a.k.a (Caesar Cipher)

update 2009/01/09 : I made a JavaScript version you can play with.

There was a text advert on Daring Fireball which seemed to be obviously a shifted text. (i.e. the rotation of an intelligible text was used). That prompted me to try and decode it. I’m lazy, so i didn’t want to do it by hand. The scripting laguage that I currently use is php, so I looked for a text rotation method in php, but the only one I could find is rot_13, which rotates the text by 13, but that didn’t give me the answer. So I coded my own arbitrary rotation function. Here it is :

$str="Ztte pc tnt dc BprWtxhi iwxh lttz. Hdbtiwx cv'h vdxcv sdlc...";
$rot = 11;
print "rotation = $rot . Rotated text: ". rot_n($str,$rot) . "\n";
function rot_n($str,$rot){
	$upperOffset = 65;
	$lowerOffset = 97;
	$ret="";
	for($i=0; $i<strlen($str); $i++){
		$c = ord(substr($str,$i,1));
		if($c>64 && $c < 91){
			$ret.=chr(($c-$upperOffset+$rot)%26+$upperOffset);
		}
		else {
			if( $c>96 && $c<123){
			    $ret.=chr(($c-$lowerOffset+$rot)%26+$lowerOffset);
			}else {
				$ret.=chr($c);
			}
		}
	}
	return $ret;
}

You can use this to code and decode :-). Maybe i’ll do a javascript version of this function.Done and commited in github.