A toy cypher written in PHP. (I have no idea why I wrote this...)

xor.php

<?php

function xor_cipher($data, $key) {
    $data = bitify($data);
    $key = bitify($key);
    $cipher = array();
    $k_i = 0;
    for($d_i=0; $d_i<count($data); $d_i++) {
        $d = $data[$d_i];
        $k = $key[$k_i];
        $c = $d ^ $k;
        $cipher[] = $c;
        $k_i<(count($key)-1)?$k_i++:$k_i=0;
    }
    return unbitify($cipher);
}

function bitify($data) {
    $final = array();
    for($i = 0; $i < strlen($data); $i++) {
        $char = $data[$i];
        $ord = ord($char);
        $byte = sprintf('%08b', $ord);
        for($j = 0; $j < 8; $j++) {
            $bit = $byte[$j];
            $final[] = intval($bit);
        }
    }
    return $final;
}

function unbitify($data) {
    $final = '';
    for($i = 0; $i < count($data); $i+=8) {
        $byte = implode(array($data[$i], $data[$i+1], $data[$i+2], $data[$i+3], $data[$i+4], $data[$i+5], $data[$i+6], $data[$i+7]));
        $ord = bindec($byte);
        $char = chr($ord);
        $final .= $char;
    }
    return $final;
}

function swizz_cipher($data, $key) {
    $data = bitify($data);
    $key = bitify($key);
    $cipher = array();
    $k_i = 0;
    for($d_i=0; $d_i<count($data); $d_i++) {
        $d = $data[$d_i];
        $k = $key[$k_i];
        $p = $d_i>0?$cipher[$d_i-1]:0;
        $t = $k ^ $p;
        $c = $d ^ $t;
        $cipher[] = $c;
        $k_i<(count($key)-1)?$k_i++:$k_i=0;
    }
    return unbitify($cipher);
}

function swizz_decipher($cipher, $key) {
    $cipher = bitify($cipher);
    $key = bitify($key);
    $f_key = array();
    $k_i = 0;
    foreach($cipher as $bit) {
        $f_key[] = $key[$k_i];
        $k_i<(count($key)-1)?$k_i++:$k_i=0;
    }
    $r_cipher = array_reverse($cipher);
    $r_key = array_reverse($f_key);
    $data = array();
    $k_i = 0;
    for($d_i=0; $d_i<count($r_cipher); $d_i++) {
        $t = $d_i<(count($r_cipher)-1)?$r_cipher[$d_i+1]:0;
        $c = $r_cipher[$d_i];
        $k = $r_key[$d_i];
        $p = $t ^ $k;
        $d = $p ^ $c;
        $data[] = $d;
    }
    $r_data = array_reverse($data);
    return unbitify($r_data);
}

$data = "Hello, world!";
$key = "ola";

$cipher = swizz_cipher($data, $key);
$decipher = swizz_decipher($cipher, $key);

var_dump($decipher);