Secret key for wireless communication in cyber-physical automotive systems

• US 10,129,022 B1
• Filed: 02/22/2017
• Issued: 11/13/2018
• Est. Priority Date: 02/22/2016
• Status: Active Grant

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Al Faruque, Mohammad Abdullah, Wan, Jiang, Lopez, Anthony
• Primary Examiner(s): Lwin, Maung T
• Application Number:
  US15/439,102
• Time in Patent Office: 629 Days
• Field of Search: None
• CPC Class Codes: H04L 63/0428 wherein the data content is protected, e.g. by encrypting or encapsulating the payload
• 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 9/001 using chaotic signals
• CPC Class Codes: H04L 9/002 Countermeasures against attacks on cryptographic mechanisms network architectures or network communication protocols for protection against malicious traffic H04L63/1441
• CPC Class Codes: H04L 9/0866 involving user or device identifiers, e.g. serial number, physical or biometrical information, DNA, hand-signature or measurable physical characteristics
• CPC Class Codes: H04W 12/03 Protecting confidentiality, e.g. by encryption
• CPC Class Codes: H04W 12/041 Key generation or derivation
• CPC Class Codes: H04W 12/047 without using a trusted network node as an anchor
• CPC Class Codes: H04W 12/79 Radio fingerprint
• CPC Class Codes: H04W 4/40 for vehicles, e.g. vehicle-to-pedestrians [V2P]

Abstract

A key generation technique exploiting the randomness of a wireless channel to generate secret keys to secure automotive wireless communication using symmetric cryptography is presented. Moreover, the algorithm of the present technique solves the challenging key exchange problem in automotive wireless communication with low costs in terms of performance and code size. As demonstrated, the proposed algorithm can generate secret keys with 67% average min-entropy. Furthermore, the proposed technique can achieve up to 10× performance and 20× code size reduction in comparison to the state-of-the-art hybrid cryptographic algorithms.

Claims

1. A method of generating a key to effectively secure wireless communications between a first communication node and a second communication node, wherein a first cyber-physical system is disposed within the first communication node and a second cyber-physical system is disposed within the second communication node, wherein each cyber-physical system performs an encryption and decryption of said wireless communications, wherein the method comprises:

a. sending and receiving a predefined group of probe signals, of predefined size (“

G_size”

), between the first communication node and the second communication node via a wireless channel, wherein the group of probe signals are sent for evaluating randomness of a channel gain of the wireless channel;

b. collecting a plurality of received signal strength (“

RSS”

) values from the wireless channel;

c. obtaining a plurality of filtered RSS values by filtering the plurality of RSS values with a high-pass filter defined by an impulse frequency response of the wireless channel, wherein the plurality of filtered RSS values contain information needed to generate the key of required length, K_length;

d. generating a set of bits, comprising;

i. calculating an upper threshold, Th_up, and a lower threshold, Th_lo, based on a mean and a variation of the plurality of filtered RSS values; and

ii. assigning each filtered RSS value greater than Th_up to 1 and assigning each filtered RSS value less than Th_lo to 0, wherein each filtered RSS value between Th_up and Th_lo is discarded;

e. generating the key having a length L, by collecting the set of bits; and

f. verifying a length, L, of the key (104), wherein if L is less than K_length, then steps a-f are repeated until L is greater than or equal to K_length,

wherein the key is used by the first and second cyber-physical systems to encrypt and decrypt the wireless communications between the first and second communication nodes.

2. The method of claim 1, wherein each probe signal is exchanged within a time period less than a coherence time (“

T_c”

) of the wireless channel between the first communication node and the second communication node.

3. The method of claim 2, wherein a time interval (“

τ

_step”

) between exchanging each probe signal is not less than T_c.

4. The method of claim 3, wherein the plurality of RSS values are collected within time period defined by G_size×

τ

_step.

5. The method of claim 1 further comprising performing a mismatch check to remove one or more mismatch bits from the set of bits.

6. The method of claim 1 further comprising determining an energy and performance-aware optimization, wherein said optimization is formulated as a linear optimization problem to be minimized:

W₁*(KeyGenOHR_p+CryptOHR_p)+W₂*(KeyGenOHR_e+CryptOHR_e),

wherein W₁ is a pre-defined weight performance, W₂ is a predefined energy overhead, KeyGenO H R_p is a key generation performance overhead, KeyGenO H R_e is a key generation energy overhead, CryptO H R_p is a cryptographic algorithm performance overhead and CryptO H R_e is a cryptographic algorithm energy overhead, wherein solving the linear optimization problem provides an optimized solution for the cryptographic algorithm, the K_length, and a time interval for which the cryptographic algorithm or the key is effective.

7. The method of claim 1, wherein the first communication node is a vehicle or infrastructure.

8. The method of claim 1, wherein the second communication node is a vehicle or infrastructure.

9. A system (200) for generating a key to effectively secure wireless communications between a first communication node (215) and a second communication node (217), wherein a first cyber-physical system (201) is disposed at the first communication node (215) and a second cyber-physical system (221) is disposed at the second communication node (217), wherein each cyber-physical system performs an encryption and decryption of said wireless communications, wherein the system (200) comprises:

a. a first transceiver (203) disposed at the first communication node (215);

b. a second transceiver (219) disposed at the second communication node (217), wherein the second transceiver (219) is linked to the first transceiver (203) by a wireless channel;

c. a processor, operatively coupled to the first transceiver (203); and

d. a memory operatively coupled to the processor, configured to store digitally-encoded instructions that, when executed by the processor, cause the processor to perform operations comprising;

i. sending and receiving a predefined group of probe signals of predefined size (“

G_size”

), between the first transceiver (203) and the second transceiver (219) via the wireless channel, wherein the group of probe signals are sent for evaluating randomness of a channel gain of the wireless channel;

ii. collecting a plurality of received signal strength (“

RSS”

) values from the wireless channel;

iii. obtaining a plurality of filtered RSS values by filtering the plurality of RSS values with a high-pass filter defined by an impulse frequency response of the wireless channel, wherein the plurality of filtered RSS values contain information needed to generate the key of required length, K_length;

iv. generating a set of bits, comprising;

A. calculating an upper threshold, Th_up, and a lower threshold, Th_lo, based on a mean and a variation of the plurality of filtered RSS values; and

B. assigning each filtered RSS value greater than Th_up to 1 and assigning each filtered RSS value less than Th_lo to 0, wherein each filtered RSS value between Th_up and Th_lo is discarded;

v. generating the key having a length L, by collecting the set of bits;

vi. performing a mismatch check to remove one or more mismatch bits from the set of bits of the key;

vii. determining and applying an energy and performance-aware optimization, wherein said optimization is formulated as a linear optimization problem to be minimized, wherein solving the linear optimization problem provides an optimized solution for the K_length and a time interval for which the key is effective; and

viii. verifying a length, L, of the key, wherein if L is less than K_length, then steps i-viii are repeated until L is greater than or equal to K_length,

wherein the key is used by the first and second cyber-physical systems (201, 221) to encrypt and decrypt the wireless communications between the first and second communication nodes (215, 217).

10. The system of claim 9, wherein each probe signal is exchanged within a time period less than a coherence time (“

T_c”

) of the wireless channel between the first communication node and the second communication node, wherein a time interval (“

τ

_step”

) between exchanging each probe signal is not less than T_c.

11. The system of claim 10, wherein the plurality of RSS values are collected within time period defined by G_size×

τ

_step.

12. The system of claim 9, wherein said linear optimization problem to be minimized is:

W₁*(KeyGenOHR_p+CryptOHR_p)+W₂*(KeyGenOHR_e+CryptOHR_e),

wherein W₁ is a pre-defined weight performance, W₂ is a predefined energy overhead, KeyGenO H R_p is a key generation performance overhead, KeyGenO H R_e is a key generation energy overhead, CryptO H R_p is a cryptographic algorithm performance overhead and CryptO H R_e is a cryptographic algorithm energy overhead, wherein solving the linear optimization problem provides an optimized solution for the cryptographic algorithm, the K_length, and a time interval for which the cryptographic algorithm or the key is effective.

13. A system (200) for generating a key to effectively secure wireless communications between a first communication node (215) and a second communication node (217), wherein a first cyber-physical system (201) is disposed at the first communication node (215) and a second cyber-physical system (221) is disposed at the second communication node (217), wherein each cyber-physical system performs an encryption and decryption of said wireless communications, wherein the system (200) comprises:

a. a first transceiver (203) disposed at the first communication node (215);

b. a second transceiver (219) disposed at the second communication node (217), wherein the second transceiver (219) is linked to the first transceiver (203) by a wireless channel;

c. a processor, operatively coupled to the first transceiver (203); and

d. a memory operatively coupled to the processor, configured to store digitally-encoded instructions that, when executed by the processor, cause the processor to perform operations comprising;

i. sending and receiving a predefined group of probe signals, of predefined size (“

G_size”

), between the first transceiver (203) and the second transceiver (219) via the wireless channel, wherein the group of probe signals are sent for evaluating randomness of a channel gain of the wireless channel;

ii. collecting a plurality of received signal strength (“

RSS”

) values from the wireless channel;

iii. obtaining a plurality of filtered RSS values by filtering the plurality of RSS values with a high-pass filter defined by an impulse frequency response of the wireless channel, wherein the plurality of filtered RSS values contain information needed to generate the key of required length, K_length;

iv. generating a set of bits, comprising;

A. calculating an upper threshold, Th_up, and a lower threshold, Th_lo, based on a mean and a variation of the plurality of filtered RSS values; and

B. assigning each filtered RSS value greater than Th_up to 1 and assigning each filtered RSS value less than Th_lo to 0, wherein each filtered RSS value between Th_up and Th_lo is discarded;

v. generating the key having a length L, by collecting the set of bits; and

vi. verifying a length, L, of the key, wherein if L is less than K_length, then steps i-ix are repeated until L is greater than or equal to K_length;

wherein the key is used by the first and second cyber-physical systems (201, 221) to encrypt and decrypt the wireless communications between the first and second communication nodes (215, 217).

14. The system of claim 13, wherein each probe signal is exchanged within a time period less than a coherence time (“

T_c”

) of the wireless channel between the first communication node and the second communication node.

15. The system of claim 14, wherein a time interval (“

τ

_step”

) between exchanging each probe signal is not less than T_c.

16. The system of claim 15, wherein the plurality of RSS values are collected within time period defined by G_size×

τ

_step.

17. The system of claim 13, wherein operations performed by the processor further comprises performing a mismatch check to remove one or more mismatch bits from the set of bits of the key.

18. The system of claim 13, wherein operations performed by the processor further comprises determining and applying an energy and performance-aware optimization, wherein said optimization is formulated as a linear optimization problem to be minimized, wherein said linear optimization problem to be minimized is:

W₁*(KeyGenOHR_p+CryptOHR_p)+W₂*(KeyGenOHR_e+CryptOHR_e),

wherein W₁ is a pre-defined weight performance, W₂ is a predefined energy overhead, KeyGenO H R_p is a key generation performance overhead, KeyGenO H R_e is a key generation energy overhead, CryptO H R_p is a cryptographic algorithm performance overhead and CryptO H R_e is a cryptographic algorithm energy overhead, wherein solving the linear optimization problem provides an optimized solution for the cryptographic algorithm, the K_length, and a time interval for which the cryptographic algorithm or the key is effective.

19. The system of claim 13, wherein the first communication node is a vehicle or infrastructure.

20. The system of claim 13, wherein the second communication node is a vehicle or infrastructure.