Sharing system access using a mobile device

1. A control unit, comprising:

a processor; and

memory having program instructions stored therein that are executable by the processor to cause the control unit to perform operations including:

performing a Bluetooth pairing operation with a first mobile device, wherein the Bluetooth pairing operation includes the control unit sending, to the first mobile device, wireless credentials usable by the first mobile device to determine a changing communication address of the control unit, and wherein the first mobile device is configured to share the wireless credentials with a second mobile device, and wherein the wireless credentials include a public media access control (MAC) address and identity resolving key (IRK) of the control unit;

establishing, with the second mobile device, a Bluetooth link, wherein the second mobile device is addressed by the control unit using an initial IRK of the second mobile device;

receiving, from the second mobile device over the Bluetooth link, a different IRK to be used for subsequent communications;

receiving, from the second mobile device, a communication directed to the changing communication address of the control unit, wherein the communication is indicative of a request from the second mobile device to access a system controlled by the control unit; and

in response to receiving the request, determining whether to enable the second mobile device to access to the system controlled by the control unit.

2. The control unit of claim 1 , wherein the operations further include:

receiving, from the first mobile device, wireless credentials of the second mobile device that include the initial IRK; and

performing an authentication based on the wireless credentials of the second mobile device in order to establish the Bluetooth link with the second mobile device.

3. The control unit of claim 1 , wherein the operations further include:

deriving a cryptographic key based on a sharing cryptographic key established with the first mobile device during the Bluetooth pairing operation; and

performing an authentication by decrypting at least a portion of the communication with the derived cryptographic key.

4. The control unit of claim 1 , wherein the control unit is an electronic control unit (ECU) configured to enable physical entry into the system.

5. A non-transitory computer readable medium having program instructions stored therein that are executable by a second mobile device to perform operations comprising:

receiving, from a first mobile device, first wireless credentials of a control unit configured to control access to a system, wherein the first wireless credentials include a first public media access control (MAC) address and an identity resolving key (IRK) of the control unit, wherein the first mobile device obtained the first wireless credentials in a Bluetooth pairing operation with the control unit;

providing, to the first mobile device, second wireless credentials of the second mobile device, wherein the second wireless credentials include a second public media access control (MAC) address and an initial identity resolving key (IRK) of the second mobile device;

establishing a Bluetooth link with the control unit using the first and second wireless credentials, wherein the establishing includes determining a changing communication address of the control unit based on the first wireless credentials;

changing the initial IRK to a different IRK and communicating the different IRK to the control unit over the established Bluetooth link; and

sending, over the established Bluetooth link, a request to obtain access to the system controlled by the control unit.

6. The computer readable medium of claim 5 , wherein the operations further comprising:

receiving, from the first mobile device, a second link cryptographic key derived from a sharing cryptographic key established between the first mobile device and the control unit during the Bluetooth pairing operation; and

encrypting the request with the second link cryptographic key.

7. The computer readable medium of claim 6 , wherein the second link cryptographic key is generated by applying a key derivation function (KDF) to the sharing cryptographic key, a first link cryptographic key established during the Bluetooth pairing operation for communications between the first mobile device and the control unit, and a counter value, the counter value being indicative of a number of devices that have received authorization information for accessing the system.

8. The computer readable medium of claim 6 , wherein the operations further comprise:

receiving, from the first mobile device, a beacon cryptographic key derived from the sharing cryptographic key; and

sending, to the control unit, a beacon including a payload encrypted with the beacon cryptographic key, wherein the encrypted payload is usable to authenticate the second mobile device to the control unit.

9. The computer readable medium of claim 8 , wherein the beacon cryptographic key is generated by the first mobile device applying a key derivation function (KDF) to the sharing cryptographic key and a counter value, the counter value being indicative of a number of devices that have received authorization information for accessing the system.

10. The computer readable medium of claim 5 , wherein the control unit is an electronic control unit (ECU) configured to unlock a door of the system.

11. A method, comprising:

receiving, at a second mobile device from a first mobile device, first wireless credentials of a control unit configured to control access to a system, wherein the first wireless credentials include a first public media access control (MAC) address and an identity resolving key (IRK) of the control unit, wherein the first mobile device obtained the first wireless credentials in a Bluetooth pairing operation with the control unit;

providing, by the second mobile device to the first mobile device, second wireless credentials of the second mobile device, wherein the second wireless credentials include a second public media access control (MAC) address and an initial identity resolving key (IRK) of the second mobile device;

establishing, by the second mobile device, a Bluetooth link with the control unit using the first and second wireless credentials, wherein the establishing includes determining a changing communication address of the control unit based on the first wireless credentials;

changing, by the second mobile device, the initial IRK to a different IRK and communicating the different IRK to the control unit over the established Bluetooth link; and

sending, by the second mobile device over the established Bluetooth link, a request to obtain access to the system controlled by the control unit.

12. The method of claim 11 , further comprising:

receiving, at the second mobile device from the first mobile device, a beacon cryptographic key derived from a sharing cryptographic key established between the first mobile device and the control unit.

13. The method of claim 12 , wherein the beacon cryptographic key is generated by the first mobile device applying a key derivation function (KDF) to the sharing cryptographic key and a counter value, the counter value being indicative of a number of devices that have received authorization information for accessing the system.

14. The method of claim 12 , wherein the establishing includes:

sending, to the control unit, a beacon including a payload encrypted with the beacon cryptographic key.

15. The method of claim 14 , further comprising:

receiving, at the second mobile device from the first mobile device, a second link cryptographic key derived from the sharing cryptographic key; and

using, by the second mobile device, the second link cryptographic key to encrypt traffic directed to the control unit after being authenticated.

16. The method of claim 15 , wherein the second link cryptographic key is generated by applying a key derivation function (KDF) to the sharing cryptographic key, a first link key established during the Bluetooth pairing operation, and a counter value, the counter value being indicative of a number of devices that have received authorization information for accessing the system.

17. The method of claim 11 , wherein the control unit is an electronic control unit (ECU) configured to operate an entry mechanism of the system.

18. The method of claim 12 , wherein the sharing cryptographic key is established by a Diffie-Hellman exchange between the first mobile device and the control unit.