JS AlPHABET Shifting Cipher Randomized V2

<script>
var possible = "ABCGDEFGHIJKLMNOPQRSTUVWXYZ";
var text = "";
for(var i=1; i<26; i++){
text+=possible.charAt(Math.floor(Math.random()*possible.length))
text+=(Math.floor(Math.random()*possible.length))
document.writeln(text+":ABCDEFGHIJKLMNOPQRSTUVWXYZ\n\n");
text='';
}
</script>