C# simple custom encrypting

Question

I'm making a simple custom encrypting in C#.NET, the encryption passes succesfully, but the decrypting goes wrong. The algorithm is very intuitive, but I don't know why it's decrypted wrong. Here is my code:

 private void button1_Click(object sender, RoutedEventArgs e)
        {
            //Encrypting 
            byte[] initial_text_bytes = Encoding.UTF8.GetBytes(initial_text_tb.Text);
            byte[] secret_word_bytes = Encoding.UTF8.GetBytes(secret_word_tb.Text);
            byte[] encrypted_bytes = new byte[initial_text_bytes.Length];




            int secret_word_index = 0;
            for (int i=0; i < initial_text_bytes.Length; i++)
            {
                if (secret_word_index == secret_word_bytes.Length)
                {
                    secret_word_index = 0;
                }
                encrypted_bytes[i] = (byte)(initial_text_bytes[i] + initial_text_bytes[secret_word_index]);
                secret_word_index++;
            }



          //  String s = Encoding.UTF8.GetString(encrypted_bytes);
                //new String(Encoding.UTF8.GetChars(encrypted_bytes));

            text_criptat_tb.Text = Convert.ToBase64String(encrypted_bytes);


        }

        private void button2_Click(object sender, RoutedEventArgs e)
        {
            //Decrypting
            byte[] initial_text_bytes = Encoding.UTF8.GetBytes(text_criptat_tb.Text);
            byte[] secret_word_bytes = Encoding.UTF8.GetBytes(secret_word_tb.Text);
            byte[] encrypted_bytes = new byte[initial_text_bytes.Length];

            int secret_word_index = 0;
            for (int i = 0; i < initial_text_bytes.Length; i++)
            {
                if (secret_word_index == secret_word_bytes.Length)
                {
                    secret_word_index = 0;
                }
                encrypted_bytes[i] = (byte)(initial_text_bytes[i] - initial_text_bytes[secret_word_index]);
                secret_word_index++;
            }
           // String s = new String(Encoding.UTF8.GetChars(encrypted_bytes));

            initial_text_tb.Text = Convert.ToBase64String(encrypted_bytes);


        }

And this is what I get when I encrypt: After encrypting And this is when I decrypt: After decrypting Thanks

"I'm making a simple custom encrypting " - Don't write your own encryption. It will be flawed... — Mitch Wheat
– Mitch Wheat, Commented Feb 21, 2012 at 23:58
You don't seem to be converting back from base64 anywhere... — moonshadow
– moonshadow, Commented Feb 22, 2012 at 0:01

Guffa · Accepted Answer · 2012-02-22 00:11:07Z

I see four problems with the code.

1. You are adding bytes from the initial text instead of the secret word.

Here:

encrypted_bytes[i] = (byte)(initial_text_bytes[i] + initial_text_bytes[secret_word_index]);

Use instead:

encrypted_bytes[i] = (byte)(initial_text_bytes[i] + secret_word_bytes[secret_word_index]);

2. You are using `Encoding.UTF8.GetBytes` to try to decode the base-64 string.

Here:

byte[] initial_text_bytes = Encoding.UTF8.GetBytes(text_criptat_tb.Text);

Use instead:

byte[] initial_text_bytes = Convert.FromBase64String(text_criptat_tb.Text);

3. You are subtracting bytes from the inital text intead of the secret word.

Here:

encrypted_bytes[i] = (byte)(initial_text_bytes[i] - initial_text_bytes[secret_word_index]);

Use instead:

encrypted_bytes[i] = (byte)(initial_text_bytes[i] - secret_word_bytes[secret_word_index]);

4. You are using `Convert.ToBase64String` to try to decode the UTF-8 data.

Here:

initial_text_tb.Text = Convert.ToBase64String(encrypted_bytes);

Use instead:

initial_text_tb.Text = Encoding.UTF8.GetString(encrypted_bytes);

Collectives™ on Stack Overflow

C# simple custom encrypting

1 Answer 1

1. You are adding bytes from the initial text instead of the secret word.

2. You are using `Encoding.UTF8.GetBytes` to try to decode the base-64 string.

3. You are subtracting bytes from the inital text intead of the secret word.

4. You are using `Convert.ToBase64String` to try to decode the UTF-8 data.

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Collectives™ on Stack Overflow

1 Answer 1

1. You are adding bytes from the initial text instead of the secret word.

2. You are using Encoding.UTF8.GetBytes to try to decode the base-64 string.

3. You are subtracting bytes from the inital text intead of the secret word.

4. You are using Convert.ToBase64String to try to decode the UTF-8 data.

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Your Answer

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2. You are using `Encoding.UTF8.GetBytes` to try to decode the base-64 string.

4. You are using `Convert.ToBase64String` to try to decode the UTF-8 data.