加密过滤器特别适用于文件/数据流的加密。
本特性已自 PHP 7.1.0 起废弃。强烈建议不要使用本特性。
mcrypt.* 和
mdecrypt.* 使用 libmcrypt 提供了对称的加密和解密。这两组过滤器都支持
mcrypt 扩展库中相同的算法，格式为
mcrypt.ciphername，其中
ciphername 是密码的名字，将被传递给
mcrypt_module_open()。有以下五个过滤器参数可用：
| 参数 | 是否必须 | 默认值 | 取值举例 |
|---|---|---|---|
| mode | 可选 | cbc | cbc、cfb、ecb、nofb、ofb、stream |
| algorithms_dir | 可选 | ini_get('mcrypt.algorithms_dir') | algorithms 模块的目录 |
| modes_dir | 可选 | ini_get('mcrypt.modes_dir') | modes 模块的目录 |
| iv | 必须 | N/A | 典型为 8、16 或 32 字节的二进制数据。根据密码而定 |
| key | 必须 | N/A | 典型为 8、16 或 32 字节的二进制数据。根据密码而定 |
示例 #1 用 Blowfish 算法加解密
<?php
// 假设之前已经生成了 $key
$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);
// 解密
$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 $data;
?>示例 #2 将文件以 SHA256 HMAC 的 AES-128 CBC 加密
<?php
AES_CBC::encryptFile($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']; }
}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.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.