Program verification apparatus and method, and signature system based on program verification

A program verification apparatus comprising:

• a storing device to store a plurality of statements in correspondence with values of respective risk levels of the statements;
• an obtaining device configured to refer to a signature included in a signed module, and thereby to obtain a value indicating a risk level of the signed module;
• an input device configured to input a to-be-verified program including a plurality of statements or signed modules;
• a calculating device configured to determine values of first risk levels of the statements included in the to-be-verified program by referring to the storing device, determine values of second risk levels of the signed modules included in the to-be-verified program by using the obtaining device, and calculate a maximum value of a risk level of the to-be-verified program from the values of the first risk levels and the values of the second risk levels;
• and
• an output device configured to output a verification result including the maximum value of the risk level.