PHP 7.1.0 Alpha 2 Released

mcrypt_decrypt

(PHP 4 >= 4.0.2, PHP 5, PHP 7)

mcrypt_decryptDecrypts crypttext with given parameters

Descrição

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

Decrypts the data and returns the unencrypted data.

Parâmetros

cipher

Uma das constantes MCRYPT_ciphername, ou o nome do algoritmo como string.

key

The key with which the data was encrypted. If the provided key size is not supported by the cipher, the function will emit a warning and return FALSE

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

Uma das constantes MCRYPT_MODE_modename, ou uma das strings: "ecb", "cbc", "cfb", "ofb", "nofb" ou "stream".

iv

Utilizado para a inicialização dos modos CBC, CFB, OFB, e em alguns algoritmos em modo STREAM. Se o tamanho do IV fornecido não for surportado no modo chaining ou um IV não for fornecido para um modo chaining que necessite, a função emitirá um warning e refornará FALSE.

Valor Retornado

Returns the decrypted data as a string ou FALSE em caso de falha.

Changelog

Versão Descrição
5.6.0 Invalid key and iv sizes are no longer accepted. mcrypt_decrypt() will now throw a warning and return FALSE if the inputs are invalid. Previously keys and IVs were padded with '\0' bytes to the next valid size.

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User Contributed Notes 7 notes

up
27
eddiec at stararcher dot com
10 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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9
evangelion207 at hotmail dot com
5 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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7
david at sickmiller dot com
7 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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7
beltrachi
4 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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1
Anonymous
5 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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0
pnz dot r00t at yandex dot ru
3 months ago
When i using this function i find some problem, with adding additional binary symbols in decode message.
$sDecrypt – «2433091»
$sDecrypt strlen – 16 (before trim)
$sDecrypt – «2433091»
$sDecrypt strlen – 7 (after trim)
At local PC this problem solved by using trim/trim, but if I send my encrypt message to sever, and try encrypt them, I see that my message is not 16 symbols, as it was in my local pc, it is 32 sybmols, after encode. And trim function not working. I look at symbols code and what I see
    50
    52
    51
    51
    48
    57
    49
    0
    0
    0
    0
    0
    0
    0
    0
    0
    10
    158
    112
    183
    154
    27
    95
    85
    42
    35
    95
    54
    227
    41
    179
    77
After “tabulation symbols” I get some junk symbols, and  I solve this problems like this.
After mcrypt_decrypt I use this code
$plaintext_dec = substr($plaintext_dec, 0, strpos($plaintext_dec, "\0"));
I think it is not best resolution for this problem, but I solve my problem :)
up
-13
artaxerxes2 at iname dot com
3 years 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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