Caesar Cipher in JavaScript

README.MD

Caesar Cipher in JavaScript

A quick implementation of Caesar Cipher in JavaScript using a custom defined modulo function. For more details please check: http://www.codeavenger.com/2017/05/19/JavaScript-Modulo-operation-and-the-Caesar-Cipher.html

caesarcipher.js

// Function will implement Caesar Cipher to
// encrypt / decrypt the msg by shifting the letters
// of the message acording to the key
function encrypt(msg, key)
{
    var encMsg = "";

    for(var i = 0; i < msg.length; i++)
    {
        var code = msg.charCodeAt(i);

        // Encrypt only letters in 'A' ... 'Z' interval
        if (code >= 65 && code <= 65 + 26 - 1)
        {
            code -= 65;
            code = mod(code + key, 26);
            code += 65;
        }

        encMsg += String.fromCharCode(code);
    }

    return encMsg;
}


// Modulo function: n mod p
function mod(n, p)
{
    if ( n < 0 )
        n = p - Math.abs(n) % p;

    return n % p;
}

test_caesarcipher.js

var msg = "ABCDEFGHIJKLMNOPQRSTUVWXYZ.";
var ok = true;

// Encrypt with a wide range of keys
// ... then try to decrypt imediately
for(var i = 0; i < 300; i++)
{
    var encMsg = encrypt(msg, i);
    var decMsg = encrypt(encMsg, -1 * i);

    if ( msg != decMsg )
        ok = false;

    console.log(i, msg, encMsg, decMsg);
}

console.log("Correct: " + ok);