A first IoT, Internet of Things, device for operating in an IoT network of the first IoT device through an nth IoT device (100-n), where n is a natural number equal to or greater than 2, the first IoT device comprising: a key generator configured to store a master key and including a key generation logic for generating a private key based on the master key; a communication unit configured to communicate with the second IoT device through the nth IoT device (100-n) in the IoT network; and an arithmetic unit configured to perform processes of: (a) determining whether the first IoT device is a master device in the IoT network; (b) when the first IoT device is determined to be the master device in the IoT network, generating a second private key through an n th private key respectively corresponding to the second IoT device through the nth IoT device (100-n) by using the key generator and transmitting the second private key through the nth private key to the second IoT device through the n th IoT device (100-n), respectively, via the communication unit; and (c) when the first IoT device is determined to be not the master device in the IoT network, receiving a first private key corresponding to the first IoT device from one of the second IoT device through the n th IoT device (100-n) determined as the master device, wherein the process (b) comprises processes of: (b-1) receiving a second normal key through an n th normal key from the second IoT device through the n th IoT device (100-n), respectively, via the communication unit; (b-2) generating the second private key through the n th private key based on the master key and the second normal key through the n th normal key by using the key generator; and (b-3) transmitting the second private key through the n th private key to the second IoT device through the n th IoT device (100-n), respectively. a key generator configured to store a master key and including a key generation logic for generating a private key based on the master key; a communication unit configured to communicate with the second IoT device through the nth IoT device (100-n) in the IoT network; and an arithmetic unit configured to perform processes of: (a) determining whether the first IoT device is a master device in the IoT network; (b) when the first IoT device is determined to be the master device in the IoT network, generating a second private key through an n th private key respectively corresponding to the second IoT device through the nth IoT device (100-n) by using the key generator and transmitting the second private key through the nth private key to the second IoT device through the n th IoT device (100-n), respectively, via the communication unit; and (c) when the first IoT device is determined to be not the master device in the IoT network, receiving a first private key corresponding to the first IoT device from one of the second IoT device through the n th IoT device (100-n) determined as the master device, wherein the process (b) comprises processes of: (b-1) receiving a second normal key through an n th normal key from the second IoT device through the n th IoT device (100-n), respectively, via the communication unit; (b-2) generating the second private key through the n th private key based on the master key and the second normal key through the n th normal key by using the key generator; and (b-3) transmitting the second private key through the n th private key to the second IoT device through the n th IoT device (100-n), respectively. (a) determining whether the first IoT device is a master device in the IoT network; (b) when the first IoT device is determined to be the master device in the IoT network, generating a second private key through an n th private key respectively corresponding to the second IoT device through the nth IoT device (100-n) by using the key generator and transmitting the second private key through the nth private key to the second IoT device through the n th IoT device (100-n), respectively, via the communication unit; and (c) when the first IoT device is determined to be not the master device in the IoT network, receiving a first private key corresponding to the first IoT device from one of the second IoT device through the n th IoT device (100-n) determined as the master device, wherein the process (b) comprises processes of: (b-1) receiving a second normal key through an n th normal key from the second IoT device through the n th IoT device (100-n), respectively, via the communication unit; (b-2) generating the second private key through the n th private key based on the master key and the second normal key through the n th normal key by using the key generator; and (b-3) transmitting the second private key through the n th private key to the second IoT device through the n th IoT device (100-n), respectively. (b-1) receiving a second normal key through an n th normal key from the second IoT device through the n th IoT device (100-n), respectively, via the communication unit; (b-2) generating the second private key through the n th private key based on the master key and the second normal key through the n th normal key by using the key generator; and (b-3) transmitting the second private key through the n th private key to the second IoT device through the n th IoT device (100-n), respectively.