Encryption - Decryption In JavaScript Like A Student Thought

A student thought

An algorithm may be similar to basic algorithms of Information Security books.

I'm thankful to my colleague Mr.Jayesh Patel and my cousin Maulik Trivedi, currently a computer engineering student at Marwadi College of Engineering and Technology, Rajkot.

I will describe an algorithm with practical steps proven with JavaScript code, or you can perform it in any language you choose.

The graphic layout of the tool works on this algorithm and depends on your thoughts.

I am designing a webpage like the following screenshot,

Description of algorithm

A simple algorithm works with & plays with an ASCII value of characters. The algorithm works within the following six different steps.

Step 1. Convert input string characters in respected ASCII codes & store them in an array like the following example of JavaScript code.

for(i = 0; i < inputString.length; i++)    
{    
    asciiArr[i] = inputString[i].charCodeAt(0);    
}   

Step 2. Fill the A to Z array in capital or small letters,

for(i = 0, code = 65; i < 26; i++, code++)    
{    
    atozArr[i] = String.fromCharCode(code);    
} 

Step 3. Choose randomly single character index from A to Z and differentiate its position in one variable & its respected ASCII value in the second variable.

Write a function outside the main function of your code. Note. I am referencing a function returning a random value from the minimum-maximum range.

position = randomIndexFromInterval(0, atozArr.length - 1);    
positionAscii = atozArr[position].charCodeAt(0);    
    
function randomIndexFromInterval(min, max)    
{    
    return Math.floor(Math.random() * (max - min + 1) + min);    
}   

Step 4. Addition of every input String each element to positionAscii.

for(i = 0; i < inputString.length; i++)    
{    
    encryptedString[i] = parseInt(asciiArr[i]) + parseInt(atozArr[position].charCodeAt(0));    
}  

Step 5. Attachment of the key to the encrypted string or not it's your choice & it's your modification scenario. Here I am attaching a key with an encrypted string.

Step 6. Finally, your encryption is ready to send.

for(i = 0; i < encryptedString.length; i++)    
{    
    outputString.innerHTML = outputString.innerHTML + String.fromCharCode(encryptedString[i]);    
}   

Here outputString is an HTML element to display output on a webpage. For the decryption process, reverse steps apply.

Plain Text

Hi, I am writing a blog on blogspot.com.

Cypher Text

¾u?u¶ÂuÌǾɾüu¶u·ÁļuÄÃu·ÁļÈÅÄÉ?¸ÄÂU

Note. Every time, the ciphertext will change due to selecting a random position from A to Z.

So guys, here is an output screenshot of my web browser Mozilla Firefox.

JavaScript Code for Practice

function encryption()    
{    
    var inputString = document.getElementById("input")    
        .value;    
    var outputString = document.getElementById("enc");    
    var asciiArr = new Array();    
    var atozArr = new Array();    
    var encryptedString = new Array();    
    if(inputString.length != 0)    
    {    
        outputString.innerHTML = "";    
        //First Step: Convert all characters in ascii code       
        for(i = 0; i < inputString.length; i++)    
        {    
            asciiArr[i] = inputString[i].charCodeAt(0);    
        }    
        //Second Step: Fill AtoZ array in capital or small letters       
        for(i = 0, code = 65; i < 26; i++, code++)    
        {    
            atozArr[i] = String.fromCharCode(code);    
        }    
        //Third Step: Choose random single character index from A to Z      
        position = randomIndexFromInterval(0, atozArr.length - 1);    
        positionAscii = atozArr[position].charCodeAt(0);    
        //Fourth Step: Addition of every inputString element to positionAscii      
        for(i = 0; i < inputString.length; i++)    
        {    
            encryptedString[i] = parseInt(asciiArr[i]) + parseInt(atozArr[position].charCodeAt(0));    
        }    
        //Fifth Step: Attach key to encrypted string      
        encryptedString[asciiArr.length] = positionAscii;    
        //Sixth Step: Finally your encryption is ready to send      
        for(i = 0; i < encryptedString.length; i++)    
        {    
            outputString.innerHTML = outputString.innerHTML + String.fromCharCode(encryptedString[i]);    
        }    
        document.getElementById("inputBox")    
            .value = outputString.innerHTML;    
    }    
    else    
    {    
        document.getElementById("enc")    
            .innerHTML = "Error: Value can not be empty.";    
        return false;    
    }    
}    
    
function decryption()    
{    
    var inputBox = document.getElementById("inputBox");    
    var plainText = document.getElementById("dec");    
    if(inputBox.value != 0)    
    {    
        var encryptedString = inputBox.value;    
        var key = encryptedString[encryptedString.length - 1];    
        var decryptedString = new Array();    
        for(i = 0; i < encryptedString.length - 1; i++)    
        {    
            decryptedString[i] = encryptedString[i].charCodeAt(0) - key.charCodeAt(0);    
        }    
        plainText.innerHTML = "";    
        for(i = 0; i < decryptedString.length; i++)    
        {    
            plainText.innerHTML = plainText.innerHTML + String.fromCharCode(decryptedString[i]);    
        }    
    }    
    else    
    {    
        document.getElementById("dec")    
            .innerHTML = "Error: Value can not be empty.";    
        return false;    
    }    
}    
    
function randomIndexFromInterval(min, max)    
{    
    return Math.floor(Math.random() * (max - min + 1) + min);    
}