func (key *ObjectKey) Unseal(extKey []byte, sealedKey SealedKey, domain, bucket, object string) error {
	var unsealConfig sio.Config
	switch sealedKey.Algorithm {
	default:
		return Errorf("The sealing algorithm '%s' is not supported", sealedKey.Algorithm)
	case SealAlgorithm:
		mac := hmac.New(sha256.New, extKey)
		mac.Write(sealedKey.IV[:])
		mac.Write([]byte(domain))
		mac.Write([]byte(SealAlgorithm))