EDPoint.fromBytes constructor

EDPoint.fromBytes({ required CurveED curve, required List<int> data, BigInt? order, })

Factory constructor to create an EDPoint from a byte representation.

Parameters:

• curve: The Edwards curve associated with the point.
• data: The byte array representing the point's coordinates.
• order: The order of the point (optional).

Implementation

factory EDPoint.fromBytes({
  required CurveED curve,
  required List<int> data,
  BigInt? order,
}) {
  data = data.clone();
  final p = curve.p;
  final expLen = (p.bitLength + 1 + 7) ~/ 8;

  if (data.length != expLen) {
    throw ArgumentException.invalidOperationArguments(
      "EDPoint",
      name: "data",
      reason: "Incorrect bytes length.",
      expecteLen: expLen,
    );
  }

  final x0 = (data[expLen - 1] & 0x80) >> 7;
  data[expLen - 1] &= 0x80 - 1;

  final y = BigintUtils.fromBytes(data, byteOrder: Endian.little);

  final x2 =
      (y * y - BigInt.from(1)) *
      BigintUtils.inverseMod(curve.d * y * y - curve.a, p) %
      p;
  BigInt x = ECDSAUtils.modularSquareRootPrime(x2, p);
  if (x.isOdd != (x0 == 1)) {
    x = (-x) % p;
  }
  final t = x * y;
  return EDPoint(
    curve: curve,
    x: x,
    y: y,
    z: BigInt.one,
    t: t,
    generator: false,
    order: order,
  );
}