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:
<?php
$retval = mcrypt_decrypt( ...etc ...);
$retval = rtrim($retval, "\0"); // trim ONLY the nulls at the END
?>
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_nombredelcifrado, o el nombre del algoritmo como string. -
key -
La clave con la cual los datos fueron cifrados. Si la clave proporcionada no está soportada por el cifrador, la función emitirá una advertencia y devolverá
FALSE -
data -
La información que será descifrada con el cifrador y modo dados por los parámetros
cipherymode. Si el tamaño de la información no es n * blocksize, la información será rellenada con '\0'. -
mode -
Una de las constantes
MCRYPT_MODE_nombredelmodo, o una de las siguientes strings: "ecb", "cbc", "cfb", "ofb", "nofb" o "stream". -
iv -
Used for the initialization in CBC, CFB, OFB modes, and in some algorithms in STREAM mode. If the provided IV size is not supported by the chaining mode or no IV was provided, but the chaining mode requires one, the function will emit a warning and return
FALSE.
Valores devueltos
Devuelve los datos descifrados en formato cadena o FALSE en caso de error.
Historial de cambios
| Versión | Descripción |
|---|---|
| 5.6.0 |
Tamaños incorrectos en key y iv
ya no son admitidos. mcrypt_decrypt() emitirá
una advertencia y devolverá FALSE si los datos de entrada son incorrectos. Anteriormente la clave y
el IV eran rellenados con bytes '\0' hasta el siguiente tamaño válido.
|
add a note
User Contributed Notes 6 notes
eddiec at stararcher dot com ¶
9 years ago
david at sickmiller dot com ¶
6 years ago
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
?>
evangelion207 at hotmail dot com ¶
3 years ago
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..
beltrachi ¶
3 years ago
Caution, MCRYPT_RIJNDAEL_256 is not equivalent to AES_256.
The way to make RIJNDAEL be decrypted from AES with openssl is to use MCRYPT_RIJNDAEL_128 and padd the string to encrypt before encrypting with the follwing function:
<?php
function pkcs5_pad ($text, $blocksize) {
$pad = $blocksize - (strlen($text) % $blocksize);
return $text . str_repeat(chr($pad), $pad);
}
?>
On the decryption, the choosing of AES_256 or AES_128, etc. is based on the keysize used in the crypting. In my case it was a 128bit key so I used AES_128.
Anonymous ¶
4 years ago
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, -$padding);
?>
artaxerxes2 at iname dot com ¶
1 year ago
To decrypt data coming from MySQL's AES_ENCRYPT function:
<?php
function mysql_aes_key($key)
{
$new_key = str_repeat(chr(0), 16);
for($i=0,$len=strlen($key);$i<$len;$i++)
{
$new_key[$i%16] = $new_key[$i%16] ^ $key[$i];
}
return $new_key;
}
function aes_decrypt($encrypted,$key)
{
// if $encrypted is HEXed, then return it to binary
$encrypted = pack('H*',$encrypted);
$key = mysql_aes_key($key);
return rtrim(mcrypt_decrypt(MCRYPT_RIJNDAEL_128,$key,$encrypted,MCRYPT_MODE_ECB,''),"\x00..\x1F");
}
?>
adapted from the article "Replicating MySQL AES Encryption Methods With PHP" (dated 2012-05-20) found somewhere online.
