Abstract: An RFID tag used to purchase service related to the RFID tag containing purchase information, a service purchase system using the RFID tag, and a service purchase method thereof. The RFID tag provides content information, right information, and purchase information. Therefore, when purchasing service products such as contents, user convenience can be increased and reliability can be guaranteed.

Abstract: A security method using an electronic signature, which improves the performance of an electronic signature authentication by generating and verifying an electronic signature using a mediator, and acquires a forward security in an electronic signature generation and verification by adding a forward secure signature of semi-trusted party (SEM) to a partial signature value generated based on a secret key piece of the SEM. A public key and an optional secret key composed of two kinds of pieces are generated by a certificate authority in response to a request from a user terminal device. The secret key pieces are issued to the user terminal device and a semi-trusted party not to be overlapped with each other. A first signature piece generated from the issued pieces of the private key is transmitted to the user terminal device from the semi-trusted party when a certificate of the user terminal device is still valid.

Abstract: A tag generation method for generating tags used in data packets in a broadcast encryption system is provided. The method includes detecting at least one revoked leaf node; setting a node identification (node ID) assigned to at least one node among nodes assigned node IDs at a layer 0 and to which the at least one revoked leaf node is subordinate, to a node path identification (NPID) of the at least one revoked leaf node at the layer 0; generating a tag list in the layer 0 by combining the NPID of each of the at least one revoked leaf nodes at the layer 0 in order of increment of node IDs of the corresponding at least one revoked leaf nodes; and generating a tag list in a lowest layer by repeatedly performing the setting and generation operation down to the lowest layer.

Abstract: A hybrid broadcast encryption method is provided. The hybrid broadcast encryption method includes setting initialization values, generating a node secret using the initialization values; generating a private secret using the node secret; sending the node secret and the private secret; generating a broadcast message based on a revoked group; encrypting a session key using a key encryption key (KEK) which is allocated to every user group and the broadcast message; and broadcasting to every user the encrypted session key and the broadcast message.

Abstract: A method of generating prevention and control data to verify validity of data to be transmitted, and an apparatus to perform the method, the method including generating the prevention and control data according to composing information of the data to be transmitted, and transmitting the prevention and control data along with the data to be transmitted to verify the validity of the data to be transmitted.

Abstract: A user key management method for a broadcast encryption includes assigning node path identifiers (IDs) to nodes arranged in sequence; assigning random seed value keys to the nodes according to the node path IDs; generating key values by repeatedly applying a hash function to the assigned random seed value keys; and assigning the generated key values to the nodes in sequence. Accordingly, it is possible to reduce the transmission overhead that is most important matter in the broadcast encryption to less than the number of the revoked users. Further, there is an advantage that the transmission overhead of the exemplary embodiments of the present invention is remarkably reduced compared with the Subset Difference method.

Abstract: A method of managing a user key for a broadcast encryption. The method includes assigning numbers to respective users and arranging the users on a ring-shaped structure in order to map hash chains onto the respective nodes of a ring-shaped structure. The method further includes making random node keys correspond to the respective nodes, one by one, constructing the hash chains from the corresponding node keys using a hash function, and successively mapping the constructed hash chains onto the nodes of the ring-shaped structure.

Abstract: An apparatus and method for generating a key for a broadcast encryption. The apparatus includes a node secret generator for managing a user that receives broadcast data in a tree structure and for generating a unique node secret for each node in the tree structure. The apparatus also includes an instant key generator for temporarily generating an instant key used at all nodes in common in the tree structure, and a node key generator for generating a node key for each node by operating the node secret generated at the node secret generator and the instant key generated at the instant key generator. Thus, key update can be efficiently achieved.

Abstract: A digital signature method based on identification information of one or more group members who belong to a group includes: a) a group parameter generating operation generating group public key information and group secret key information corresponding to the group; b) a member registering operation generating member secret key information using identification information of the group members who belong to the group and an identification information digest value obtained by applying a predetermined hash function to the identification information, and transmitting the member secret key information to the group members; c) a digital signing operation generating a digital signature by applying a predetermined signature algorithm to the identification information and the identification information digest value, and transmitting the generated digital signature and a message; and d) an authentication operation verifying a validity of the digital signature by applying a predetermined authentication algorithm to the

Abstract: A conference session key distribution method used in an ID-based cryptographic system includes selecting two different temporary secret keys, generating a message and generating session key generation variables using the temporary secret keys of a session initiating party. Only valid participating parties receive the session key generation variables. Each party determines the session shared key from the session key generation variables.