sensor (203);
e. the second vehicle (205) capable of transmitting a signal (211);
f. a second transceiver (206) disposed on the second vehicle;
g. a second sensor (207) disposed on the second vehicle, capable of sensing the signal (210) transmitted by the first vehicle (201); and
h. the second processor (208) operatively connected to the second transceiver (206) and the second sensor (207);
wherein the first processor (204) and the second processor (207) execute computer readable instructions that causes each processor to independently perform operations comprising:
i. sending and receiving the signals with the processor of the other vehicle;
ii. sampling a fixed number of sample points from the received signal at fixed intervals, thereby producing a plurality of sample points (212), each sample point having an index, wherein a same number of sample points is sampled by both vehicles, wherein the plurality of sample points is unique to the received signal due to the stochastic nature of the road conditions and driving behavior;
iii. quantizing the plurality of sample points, wherein the quantized sample point is either a “1” or a “0”, or invalid, wherein the quantized sample points that are “1” or “0” are valid, wherein the index values of the valid sample points are valid index values, wherein the valid quantized sample points comprise a plurality of key bits corresponding to the plurality of valid index values,
iv. transmitting the plurality of valid index values to the other vehicle;
v. receiving a plurality of valid index values from the other vehicle;
vi. comparing the two pluralities of valid index values to determine a plurality of shared valid index values;
vii. selecting the plurality of key bits corresponding to the plurality of shared valid index values, wherein the plurality of key bits thus selected comprises an encryption key;
viii. encrypting a message using the encryption key;
ix. transmitting the encrypted message to the other vehicle;
x. receiving an encrypted message from the other vehicle; and
xi. decrypting the encrypted message using the encryption key;
wherein the signals sent between the vehicles are symmetrically affected by road conditions and driving behavior in a manner observable to the vehicles, wherein the received signals are used to generate symmetric encryption keys, wherein instructions for quantizing the sample points are the same for both vehicles, wherein the encryption keys generated are identical, wherein as a result, the first vehicle is able to correctly decrypt the message from the second vehicle and the second vehicle is able to correctly decrypt the message from the first vehicle.

### Claim 11 (depends on 10)

The system of claim 10, wherein the signals are visible light signals, wherein the stochastic process is a fluctuation in a signal strength of the visible light signals caused by road conditions and driving behavior.

### Claim 12 (depends on 11)

The system of claim 11, wherein the visible light signals are generated by headlights or taillights of the vehicles.

### Claim 13 (depends on 10)

The system (200) of claim 10, wherein the first and second sensors are photodetectors capable of detecting the light signals.

### Claim 14 (depends on 10)

The system of claim 10, wherein the signals are radio frequency (RF) signals, wherein the stochastic process is a fluctuation of RF signal strength caused by road conditions and driving behavior.

### Claim 15 (depends on 10)

The system (200) of claim 10, wherein the quantization rule comprises an upper and a lower threshold, wherein the key bit is a 1 if the sample value is greater than the upper threshold, wherein the key bit is a 0 if the sample is below the lower threshold, wherein the sample is invalid otherwise.

### Claim 16 (depends on 15)

The system (200) of claim 15, wherein the threshold values vary depending on the sample index value corresponding to the sample point.