code: def verify_signature!
        node      = original.at("#{prefix}/ds:Signature/ds:SignedInfo", NS_MAP)
        canoned   = node.canonicalize(C14N)
  
        unless x509.public_key.verify(signature_method.new, decoded_signature_value, canoned)
          raise SignatureError.new("Signature validation error: Possible canonicalization mismatch", "This canonicalizer returns #{canoned}")
        end
      end
docs: Tests correctness of the signature (and hence digests)