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']; }
}