An information processing system includes a unit that selects a time stamp authority to which a request for generation of a time stamp, the time stamp authority to be selected is different from a time stamp authority selected in a last selection process which has been performed; a unit that acquires the time stamp from the selected time stamp authority; a unit that generates link information specifying an order in which time stamps; a controller that causes verification information including the time stamp, identification information of the time stamp authority, the link information, that are associated with each other; a unit that receives a time stamp verification request with regard to digital data; and a unit that compares an invalidated time stamp applied to digital data to be verified with a time stamp to thereby specify a time range in which the invalidated time stamp is applied.