The present invention provides a system to ensure security of data in a computer network system. A center certifies a public-key of user of the system and distributes a secret-key. A first system comprises the center in a network, an information provider and a plurality of users. The center identifies utilization status by requests of the secret-key. The data is encrypted by the secret-key and is stored and transferred, while the data to be stored and transferred is encrypted by a secret-key different from the secret-key of the transferred data. An original data label is added to the original data, and an edit label is added to the edited data, and the center does not store the data and stores only the original data label and the edit label. A second system comprises a center and an information provider in a network, and a plurality of users utilizing the network. The center stores the original data and editing scenario, and also the original data label, user label and edit label. The data is not transferred between the users, but data label encrypted by the public-key is transferred. In electronic commerce system, every data is distributed through a mediator in the network, data which is transferred from a maker to a user is encrypted by a secret-key for encryption, and data which is transferred from the user to the maker is encrypted by a secret-key for re-encryption.