open_len method
Implementation
Uint8List open_len(Uint8List box, final int boxoff, final int boxlen) {
// check message
if (!(box != null &&
box.length >= (boxoff + boxlen) &&
boxlen >= boxzerobytesLength)) return null;
return open_nonce_len(box, boxoff, box.length - boxoff, _generateNonce());
}