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(PHP 4 >= 4.0.2, PHP 5)
mdecrypt_generic — Decrypts data
This function decrypts data. Note that the length of the returned string can in fact be longer than the unencrypted string, due to the padding of the data.
Beispiel #1 mdecrypt_generic() Example
<?php
/* Data */
$key = 'this is a very long key, even too long for the cipher';
$plain_text = 'very important data';
/* Open module, and create IV */
$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);
/* Initialize encryption handle */
if (mcrypt_generic_init($td, $key, $iv) != -1) {
/* Encrypt data */
$c_t = mcrypt_generic($td, $plain_text);
mcrypt_generic_deinit($td);
/* Reinitialize buffers for decryption */
mcrypt_generic_init($td, $key, $iv);
$p_t = mdecrypt_generic($td, $c_t);
/* Clean up */
mcrypt_generic_deinit($td);
mcrypt_module_close($td);
}
if (strncmp($p_t, $plain_text, strlen($plain_text)) == 0) {
echo "ok\n";
} else {
echo "error\n";
}
?>
The example above shows how to check if the data before the encryption is the same as the data after the decryption. It is very important to reinitialize the encryption buffer with mcrypt_generic_init() before you try to decrypt the data.
The decryption handle should always be initialized with mcrypt_generic_init() with a key and an IV before calling this function. Where the encryption is done, you should free the encryption buffers by calling mcrypt_generic_deinit(). See mcrypt_module_open() for an example.
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
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;
}
?>
<?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 $encrypted_data;
}
?>
It is generally not recommended to just use rtrim to remove the padding.
Use rtrim($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);
}
?>
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.
On Win32 systems with PHP 5, you must use the newer libmcrypt.dll file, otherwise mdecrypt_generic will not work.
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.
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);
?>
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