MD5 vs SHA1

MD5 vs SHA1

Saturday, July 05, 2008 Pablo Santos dotnet 8 Comments

Plastic relies on hashes for certain operations related to file and directory contents.

Hashes can take some time to be calculated so choosing the right one can be important.

We're currently using MD5. Is it faster or slower than SHA1?

Here's the code I used to recursively calculate the hashes of the files of an entire directory:

    class Hasher
    {
        static void Main(string[] args)
        {
            string path =
               args.Length > 0 ? args[0] :
                   Environment.CurrentDirectory;
            string hashtype = args.Length > 1 ? args[1] : "md5";
            Hasher calculator = new Hasher();
            int ini = Environment.TickCount;
            calculator.Calculate(path, hashtype);
            Console.WriteLine(
                "Time hashing {0} files {1} ms. Method {2}",
                calculator.mCount,
                Environment.TickCount - ini,
                hashtype);
        }

        int mCount = 0;
        int mConvert = 0;

        void Calculate(string root, string hashtype)
        {
            string[] files = Directory.GetFiles(root, "*");

            foreach( string file in files )
            {
                Console.Write("Hashing {0}: ", file);
                FileStream st = new FileStream(
                    file,
                    System.IO.FileMode.Open,
                    System.IO.FileAccess.Read,
                    System.IO.FileShare.ReadWrite);
                string hash;
                if( hashtype == "sha1" )
                    hash = CalcSHA1HashCode(st);
                else
                    hash = CalcMD5HashCode(st);
                Console.WriteLine(hash);
                st.Close();
                ++mCount;
            }

            string[] directories =
                Directory.GetDirectories(root, "*");
            foreach( string directory in directories )
                Calculate(directory, hashtype);
        }

        string CalcMD5HashCode(FileStream file)
        {
            MD5CryptoServiceProvider md5Provider =
                new MD5CryptoServiceProvider();
            Byte[] hash = md5Provider.ComputeHash(file);
            return Convert.ToBase64String(hash);
        }

        string CalcSHA1HashCode(FileStream file)
        {
            SHA1CryptoServiceProvider sh1Provider =
                new SHA1CryptoServiceProvider();
            Byte[] hash = sh1Provider.ComputeHash(file);
            return Convert.ToBase64String(hash);
        }
    }

And the results:
Time hashing 1379 files 3676 ms. Method sha1
Time hashing 1379 files 3515 ms. Method md5

So almost no difference between the two methods. Mono and .NET obtain the same results too.

What can really be a difference (obviously) is the filesystem status: the first time you try it on a directory it will be much (about 10 times) slower! And here Linux systems normally win the battle due to their cache management strategies.

Pablo Santos

I'm the CTO and Founder at Códice.
I've been leading Plastic SCM since 2005. My passion is helping teams work better through version control.
I had the opportunity to see teams from many different industries at work while I helped them improving their version control practices.
I really enjoy teaching (I've been a University professor for 6+ years) and sharing my experience in talks and articles.
And I love simple code. You can reach me at @psluaces.