PHP 5.6.0RC3 is available

mcrypt_decrypt

(PHP 4 >= 4.0.2, PHP 5)

mcrypt_decryptDecrypts crypttext with given parameters

Descrizione

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

Decrypts the data and returns the unencrypted data.

Elenco dei parametri

cipher

Una tra le costanti MCRYPT_ciphername, oppure il nome dell'algoritmo sotto forma di stringa.

key

The key with which the data was encrypted. If it's smaller than the required keysize, it is padded with '\0'.

data

The data that will be decrypted with the given cipher and mode. If the size of the data is not n * blocksize, the data will be padded with '\0'.

mode

Una tra le costanti MCRYPT_MODE_modename, oppure una tra le seguenti stringhe: "ecb", "cbc", "cfb", "ofb", "nofb" o "stream".

iv

Usato per l'inizializzazione nei modi CBC, CFB, OFB, e in alcuni algoritmi nel modo STREAM. iSe non si fornisce un IV, quando รจ necessario per un algoritmo, la funzione restituisce un avvertimento e utilizza and uses un IV con tutti i byte impostati a "\0".

Valori restituiti

Returns the decrypted data as a string.

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User Contributed Notes 6 notes

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2
beltrachi
2 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.
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2
eddiec at stararcher dot com
9 years ago
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
?>
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2
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..
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2
david at sickmiller dot com
5 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
?>
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0
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.
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0
Anonymous
3 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);
?>
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