According to an aspect of the embodiment, there is provided a transmitting apparatus, including a data storage, a first key storage, a second key storage, an additional information generating unit, a first authenticator generating unit, a second authenticator generating unit, a third authenticator generating unit, and a packet transmitting unit. a judging unit that judges the candidate is admitted as the second authenticator, when the candidate contains a common part of the first authenticator. a third authenticator generating unit generates a third authenticator based on a second authenticator that is a second authenticator candidate contains a common part of the first authenticator. The packet transmitting unit transmits a packet including the data and the third authenticator.