mcrypt_decrypt

(PHP 4 >= 4.0.2, PHP 5)

mcrypt_decrypt — Desencripta texto cifrado con los parámetros dados

Descripción

string mcrypt_decrypt ( string $cipher , string $key , string $data , string $mode [, string $iv ] )

Desencripta data y devuelve los datos sin cifrar.

Parámetros

cipher: Una de las constantes MCRYPT_ciphername, o el nombre del algoritmo en formato cadena.
key: La clave con la cual los datos fueron encriptados. Si es más pequeña de lo requerido, se rellena con '\0'.
data: La información que será descifrada con el cifrador y modo dados por los parámetros cipher y mode. Si el tamaño de la información no es n * blocksize, la información será rellenada con '\0'.
mode: Una de las constantes MCRYPT_MODE_modename, o una de las siguientes cadenas: "ecb", "cbc", "cfb", "ofb", "nofb" o "stream".
iv: El parámetro iv es utilizado para la inicialización en modo CBC, CFB, OFB, y en algunos algoritmos en modo STREAM. Si no se indica ningún IV, mientras sea necesario para un algoritmo, la función genera un warning y utiliza un IV con todos sus bytes seteados a '\0'.

Valores devueltos

Devuelve los datos desencriptados en formato cadena.

mcrypt_ecb

mcrypt_create_iv

Last updated: Fri, 20 May 2011

add a note User Contributed Notes mcrypt_decrypt

evangelion207 at hotmail dot com 17-Apr-2011 03:24


Be careful, sometimes mcrypt_decrypt return additional white spaces to the uncrypted string; use trim() for deleting them. I was like 2 hours searching the error and it was that..

maciej at wiercinski dot net 09-Apr-2011 07:59


If you want to combine mcrypt with MySQL's AES_DECRYPT / AES_ENCRYPT function, please keep in mind that it uses PKCS5 padding (code from note above works just fine), what is not mentioned in MySQL's documentation at all.

Anonymous 24-Nov-2010 11:41


To remove PKCS7 padding:





<?php


    $decrypted = mdecrypt_generic($td, base64_decode($enc_auth_token));


    $dec_s = strlen($decrypted);


    $padding = ord($decrypted[$dec_s-1]);


    $decrypted = substr($decrypted, 0, -$padding);


?>

uramihsayibok, gmail, com 18-Oct-2009 06:17


kooktroop's example (09-Jul-2004) may be a bit misleading. Using a random IV for encryption, then another random IV for decryption? If you run it, it works!



That's because ECB doesn't use an IV. For modes that do use one you need the same one for encryption and decryption.



For example, Rijndael-256 (aka AES-256) and CFB:

<?php



$text = "The quick brown fox jumps over the lazy dog.";

$key = "haseveryletter";



$iv = mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_CFB), MCRYPT_RAND);

$encrypted = mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $key, $text, MCRYPT_MODE_CFB, $iv);



// create a new IV

$newiv = mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_CFB), MCRYPT_RAND);

$corrupt = mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $key, $encrypted, MCRYPT_MODE_CFB, $newiv);

echo $corrupt; // [binary junk...]he lazy dog



$good = mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $key, $encrypted, MCRYPT_MODE_CFB, $iv);

echo $good; // The quick brown fox jumps over the lazy dog



?>



Rijndael can sync up on each block so only the first one (here, 256 bits = 32 characters long) will be corrupted. Not necessarily true for other algorithms...

david at sickmiller dot com 03-Oct-2008 07:20


I was wrong about ColdFusion always padding with EOT.  By default, ColdFusion uses PKCS#5 padding.  See the comments on http://us3.php.net/manual/en/ref.mcrypt.php for pkcs5_(un)pad functions

david at sickmiller dot com 02-Oct-2008 05:15


If you happen to be decrypting something encrypted in ColdFusion, you'll discover that its encrypt function apparently pads the plaintext with ASCII 4, the "end of transmission" character.



Building on eddiec's code, you can remove both nulls and EOTs with this:



<?php

    $retval = mcrypt_decrypt( ...etc ...);

    $retval = rtrim($retval, "\0\4");     // trim ONLY the nulls and EOTs at the END

?>

smp_info at yahoo dot com 11-Oct-2007 06:27


Since the returned data seems to be still padded with extra characters, you can get *only* the original data that was encrypted by str_replace()'ing the \x0 characters.



<?php

$decryptedData = str_replace("\x0", '', $encryptedData);

?>

eddiec at stararcher dot com 14-Jul-2005 01:26


It appears that mcrypt_decrypt pads the *RETURN STRING* with nulls ('\0') to fill out to n * blocksize.  For old C-programmers, like myself, it is easy to believe the string ends at the first null.  In PHP it does not:





    strlen("abc\0\0") returns 5 and *NOT* 3


    strcmp("abc", "abc\0\0") returns -2 and *NOT* 0





I learned this lesson painfully when I passed a string returned from mycrypt_decrypt into a NuSoap message, which happily passed the nulls along to the receiver, who couldn't figure out what I was talking about.





My solution was:


<?


    $retval = mcrypt_decrypt( ...etc ...);


    $retval = rtrim($retval, "\0");     // trim ONLY the nulls at the END


?>

kooktroop at gmail dot com 09-Jul-2004 10:13


Following on from the mcrypt_encrypt() example:



<?php

$text = "boggles the inivisble monkey will rule the world";

$key = "This is a very secret key";



$iv_size = mcrypt_get_iv_size(MCRYPT_XTEA, MCRYPT_MODE_ECB);

$iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);

echo strlen($text) . "<br>";



$enc = mcrypt_encrypt(MCRYPT_XTEA, $key, $text, MCRYPT_MODE_ECB, $iv);

echo strlen($enc) . "<br>";

   

$iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);

$key = "This is a very secret key";

$text = "Meet me at 11 o'clock behind the monument.";

echo strlen($text) . "<br>";



$crypttext = mcrypt_decrypt(MCRYPT_XTEA, $key, $enc, MCRYPT_MODE_ECB, $iv);

echo "$crypttext<br>";

?>

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