How to Create an MD5 Hash of a String in C# and Displaying a Gravatar Image

The MD5 (message-digest algorithm) in used in a wide variety of cryptographic applications, and is commonly used to verify data integrity.

The following code will show you how to create a simple utility class that converts strings into MD5 hashes, and an example of its usage by creating a Gravatar image link.

The HashUtil class

public class HashUtil
{
    public static string CreateMD5(string input)
    {
        if (string.IsNullOrEmpty(input))
        {
            throw new ArgumentNullException("input");
        }

        using (var md5 = MD5.Create())
        {
            byte[] inputBytes = Encoding.ASCII.GetBytes(input);
            byte[] hash = md5.ComputeHash(inputBytes);

            // convert byte array to hex string
            var sb = new StringBuilder();
            for (int i = 0; i < hash.Length; i++)
            {
                sb.Append(hash[i].ToString("X2"));
            }

            return sb.ToString();
        }
    }
}

Example usage

The following example creates an MD5 hash of an email address and then builds a Gravatar URL.

string hash = HashUtil.CreateMD5("[email protected]");
string url = String.Format("//www.gravatar.com/avatar/{0}?d=mm", hash);