mdecrypt_generic

(PHP 4 >= 4.0.2, PHP 5, PHP 7 < 7.2.0, PECL mcrypt >= 1.0.0)

mdecrypt_generic — Decrypts data

Warning

This function has been DEPRECATED as of PHP 7.1.0 and REMOVED as of PHP 7.2.0. Relying on this function is highly discouraged.

Description

mdecrypt_generic(resource $td, string $data): string

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.

Parameters

td: An encryption descriptor returned by mcrypt_module_open()
data: Encrypted data.

Return Values

Returns decrypted string.

Examples

Example #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.

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User Contributed Notes 11 notes

down

jakub dot lopuszanski at nasza-klasa dot pl ¶

11 years 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.

down

nytro_rst at yahoo dot com ¶

15 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;

}

?>

down

Ulysse ¶

10 years 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.

down

Anonymous ¶

15 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;
}
?>

down

Peter Bailey ¶

12 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 );

?>

down

trashmail dot hashishin at gmail dot com ¶

14 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

down

robbie [at] averill [dot] co [dot] nz ¶

19 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.

down

Silvan ¶

17 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);
}

?>

down

php at pcwize dot com ¶

18 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.

down

drew at expressdynamics dot com ¶

19 years ago

On Win32 systems with PHP 5, you must use the newer libmcrypt.dll file, otherwise mdecrypt_generic will not work.

down

jon@jonroig dot com ¶

20 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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mdecrypt_generic

Description

Parameters

Return Values

Examples

See Also

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User Contributed Notes 11 notes