How do I calculate a MD5 hash from a string?

It is a common practice to store passwords in databases using a hash. MD5 (defined in RFC 1321) is a common hash algorithm, and using it from C# is easy.

Here’s an implementation of a method that converts a string to an MD5 hash, which is a 32-character string of hexadecimal numbers.

public string CalculateMD5Hash(string input)  
{  
  // step 1, calculate MD5 hash from input  
  MD5 md5 = System.Security.Cryptography.MD5.Create();  
  byte[] inputBytes = System.Text.Encoding.ASCII.GetBytes(input);  
  byte[] hash = md5.ComputeHash(inputBytes);  
  
  // step 2, convert byte array to hex string  
  StringBuilder sb = new StringBuilder();  
  for (int i = 0; i < hash.Length; i++)  
  {  
      sb.Append(hash[i].ToString("X2"));  
  }  
  return sb.ToString();  
}  

An example call:

string hash = CalculateMD5Hash("abcdefghijklmnopqrstuvwxyz");

…returns a string like this:

C3FCD3D76192E4007DFB496CCA67E13B

To make the hex string use lower-case letters instead of upper-case, replace the single line inside the for loop with this line:

sb.Append(hash[i].ToString("x2"));

The difference is the ToString method parameter.