Patent ID: 8340284

Claim:
A key generation device comprising: a calculation unit that calculates three groups G, G′ and G T of the same order for which there exist a bilinear map from group G and group G′ to group G T and an isomorphic map from group G′ to group G, a receiving unit that receives a random number, an identity, a master key that includes secret hierarchical elements of group G′ in number proportional to a number of hierarchical layers that is a variable representing a depth of hierarchical structure of the identity, and a public key that includes the number of hierarchical layers and hierarchical elements that are a set of the isomorphic map of values of the secret hierarchical elements and does not include the secret hierarchical elements, to generate a secret key; and a generating unit that generates specific two random number elements based on the input random number, and generates the secret key that includes elements each obtained by raising the secret hierarchical elements to a power of each of the two random number elements.