/**
* 加密函數
* @param string $txt 需要加密的字符串
* @param string $key 密鑰
* @return string 返回加密結果
*/
function atom_encrypt($txt, $key = '')
{
if (empty($txt)) return $txt;
$key = md5($key);
$chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_.";
$ikey = sha1($key);
$nh1 = rand(0, 64);
$nh2 = rand(0, 64);
$nh3 = rand(0, 64);
$ch1 = $chars{$nh1};
$ch2 = $chars{$nh2};
$ch3 = $chars{$nh3};
$nhnum = $nh1 + $nh2 + $nh3;
$knum = 0;
$i = 0;
while (isset($key{$i})) $knum += ord($key{$i++});
$mdKey = substr(md5(md5(md5($key . $ch1) . $ch2 . $ikey) . $ch3), $nhnum % 8, $knum % 8 + 16);
$txt = base64_encode(time() . '_' . $txt);
$txt = str_replace(array('+', '/', '='), array('-', '_', '.'), $txt);
$tmp = '';
$j = 0;
$k = 0;
$tlen = strlen($txt);
$klen = strlen($mdKey);
for ($i = 0; $i < $tlen; $i++) {
$k = $k == $klen ? 0 : $k;
$j = ($nhnum + strpos($chars, $txt{$i}) + ord($mdKey{$k++})) % 64;
$tmp .= $chars{$j};
}
$tmplen = strlen($tmp);
$tmp = substr_replace($tmp, $ch3, $nh2 % ++$tmplen, 0);
$tmp = substr_replace($tmp, $ch2, $nh1 % ++$tmplen, 0);
$tmp = substr_replace($tmp, $ch1, $knum % ++$tmplen, 0);
return $tmp;
}

/**
* 解密函數
* @param string $txt 需要解密的字符串
* @param string $key 密匙
* @return string 字符串類型的返回結果
*/
function atom_decrypt($txt, $key = '', $ttl = 0)
{
if (empty($txt)) return $txt;
$key = md5($key);
$chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_.";
$ikey = sha1($key);
$knum = 0;
$i = 0;
$tlen = @strlen($txt);
while (isset($key{$i})) $knum += ord($key{$i++});
$ch1 = @$txt{$knum % $tlen};
$nh1 = strpos($chars, $ch1);
$txt = @substr_replace($txt, '', $knum % $tlen--, 1);
$ch2 = @$txt{$nh1 % $tlen};
$nh2 = @strpos($chars, $ch2);
$txt = @substr_replace($txt, '', $nh1 % $tlen--, 1);
$ch3 = @$txt{$nh2 % $tlen};
$nh3 = @strpos($chars, $ch3);
$txt = @substr_replace($txt, '', $nh2 % $tlen--, 1);
$nhnum = $nh1 + $nh2 + $nh3;
$mdKey = substr(md5(md5(md5($key . $ch1) . $ch2 . $ikey) . $ch3), $nhnum % 8, $knum % 8 + 16);
$tmp = '';
$j = 0;
$k = 0;
$tlen = @strlen($txt);
$klen = @strlen($mdKey);
for ($i = 0; $i < $tlen; $i++) {
$k = $k == $klen ? 0 : $k;
$j = strpos($chars, $txt{$i}) - $nhnum - ord($mdKey{$k++});
while ($j < 0) $j += 64;
$tmp .= $chars{$j};
}
$tmp = str_replace(array('-', '_', '.'), array('+', '/', '='), $tmp);
$tmp = trim(base64_decode($tmp));
if (preg_match("/\d{10}_/s", substr($tmp, 0, 11))) {
if ($ttl > 0 && (time() - substr($tmp, 0, 11) > $ttl)) {
$tmp = NULL;
} else {
$tmp = substr($tmp, 11);
}
}
return $tmp;
}