mcrypt_ofb
We found that sometimes the resulting padding is not null characters "\0" but rather one of several control characters.
If you know your data is not supposed to have any trailing control characters "as we did" you can strip them like so.
<?php
$data = mdecrypt_generic( $cipher, $data );
// Strip trailing control-character padding
$data = preg_replace( "/\p{Cc}*$/u", "", $data );
?>
mdecrypt_generic
(PHP 4 >= 4.0.2, PHP 5)
mdecrypt_generic — データを復号する
説明
string mdecrypt_generic
( resource
$td
, string $data
)この関数は、データを復号します。データのパディングが行われるため、 返される文字列の長さは暗号化前の文字列よりも長くなる可能性があることに 注意してください。
例
例1 mdecrypt_generic() の例
<?php
/* データ */
$key = 'this is a very long key, even too long for the cipher';
$plain_text = 'very important data';
/* モジュールをオープンし、IV を作成します */
$td = mcrypt_module_open('des', '', 'ecb', '');
$key = substr($key, 0, mcrypt_enc_get_key_size($td));
$iv_size = mcrypt_enc_get_iv_size($td);
$iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
/* 暗号化ハンドルを初期化します */
if (mcrypt_generic_init($td, $key, $iv) != -1) {
/* データを暗号化します */
$c_t = mcrypt_generic($td, $plain_text);
mcrypt_generic_deinit($td);
/* 復号のため、バッファを再度初期化します */
mcrypt_generic_init($td, $key, $iv);
$p_t = mdecrypt_generic($td, $c_t);
/* 後始末をします */
mcrypt_generic_deinit($td);
mcrypt_module_close($td);
}
if (strncmp($p_t, $plain_text, strlen($plain_text)) == 0) {
echo "ok\n";
} else {
echo "error\n";
}
?>
上記の例は、暗号化前のデータと復号したデータと同じであるかどうかを 調べる方法を示すものです。データを復号する前に mcrypt_generic_init() で暗号化バッファを再度 初期化しておくことが重要です。
この関数をコールする前に、常に mcrypt_generic_init() でキーと IV を使用して 復号ハンドルを初期化しておくべきです。暗号化が終了した際には mcrypt_generic_deinit() をコールして暗号化 バッファを開放すべきです。 mcrypt_module_open() の例を参照ください。
参考
- mcrypt_generic() - データを暗号化する
- mcrypt_generic_init() - 暗号化に必要な全てのバッファを初期化する
- mcrypt_generic_deinit() - 暗号化モジュールを終了する
add a note
User Contributed Notes
mdecrypt_generic
Peter Bailey
19-Mar-2012 05:49
trashmail dot hashishin at gmail dot com
01-Jun-2010 12:46
Whenever you need to decrypt files encrypted with dot.net (and others?) you can use the following settings:
Encryption: 'rijndael-256'
Mode: 'cbc'
Padding-Mode: Zeros
iv: "yes"
encode the data with base64 to send them to your php script
Anonymous
21-Mar-2009 07:31
Here's a quick snippet for removing PKCS7 padding:
<?php
function unpadPKCS7($data, $blockSize) {
$length = strlen ( $data );
if ($length > 0) {
$first = substr ( $data, - 1 );
if (ord ( $first ) <= $blockSize) {
for($i = $length - 2; $i > 0; $i --)
if (ord ( $data [$i] != $first ))
break;
return substr ( $data, 0, $i );
}
}
return $data;
}
?>
nytro_rst at yahoo dot com
09-Feb-2009 03:33
<?php
// Parameters:
// $text = The text that you want to encrypt.
// $key = The key you're using to encrypt.
// $alg = The algorithm.
// $crypt = 1 if you want to crypt, or 0 if you want to decrypt.
function cryptare($text, $key, $alg, $crypt)
{
$encrypted_data="";
switch($alg)
{
case "3des":
$td = mcrypt_module_open('tripledes', '', 'ecb', '');
break;
case "cast-128":
$td = mcrypt_module_open('cast-128', '', 'ecb', '');
break;
case "gost":
$td = mcrypt_module_open('gost', '', 'ecb', '');
break;
case "rijndael-128":
$td = mcrypt_module_open('rijndael-128', '', 'ecb', '');
break;
case "twofish":
$td = mcrypt_module_open('twofish', '', 'ecb', '');
break;
case "arcfour":
$td = mcrypt_module_open('arcfour', '', 'ecb', '');
break;
case "cast-256":
$td = mcrypt_module_open('cast-256', '', 'ecb', '');
break;
case "loki97":
$td = mcrypt_module_open('loki97', '', 'ecb', '');
break;
case "rijndael-192":
$td = mcrypt_module_open('rijndael-192', '', 'ecb', '');
break;
case "saferplus":
$td = mcrypt_module_open('saferplus', '', 'ecb', '');
break;
case "wake":
$td = mcrypt_module_open('wake', '', 'ecb', '');
break;
case "blowfish-compat":
$td = mcrypt_module_open('blowfish-compat', '', 'ecb', '');
break;
case "des":
$td = mcrypt_module_open('des', '', 'ecb', '');
break;
case "rijndael-256":
$td = mcrypt_module_open('rijndael-256', '', 'ecb', '');
break;
case "xtea":
$td = mcrypt_module_open('xtea', '', 'ecb', '');
break;
case "enigma":
$td = mcrypt_module_open('enigma', '', 'ecb', '');
break;
case "rc2":
$td = mcrypt_module_open('rc2', '', 'ecb', '');
break;
default:
$td = mcrypt_module_open('blowfish', '', 'ecb', '');
break;
}
$iv = mcrypt_create_iv(mcrypt_enc_get_iv_size($td), MCRYPT_RAND);
$key = substr($key, 0, mcrypt_enc_get_key_size($td));
mcrypt_generic_init($td, $key, $iv);
if($crypt)
{
$encrypted_data = mcrypt_generic($td, $text);
}
else
{
$encrypted_data = mdecrypt_generic($td, $text);
}
mcrypt_generic_deinit($td);
mcrypt_module_close($td);
return $encrypted_data;
}
?>
Silvan
17-Aug-2007 12:34
It is generally not recommended to just use rtrim to remove the padding.
Use rtrim($str, "\0") for strings that do not end in "\0" or store the data length during encryption.
(Although data containing "\0" sometimes gets corrupted during encryption so these types of data actually should be packed.)
For example:
<?php
function encrypt($original_data)
{
$length = strlen($original_data);
$data_to_encrypt = $length.'|'.$original_data;
// Encrypt the data including its length.
// Do not save the length unencrypted, as this could be a (minor) security risk
}
function decrypt($cypher)
{
// Decrypt the cypher data first
// Next retrieve the original data
list($length, $padded_data) = explode('|', $decrypted_data, 2);
$original_data = substr($padded_data, 0, $length);
}
?>
php at pcwize dot com
12-Oct-2006 02:59
Just confirming the .DLL issues. With 4.3.4 you need the older .DLL. I'm guessing any version of PHP4 needs the older .DLL. With PHP5 you need the newer one.
drew at expressdynamics dot com
05-Jul-2005 10:07
On Win32 systems with PHP 5, you must use the newer libmcrypt.dll file, otherwise mdecrypt_generic will not work.
robbie [at] averill [dot] co [dot] nz
24-Mar-2005 03:15
I have noticed that sometimes when the binary ciphertext is longer than the plaintext, the decrypted plaintext can have some little boxes/squares next to it as 'padding'. I also noticed that you can't cut and paste them to be able to edit them out, but i did find a solution.
Just call rtrim() around the string and it removes them.
jon@jonroig dot com
07-Apr-2004 07:29
Here's a bit of encrypt/decrypt code.
If you're using this on the win32 platform, BEWARE! The latest DLL (19-Jan-2004) contains a bug that keeps mdecrypt_generic from functioning. Nearly drove me over the edge... The 30-Dec-2002 version seems to work with no trouble.
<?
$key = "this is a secret key";
$input = "Let us meet at 9 o'clock at the secret place.";
$td = mcrypt_module_open('tripledes', '', 'ecb', '');
$iv = mcrypt_create_iv (mcrypt_enc_get_iv_size($td), MCRYPT_RAND);
mcrypt_generic_init($td, $key, $iv);
$encrypted_data = mcrypt_generic($td, $input);
mcrypt_generic_deinit($td);
mcrypt_module_close($td);
echo "Encrypt: ".$encrypted_data;
echo "<br><br>";
$td = mcrypt_module_open('tripledes', '', 'ecb', '');
$iv = mcrypt_create_iv (mcrypt_enc_get_iv_size($td), MCRYPT_RAND);
$key = substr($key, 0, mcrypt_enc_get_key_size($td));
mcrypt_generic_init($td, $key, $iv);
$decrypted_data = mdecrypt_generic($td, $encrypted_data);
echo "Decrypt: ".$decrypted_data;
mcrypt_generic_deinit($td);
mcrypt_module_close($td);
?>