| CPC E05F 15/668 (2015.01) [E05F 15/77 (2015.01); G07C 9/00857 (2013.01); G07C 2009/00865 (2013.01)] | 17 Claims |

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1. A method of effecting secure communications for a first device and a second device, the method comprising:
transmitting a first public key of the first device to the second device;
transmitting a second public key of the second device to the first device;
determining, at the first device, a shared secret session key based at least in part upon a first private key of the first device and the second public key of the second device;
determining, at the second device, the shared secret session key based at least in part upon a second private key of the second device and the first public key of the first device;
transmitting, from the first device to the second device, a first message encrypted using the shared secret session key, the first message including a first fixed code and a first changing code;
transmitting, from the second device to the first device, a second message encrypted using the shared secret session key, the second message including a second fixed code and a second changing code;
transmitting, from the first device to the second device, a third message encrypted using the shared secret session key, the third message including the first fixed code and a changed version of the first changing code;
validating, by the second device, the third message based at least in part on the first fixed code, the first changing code, and the changed version of the first changing code;
transmitting, from the second device to the first device, a fourth message encrypted using the shared secret session key in response to the second device validating the third message, the fourth message including the second fixed code, a changed version of the second changing code, and a long-term key;
transmitting, from the first device to the second device, a fifth message encrypted using the long-term key;
decrypting, by the second device, the fifth message using the long-term key; and
performing, by the second device, an action in response to validating the fifth message.
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