// may be cryptographically bound to the object's path the same bucket/object as during sealing
// must be provided. On success the ObjectKey contains the decrypted sealed key.
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: