A digital signature method to generate a signature for an electronic document, the method including: initializing a signature t of each of the document segments of electronic document and twice raising the signature t to the power of a hash value of each of the document segments and digitally signing the raised signature to produce a signature s serving as the signature of the electronic document; and revising a document segment; wherein, in the revising, to delete a document segment, the signature t is raised twice to the power of the hash value of the document segment unless the document segment is sanitization prohibited, or the signature t is raised to the power of the hash value of the document if the document segment is sanitization prohibited, and the document segment is deleted; to sanitize a document segment, the document segment is replaced with the hash value thereof.