public static BigInteger ShanksAlgorithm(BigInteger alpha, BigInteger beta, BigInteger n)
{
return(BabyStepGiantStep.bsgs2(alpha, beta, n));
BigInteger m = (n - 1).Sqrt() + 1;
BigInteger a = BigInteger.ModPow(alpha, m, n);
BigInteger b = ExtendedGCD(alpha, n)[1];
List <BigInteger[]> L1 = new List <BigInteger[]>();
List <BigInteger[]> L2 = new List <BigInteger[]>();
for (int ii = 0; ii < m; ii++)
{
L1.Add(new BigInteger[] { ii, BigInteger.ModPow(a, ii, n) });
BigInteger second = beta * BigInteger.Pow(b, ii) % n;
while (second < 0)
{
second += n;
}
L2.Add(new BigInteger[] { ii, second });
}
L1 = L1.OrderBy(x => x[1]).ToList();
L2 = L2.OrderBy(x => x[1]).ToList();
int i = 0;
int j = 0;
bool found = false;
while (!found && i < m && j < m)
{
if (L1[j][1] == L2[i][1])
{
return(m * L1[j][0] + L2[i][0] % n);
}
else if (BigInteger.Abs(L1[j][1]) > BigInteger.Abs(L2[i][1]))
{
i += 1;
}
else
{
j += 1;
}
}
return(-1);
}
private void DoMagicBtn_Click(object sender, EventArgs e)
{
BSGSProgressBar.Value = 0;
BigInteger a, b, m, answer;
a = 0;
b = 0;
m = 0;
answer = 0;
ResultLabel.Visible = false;
ResultLabel.ForeColor = Color.Red;
BigInteger.TryParse(ABox.Text, out a);
BigInteger.TryParse(BBox.Text, out b);
BigInteger.TryParse(MBox.Text, out m);
if (a < 2 || b < 0 || m < 3 || b > m)
{
ResultLabel.Text = "Неправильный ввод данных";
}
else if (!(CryptoMath.isPrime(m)))
{
ResultLabel.Text = "М должно быть простым";
}
else
{
if (m.ToString().Length > 10)
{
ResultLabel.Text = "Слишком большое М - \nВозможна нехватка памяти";
ResultLabel.Visible = true;
}
try
{
BSGSProgressBar.Visible = true;
this.Enabled = false;
answer = BabyStepGiantStep.bsgs2(a, b, m, BSGSProgressBar);
}
catch (OutOfMemoryException)
{
ResultLabel.Text = "Нехватка оперативной памяти";
ResultLabel.Visible = true;
this.Enabled = true;
return;
}
if (answer == -1)
{
ResultLabel.Text = "Такого Х не найдено";
}
else
{
ResultLabel.ForeColor = Color.Green;
ResultLabel.Text = $"X = {answer}";
if (BigInteger.ModPow(a, answer, m) != b)
{
ResultLabel.Text += "?";
}
}
}
BSGSProgressBar.Visible = false;
ResultLabel.Visible = true;
this.Enabled = true;
}
