Filtros de Criptografia

Os filtros mcrypt.* e mdecrypt.* permitem criptografar e descriptografar usando libmcrypt. Ambos os conjuntos de filtros suportam os mesmos algoritmos disponíveis na extensão mcrypt na forma de mcrypt.ciphername onde ciphername é o nome da cifra como seria passada para mcrypt_module_open(). Os cinco filtros a seguir estão disponíveis:

Parâmetros para os filtros mcrypt
Parâmetro É Necessário? Valor Padrão Exemplos de Valores
mode Opcional cbc cbc, cfb, ecb, nofb, ofb, stream
algorithms_dir Opcional ini_get('mcrypt.algorithms_dir') Localização do módulos de algoritmos
modes_dir Opcional ini_get('mcrypt.modes_dir') Localização do módulos de modos
iv Necessário N/A Tipicamente 8, 16, or 32 bytes de dados binários. Dependa da cifra.
key Necessário N/A Tipicamente 8, 16, or 32 bytes de dados binários. Dependa da cifra.

Exemplo #1 Criptografando saída de arquivo usando 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);
?>

Exemplo #2 Lendo um arquivo criptografado

<?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 2 notes

up
7
Uwe Ohse
8 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.
up
3
Maarten Bodewes
3 months ago
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.
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