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The following example code shows how to calculate the MD5 Checksum of a file in C-Sharp:

[csharp]
using System;
using System.Collections.Generic;
using System.Text;
using System.IO;
using System.Security.Cryptography;

class Program
{
static void Main(string[] args)
{
if (args.Length <= 0) // No Arguments passed, exit
{
Console.WriteLine("Drag and Drop a file onto this exe to get it’s MD5 hash.");
Console.Read();
return;
}
if (File.Exists(args[0]) == false) // Invalid Argument passed, exit
{
Console.WriteLine("Drag and Drop a file onto this exe to get it’s MD5 hash.");
Console.Read();
return;
}

Console.WriteLine(GetMD5HashFromFile(args[0])); // Compute MD5 hash
Console.Read(); // Wait for user input
}

private static string GetMD5HashFromFile(string fileName)
{
FileStream file = new FileStream(fileName, FileMode.Open);
MD5 md5 = new MD5CryptoServiceProvider();
byte[] retVal = md5.ComputeHash(file);
file.Close();

StringBuilder sb = new StringBuilder();
for (int i = 0; i < retVal.Length; i++)
{
sb.Append(retVal[i].ToString("x2"));
}
return sb.ToString();
}
}

[/csharp]

You may also want to use it as a stand alone function:

[csharp]
private static string GetMD5HashFromFile(string fileName)
{
FileStream file = new FileStream(fileName, FileMode.Open);
System.Security.Cryptography.MD5 md5 = new System.Security.Cryptography.MD5CryptoServiceProvider();
byte[] retVal = md5.ComputeHash(file);
file.Close();

StringBuilder sb = new StringBuilder();
for (int i = 0; i < retVal.Length; i++)
{
sb.Append(retVal[i].ToString("x2"));
}
return sb.ToString();
}
[/csharp]