mcrypt_encrypt

(PHP 4 >= 4.0.2, PHP 5, PHP 7 < 7.2.0, PECL mcrypt >= 1.0.0)

mcrypt_encrypt — Encrypts plaintext with given parameters

Warnung

Diese Funktion wurde in PHP 7.1.0 als DEPRECATED (veraltet) markiert und wurde in PHP 7.2.0 ENTFERNT. Von der Verwendung dieser Funktion wird dringend abgeraten.

Beschreibung

mcrypt_encrypt(
    string $cipher,
    string $key,
    string $data,
    string $mode,
    string $iv = ?
): string|false

Encrypts the data and returns it.

Parameter-Liste

cipher

Eine der Konstanten von MCRYPT_ciphername oder der Name eines Algorithmus als Zeichenkette.

key

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

The returned crypttext can be larger than the size of the data that was given by data.

mode

Eine der MCRYPT_MODE_modename-Konstanten oder eine der folgenden Zeichenketten: "ecb", "cbc", "cfb", "ofb", "nofb" oder "stream".

iv

Wird für die Initialisierung in den Modi CBC, CFB oder OFB und von einigen Algorithmen im STREAM-Modus verwendet. Wird die Länge des angegebenen IV vom Betriebsmodus nicht unterstützt, oder wurde kein IV angegeben aber der Betriebsmodus benötigt einen, so wird diese Funktion eine Warnung ausgeben und false zurückgeben.

Rückgabewerte

Returns the encrypted data as a string Bei einem Fehler wird false zurückgegeben..

Beispiele

Beispiel #1 mcrypt_encrypt() Example

<?php
    # --- ENCRYPTION ---

    # the key should be random binary, use scrypt, bcrypt or PBKDF2 to
    # convert a string into a key
    # key is specified using hexadecimal
    $key = pack('H*', "bcb04b7e103a0cd8b54763051cef08bc55abe029fdebae5e1d417e2ffb2a00a3");
    
    # show key size use either 16, 24 or 32 byte keys for AES-128, 192
    # and 256 respectively
    $key_size =  strlen($key);
    echo "Key size: " . $key_size . "\n";
    
    $plaintext = "This string was AES-256 / CBC / ZeroBytePadding encrypted.";

    # create a random IV to use with CBC encoding
    $iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
    $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
    
    # creates a cipher text compatible with AES (Rijndael block size = 128)
    # to keep the text confidential 
    # only suitable for encoded input that never ends with value 00h
    # (because of default zero padding)
    $ciphertext = mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $key,
                                 $plaintext, MCRYPT_MODE_CBC, $iv);

    # prepend the IV for it to be available for decryption
    $ciphertext = $iv . $ciphertext;
    
    # encode the resulting cipher text so it can be represented by a string
    $ciphertext_base64 = base64_encode($ciphertext);

    echo  $ciphertext_base64 . "\n";

    # === WARNING ===

    # Resulting cipher text has no integrity or authenticity added
    # and is not protected against padding oracle attacks.
    
    # --- DECRYPTION ---
    
    $ciphertext_dec = base64_decode($ciphertext_base64);
    
    # retrieves the IV, iv_size should be created using mcrypt_get_iv_size()
    $iv_dec = substr($ciphertext_dec, 0, $iv_size);
    
    # retrieves the cipher text (everything except the $iv_size in the front)
    $ciphertext_dec = substr($ciphertext_dec, $iv_size);

    # may remove 00h valued characters from end of plain text
    $plaintext_dec = mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $key,
                                    $ciphertext_dec, MCRYPT_MODE_CBC, $iv_dec);
    
    echo  $plaintext_dec . "\n";
?>

Das oben gezeigte Beispiel erzeugt folgende Ausgabe:

Key size: 32
ENJW8mS2KaJoNB5E5CoSAAu0xARgsR1bdzFWpEn+poYw45q+73az5kYi4j+0haevext1dGrcW8Qi59txfCBV8BBj3bzRP3dFCp3CPQSJ8eU=
This string was AES-256 / CBC / ZeroBytePadding encrypted.

Siehe auch

mcrypt_decrypt() - Decrypts crypttext with given parameters
mcrypt_module_open() - Opens the module of the algorithm and the mode to be used

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User Contributed Notes 14 notes

down

scott at paragonie dot com ¶

9 years ago

If you're writing code to encrypt/encrypt data in 2015, you should use openssl_encrypt() and openssl_decrypt(). The underlying library (libmcrypt) has been abandoned since 2007, and performs far worse than OpenSSL (which leverages AES-NI on modern processors and is cache-timing safe).

Also, MCRYPT_RIJNDAEL_256 is not AES-256, it's a different variant of the Rijndael block cipher. If you want AES-256 in mcrypt, you have to use MCRYPT_RIJNDAEL_128 with a 32-byte key. OpenSSL makes it more obvious which mode you are using (i.e. 'aes-128-cbc' vs 'aes-256-ctr').

OpenSSL also uses PKCS7 padding with CBC mode rather than mcrypt's NULL byte padding. Thus, mcrypt is more likely to make your code vulnerable to padding oracle attacks than OpenSSL.

Finally, if you are not authenticating your ciphertexts (Encrypt Then MAC), you're doing it wrong.

Further reading:

https://paragonie.com/blog/2015/05/using-encryption-and-authentication-correctly

https://paragonie.com/blog/2015/05/if-you-re-typing-word-mcrypt-into-your-code-you-re-doing-it-wrong

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jesse at pctest dot com ¶

19 years ago

Solving 3DES incompatibilities with .NET's TripleDESCryptoServiceProvider

mcrypt's 3DES only accepts 192 bit keys, but Microsoft's .NET and many other tools accept both 128 and 192 bit keys.
If your key is too short, mcrypt will 'helpfully' pad null characters onto the end, but .NET refuses to use a key where the last third is all null (this is a Bad Key). This prevents you from emulating mcrypt's "short key" behaviour in .NET.

How to reconcile this? A little DES theory is in order
3DES runs the DES algorithm three times, using each third of your 192 bit key as the 64 bit DES key

Encrypt Key1 -> Decrypt Key2 -> Encrypt Key3

and both .NET and PHP's mcrypt do this the same way.
The problem arises in short key mode on .NET, since 128 bits is only two 64 bit DES keys
The algorithm that they use then is:

Encrypt Key1 -> Decrypt Key2 -> Encrypt Key1

mcrypt does not have this mode of operation natively.
but before you go and start running DES three times yourself, here's a Quick Fix
<?php
$my_key = "12345678abcdefgh"; // a 128 bit (16 byte) key
$my_key .= substr($my_key,0,8); // append the first 8 bytes onto the end
$secret = mcrypt_encrypt(MCRYPT_3DES, $my_key, $data, MCRYPT_MODE_CBC, $iv);  //CBC is the default mode in .NET
?>

And, like magic, it works.

There's one more caveat: Data padding
mcrypt always pads data will the null character
but .NET has two padding modes: "Zeros" and "PKCS7"
Zeros is identical to the mcrypt scheme, but PKCS7 is the default.
PKCS7 isn't much more complex, though:
instead of nulls, it appends the total number of padding bytes (which means, for 3DES, it can be a value from 0x01 to 0x07)
if your plaintext is "ABC", it will be padded into:
0x41 0x42 0x43 0x05 0x05 0x05 0x05 0x05

You can remove these from a decrypted string in PHP by counting the number of times that last character appears, and if it matches it's ordinal value, truncating the string by that many characters:
<?php
    $block = mcrypt_get_block_size('tripledes', 'cbc');
    $packing = ord($text{strlen($text) - 1});
    if($packing and ($packing < $block)){
      for($P = strlen($text) - 1; $P >= strlen($text) - $packing; $P--){
    if(ord($text{$P}) != $packing){
      $packing = 0;
    }
      }
    }
    $text = substr($text,0,strlen($text) - $packing);
?>

And to pad a string that you intend to decrypt with .NET, just add the chr() value of the number of padding bytes:
<?php
    $block = mcrypt_get_block_size('tripledes', 'cbc');
    $len = strlen($dat);
    $padding = $block - ($len % $block);
    $dat .= str_repeat(chr($padding),$padding);
?>

That's all there is to it.
Knowing this, you can encrypt, decrypt, and duplicate exactly any .NET 3DES behaviour in PHP.

down

your dot brother dot t at hotmail dot com ¶

9 years ago

The encryption has no authenticity check. It can be achieved with three methods, described in http://en.wikipedia.org/wiki/Authenticated_encryption#Approaches_to_Authenticated_Encryption
Encrypt-then-MAC (EtM), Encrypt-and-MAC (E&M), MAC-then-Encrypt (MtE).

The following is a suggestion for MtE:

<?php 
        public static function getMacAlgoBlockSize($algorithm = 'sha1')
        {
            switch($algorithm)
            {
                case 'sha1':
                {
                    return 160;
                }
                default:
                {
                    return false;
                    break;
                }
            }
        }

        public static function decrypt($message, $key, $mac_algorithm = 'sha1',
                                           $enc_algorithm = MCRYPT_RIJNDAEL_256, $enc_mode = MCRYPT_MODE_CBC)
        {
            $message= base64_decode($message);
            $iv_size = mcrypt_get_iv_size($enc_algorithm, $enc_mode);

            $iv_dec = substr($message, 0, $iv_size);
            $message= substr($message, $iv_size);

            $message= mcrypt_decrypt($enc_algorithm, $key, $message, $enc_mode, $iv_dec);

            $mac_block_size = ceil(static::getMacAlgoBlockSize($mac_algorithm)/8);
            $mac_dec = substr($message, 0, $mac_block_size);
            $message= substr($message, $mac_block_size);

            $mac = hash_hmac($mac_algorithm, $message, $key, true);

            if($mac_dec == $mac)
            {
                return $password;
            }
            else
            {
                return false;
            }
        }

        public static function encrypt($message, $key, $mac_algorithm = 'sha1',
                                           $enc_algorithm = MCRYPT_RIJNDAEL_256, $enc_mode = MCRYPT_MODE_CBC)
        {

            $mac = hash_hmac($mac_algorithm, $message, $key, true);
            $mac = substr($mac, 0, ceil(static::getMacAlgoBlockSize($mac_algorithm)/8));
            $message= $mac . $message;

            $iv_size = mcrypt_get_iv_size($enc_algorithm, $enc_mode);
            $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);

            $ciphertext = mcrypt_encrypt($enc_algorithm, $key,
                                         $message, $enc_mode, $iv);

            return base64_encode($iv . $ciphertext);
        }
?>

down

Anonymous ¶

13 years ago

In the other notes there are some misconceptions about crypto and the IV, especially for CBC mode.



The most important point: Encryption DOES NOT provide any proof of data integrity or authentication WHATSOEVER. If you need to be sure that the data is secret and not tampered with, you need to encrypt THEN use a keyed HMAC.



For CBC mode, the IV DOES NOT need to be secret. It can be sent along with the plaintext. It needs to be UNIQUE and RANDOM. So that every message is encrypted with a different IV.



The best way to generate an IV is to use mcrypt_create_iv().



Keys must be binary, not ASCII. To create a key from a password:



<?php

$password = "MyPassword!1!";

$aes256Key = hash("SHA256", $password, true); //we want a 32 byte binary blob

?>

down

Scott.a.Herbert at googlemail.com ¶

12 years ago

It is always better to use a standard encryption cipher's rather than to "roll your own", firstly the standard cipher has been tested by world class crypto-analysis's where as unless your a world class crypto-analysis (and if you are why are you even thinking of rolling your own?!?) you won't have the skills needed to even test it (for example if you just XOR each character with a key, it may look secure (the text will be different) but if you count the number of times a character is repeated you see whatever the letter "E" encrypts to occurs more often then the encrypted "Z" (assuming English language plain text)

Secondly, you may think that the hidden nature of your cipher makes it more secure, but the fact is that your cipher is likely *only* secure because it's secret, if someone what able to break-in to your site and steal your code (but not your key) they maybe able break you encrypted data, if someone broke in and found you where using Blowfish (for example) it wouldn't help them.

down

MadMass ¶

11 years ago

Note that the IV must be the same for mcrypt_encrypt and mcrypt_decrypt, otherwise you will have corrupted data after decryption.

down

Anonymous ¶

13 years ago

I've noticed some people using a-z, A-Z and 0-9 for keys and stating things like "16 characters is a 128-bit key". This isn't true. Using only these characters, you will get at most 6 bits of entropy per chartacter:

log2(26 + 26 + 10) = 5.954196310386876

So you're actually only getting 95 bits of entropy in 16 characters, which is 0.0000000117% of the keyspace you would get if you were using the full range.

In order to get the full entropy from a key using just a-z, A-Z and 0-9 you should multiply your key length by 1.3333 to account for the 2 bits of lost entropy per byte.

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Anonymous ¶

17 years ago

I should mention that ECB mode ignores the IV, so it is misleading to show an example using both MCRYPT_MODE_ECB and an IV (the example in the manual shows the same thing).  Also, it's important to know that ECB is useful for random data, but structured data should use a stronger mode like MCRYPT_MODE_CBC

Also, rtrim($decryptedtext, "\0") would be a better option to remove NULL padding than my lazy trim()...

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-3

Robin Leffmann ¶

14 years ago

Contrary to what is implied in the mcrypt_encrypt() manual page, as well as the info given regarding the CBC vs CFB modes, mcrypt_encrypt() works just fine for encrypting binary data as well.
 
A simple example verifies that the decrypted output is binary identical once cut to its original length:
 
<?php

// 448-bit key (56 bytes) - the only size that mcrypt/php uses for the Blowfish cipher
// (using a smaller key works just fine, as mcrypt appends \0 to reach proper key-size)
$key = 'SADFo92jzVnzSj39IUYGvi6eL8v6RvJH8Cytuiouh547vCytdyUFl76R';

// Blowfish/CBC uses an 8-byte IV
$iv = substr( md5(mt_rand(),true), 0, 8 );

// do 50 encrypt/decrypt operations on some random data, and verify integrity with md5()
for( $i = 0; $i < 50; $i++ )
{
    // create a random, binary string of random length
    $size = mt_rand( 25000, 500000 );
    $c = 0; $data = null;
    while( $c++ * 16 < $size )
        $data .= md5( mt_rand(), true );
    $data = substr( $data, 0, $size );
    $cksum = md5( $data );

    // encrypt using Blowfish/CBC
    $enc = mcrypt_encrypt( MCRYPT_BLOWFISH, $key, $data, MCRYPT_MODE_CBC, $iv );

    echo $size . ' -> ' . strlen( $enc ) . ' -> ';

    // decrypt (using same IV - a must for the CBC mode)
    $dec = mcrypt_decrypt( MCRYPT_BLOWFISH, $key, $enc, MCRYPT_MODE_CBC, $iv );

    // cut the output with substr(), NOT by using rtrim() as is suggested in some of
    // the mcrypt manual pages - this is binary data, not plaintext
    echo ( md5(substr($dec, 0, $size)) == $cksum ? 'ok' : 'bad' ) . PHP_EOL;
}

?>

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-5

stefan at katic dot me dot rs ¶

10 years ago

I was trying (and succeeded) to encrypt and decrypt in JAVA, pass it to php, and do it again,without corrupting data when I noticed something interesting. So, my code goes like this:
$data = 'one';
$key = '1234567890123456';

function encrypt($data, $key){
    return base64_encode(
    mcrypt_encrypt(
        MCRYPT_RIJNDAEL_128,
        $key,
        $data,
        MCRYPT_MODE_CBC,
        "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
    )
);
}
function decrypt($data, $key){
    $decode = base64_decode($data);
    return mcrypt_decrypt(
                    MCRYPT_RIJNDAEL_128,
                    $key,
                    $decode,
                    MCRYPT_MODE_CBC,
                    "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
            );
    
    
}
$encrypted = encrypt($data, $key);
$decrypted= decrypt($encrypted, $key);

//In the beginning, I thought something's wrong, because I did '===' comparison between $decrypted and $data. It didn't work (but later started working, again, dont know why...) So, I dumped both:
var_dump($data);
var_dump($decrypted);
//Results:
string(16) "one" 
string(16) "one" 
//Clearly, the length of both is 3, not 16. Just wanted to let you know what could happen, and I really don't know if this is a bug... 
Thanks,
S.

down

-2

Anonymous ¶

6 years ago

<?php
# Vernam Cipher (One-time pad)
$k1 = '1.key';
$k2 = '2.key';
$d = 'The quick brown fox jumped over the lazy dog';
VernamCipher::createTestKeyFile($k1, 1024);
copy($k1, $k2);
$c1 = new VernamCipher($k1);
$eD = $c1->encryptWithHMAC($d);
echo 'Encrypted: ', bin2hex($eD);
$c2 = new VernamCipher($k2);
echo PHP_EOL, 'Decrypted: ', $c2->decryptWithHMAC($eD);

class VernamCipher
{
    const DEFAULT_HMAC_ALGO = 'sha3-256';
    const DEFAULT_HMAC_KEY_LENGTH = 16;
    const DEFAULT_HMAC_HASH_LENGTH = 32;
    private $keyFilePath;
    private $keyFileHandler;
    private $deferredFtruncate = false;
    private $deferredFtruncatePos;
    private $hmacAlgo = self::DEFAULT_HMAC_ALGO;
    private $hmacKeyLength = self::DEFAULT_HMAC_KEY_LENGTH;
    private $hmacHashLength = self::DEFAULT_HMAC_HASH_LENGTH;

    function __construct(string $keyFilePath, string $hmacAlgo = self::DEFAULT_HMAC_ALGO, int $hmacKeyLength = self::DEFAULT_HMAC_KEY_LENGTH)
    {
        $this->keyFilePath = $keyFilePath;
        $this->openKeyFile();
        
        if($hmacAlgo !== self::DEFAULT_HMAC_ALGO) {
            if(in_array($hmacAlgo, hash_algos())) {
                $this->hmacAlgo = $hmacAlgo;
                $this->hmacHashLength = strlen(hash($this->hmacAlgo, '', true));
            }
            else {
                $this->hmacAlgo = self::DEFAULT_HMAC_ALGO;
                $this->hmacHashLength = self::DEFAULT_HMAC_HASH_LENGTH;
            }
        }
        
        if($hmacKeyLength !== self::DEFAULT_HMAC_KEY_LENGTH) {
            $this->hmacKeyLength = $hmacKeyLength;
        }
    }
    public function encryptWithHMAC(string $data)
    {
        $hmacKey = $this->getBytes($this->hmacKeyLength);
        $encData = $this->encrypt($data);
        $dataHmac = $this->hashHmac($encData, $hmacKey);
        
        return $dataHmac.$encData;
    }
    public function decryptWithHMAC(string $data)
    {
        $dataLength = strlen($data);

        if($dataLength < $this->hmacHashLength)
            throw new Exception('data length '.$dataLength.' < hmac length '. $this->hmacHashLength);
        
        $dataHmacRemote = substr($data, 0, $this->hmacHashLength);
        $dataOnly = substr($data, $this->hmacHashLength);
        
        $hmacKey = $this->getBytes($this->hmacKeyLength, false);
        $dataHmacLocal = $this->hashHmac($dataOnly, $hmacKey);
        
        if(hash_equals($dataHmacLocal, $dataHmacRemote) === false)
            throw new Exception('Hashes not equals, remote: '.bin2hex($dataHmacRemote).' local:'. bin2hex($dataHmacLocal));
    
        $this->deferredFtruncate();

        return $this->encrypt($dataOnly);
    }
    public function encrypt(string $data) : string
    {
        $dataLength = strlen($data);
        $bytes = $this->getBytes($dataLength);
        for($i=0;$i<$dataLength;$i++)
            $data{$i} = $data{$i} ^ $bytes{$i};
        
        return $data;
    }
    public function decrypt(string $data) : string
    {
        return $this->encrypt($data);
    }
    private function hashHmac($data, $key)
    {
        return hash_hmac($this->hmacAlgo, $data, $key, true);
    }
    # Don't use in production. You must use true random number generator.
    public static function createTestKeyFile(string $filePath, int $size)
    {
        file_put_contents($filePath, random_bytes($size));
    }
    private function deferredFtruncate()
    {
        if(!$this->deferredFtruncate)
            return;
        
        ftruncate($this->keyFileHandler, $this->deferredFtruncatePos);
        $this->deferredFtruncate = false;
    }
    public function getBytes(int $length, $truncateNow = true) : string
    {
        fseek($this->keyFileHandler, 0, SEEK_END);
        $currentPos = ftell($this->keyFileHandler);

        if($currentPos < $length)
            throw new Exception('Not enough key materials, key size: '. $currentPos. ' needed: '.$length);

        fseek($this->keyFileHandler, -$length, SEEK_END);
        $bytes = fread($this->keyFileHandler, $length);
        
        if($truncateNow)
            ftruncate($this->keyFileHandler, $currentPos - $length);
        else {
            $this->deferredFtruncate = true;
            $this->deferredFtruncatePos = $currentPos - $length;
        }

        return $bytes;
    }
    private function openKeyFile()
    {
        if($this->keyFileHandler)
            return;

        if(($this->keyFileHandler = fopen($this->keyFilePath, 'rb+')) === false)
            throw new Exception('Cant open key file: '.$this->keyFilePath);
        
        if(!flock($this->keyFileHandler, LOCK_EX | LOCK_NB))
            throw new Exception('Cant lock key file: '.$this->keyFilePath);
    }
}
?>

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-5

stonecypher at gmail dot com ¶

18 years ago

Most of the user-written cipher examples here are badly broken, and there are a few cases where the manual says things that are outright incorrect, such as that it's "safe to transmit the initialization vector in plaintext" (this is incorrect: see Ciphers By Ritter, http://www.ciphersbyritter.com/GLOSSARY.HTM#IV ,  for details.)

mcrypt itself is perfectly safe, but correct and therefore safe usage is inobvious.  It is important to use a cryptographic library correctly; a simple usage error, even when it produces results that can be unpacked at the other side, can render a strong algorithm completely useless.

The initialization vector must be permuted with a recoverable noise source (an arbitrary md5 hash is acceptable, since it's just a fake OTP and its origin contents are wholly unimportant.) 

Passwords should be remade with a salted one-way hash (md5 is again acceptable even though it's been damaged, since the only thing you could recover from a cracked md5 hash is the source data to generate the password, which is useless.) 

It's important to use a sane block mode (OFB is unsafe for almost all algorithms; never use it.  Prefer CBC in all cases except where you need to deal with a degraded signal and cannot retransmit.)

A correct usage example is actually pretty long and needs a lot of explanation, so I developed a safe wrapper library which doesn't constrain usage and which comments itself very heavily.  It's appropriate for use or for learning.  Please see my blog for details on Stone PHP SafeCrypt:

http://blog.sc.tri-bit.com/archives/101

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-5

leilond at hotmail dot com ¶

8 years ago

I always use this method to prevent a lot of errors

function encrypt( $string ) {
  $algorithm = 'rijndael-128'; // You can use any of the available
  $key = md5( "mypassword", true); // bynary raw 16 byte dimension.
  $iv_length = mcrypt_get_iv_size( $algorithm, MCRYPT_MODE_CBC );
  $iv = mcrypt_create_iv( $iv_length, MCRYPT_RAND );
  $encrypted = mcrypt_encrypt( $algorithm, $key, $string, MCRYPT_MODE_CBC, $iv );
  $result = base64_encode( $iv . $encrypted );
  return $result;
}
function decrypt( $string ) {
  $algorithm =  'rijndael-128';
  $key = md5( "mypassword", true );
  $iv_length = mcrypt_get_iv_size( $algorithm, MCRYPT_MODE_CBC );
  $string = base64_decode( $string );
  $iv = substr( $string, 0, $iv_length );
  $encrypted = substr( $string, $iv_length );
  $result = mcrypt_decrypt( $algoritmo, $key, $encrypted, MCRYPT_MODE_CBC, $iv );
  return $result;
}

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-5

gm dot outside+php at gmail dot com ¶

10 years ago

Please note that the following part of the documentation is no longer true (after commit: http://git.php.net/?p=php-src.git;a=commit;h=a861a3a93d89a50ce58e1ab1abef1eb501f97483):

> key
> The key with which the data will be encrypted. If it's smaller than the required keysize, it is padded with '\0'. It is better not to use ASCII strings for keys.

That commit changed the behaviour to be strict and if the keysize is smaller than the required size a warning will be issued as follows:

Warning: mcrypt_encrypt(): Key of size 10 not supported by this algorithm. Only keys of size 16 supported in script.php on line 5

and the mcrypt_encode() will return failure.

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