FromBytes method

bool FromBytes(Uint8List s)

Implementation

bool FromBytes(Uint8List s) {
  var u = FieldElement();
  var v = FieldElement();
  var v3 = FieldElement();
  var vxx = FieldElement();
  var check = FieldElement();

  FeFromBytes(Y, s);
  FeOne(Z);
  FeSquare(u, Y);
  FeMul(v, u, d);
  FeSub(u, u, Z); // y = y^2-1
  FeAdd(v, v, Z); // v = dy^2+1

  FeSquare(v3, v);
  FeMul(v3, v3, v); // v3 = v^3
  FeSquare(X, v3);
  FeMul(X, X, v);
  FeMul(X, X, u); // x = uv^7

  fePow22523(X, X); // x = (uv^7)^((q-5)/8)
  FeMul(X, X, v3);
  FeMul(X, X, u); // x = uv^3(uv^7)^((q-5)/8)

  var tmpX = Uint8List(32);
  var tmp2 = Uint8List(32);

  FeSquare(vxx, X);
  FeMul(vxx, vxx, v);
  FeSub(check, vxx, u); // vx^2-u
  if (FeIsNonZero(check) == 1) {
    FeAdd(check, vxx, u); // vx^2+u
    if (FeIsNonZero(check) == 1) {
      return false;
    }
    FeMul(X, X, SqrtM1);

    FeToBytes(tmpX, X);
    for (var i = 0; i < tmp2.length; i++) {
      tmp2[31 - i] = tmp2[i];
    }
  }

  if (FeIsNegative(X) != (s[31] >> 7)) {
    FeNeg(X, X);
  }

  FeMul(T, X, Y);
  return true;
}