code: def verify_digests!
        references.each do |reference|
          node    = referenced_node(reference.uri)
          canoned = node.canonicalize(C14N, reference.namespaces)
          digest  = reference.digest_method.digest(canoned)
  
          if digest != reference.decoded_digest_value
            raise SignatureError.new("Reference validation error: Digest mismatch for #{reference.uri}")
          end
        end
      end
docs: Tests that the document content has not been edited