caesarCipher.js

// enciphering
plaintext = "DEFEND THE EAST WALL OF THE CASTLE";  
var key = 3;
ciphertext = "";    var re = /[a-z]/;
for(i=0; i<plaintext.length; i++){ 
   if(re.test(plaintext.charAt(i))) ciphertext += String.fromCharCode((plaintext.charCodeAt(i) - 97 + key)%26 + 97); 
   else ciphertext += plaintext.charAt(i); 
} 

// deciphering
plaintext2 = "";    
for(i=0; i<ciphertext.length; i++){ 
    if(re.test(ciphertext.charAt(i))) plaintext2 += String.fromCharCode((ciphertext.charCodeAt(i) - 97 + 26 - key)%26 + 97); 
    else plaintext += ciphertext.charAt(i); 
} 

alert(plaintext)
alert(ciphertext)
alert(plaintext2)