docs: @Nonnull
      public static SecretKey toAes128Key(@Nonnull String s) {
          try {
              // turn secretKey into 256 bit hash
              MessageDigest digest = MessageDigest.getInstance("SHA-256");
              digest.reset();
              digest.update(s.getBytes(StandardCharsets.UTF_8));
  
              // Due to the stupid US export restriction JDK only ships 128bit version.
              return new SecretKeySpec(digest.digest(),0,128/8, "AES");
          } catch (NoSuchAlgorithmException e) {
              throw new Error(e);
          }
      }