isSignature function
Implementation
bool isSignature(Uint8List value) {
Uint8List r = value.sublist(0, 32);
Uint8List s = value.sublist(32, 64);
return value.length == 64 &&
_compare(r, ecGroupOrder as Uint8List) < 0 &&
_compare(s, ecGroupOrder as Uint8List) < 0;
}