is there a rationale for doing the signatures like they do? do they need to support multiple parts of the document signed by different people? I think a model w

is there a rationale for doing the signatures like they do? do they need to support multiple parts of the document signed by different people? I think a model where you just sign a blob of data seems much more straight forward and doesn't have any of these problems. the blob signing model does have some problems. for example lets say in the blob signing model for OOXML you would just sign a zip file that has all the xml files. the problem is the person doing the signature could try and craft the zip or the files in such a way that the document renders differently for different people. this is a problem but it is not as bad as the problem where someone who is not the author can create a new document based on an existing signed document because the signature scheme is very difficult to implement correctly.