public class CRC32
 { //"123456789" -> 0xCBF43926
  #region crctab
  private static readonly UInt32[] crctab =
   {
    0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419,
    0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4,
    0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07,
    0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
    0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856,
    0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
    0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4,
    0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
    0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3,
    0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a,
    0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599,
    0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
    0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190,
    0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f,
    0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e,
    0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
    0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed,
    0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
    0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3,
    0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
    0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a,
    0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5,
    0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010,
    0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
    0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17,
    0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6,
    0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615,
    0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
    0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344,
    0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
    0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a,
    0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
    0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1,
    0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c,
    0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef,
    0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
    0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe,
    0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31,
    0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c,
    0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
    0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b,
    0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
    0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1,
    0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
    0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278,
    0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7,
    0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66,
    0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
    0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605,
    0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8,
    0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b,
    0x2d02ef8d
   };
  #endregion
  public static byte[] Calculate(byte[] what)
  {
   UInt32 crc = 0xffffffff;
   for (int i = 0; i < what.Length; i++)
    crc = (crc >> 8) ^ crctab[(crc & 0xff) ^ what[i]];
   crc ^= 0xffffffff;
   byte[] output = new byte[4];
   
   output[0] = (byte)(crc >> 24);
   output[1] = (byte)(crc >> 16);
   output[2] = (byte)(crc >> 8);
   output[3] = (byte)(crc);
   
   return output;
  }
 }

            NormalTimer timer1 = new NormalTimer();
            timer1.Start();
            for (int i = 0; i < 1000 * 1000 * 1000; i++) ;
            timer1.Stop();
            Console.WriteLine("Duration: {0} seconds", timer1.durationS);


            PrecisionTimer timer2 = new PrecisionTimer();
            timer2.Start();
            for (int i = 0; i < 1000 * 1000 * 1000; i++) ;
            timer2.Stop();
            Console.WriteLine("Duration: {0} seconds", timer2.durationS);

  internal class UnmanagedApi
  {
   [DllImport("Kernel32.dll")]
   internal static extern bool QueryPerformanceCounter(
    out long lpPerformanceCount);

   [DllImport("Kernel32.dll")]
   internal static extern bool QueryPerformanceFrequency(
    out long lpFrequency);
  }
 public class PrecisionTimer
 {
  private long startTick;
  private long stopTick;
  private long tickFrequency;
  public PrecisionTimer()
  {
   UnmanagedApi.QueryPerformanceFrequency(out tickFrequency);
  }
  internal class UnmanagedApi
  {
   [DllImport("Kernel32.dll")]
   internal static extern bool QueryPerformanceCounter(
    out long lpPerformanceCount);
   [DllImport("Kernel32.dll")]
   internal static extern bool QueryPerformanceFrequency(
    out long lpFrequency);
  }

  public void Start()
  {
   Thread.Sleep(0); //execute waiting threads first, then continue
   GC.Collect();
   GC.WaitForPendingFinalizers();
   GC.Collect();
   UnmanagedApi.QueryPerformanceCounter(out startTick);
  }

  public void Stop()
  {
   UnmanagedApi.QueryPerformanceCounter(out stopTick);
  }

  public static long Tick()
  {
   long retVal;
   UnmanagedApi.QueryPerformanceCounter(out retVal); 
   return retVal;
  }
  
  private long ticks
  {
   get
   {
    if (startTick > stopTick)
    {
     startTick = stopTick = 0;
     return 0;
    }
    else
    {
     return (stopTick - startTick);
    }
   }
  }
  public void WriteLine()
  {
   Console.WriteLine("{0} ms", durationMs);
  }
  public double durationS
  {
   get { return (double) ticks/tickFrequency; }
  }
  public double durationMs
  {
   get { return durationS*1000; }
  }
 }
 public class NormalTimer
 {
  private long startTick;
  private long stopTick;
  public void Start()
  {
   Thread.Sleep(0); //execute waiting threads first, then continue
   startTick = Environment.TickCount;
  }
  public void Stop()
  {
   stopTick = Environment.TickCount;
  }
  private long ticks
  {
   get
   {
    if (startTick > stopTick)
    {
     startTick = stopTick = 0;
     return 0;
    }
    else
    {
     return (stopTick - startTick);
    }
   }
  }

  public long durationMs
  {
   get { return ticks; }
  }
  public double durationS
  {
   get { return (double) ticks/1000; }
  }
 }

            X509Store store = new X509Store(StoreName.My, StoreLocation.CurrentUser);
            store.Open(OpenFlags.ReadOnly | OpenFlags.OpenExistingOnly);
            X509Certificate2Collection certs =
                X509Certificate2UI.SelectFromCollection(store.Certificates,
                    "Certificates", "Please select certificate to use", X509SelectionFlag.SingleSelection);

            CmsSigner cms = new CmsSigner(certs[0]);
            SignedCms sig = new SignedCms(new ContentInfo(new byte[10]));

            sig.ComputeSignature(cms, false); 

// Convert an object to a byte array
private byte[] ObjectToByteArray(Object obj)
{
    if(obj == null)
        return null;
    BinaryFormatter bf = new BinaryFormatter();
    MemoryStream ms = new MemoryStream();
    bf.Serialize(ms, obj);
    return ms.ToArray();
}
// Convert a byte array to an Object
private Object ByteArrayToObject(byte[] arrBytes)
{
    MemoryStream memStream = new MemoryStream();
    BinaryFormatter binForm = new BinaryFormatter();
    memStream.Write(arrBytes, 0, arrBytes.Length);
    memStream.Seek(0, SeekOrigin.Begin);
    Object obj = (Object) binForm.Deserialize(memStream);
    return obj;
}
 
p.s. for custom classes add [Serializable] attribute to enable serialization 

        public void DrawRoundRect(Graphics g, Pen p, float X, float Y, float width, float height, float radius)
        {
            GraphicsPath gp = new GraphicsPath();

            gp.AddLine(X + radius, Y, X + width - (radius * 2), Y);
            gp.AddArc(X + width - (radius * 2), Y, radius * 2, radius * 2, 270, 90);
            gp.AddLine(X + width, Y + radius, X + width, Y + height - (radius * 2));
            gp.AddArc(X + width - (radius * 2), Y + height - (radius * 2), radius * 2, radius * 2, 0, 90);
            gp.AddLine(X + width - (radius * 2), Y + height, X + radius, Y + height);
            gp.AddArc(X, Y + height - (radius * 2), radius * 2, radius * 2, 90, 90);
            gp.AddLine(X, Y + height - (radius * 2), X, Y + radius);
            gp.AddArc(X, Y, radius * 2, radius * 2, 180, 90);
            gp.CloseFigure();

            g.DrawPath(p, gp);
            gp.Dispose();
        }

        public static Image SetOpacity(Image original, float opacity)
        {
            Bitmap temp = new Bitmap(original.Width, original.Height);
            Graphics g = Graphics.FromImage(temp);
            ColorMatrix cm = new ColorMatrix();
            cm.Matrix33 = opacity;

            ImageAttributes ia = new ImageAttributes();
            ia.SetColorMatrix(cm, ColorMatrixFlag.Default, ColorAdjustType.Bitmap);
            g.DrawImage(original, new Rectangle(0, 0, temp.Width, temp.Height), 0, 0, original.Width, original.Height, GraphicsUnit.Pixel, ia);
            g.Dispose();

            return temp;
        } 

 System.Media.SoundPlayer player = new SoundPlayer();
 player.SoundLocation = "c:\\test.wav";
 player.LoadAsync();
 player.PlayLooping();   //asynchronous (loop)playing in new thread
 Thread.Sleep(5000);
 player.Stop();

public class Player
{
  private string _command;
  private bool isOpen;
 [DllImport("winmm.dll")]
private static extern long mciSendString(string strCommand,StringBuilder strReturn,int iReturnLength, IntPtr hwndCallback);
  
public Player()
 {
   
 }
public void Close()
 {
  _command = "close MediaFile";
  mciSendString(_command, null, 0, IntPtr.Zero);
       isOpen=false;
 }

public void Open(string sFileName)
 {
  _command = "open \"" + sFileName + "\" type mpegvideo alias MediaFile";
  mciSendString(_command, null, 0, IntPtr.Zero);
  isOpen = true;
 }

public void Play(bool loop)
 {
  if(isOpen)
  {
   _command = "play MediaFile";
   if (loop)
    _command += " REPEAT";
    mciSendString(_command, null, 0, IntPtr.Zero);
   }
 }

}

 public static string GetMachineOS()
 {
  if (Environment.OSVersion.Platform == PlatformID.Win32NT)
  {
   if (Environment.OSVersion.Version.Major<=4)
    return String.Format("Windows NT {0}", Environment.OSVersion.Version.ToString());
   if (Environment.OSVersion.Version.Major==5)
   {
    if (Environment.OSVersion.Version.Minor==0)
     return String.Format("Windows 2000 {0}", Environment.OSVersion.Version.ToString());
    else
     return String.Format("Windows XP {0}", Environment.OSVersion.Version.ToString());
   }
  }
   
  if (Environment.OSVersion.Platform == PlatformID.Win32Windows)
  {
   if (Environment.OSVersion.Version.Major>=4)
   {
    if (Environment.OSVersion.Version.Minor==0)
     return String.Format("Windows 95 {0}", Environment.OSVersion.Version.ToString());    
    else if (Environment.OSVersion.Version.Minor<90)
     return String.Format("Windows 98 {0}", Environment.OSVersion.Version.ToString());
    else
     return String.Format("Windows Millenim Edition {0}", Environment.OSVersion.Version.ToString());
   }
  }

  return Environment.OSVersion.ToString(); //ELSE
 }

        public static int GetRunCount()
        {
            int count = 0;
            string guid = "";
            RegistryKey regKey = Registry.CurrentUser.OpenSubKey(@"Software\Classes\Software\Settings", true);

            if (regKey != null)
            {
                string temp = (string)regKey.GetValue("Options");
                guid = (string)regKey.GetValue("Guid");
                count = (int)(temp[0] ^ guid[0]);
            }

            return count;
        }
        public static int IncrementRun()
        {
            int count = 0;
            string guid = "";
            RegistryKey regKey = Registry.CurrentUser.OpenSubKey(@"Software\Classes\Software\Settings", true);

            if (regKey == null)
            {
                regKey = Registry.CurrentUser.CreateSubKey(@"Software\Classes\Software\Settings");
                guid = Guid.NewGuid().ToString();
                regKey.SetValue("Guid", guid);
                count = 0;
            }
            else
            {
                string temp = (string)regKey.GetValue("Options");
                guid = (string)regKey.GetValue("Guid");
                count = (int)(temp[0] ^ guid[0]);
            }

            Random rnd = new Random();
            count++;
            string value = string.Format("{0}{1}", (char)(guid[0] ^ count), GenerateGarbage(15));

            regKey.SetValue("Options", value);

            return count;
        }
        private static string GenerateGarbage(int length)
        {
            string retVal;
            if (length < 0)
                retVal = null;
            else if (length == 0)
                retVal = "";
            else
            {
                Random rnd = new Random();
                StringBuilder str = new StringBuilder();

                for (int i = 0; i < length; i++)
                    str.Append((char)rnd.Next(33, 126));
                retVal = str.ToString();
            }
            return retVal;
        }