Encrypt/Decrypt String

function str_encrypt($v, $k){
    if ($v){
        $g = strlen($k)-1;
        $e = strlen($v);
        for ($i = 0; $i < $e; $i++){
            $j = $i;
            while ($j > $g){
                $j = $j - $g;
            }
            $h = ord($v[$i]);
            $l = ord($k[$j]);
            $f = $h + $l + $i - $j;
            if ($f >= 256){
                $b[$i] = chr($f - 255);
            }else{
                $b[$i] = chr($f);
            }
        }
        $b = implode($b);
        return $b;
    }
}

function str_decrypt($v, $k){
    if ($v){
        $g = strlen($k)-1;
        $e = strlen($v);
        for ($i = 0; $i < $e; $i++){
            $j = $i;
            while ($j > $g){
                $j = $j - $g;
            }
            $h = ord($v[$i]);
            $l = ord($k[$j]);
            $f = $h - $l - $i + $j;
            if ($f < 0){
                $b[$i] = chr($f + 255);
            }else{
                $b[$i] = chr($f);
            }
        }
        $b = implode($b);
        return $b;
    }
}