Encryption Build From Scratch

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• Download source - 7.2 KB

Introduction

As a student, I was going through crypto streams and for some strange reason I couldn't get them to encrypt more than 16 characters at a time. I thought to myself, "How does this work exactly?" I set out to reinvent the wheel, if you will, and this is what I came up with.

Background

My first attempt at rewriting encryption from scratch was actually really simple. What I did was take each character of a string and get its ASCII value. Then I took this number and multiplied it by 2 before converting it back into a character. To decrypt, I did the exact same thing, but instead of multiplying, I divided by 2.

public string encrypt(string myString) 
{
    int currentCharNum = 0; 
    int encryptedCharNum = 0; 
    string encryptedText = ""; 

    foreach (char currentChar in myString) 
    {
        currentCharNum = currentChar; 
        //This implicitly converts the char to its ascii value 

        encryptedStringNum = currentCharNum * 2; 
        //multiplies the value with 2 

        encryptedText += (char)encryptedStringNum; 
        //explicitly converts the NEW ENCRYPTED value to a 

        //char and adds it to the final string 

    } 
    return encryptedText; 
}

Using this method, encrypting the string "Hello Harvey!!!" would return "����@�����BBB". Now this was awesome; I actually did it! However, there were some weaknesses. I noticed that the "!!!" at the end of the original string returned "BBB". This was a problem because if you noticed the patterns, you could crack this if you really wanted to.

Version 2 was another story. This time I implemented a key to be used with the encryption instead of just multiplying everything by 2! Let's say you wanted to encrypt the string "Hello Harvey!!!" with a key of "2 4 6".

The H is multiplied by 2,

The e is multiplied by 4,

The l is multiplied by 6,

The l is multiplied by 2,

The o is multiplied by 4 and so on...

The resulting encrypted string would now be "ư�ưʈ�€ư�Ljɞ� �B". Now the "!!!" at the end isn't all the same characters in the encrypted string!

Using the Code

The first major method I had to write was to get these key numbers out of the text box and into an array.

public ArrayList myKey = new ArrayList();

public void getKey(string keyString) 
{
    myKey.Clear();
    keyString.Trim(); 
    //trimming variable so no white space exists at front or back 

    
    myKey.AddRange(keyString.Split(new char[] {' '})); 
    //adding individual numbers to arrayList

    
    int[] key = new int[myKey.Count]; 
    //initializing an int array to put the individual numbers in

    
    int counter = 0; //initializing counter to 0 

    
    foreach (string item in myKey)
    {
        try 
        {
            key[counter] = Int32.Parse(item); 
            counter++;
        }
        catch (FormatException) 
        {
            MessageBox.Show("Characters Not Allowed As Key");
            textBox1.Text = ""; 
        }
        catch (Exception E) 
        {
            MessageBox.Show("Error: \n \n" + E);
        }    }
    counter = 0;
}

The 2nd method did the actual encrypting.

public string encrypt(string fileContents)
{
    lblCharCount.Text = fileContents.Length.ToString();
    
    int currentCharNum = 0;
    int encryptedStringNum = 0;
    int keyIndex = myKey.Count - 1;
    
    progressBar1.Maximum = fileContents.Length;
    progressBar1.Value = 0;
    
    string encryptedText = "";
    
    foreach (char currentChar in fileContents)
    {
        currentCharNum = currentChar;
        encryptedStringNum = 
            currentCharNum * Int32.Parse(myKey[keyIndex].ToString());
        encryptedText += (char)encryptedStringNum;
        
        progressBar1.Value += 1;
        
        if (keyIndex == myKey.Count - 1)
        {
            keyIndex = 0;
        }
        else
        {
            keyIndex++;
        }
    }
    
    try
    {
        FileStream writeEncryped = 
            new FileStream(txbTarget.Text, 
            FileMode.Create, FileAccess.Write);
        StreamWriter writeEncryptedWriter = new StreamWriter(writeEncryped);
        
        writeEncryptedWriter.Write(encryptedText);
        
        writeEncryped.Flush();
        writeEncryptedWriter.Close();
        writeEncryped.Close();
    }
    catch (FileNotFoundException)
    {
        MessageBox.Show("File Not Found");
    }
    catch (Exception E)
    {
        MessageBox.Show("Error: \n\n" + E);
    }
    return encryptedText;
}   

You might have noticed that the block has a file stream in it. I actually implemented my encryption model to encrypt entire text files.

Known Issues

This application is still a work in progress, so there are some issues I'll list here. The main setback is that I have no check to ensure that the encrypted character stays in the bounds of the ASCII table. So, if the final answer/encrypted character value is above 65535, it moans. The second issue is that when you're encrypting huge text files -- of 500000 characters, for example -- it takes some time to display the encrypted text in the text box. I'm not sure why it does this, but I think it's because of the high ASCII values.

Notes

I used sharpDevelop 2.2 to write this program, but it should work in 2.0 as well.

History

• 14 November, 2007 -- Original version posted