Question

Need to get MD5 hash from string.
Get an error MD5 is null.
I am tying to get a 32 character MD5 hash from a string.

using (System.Security.Cryptography.MD5 md5 = 
       System.Security.Cryptography.MD5.Create("TextToHash"))
{
    byte[] retVal = md5.Hash;
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < retVal.Length; i++)
    {
        sb.Append(retVal[i].ToString("x2"));
    }
}

Answer 1

Need to get MD5 hash from string.

Then first you need to convert your string to binary data in some form. How you do that will depend on your requirements, but it’ll probably be Encoding.GetBytes for some encoding… you need to work out which encoding though. Does this hash need to match the hash created somewhere else, for example?

Get an error MD5 is null.

That’s because you’re using MD5.Create incorrectly. The argument is an algorithm name. You should almost certainly just use the parameterless overload instead.

I suspect you want something like:

byte[] hash;
using (MD5 md5 = MD5.Create())
{
    hash = md5.ComputeHash(Encoding.UTF8.GetBytes(text));
}
// Now convert the binary hash into text if you must...