A security chip and an application processor may be included in a device configured to engage in encrypted communications with an external client, including public key infrastructure communications, in an environment where a certificate authority is absent. The security chip may provide the application processor with a device public key from among a pair of device keys related to public key infrastructure communications, receive a request from the application processor to generate a digital signature on a certificate form including the device public key, provide the application processor with a digital signature generated based on an encryption operation using a certificate authority private key, and receive and store a certificate including the digital signature from the application processor.