Encryption Filters

mcrypt.* and mdecrypt.* provide symmetric encryption and decryption using libmcrypt. Both sets of filters support the same algorithms available to mcrypt extension in the form of mcrypt.ciphername where ciphername is the name of the cipher as it would be passed to mcrypt_module_open(). The following five filter parameters are also available:

mcrypt filter parameters
Parameter Required? Default Sample Values
mode Optional cbc cbc, cfb, ecb, nofb, ofb, stream
algorithms_dir Optional ini_get('mcrypt.algorithms_dir') Location of algorithms modules
modes_dir Optional ini_get('mcrypt.modes_dir') Location of modes modules
iv Required N/A Typically 8, 16, or 32 bytes of binary data. Depends on cipher
key Required N/A Typically 8, 16, or 32 bytes of binary data. Depends on cipher

Beispiel #1 Encrypting file output using 3DES

<?php
$passphrase 
'My secret';

/* Turn a human readable passphrase
 * into a reproducable iv/key pair
 */
$iv substr(md5('iv'.$passphrasetrue), 08);
$key substr(md5('pass1'.$passphrasetrue) . 
               
md5('pass2'.$passphrasetrue), 024);
$opts = array('iv'=>$iv'key'=>$key);

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

Beispiel #2 Reading an encrypted file

<?php
$passphrase 
'My secret';

/* Turn a human readable passphrase
 * into a reproducable iv/key pair
 */
$iv substr(md5('iv'.$passphrasetrue), 08);
$key substr(md5('pass1'.$passphrasetrue) . 
               
md5('pass2'.$passphrasetrue), 024);
$opts = array('iv'=>$iv'key'=>$key);

$fp fopen('secret-file.enc''rb');
stream_filter_append($fp'mdecrypt.tripledes'STREAM_FILTER_READ$opts);
$data rtrim(stream_get_contents($fp));
fclose($fp);

echo 
$data;
?>
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User Contributed Notes 1 note

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1
Uwe Ohse
5 months ago
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.
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