A digital signature program includes computer-executable instructions for giving a numerical value in a state where header information necessary for playback of each partial data item may be added to the partial data item resulting from the division to a one-way function to generate an output value sequence of the one-way function concerning the multiple partial data items. The program also includes computer-executable instructions for generating binary trees concerning the streaming data, having leaves including only the output values in the output value sequence; and computer-executable instructions for using an output value indicating a root of the generated binary trees to generate a digital signature of a signer for the streaming data.