Los filtros de cifrado son especialmente útiles para el cifrado de archivos y flujos.
Esta característica ha sido declarada OBSOLETA a partir de PHP 7.0.1. Su uso está totalmente desaconsejado.
mcrypt.* y mdecrypt.* ofrecen
encripción y desencripción simétrica usando libmcrypt. Ambos conjuntos de
filtros soportan los mismos algoritmos disponibles a la extensión mcrypt en la forma de
mcrypt.ciphername, en donde
ciphername es el nombre del cifrado que debe ser
pasado a mcrypt_module_open(). Los siguientes cinco
parámetros se encuentran disponibles también:
| Parámetro | ¿Requerido? | Por omisión | Valores de ejemplo |
|---|---|---|---|
| mode | Optional | cbc | cbc, cfb, ecb, nofb, ofb, stream |
| algorithms_dir | Optional | ini_get('mcrypt.algorithms_dir') | Ubicación de los módulos de los algoritmos |
| modes_dir | Optional | ini_get('mcrypt.modes_dir') | Ubicación de los módulos de los modos |
| iv | Required | N/A | Típicamente 8, 16, o 32 bytes de datos binarios. Depende del cifrado |
| key | Required | N/A | Típicamente 8, 16, o 32 bytes de datos binarios. Depende del cifrado |
Ejemplo #1 Encriptar/Desencriptar con Blowfish
<?php
//$key que se supone que ha sido generado previamente
$iv_size = mcrypt_get_iv_size(MCRYPT_BLOWFISH, MCRYPT_MODE_CBC);
$iv = mcrypt_create_iv($iv_size, MCRYPT_DEV_URANDOM);
$fp = fopen('encrypted-file.enc', 'wb');
fwrite($fp, $iv);
$opts = array('mode'=>'cbc','iv'=>$iv, 'key'=>$key);
stream_filter_append($fp, 'mcrypt.blowfish', STREAM_FILTER_WRITE, $opts);
fwrite($fp, 'message to encrypt');
fclose($fp);
//desencriptar...
$fp = fopen('encrypted-file.enc', 'rb');
$iv = fread($fp, $iv_size = mcrypt_get_iv_size(MCRYPT_BLOWFISH, MCRYPT_MODE_CBC));
$opts = array('mode'=>'cbc','iv'=>$iv, 'key'=>$key)
stream_filter_append($fp, 'mdecrypt.blowfish', STREAM_FILTER_READ, $opts);
$data = rtrim(stream_get_contents($fp));//trims off null padding
fclose($fp);
echo $data;
?>Ejemplo #2 Encriptar el archivo usando AES-128 CBC con SHA256 HMAC en PHP 5.5+
<?php
AES_CBC::encryptFile($password, "plaintext.txt", "encrypted.enc");
AES_CBC::decryptFile($password, "encrypted.enc", "decrypted.txt");
class AES_CBC
{
protected static $KEY_SIZES = array('AES-128'=>16,'AES-192'=>24,'AES-256'=>32);
protected static function key_size() { return self::$KEY_SIZES['AES-128']; } //default AES-128
public static function encryptFile($password, $input_stream, $aes_filename){
$iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
$fin = fopen($input_stream, "rb");
$fc = fopen($aes_filename, "wb+");
if (!empty($fin) && !empty($fc)) {
fwrite($fc, str_repeat("_", 32) );//marcador de posición, SHA256 HMAC irá aquí más tarde
fwrite($fc, $hmac_salt = mcrypt_create_iv($iv_size, MCRYPT_DEV_URANDOM));
fwrite($fc, $esalt = mcrypt_create_iv($iv_size, MCRYPT_DEV_URANDOM));
fwrite($fc, $iv = mcrypt_create_iv($iv_size, MCRYPT_DEV_URANDOM));
$ekey = hash_pbkdf2("sha256", $password, $esalt, $it=1000, self::key_size(), $raw=true);
$opts = array('mode'=>'cbc', 'iv'=>$iv, 'key'=>$ekey);
stream_filter_append($fc, 'mcrypt.rijndael-128', STREAM_FILTER_WRITE, $opts);
$infilesize = 0;
while (!feof($fin)) {
$block = fread($fin, 8192);
$infilesize+=strlen($block);
fwrite($fc, $block);
}
$block_size = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
$padding = $block_size - ($infilesize % $block_size);//$padding es un número del 1 al 16
fwrite($fc, str_repeat(chr($padding), $padding) );//realizar el relleno de PKCS7
fclose($fin);
fclose($fc);
$hmac_raw = self::calculate_hmac_after_32bytes($password, $hmac_salt, $aes_filename);
$fc = fopen($aes_filename, "rb+");
fwrite($fc, $hmac_raw);//sobrescribir el marcador de posición
fclose($fc);
}
}
public static function decryptFile($password, $aes_filename, $out_stream) {
$iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
$hmac_raw = file_get_contents($aes_filename, false, NULL, 0, 32);
$hmac_salt = file_get_contents($aes_filename, false, NULL, 32, $iv_size);
$hmac_calc = self::calculate_hmac_after_32bytes($password, $hmac_salt, $aes_filename);
$fc = fopen($aes_filename, "rb");
$fout = fopen($out_stream, 'wb');
if (!empty($fout) && !empty($fc) && self::hash_equals($hmac_raw,$hmac_calc)) {
fread($fc, 32+$iv_size);//skip sha256 hmac and salt
$esalt = fread($fc, $iv_size);
$iv = fread($fc, $iv_size);
$ekey = hash_pbkdf2("sha256", $password, $esalt, $it=1000, self::key_size(), $raw=true);
$opts = array('mode'=>'cbc', 'iv'=>$iv, 'key'=>$ekey);
stream_filter_append($fc, 'mdecrypt.rijndael-128', STREAM_FILTER_READ, $opts);
while (!feof($fc)) {
$block = fread($fc, 8192);
if (feof($fc)) {
$padding = ord($block[strlen($block) - 1]);//asume el relleno del PKCS7
$block = substr($block, 0, 0-$padding);
}
fwrite($fout, $block);
}
fclose($fout);
fclose($fc);
}
}
private static function hash_equals($str1, $str2) {
if(strlen($str1) == strlen($str2)) {
$res = $str1 ^ $str2;
for($ret=0,$i = strlen($res) - 1; $i >= 0; $i--) $ret |= ord($res[$i]);
return !$ret;
}
return false;
}
private static function calculate_hmac_after_32bytes($password, $hsalt, $filename) {
static $init=0;
$init or $init = stream_filter_register("user-filter.skipfirst32bytes", "FileSkip32Bytes");
$stream = 'php://filter/read=user-filter.skipfirst32bytes/resource=' . $filename;
$hkey = hash_pbkdf2("sha256", $password, $hsalt, $iterations=1000, 24, $raw=true);
return hash_hmac_file('sha256', $stream, $hkey, $raw=true);
}
}
class FileSkip32Bytes extends php_user_filter
{
private $skipped=0;
function filter($in, $out, &$consumed, $closing) {
while ($bucket = stream_bucket_make_writeable($in)) {
$outlen = $bucket->datalen;
if ($this->skipped<32){
$outlen = min($bucket->datalen,32-$this->skipped);
$bucket->data = substr($bucket->data, $outlen);
$bucket->datalen = $bucket->datalen-$outlen;
$this->skipped+=$outlen;
}
$consumed += $outlen;
stream_bucket_append($out, $bucket);
}
return PSFS_PASS_ON;
}
}
class AES_128_CBC extends AES_CBC {
protected static function key_size() { return self::$KEY_SIZES['AES-128']; }
}
class AES_192_CBC extends AES_CBC {
protected static function key_size() { return self::$KEY_SIZES['AES-192']; }
}
class AES_256_CBC extends AES_CBC {
protected static function key_size() { return self::$KEY_SIZES['AES-256']; }
}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.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.