XML signature 101

 Notes:

• There are two canonicalization processes; one is to canonicalize "<SignedInfo>"; the other is to canonialize "referenced" xml elment.
• Canonicalization doesn't indent xml elements. So you cannot add even white spaces to elements' content after signing. 
• What c14n does is to normalize attributes, so you can put spaces around attribute names, reorder attributes afer signing.

XML signature standard 1.1: https://www.w3.org/TR/xmldsig-core1/#sec-Overview