Abstract: A terminal of a user as an issuer of electronic information calculates a Digest value for a content and sends this Digest value and a key ID of the issuer user to an authentication center server device. The authentication center server device searches a key storage for a secret key corresponding to this key ID, generates a signature value by encrypting the Digest value with this secret key and responds the signature value to the user terminal. The user terminal forms an undersigned content by attaching the received signature value and key ID to signature object electronic information, and issues this content to a recipient. The terminal of the recipient user calculates a Digest value for the content in the undersigned content, and sends this Digest value, the signature value and the attachment key ID to the authentication center server device.

Abstract: A program capable of improving security of an information processing device handling a plurality of transactions. User identification information input section receives user identification information input thereto and identifying a user, and certificate acquiring section acquires a certificate certifying authenticity of the user. Correspondence storing section stores information indicating the correspondence between the user identification information and the certificate. When accessed from a certain user, certificate identifying section identifies, based on the user identification information from the user, a corresponding certificate. Based on the certificate identified by the certificate identifying section, user certification section verifies whether or not the user is an authentic user.