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
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
Tests that the document content has not been edited