Why would MD5 be slower than SHA256 in my C# code?

Question

Here's the code:

static byte[] hashWithMd5(string text)
{
   using (var hasher = MD5.Create())
   {
       byte[] inputBytes = Encoding.ASCII.GetBytes(text);
       byte[] hash = hasher.ComputeHash(inputBytes);
       return hash;
   }
}

Code for SHA256 is the same except that SHA256Managed.Create() is called.

Each is run one million times to hash the same hard-coded 20-characters string. Time is measured using DateTime.UtcNow. Release is targeted, code runs outside debugger. Target framework version is 4.5.2.

The results are:

x64
MD5 - 5.89 seconds
SHA256Managed - 2.97 seconds

x86
MD5 - 6.68 seconds
SHA256Managed - 3.57 seconds

So no matter what configuration is run SHA256 turns out notably faster than MD5.

How could this realistically happen? Isn't SHA256 more computationally intensive?

Seems like it's just a bad implementation https://stackoverflow.com/a/14850676/1816580 — Artjom B., Dec 25 '20 at 10:25
x86 will run slower than x64. The pipelining of the microprocessor will run x64 faster than x64. — jdweng, Dec 25 '20 at 10:31
`DateTime.UtcNow` isn't a best measurement tool, Benchmark .NET or even `Stopwatch` will be better — Pavel Anikhouski, Dec 26 '20 at 15:51

Athanasios Kataras · Answer 1 · 2020-12-25T11:20:15.713

Multiple reasons why this might happen. While md5 is generally faster than sha2 you can check this: https://security.stackexchange.com/questions/95696/which-hash-algorithm-takes-longer-time-if-we-compare-between-md5-or-sha256

So it depends on various factors:

Hardware acceleration, based on your machine. If sha256 uses the GPU, you'll see much faster results.
Implementation details (as mentioned in the comment). On unix it is generally faster with md5 as expected.

Check this paper here: https://www.google.com/url?sa=t&source=web&rct=j&url=https://iopscience.iop.org/article/10.1088/1742-6596/978/1/012116/pdf&ved=2ahUKEwjx99e8_-jtAhVGzRoKHXM_DE4QFjAMegQICRAB&usg=AOvVaw1VVgJ-fEQddNca2P4OQi8p Your results, seem to confirm the Θ(n) mentioned, but not the slightly higher results.

Why would MD5 be slower than SHA256 in my C# code?

1 Answers1