byte[] MD5hash (byte[] data)
 {
    // This is one implementation of the abstract class MD5.
    MD5 md5 = new MD5CryptoServiceProvider();

    byte[] result = md5.ComputeHash(data);

    return result;
 }

//引入命名空间
using System;
using System.Security.Cryptography;
using System.Text;

class Example
{
    // Hash an input string and return the hash as
    // a 32 character hexadecimal string.
    static string getMd5Hash(string input)
    {
        // Create a new instance of the MD5CryptoServiceProvider object.
        MD5CryptoServiceProvider md5Hasher = new MD5CryptoServiceProvider();

        // Convert the input string to a byte array and compute the hash.
        byte[] data = md5Hasher.ComputeHash(Encoding.Default.GetBytes(input));

        // Create a new Stringbuilder to collect the bytes
        // and create a string.
        StringBuilder sBuilder = new StringBuilder();

        // Loop through each byte of the hashed data 
        // and format each one as a hexadecimal string.
        for (int i = 0; i < data.Length; i++)
        {
            sBuilder.Append(data[i].ToString("x2"));
        }

        // Return the hexadecimal string.
        return sBuilder.ToString();
    }

    // Verify a hash against a string.
    static bool verifyMd5Hash(string input, string hash)
    {
        // Hash the input.
        string hashOfInput = getMd5Hash(input);

        // Create a StringComparer an compare the hashes.
        StringComparer comparer = StringComparer.OrdinalIgnoreCase;

        if (0 == comparer.Compare(hashOfInput, hash))
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    static void Main()
    {
        string source = "Hello World!";
        
        string hash = getMd5Hash(source);

        Console.WriteLine("The MD5 hash of " + source + " is: " + hash + ".");

        Console.WriteLine("Verifying the hash...");

        if (verifyMd5Hash(source, hash))
        {
            Console.WriteLine("The hashes are the same.");
        }
        else
        {
            Console.WriteLine("The hashes are not same.");
        }
    }
}