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.
Filtrele de criptare
Filtrele de criptare sunt utile în special pentru criptarea fișierelor/fluxurilor.
mcrypt.* și mdecrypt.*
Avertizare
Această facilitate a fost ÎNVECHITĂ începând cu PHP 7.1.0. Utilizarea acestei facilități este foarte discurajată.
mcrypt.* și mdecrypt.*
oferă criptare și decriptare simetrică, utilizând libmcrypt.
Ambele seturi de filtre susțin aceiași algoritmi disponibili
extensiei mcrypt sub forma
mcrypt.ciphername, unde ciphername
este denumirea algoritmului de criptare, care ar fi putut fi transmis funcției
mcrypt_module_open().
De asemenea sunt disponibili și următorii cinci parametri:
| Parametrul | Necesar? | Implicit | Valori-exemple |
|---|---|---|---|
| mode | Opțional | cbc | cbc, cfb, ecb, nofb, ofb, stream |
| algorithms_dir | Opțional | ini_get('mcrypt.algorithms_dir') | Localizarea modulelor algoritmilor |
| modes_dir | Opțional | ini_get('mcrypt.modes_dir') | Localizarea modulelor modurilor |
| iv | Necesar | nu este | De obicei 8, 16, sau 32 baiți de date binare. Depinde de cifru |
| key | Necesar | nu este | De obicei 8, 16, sau 32 baiți de date binare. Depinde de cifru |
Example #1 Criptarea/Decriptarea cu Blowfish
<?php
// Se presupune că $key a fost generat anterior
$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);
// Decriptarea ...
$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 $data;
?>
Example #2 Criptarea fișierului utilizând AES-128 CBC cu SHA256 HMAC în PHP 5.5+
<?php
AES_CBC::encryptFile($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($fc, str_repeat("_", 32) );//placeholder, SHA256 HMAC will go here later
fwrite($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 is a number from 1-16
fwrite($fc, str_repeat(chr($padding), $padding) );//perform PKCS7 padding
fclose($fin);
fclose($fc);
$hmac_raw = self::calculate_hmac_after_32bytes($password, $hmac_salt, $aes_filename);
$fc = fopen($aes_filename, "rb+");
fwrite($fc, $hmac_raw);//overwrite placeholder
fclose($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]);//assume PKCS7 padding
$block = substr($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']; }
}
add a note
User Contributed Notes 2 notes
Uwe Ohse ¶
7 years ago
Maarten Bodewes ¶
7 years 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.
