Method and apparatus of generating encryption key for broadcast encryption

A method, using a hardware processor, for generating an encryption key for broadcast encryption, the method comprising:

• generating, by the hardware processor, a first encryption key with respect to all nodes, configured in a plurality of depths, from a root node to a plurality of leaf nodes;
• and
• generating, by the hardware processor, a second encryption key for a first child node connected to a sibling node of an intermediate node between the root node and the plurality of leaf nodes, wherein:
• the generating of the second encryption key comprises generating any one of first and second keys using the first encryption key of the intermediate node depending on whether the first child node, connected to a sibling node of the intermediate node, is on a left path or a right path of the sibling node,
• the generating of the second encryption key comprises generating a corresponding encryption key in a hash chain type using at least any one of the first and second encryption keys, the second encryption key being generated by applying a first hash function HL(.),
• the second encryption key is generated by a hash of the first encryption key belonging to the intermediate node, and
• the sibling node cannot determine the second encryption key of the first child node.