PHP Unconference Europe 2015

mdecrypt_generic

(PHP 4 >= 4.0.2, PHP 5)

mdecrypt_genericDesencripta datos

Descripción

string mdecrypt_generic ( resource $td , string $data )

Esta función desencripta datos. Note que la longitud de la cadena retornada puede ser mayor a la cadena no cifrada, debido al relleno de la información.

Parámetros

td

Un descriptor de cifrado devuelto por mcrypt_module_open()

data

Los datos encriptados.

Ejemplos

Ejemplo #1 Ejemplo de mdecrypt_generic()

<?php
    
/* Data */
    
$key 'esta es una clave muy larga, aún para el cifrador';
    
$plain_text 'información muy importante';

    
/* Apertura de un modo, y creación de un IV */
    
$td mcrypt_module_open('des''''ecb''');
    
$key substr($key0mcrypt_enc_get_key_size($td));
    
$iv_size mcrypt_enc_get_iv_size($td);
    
$iv mcrypt_create_iv($iv_sizeMCRYPT_RAND);

    
/* Iniciando gestor de encriptación */
    
if (mcrypt_generic_init($td$key$iv) != -1) {

        
/* Encriptación de los datos */
        
$c_t mcrypt_generic($td$plain_text);
        
mcrypt_generic_deinit($td);

        
/* Reinicialización de los buffers para desencriptación */
        
mcrypt_generic_init($td$key$iv);
        
$p_t mdecrypt_generic($td$c_t);

        
/* Finalización */
        
mcrypt_generic_deinit($td);
        
mcrypt_module_close($td);
    }

    if (
strncmp($p_t$plain_textstrlen($plain_text)) == 0) {
        echo 
"ok\n";
    } else {
        echo 
"error\n";
    }
?>

El ejemplo anterior muestra cómo chequear si los datos antes del cifrado son los mismos después de la decriptación. Es muy importante reinicializar el buffer de cifrado con mcrypt_generic_init() antes de intentar descifrar los datos.

El identificador de descifrado debería siempre ser inicializado con mcrypt_generic_init() con una clave y un IV antes de invocar a esta función. Cuando el cifrado haya terminado, se debería liberar los buffers de cifrado al invocar a mcrypt_generic_deinit() Véase mcrypt_module_open() para un ejemplo.

Ver también

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User Contributed Notes 11 notes

up
4
nytro_rst at yahoo dot com
5 years ago
<?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;
}
?>
up
3
jakub dot lopuszanski at nasza-klasa dot pl
1 year ago
For all those of you which are "surprised" by the padding (even though it is mentioned in the description of the method) please do not just "strip away everything which I do not understand".
The approach with rtrim, rtrim "\0", removing all charcodes < 16, etc. are all wrong.
The PKCS #7 padding works just as described in  RFC 5652.
To remove it, just look at the last byte of the message, and it will tell you how many bytes to remove.
For example, if the last byte is equal to \0A, then remove 10 bytes.
up
1
Anonymous
5 years ago
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;
}
?>
up
2
trashmail dot hashishin at gmail dot com
4 years ago
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
up
1
Peter Bailey
2 years ago
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 );

?>
up
0
Ulysse
11 months ago
Based on the information provided by "jakub dot lopuszanski at nasza-klasa dot pl" that in PKCS#7, the last byte contains the number of byte to remove (see RFC 5652, part 6.3), and for those like me who like to copy paste an already-made snippet:

<?php
function unpadPKCS7($data, $blocksize)
{
   
$last = substr($data, -1);
    return
substr($data, 0, strlen($data) - ord($last));
}
?>

Now you have no more reason to use rtrim() to remove the padding at the end of the result.
up
0
Silvan
7 years ago
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);
}

?>
up
0
php at pcwize dot com
8 years ago
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.
up
0
drew at expressdynamics dot com
9 years ago
On Win32 systems with PHP 5, you must use the newer libmcrypt.dll file, otherwise mdecrypt_generic will not work.
up
0
robbie [at] averill [dot] co [dot] nz
9 years ago
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.
up
0
jon@jonroig dot com
10 years ago
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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