- PHP-Resource

Encryption Filters

Encryption filters are especially useful for file/stream encryption.

mcrypt.* and mdecrypt.*

Warning

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

mcrypt.* and mdecrypt.* provide symmetric encryption and decryption using libmcrypt. Both sets of filters support the same algorithms available to mcrypt extension in the form of mcrypt.ciphername where ciphername is the name of the cipher as it would be passed to mcrypt_module_open(). The following five filter parameters are also available:

**mcrypt filter parameters**
Parameter	Required?	Default	Sample Values
mode	Optional	cbc	cbc, cfb, ecb, nofb, ofb, stream
algorithms_dir	Optional	ini_get('mcrypt.algorithms_dir')	Location of algorithms modules
modes_dir	Optional	ini_get('mcrypt.modes_dir')	Location of modes modules
iv	Required	N/A	Typically 8, 16, or 32 bytes of binary data. Depends on cipher
key	Required	N/A	Typically 8, 16, or 32 bytes of binary data. Depends on cipher

Example #1 Encrypt/Decrypt with Blowfish


<?php
//$key assumed to be previously generated
$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));//trims off null padding
fclose($fp);
echo $data;
?>

Example #2 Encrypt file using AES-128 CBC with SHA256 HMAC


<?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']; }
}