C# rastgele key üretme

public string RastgeleKey() { Random rnd = new Random(); string harfler = "ABCDEFGHIJKLMNOPRSTUVYZ"; int a, s1, s2, s3, s4, s5; a = rnd.Next(0, 10); s1 = a + 5; s2 = a % 2 + a % 3; s3 = a + a % 2; s4 = a + a % 3; s5 = a % 3 + 3; string anahtar = harfler.S