PHP Toggle Encypt Decrypt Function

PHP Toggle Encypt Decrypt Function.php

<?php

function toggleEncryption($text, $key = '') {
    // return text unaltered if the key is blank
    if ($key == '') {
        return $text;
    }

    // remove the spaces in the key
    $key = str_replace(' ', '', $key);
    if (strlen($key) < 8) {
        exit('key error');
    }
    // set key length to be no more than 32 characters
    $key_len = strlen($key);
    if ($key_len > 32) {
        $key_len = 32;
    }

    $k = array(); // key array
    // fill key array with the bitwise AND of the ith key character and 0x1F
    for ($i = 0; $i < $key_len; ++$i) {
        $k[$i] = ord($key{$i}) & 0x1F;
    }

    // perform encryption/decryption
    for ($i = 0; $i < strlen($text); ++$i) {
        $e = ord($text{$i});
        // if the bitwise AND of this character and 0xE0 is non-zero
        // set this character to the bitwise XOR of itself
        // and the ith key element, wrapping around key length
        // else leave this character alone
        if ($e & 0xE0) {
            $text{$i} = chr($e ^ $k[$i % $key_len]);
        }
    }
    return $text;
}