Patent ID: 7739492

Claim:
A decrypting method for a decrypting device configured to decrypt an encrypted message encrypted by an encrypting device, the decrypting method comprising: specifying a first decryption enabled node in a first tree structure out of nodes located on a first path ranging from a first terminal node corresponding to the decrypting device to a root node of the first tree structure, and a second decryption enabled node in a second tree structure out of nodes located on a second path ranging from a second terminal node corresponding to the decrypting device to a root node of the second tree structure as a pool for selecting the set of the first decryption enabled node and the second decryption enabled node, wherein the first decryption enabled node and the second decryption enabled node are selected by the encrypting device to encrypt the encrypted message based on a product of secret keys corresponding to each decryption device in the first tree structure and the second tree structure using a first node encryption key associated with the first decryption enabled node and a second node encryption key associated with the second decryption enabled node, and wherein the decrypting device configured to decrypt the encrypted message corresponds with the first terminal node and the second terminal node; acquiring a first node decryption key associated with the first decryption enabled node in the first tree structure and a second node decryption key associated with the second decryption enabled node in the second tree structure; and decrypting the encrypted message encrypted by the first node encryption key associated with the first decryption enabled node and the second node encryption key associated with the second decryption enabled node by use of the acquired first node decryption key and second node decryption key.