A data-processing device comprising: a holding unit arranged to hold first private-key information which is managed in the data-processing device and is not open to a user; an inputting unit arranged to input second private-key information which varies from one user to another, and public-key information; characterized in that the device further comprises: a private-key-information generating unit (22, 23, 24) arranged to generate third private-key information based on the first private-key information and the second private-key information so that the generated third private-key information and the public-key information are paired off with each other in a public-key cryptosystem algorithm in which the public-key information is used for encryption and the third private-key information is used for decryption, and store the third private-key information, wherein the stored third private-key information is not open to a verification device; a signature-information generating unit arranged to generate signature information based on information to be verified and the third private-key information; and an outputting unit arranged to output the information to be verified, the signature information and the public-key information. a holding unit arranged to hold first private-key information which is managed in the data-processing device and is not open to a user; an inputting unit arranged to input second private-key information which varies from one user to another, and public-key information; characterized in that the device further comprises: a private-key-information generating unit (22, 23, 24) arranged to generate third private-key information based on the first private-key information and the second private-key information so that the generated third private-key information and the public-key information are paired off with each other in a public-key cryptosystem algorithm in which the public-key information is used for encryption and the third private-key information is used for decryption, and store the third private-key information, wherein the stored third private-key information is not open to a verification device; a signature-information generating unit arranged to generate signature information based on information to be verified and the third private-key information; and an outputting unit arranged to output the information to be verified, the signature information and the public-key information. a private-key-information generating unit (22, 23, 24) arranged to generate third private-key information based on the first private-key information and the second private-key information so that the generated third private-key information and the public-key information are paired off with each other in a public-key cryptosystem algorithm in which the public-key information is used for encryption and the third private-key information is used for decryption, and store the third private-key information, wherein the stored third private-key information is not open to a verification device; a signature-information generating unit arranged to generate signature information based on information to be verified and the third private-key information; and an outputting unit arranged to output the information to be verified, the signature information and the public-key information.