2.5.2.1 SignedInfo Element
The SignedInfo element MUST contain the following elements:
CanonicalizationMethod, where the algorithm MUST be as specified in [Can-XML-1.0].
Reference, where the URI attribute MUST be "#idPackageObject", and DigestMethod is provided by the application.<28>
Reference, where the URI attribute MUST be "#idOfficeObject", and DigestMethod is provided by the application.<29>