Şifreleme Süzgeçleri

Şifreleme süzgeçleri öxellikle dosya/akım şifrelemesinde kullanışlıdır.

mcrypt.* ve mdecrypt.*

Uyarı

Bu özelliğin kullanımı PHP 7.1.0 itibariyle ÖNERİLMEMEKTEDİR. Bu işleve kesinlikle güvenilmemelidir.

mcrypt.* ve mdecrypt.* süzgeçleri libmcrypt kullanarak bakışımlı şifreleme ve şifre çözme yaparlar. Her iki süzgeç ailesi de mcrypt.şifreismi biçeminde mcrypt eklentisinde kullanılan algoritmaları desteklerler; buradaki şifreismi mcrypt_module_open() işlevine aktarıldığı şekliyle şifrenin ismidir. Ayrıca, aşağıdaki beş süzgeç bağımsız değişkeni de kullanılabilmektedir:

mcrypt süzgeç bağımsız değişkenleri
Bağımsız değişken Gereklilik Öntanımlı Örnek değerler
mode seçimlik cbc cbc, cfb, ecb, nofb, ofb, stream
algorithms_dir seçimlik ini_get('mcrypt.algorithms_dir') Algoritma modüllerinin yeri
modes_dir seçimlik ini_get('mcrypt.modes_dir') Kip modüllerinin yeri
iv gerekli yok Genelde 8, 16 veya 32 baytlık ikil veri. Şifreye bağlı.
key gerekli yok Genelde 8, 16 veya 32 baytlık ikil veri. Şifreye bağlı.

Örnek 1 - 3DES kullanarak şifreli dosya çıktılama

<?php
//$key evvelce üretilmiş varsayılıyor
$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);

//decrypt...
$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));//null dizesi temizleniyor
fclose($fp);
echo
$data;
?>

Örnek 2 - SHA256 HMAC ile AES-128 CBC kullanarak dosya şifreleme

<?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']; }
}
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User Contributed Notes 2 notes

up
4
Uwe Ohse
7 years 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
1
Maarten Bodewes
6 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.
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