mdecrypt_generic

(PHP 4 >= 4.0.2, PHP 5)

mdecrypt_generic — 解密数据

说明

string mdecrypt_generic ( resource $td , string $data )

解密数据。请注意，由于存在数据补齐的情况，返回字符串的长度可能和明文的长度不相等。

参数

td: 由 mcrypt_module_open() 函数创建的加密描述符。
data: 密文。

范例

Example #1 mdecrypt_generic() 例程

  <?php
     
     $key  =  'this is a very long key, even too long for the cipher' ;
     $plain_text  =  'very important data' ;

     
     $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 );

     
     if ( mcrypt_generic_init ( $td ,  $key ,  $iv ) != - 1 ) {

         
         $c_t  =  mcrypt_generic ( $td ,  $plain_text );
         mcrypt_generic_deinit ( $td );

         
         mcrypt_generic_init ( $td ,  $key ,  $iv );
         $p_t  =  mdecrypt_generic ( $td ,  $c_t );

         
         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" ;
    }
 ?>

上例中演示了如何检测解密后的数据是否和原始明文长度一致。需要着重提醒的是，在对数据进行机密之前，必须使用 mcrypt_generic_init() 函数来重新初始化缓冲区。

调用本函数之前，必须使用密钥和初始向量来调用 mcrypt_generic_init() 函数对解密句柄进行初始化。加解密工作完成之后，需要调用 mcrypt_generic_deinit() 来释放加解密缓冲区。例程请参见 mcrypt_module_open() 。

参见

mcrypt_generic() - 加密数据
mcrypt_generic_init() - 初始化加密所需的缓冲区
mcrypt_generic_deinit() - 对加密模块进行清理工作

用户评论:

[#1] Ulysse [2013-11-07 14:27:03]

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.

[#2] jakub dot lopuszanski at nasza-klasa dot pl [2013-06-25 07:16:24]

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.

[#3] Peter Bailey [2012-03-19 17:49:30]

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 ); ?>

[#4] trashmail dot hashishin at gmail dot com [2010-06-01 00:46:59]

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

[#5] Anonymous [2009-03-21 19:31:48]

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; } ?>

[#6] nytro_rst at yahoo dot com [2009-02-09 03:33:17]

<?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; } ?>

[#7] Silvan [2007-08-17 00:34:42]

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); } ?>

[#8] php at pcwize dot com [2006-10-12 14:59:08]

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.

[#9] drew at expressdynamics dot com [2005-07-05 10:07:11]

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

[#10] robbie [at] averill [dot] co [dot] nz [2005-03-24 03:15:58]

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.

[#11] jon@jonroig dot com [2004-04-07 19:29:17]

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.
<?php $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); ?>