1. An authenticity assurance system that assures authenticity of an electronic document, the authenticity assurance system comprising: a management apparatus; one or more redaction-target document structure processing apparatuses; and one or more redaction method information processing apparatuses, wherein: the management apparatus: receives the electronic document, area partitioning information, and information including a file type, a redactable signature method, and a signature output format; specifies one redaction-target document structure processing apparatus configured to process an electronic document of the file type; and inputs the electronic document and the area partitioning information into the specified redaction-target document structure processing apparatus, the specified redaction-target document structure processing apparatus: receives the electronic document and the area partitioning information from the management apparatus; divides the electronic document into one or more data sets according to the area partitioning information; generates a common data string not dependent on the file type, the common data string including the divided one or more data sets and not depending on a file type; generates an area ID for identifying at least one data set; and outputs the generated common data string and the area ID to the management apparatus, the management apparatus: specifies one redaction method information processing apparatus configured to perform the redactable signature method; and inputs the common data string and the area ID into the specified redaction method information processing apparatus, and the specified redaction method information processing apparatus: receives the common data string and the area ID from the management apparatus; generates a random number respectively for the at least one data set constituting the common data string; according to the specified redactable signature method, calculates a hash value for the common data string based on the at least one data set constituting the common data string and the generated random number; generates redactable signature method information that includes the hash value, the random number, data for calculating the random number, and the area ID; and outputs the generated redactable signature method information to the management apparatus.