Obtain MD5 file hash for all files in subdirectories in a specified path.

FileHash.cs

using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;

static class Program
{
    static MD5 md5;
    static MemoryStream ms;
    static StreamWriter sw;

    // Data directory to dump a hash.
    const string path = @"F:\VPN";

    static void Main(string[] args)
    {
        md5 = MD5.Create();
        ms = new MemoryStream();
        sw = new StreamWriter(ms);

        var start = DateTime.Now;
        Dump(new DirectoryInfo(path));
        var end = DateTime.Now;
        var elapsed = end - start;

        sw.Flush();
        ms.Seek(0, SeekOrigin.Begin);

        var rootHash = ComputeHashForStream(ms);

        Console.Error.WriteLine();
        Console.Error.WriteLine("Elapsed: {0}", elapsed);
        Console.WriteLine("Root hash: {0}", rootHash);
    }

    static void Dump(DirectoryInfo dir)
    {
        foreach (var d in dir.GetDirectories())
        {
            try { Dump(d); }
            catch (UnauthorizedAccessException) { }
        }

        foreach (var f in dir.GetFiles())
        {
            using (var s = f.OpenRead())
            {
                Console.Error.WriteLine(f.FullName);

                var hash = ComputeHashForStream(s);
                var fileName = f.FullName.Replace(path, "");
                sw.WriteLine(hash);
                Console.WriteLine("{0}\t{1}", hash, fileName);
            }
        }
    }

    static string ComputeHashForStream(Stream s)
    {
        var hash = md5.ComputeHash(s);
        var hashStr = Convert.ToBase64String(hash);
        return hashStr.Substring(0, hashStr.Length - 2);
    }
}