import 'dart:async';
import 'dart:convert';
import 'package:crypto/crypto.dart';
var pcurve = BigInt.parse('115792089237316195423570985008687907853269984665640564039457584007908834671663',radix:10); // The proven prime
var chiavePrivataBinString;
Future<void> main() async {
var gx = BigInt.parse('55066263022277343669578718895168534326250603453777594175500187360389116729240',radix:10);
var gy = BigInt.parse('32670510020758816978083085130507043184471273380659243275938904335757337482424',radix:10);
List<BigInt> gpoint = [gx, gy];
var chiaveutf = utf8.encode("p@ssw0rd");
var chiavesha = sha256.convert(chiaveutf);
var chiavePrivataBigInt = BigInt.parse(chiavesha.toString(),radix:16);
chiavePrivataBinString = chiavePrivataBigInt.toRadixString(2);

var chiavePrivataBinBigint = BigInt.parse(chiavePrivataBinString);

print("******* Public Key Generation *********");

var publicKey = await eccMultiply(gpoint,chiavePrivataBigInt);
print('publicKey:${publicKey}');

}




BigInt modinv(BigInt a,BigInt n){
    var lm=BigInt.one;
    var hm=BigInt.zero;
    BigInt low = a%(n);
    BigInt high = n;

    while (low > BigInt.one){
        var ratio = high~/low;
        var nm = hm-lm*ratio;
        var new1 = high-low*ratio;
        hm =lm;
        lm = nm;
        high = low;
        low = new1;
    }

return lm%(n);
}



ecadd(List a,List b){
    BigInt lamAdd = ((b[1]-a[1])* modinv(b[0]-a[0],pcurve))%(pcurve);
    BigInt x = (lamAdd*lamAdd-a[0]-b[0])%(pcurve);
    BigInt y;
    y = (lamAdd*(a[0]-x)-a[1])%(pcurve);
    List<BigInt> ecaddList = [x, y];
    return ecaddList;

}

ecdouble(List a){
    BigInt a0=BigInt.parse(a[0].toString());
    BigInt a1=BigInt.parse(a[1].toString());
    BigInt lam = ((BigInt.from(3)*a0*a0)* (modinv((BigInt.from(2)*a1),pcurve)) )%(pcurve);
    BigInt x = (lam*lam-BigInt.two*a0)%(pcurve);
    BigInt y = (lam*(a0-x)-a1)%(pcurve);
    List<BigInt> ecdoubleList = [x, y];
    return ecdoubleList;
}

List StringToList(scalarBin){

  var string = '${scalarBin}';
  string.split('');
  return (string.codeUnits.map((unit) {
  return new String.fromCharCode(unit);}).toList());
}

eccMultiply(genPoint,scalarHex){
    var q = new List<BigInt>();
    var scalarBin = chiavePrivataBinString;
    q=genPoint;
    List listString=StringToList(chiavePrivataBinString);


  listString.sublist(1).forEach((element)  async {

    q= ecdouble(q);
  if(element=='1'){
    q= ecadd(q,genPoint);
  }
  });
    return(q);

}