PHP encryption and decryption example analysis, _PHP tutorial

//加密
function string2secret($str)
{
 $key = "123";
 $td = mcrypt_module_open(MCRYPT_DES,'','ecb','');
 $iv = mcrypt_create_iv(mcrypt_enc_get_iv_size($td), MCRYPT_RAND);
 $ks = mcrypt_enc_get_key_size($td);
 $key = substr(md5($key), 0, $ks);
 mcrypt_generic_init($td, $key, $iv);
 $secret = mcrypt_generic($td, $str);
 mcrypt_generic_deinit($td);
 mcrypt_module_close($td);
 return $secret;
}
//解密
function secret2string($sec)
{
 $key = "123";
 $td = mcrypt_module_open(MCRYPT_DES,'','ecb','');
 $iv = mcrypt_create_iv(mcrypt_enc_get_iv_size($td), MCRYPT_RAND);
 $ks = mcrypt_enc_get_key_size($td);
 $key = substr(md5($key), 0, $ks);
 mcrypt_generic_init($td, $key, $iv);
 $string = mdecrypt_generic($td, $sec);
 mcrypt_generic_deinit($td);
 mcrypt_module_close($td);
 return trim($string);
}
echo secret2string(string2secret("11111111111111111"));
//显示结果是11111111111111111
echo '<br>'.string2secret("11111111111111111");
//显示乱码
echo '<br>';
//$string:要加密的字符串 $isEncrypt=true:加密 $isEncrypt=false:解密
function dencrypt($string, $isEncrypt = true, $key = "KEY_SPACE") {
 if (!isset($string{0}) || !isset($key{0})) {
  return false;
 }
 $dynKey = $isEncrypt &#63; hash('sha1', microtime(true)) : substr($string, 0, 40);
 $fixedKey = hash('sha1', $key);
 $dynKeyPart1 = substr($dynKey, 0, 20);
 $dynKeyPart2 = substr($dynKey, 20);
 $fixedKeyPart1 = substr($fixedKey, 0, 20);
 $fixedKeyPart2 = substr($fixedKey, 20);
 $key = hash('sha1', $dynKeyPart1 . $fixedKeyPart1 . $dynKeyPart2 . $fixedKeyPart2);
 $string = $isEncrypt &#63; $fixedKeyPart1 . $string . $dynKeyPart2 : (isset($string{339}) &#63; gzuncompress(base64_decode(substr($string, 40))) : base64_decode(substr($string, 40)));
 $n = 0;
 $result = '';
 $len = strlen($string);
 for ($n = 0; $n < $len; $n++) {
  $result .= chr(ord($string{$n}) ^ ord($key{$n % 40}));
 }
 return $isEncrypt &#63; $dynKey . str_replace('=', '', base64_encode($n > 299 &#63; gzcompress($result) : $result)) : substr($result, 20, -20);
}
echo strlen(dencrypt("12345678912345"));