According to one embodiment, a node that is a root node of a network forming a directed acyclic graph topology, which is composed of plural nodes including the node serving as the root node and having a parent-child relationship among nodes of adjacent hierarchies, includes a generating unit, an encrypting unit, and a transmitting unit. The generating unit generates a group key, and a list indicating a first node to which a distribution of the group key is inhibited. The encrypting unit encrypts the group key so as to be capable of being decrypted by a first child node other than the first node out of the child nodes of the root node. The transmitting unit transmits a first message, including an encrypted group key, which is the group key that is encrypted with respect to the first child node, and the list.