sign static method
Implementation
static Uint8List sign(Uint8List privateKey, dynamic message) {
final MiniSecretKey priv =
MiniSecretKey.fromHex(dynamicToString(privateKey));
var sk = priv.expandEd25519();
final transcript =
Sr25519.newSigningContext(utf8.encode('substrate'), message);
final signature = sk.sign(transcript);
return dynamicToUint8List(signature.encode());
}