Digital signature system

#1. Field of the Invention

#The present invention relates to a digital signature system and, in particular, to a digital signature system for performing digital signature processing using a digital certificate, which is equivalent to an official seal, issued to an organization and shared by the organization.

#2. Description of the Related Art

#In the accompanying drawings:

#FIG. 1 is an explanatory diagram showing a schematic structure of an entire digital signature system in accordance with a first embodiment of the present invention;

#FIG. 2 is a block diagram showing a structure of the digital signature system in accordance with the first embodiment of the present invention;

#First Embodiment

#FIGS. 1 and 2 show a structure of a digital signature system in accordance with an embodiment of the present invention. In these figures, identical components are denoted by identical reference numerals. First, an entire schematic structure will be described with reference to FIG. 1. As shown in FIG. 1, the digital signature system of the present invention is constituted by a server 1 and a terminal for person in charge (client) 2. The server 1 and the terminal for person in charge 2 are connected by a communication network 3 such as the Internet or the Intranet. A flow of entire processing will be briefly described. Digital data (word processor document, spreadsheet document, presentation, CSV, XML or the like) 14 prepared in the terminal for person in charge 2 is sent to the server 1 via the communication network 3. In the server 1, the digital data is received and converted into a PDF document in a digital signature request reception unit 16. The server 1 performed the digital signature processing to the digital data converted to the PDF document using a digital certificate, which is equivalent to an official seal, issued to an organization (company, department, etc.) kept in the server 1 in a digital signature unit 17, and stored it in an information memory unit 18. Note that, since the digital certificate is equivalent to an official seal, it is shared by one or more persons in charge who are authorized to apply a digital signature. The terminal for person in charge 2 takes out the stored digital data with a digital signature via the communication network 3 to refer to contents of the digital data or verify the digital signature as needed.

#Next, a specific structure of the digital signature system of the present invention will be described with reference to a block diagram of FIG. 2. In FIG. 2, reference numeral 10 denotes an certification authority that issues a digital certificate; 11, a digital certificate (including a secret key certificate and a public key certificate), which is equivalent to an official seal, issued from the certification authority 10; 12, a seal (also referred to as seal data or a digital seal) affixed to digital data when digital signature processing is performed; and 13, a hardware security module (hereinafter abbreviated as HSM) with tamper resistance for keeping the digital certificate 11 and the seal 12 while ensuring security, which is mounted in the server 1. Note that, the tamper resistance means having a structure that does not allow illegal internal analysis or alteration. It is taken for granted that the HSM 3 cannot be carried (an internal memory of the HSM 3 is destroyed if the HSM 3 is attempted to be illegally taken out of the server 1). In addition, internal information of the HSM 3 cannot be copied by a third party.