Filtros de Criptografia

Aviso

This feature has been DEPRECATED as of PHP 7.1.0. Relying on this feature is highly discouraged.

Os filtros de criptografia são especialmente úteis para criptografia de arquivo/stream.

Os filtros mcrypt.* e mdecrypt.* fornecem criptografia e descriptografia simétricas 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 passado para mcrypt_module_open(). Os cinco parâmetros de filtros a seguir também estão disponíveis:

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

Exemplo #1 Criptografar/Descriptografar com Blowfish

<?php
// assume-se que $key foi gerada anteriormente
$iv_size mcrypt_get_iv_size(MCRYPT_BLOWFISHMCRYPT_MODE_CBC);
$iv mcrypt_create_iv($iv_sizeMCRYPT_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'mensagem para criptografar');
fclose($fp);

// descriptografar...
$fp fopen('encrypted-file.enc''rb');
$iv fread($fp$iv_size mcrypt_get_iv_size(MCRYPT_BLOWFISHMCRYPT_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)); // retira o null padding
fclose($fp);
echo 
$data;
?>

Exemplo #2 Criptografar arquivo usando CBC AES-128 com HMAC SHA256 no 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']; } // padrão AES-128
  
public static function encryptFile($password$input_stream$aes_filename){
    
$iv_size mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128MCRYPT_MODE_CBC);
    
$fin fopen($input_stream"rb");
    
$fc fopen($aes_filename"wb+");
    if (!empty(
$fin) && !empty($fc)) {
      
fwrite($fcstr_repeat("_"32) ); // placeholder, HMAC SHA256 será usado aqui mais tarde
      
fwrite($fc$hmac_salt mcrypt_create_iv($iv_sizeMCRYPT_DEV_URANDOM));
      
fwrite($fc$esalt mcrypt_create_iv($iv_sizeMCRYPT_DEV_URANDOM));
      
fwrite($fc$iv mcrypt_create_iv($iv_sizeMCRYPT_DEV_URANDOM));
      
$ekey hash_pbkdf2("sha256"$password$esalt$it=1000self::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)) {
        
$block fread($fin8192);
        
$infilesize+=strlen($block);
        
fwrite($fc$block);
      }
      
$block_size mcrypt_get_block_size(MCRYPT_RIJNDAEL_128MCRYPT_MODE_CBC);
      
$padding $block_size - ($infilesize $block_size); // $padding é um número de 1-16
      
fwrite($fcstr_repeat(chr($padding), $padding) ); // realiza o padding 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); // sobrescreve o placeholder
      
fclose($fc);
    }
  }
  public static function 
decryptFile($password$aes_filename$out_stream) {
    
$iv_size mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128MCRYPT_MODE_CBC);
    
$hmac_raw file_get_contents($aes_filenamefalseNULL,  032);
    
$hmac_salt file_get_contents($aes_filenamefalseNULL32$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($fc32+$iv_size); // ignora HMAC SHA256 e salt
      
$esalt fread($fc$iv_size);
      
$iv    fread($fc$iv_size);
      
$ekey hash_pbkdf2("sha256"$password$esalt$it=1000self::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)) {
        
$block fread($fc8192);
        if (
feof($fc)) {
          
$padding ord($block[strlen($block) - 1]); // assume padding PKCS7
          
$block substr($block00-$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=100024$raw=true);
    return 
hash_hmac_file('sha256'$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
7
Uwe Ohse
1 year 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
4
Maarten Bodewes
9 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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