According to an embodiment, a communication apparatus establishes communication with an external apparatus through a higher-level device. The communication apparatus includes a main processor and a key generator. The main processor receives a data authentication request including data to be authenticated, a first key specification, and a message authentication algorithm identifier from the higher-level device. The key generator retains a key hierarchy used by an authentication protocol that is used between the higher-level device and the external apparatus, and to generate a first key by use of the key hierarchy and the first key specification. The main processor generates a message authentication code for the data to be authenticated by use of the message authentication algorithm, which is identified by the message authentication algorithm identifier, and the first key, and transmits a data authentication response including the message authentication code to the higher-level device.