加密过滤器

mcrypt.*和 mdecrypt.*使用 libmcrypt 提供了对称的加密和解密。这两组过滤器都支持 mcrypt 扩展库中相同的算法，格式为 mcrypt.ciphername，其中 ciphername是密码的名字，将被传递给 mcrypt_module_open()。有以下五个过滤器参数可用：

**mcrypt 过滤器参数**
参数	是否必须	默认值	取值举例
mode	可选	cbc	cbc, cfb, ecb, nofb, ofb, stream
algorithms_dir	可选	ini_get('mcrypt.algorithms_dir')	algorithms 模块的目录
modes_dir	可选	ini_get('mcrypt.modes_dir')	modes 模块的目录
iv	必须	N/A	典型为 8，16 或 32 字节的二进制数据。根据密码而定
key	必须	N/A	典型为 8，16 或 32 字节的二进制数据。根据密码而定

Example #1 用 3DES 将文件加密输出


<?php
$passphrase = 'My secret';

/* Turn a human readable passphrase
 * into a reproducable iv/key pair
 */
$iv = substr(md5('iv'.$passphrase, true), 0, 8);
$key = substr(md5('pass1'.$passphrase, true) .
               md5('pass2'.$passphrase, true), 0, 24);
$opts = array('iv'=>$iv, 'key'=>$key);

$fp = fopen('secert-file.enc', 'wb');
stream_filter_append($fp, 'mcrypt.tripledes', STREAM_FILTER_WRITE, $opts);
fwrite($fp, 'Secret secret secret data');
fclose($fp);
?>

Example #2 读取加密的文件


<?php
$passphrase = 'My secret';

/* Turn a human readable passphrase
 * into a reproducable iv/key pair
 */
$iv = substr(md5('iv'.$passphrase, true), 0, 8);
$key = substr(md5('pass1'.$passphrase, true) .
               md5('pass2'.$passphrase, true), 0, 24);
$opts = array('iv'=>$iv, 'key'=>$key);

$fp = fopen('secert-file.enc', 'rb');
stream_filter_append($fp, 'mdecrypt.tripledes', STREAM_FILTER_WRITE, $opts);
$data = rtrim(stream_get_contents($fp));
fclose($fp);

echo $data;
?>

User Contributed Notes

Maarten Bodewes 06-Aug-2017 12:21


The examples on this page should be destroyed with utmost urgency.



Strangely most people will fall over the use of generating the IV and 3DES key using MD5, a weak hash function, e.g. the previous note and CryptoFails blog.



http://www.cryptofails.com/post/70059608390/php-documentation-woes



A password based key derivation function should be used (bcrypt, PBKDF2).



However the use of MD-5 for key derivation however isn't that bad and if the password is strong enough (it usually isn't) then the generated DES ABC key is strong enough even now.

 

Using an identical IV for each password means that this function directly leaks information about the encrypted file. If the start of two encrypted files is identical then this function will directly leak information. For instance, if the routine encrypts multiple images then the JPEG header would be easily distinguished.



All in all these examples use deprecated routines (mcrypt), deprecated cryptographic functions (MD5 / DES) and then incorrectly perform the actual encryption. Enough reason to destroy them in the first place.

Uwe Ohse 22-Feb-2017 04:17


1) The mcrypt module has been deprecated with PHP 7.1.

What does that mean for the encryption filters?



2) deriving the IV from the secret passphrase seems wrong. This leaks information about the passphrase without need.



3) using md5() for this? Really? hash() has been available since PHP 5.1.2.



4) hashing the passphrase twice does not add any security.



5) using substr() on binary data (why, oh why, is true passed to md5()?) might lead to headaches if mbstring.func_overload is used.