A data-processing system and method for controlling synthesizing
digital-signature information. The system and method include holding
first private-key information, inputting second private-key information,
generating third private-key information based on the first private-key
information and the second private-key information, holding the third
private-key information, generating signature information based on
information to be verified and the third private-key information, and
outputting the information to be verified and the signature information.