Verschlüsselungsfilter sind besonders nützlich für die Verschlüsselung von Dateien/Streams.
Dieses Feature ist seit PHP 7.1.0 als DEPRECATED (veraltet) markiert. Von der Verwendung dieses Features wird dringend abgeraten.
mcrypt.* und mdecrypt.*
ermöglichen mit Hilfe von libmcrypt die symmetrische Ver- und
Entschlüsselung. Beide Gruppen von Filtern unterstützen die gleichen
Algorithmen, die für die Erweiterung
mcrypt in Form von
mcrypt.ciphername zur Verfügung stehen, wobei
ciphername der Name der Verschlüsselung ist, wie er
auch an die Funktion mcrypt_module_open() übergeben
werden würde. Die folgenden fünf Filterparameter sind ebenfalls verfügbar:
| Parameter | Erforderlich? | Standard | Beispielwerte |
|---|---|---|---|
| mode | Optional | cbc | cbc, cfb, ecb, nofb, ofb, stream |
| algorithms_dir | Optional | ini_get('mcrypt.algorithms_dir') | Das Verzeichnis, das die Algorithmen enthält |
| modes_dir | Optional | ini_get('mcrypt.modes_dir') | Das Verzeichnis, das die Modi enthält |
| iv | Required | N/A | Typischerweise 8, 16 oder 32 Byte Binärdaten. Abhängig von der Verschlüsselung |
| key | Required | N/A | Typischerweise 8, 16 oder 32 Byte Binärdaten. Abhängig von der Verschlüsselung |
Beispiel #1 Ver- und Entschlüsselung mit Blowfish
<?php
// $key wird als zuvor generiert angenommen
$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, 'zu verschlüsselnede Nachricht');
fclose($fp);
// entschlüsseln...
$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)); // entfernt das Null-Padding
fclose($fp);
echo $data;
?>Beispiel #2 Verschlüsseln einer Datei mit AES-128 CBC und SHA256 HMAC
<?php
AES_CBC::encryptFile($password, "klartext.txt", "verschluesselt.enc");
AES_CBC::decryptFile($password, "verschluesselt.enc", "entschluesselt.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']; } // Standard 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($fc, str_repeat("_", 32) ); // Platzhalter, hier wird später SHA256 HMAC eingefügt
fwrite($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); // $padding ist eine Zahl von 1-16
fwrite($fc, str_repeat(chr($padding), $padding) ); // PKCS7-Padding durchführen
fclose($fin);
fclose($fc);
$hmac_raw = self::calculate_hmac_after_32bytes($password, $hmac_salt, $aes_filename);
$fc = fopen($aes_filename, "rb+");
fwrite($fc, $hmac_raw); // Platzhalter überschreiben
fclose($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); // sha256 hmac und salt weglassen
$esalt = fread($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]); // PKCS7-Padding wird angenommen
$block = substr($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.