How to create your own C# Hashing Class Library

In this article I’m going to show you how to create your very own class library – also know as a dll file. We’ll be building a class containing a static text hashing method, which we’ll then call from a separate application. After reading this article you will know exactly how to create a dll file with your own methods and how to use it within other projects, and that is extremely important for any developer to know.

Creating the Class Library

First of all we must start off by creating a Class Library project from within Visual Studio – in this case we shall name it HashLibrary. Now the namespace for our dll will automatically be set to HashLibrary as well.

Next create a class and call it Hasher. We have the option of either creating a normal class or a static class. A static class is one which does not need to be instantiated. Therefore whoever consumes the class can do so by calling its methods directly, without having to create an instance of it. This is ideal for our situation because we do not need to store any data within the Hasher class – all we’ll have is a method which returns a hash value.

So make the class static by adding the static keyword before the class name as shown below:

using System;
using System.Text;

namespace HashLibrary
{
    public static class Hasher
    {
    }
}

Since the class is static, we don’t even need a constructor, as can be seen in the code. All we have is an empty class which does absolutely nothing at the moment.

So let’s make it do something. Let’s add a string hashing method as shown below.

using System;
using System.Text;
using System.Security.Cryptography;

namespace HashLibrary
{
    public static class Hasher
    {
        /// <summary>
        /// This method hashes the given text with 
        /// the SHA1CryptoServiceProvider.
        /// </summary>
        /// <param name="text">Text to hash</param>
        /// <returns>Hashed Value</returns>
        public static string HashString(string text)
        {
            // Create an instance of the SHA1 provider
            SHA1 sha = new SHA1CryptoServiceProvider();
            
            // Compute the hash 
            byte[] hashedData = sha.ComputeHash(Encoding.Unicode.GetBytes(text));

            StringBuilder stringBuilder = new StringBuilder();

            foreach (byte b in hashedData)
            {
                // Convert each byte to Hex
                stringBuilder.Append(String.Format("{0,2:X2}", b));
            }
            
            // Return the hashed value
            return stringBuilder.ToString();
        }
    }
}

Our new method HashString accepts a string parameter which is the text to be hashed. We also had to add the namespace System.Security.Cryptography because of the SHA1 and SHA1CryptoServiceProvider classes. These are the classes which actually compute the hash.

The hash is returned as a byte array so we are iterating each byte and appending it to the StringBuilder as a hex value. Finally we are returning the hashed value which is a hex representation of the binary hash.

Now if we compile the code, we end up with a file called HashLibrary.dll.

You have just created your own dll which can be used within any .NET project over and over again. And thats the beauty of a dll – it can be re-used without duplicating code, and more importantly, it can be shared between different applications.

Now let me show you how to call the HashString method in our dll.

Consuming a DLL

Create a new Windows Forms Application project and add a reference to the HashLibrary.dll we just created. Also add a button and two textboxes to the form. The first text box (txtToHash) will be for adding the text to hash, and the second textbox (txtHashed) will display the hashed text. The button will be used to call our dll and get the hashed text. Also remember to add the HashLibrary namespace to the project since we will need it to access the HashString method in our dll.

The following code shows how to access the HashString method in the dll:

private void btnHash_Click(object sender, EventArgs e)
{
    txtHashed.Text = Hasher.HashString(txtToHash.Text.Trim());
}

If you run the application you should end up with something similar to this:

And that’s it. You now know how to create your own dll and how to consume it. You can improve your dll further by adding more different static hashing methods and maybe file hashing methods as well.

I hope you enjoyed this article. Stay tuned for more soon.

Dave