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AARRHHGG!!!! PHP Strings not equal when equal...

I have been pulling my hair out today.

I'm making a system that uses some encryption. I have a 12 character string, and I encrypt it, pass it about a bit and then decrypt it.

When I look the the unencrypred and the destructed fields, they look the same, an if == fails.

Here's the result of a var_dump:

string(16) "udcKlnbI01kN"
string(12) "udcKlnbI01kN"

It looks like it's saying one string is 12 characters long and the other is 16!!!

The first one is the decrypted version, and the shorter? one is the original.

HELP!

Cris.

CrisThompsonUKAsked: 2013-05-15

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LVL 37

gr8gonzoConsultantCommented: 2013-05-15

It sounds like you're using a 128-bit block cipher for encryption/decryption, like AES-128. Block ciphers work by dealing with data that is in specifically-sized chunks of bytes, like:

16 bytes + 16 bytes + 16 bytes, etc...

So if you have data that is shorter than the block size itself, it pads the string (usually with null bytes) until the string reaches the block size.

Use trim() on the string to remove the extra characters and then compare the trimmed strings.

LVL 6

worm-getterCommented: 2013-05-15

this is a good place to start:

http://www.ibm.com/developerworks/opensource/library/os-php-encrypt/

good luck.

LVL 13

haloexpertsexchangeCommented: 2013-05-15

you probably have some invisible characters attached to the longer string, try trimming it before you do a compare.

LVL 16

Phil PhillipsDirector of DevOps & Quality AssuranceCommented: 2013-05-15

If you're going to use the decryption function in multiple places, I would even go a step further and add the trim as part of the function. That way, you don't have to remember to always to it!

Something like:

function decrypt(...) {
  //Decrypt code puts decrypted string into $result
  return trim($result, "\0");
}

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LVL 111

Ray PaseurCommented: 2013-05-15

You might want to check the character encoding carefully -- is one ISO-8859-1 and the other UTF-8? You might want to use "view source" to check the data (browsers suppress multiple blanks and EOL characters). This little code sample might be helpful. I know it works in a way that makes sense.

<?php // RAY_encrypt_decrypt.php
error_reporting(E_ALL);

// MAN PAGE: http://php.net/manual/en/ref.mcrypt.php

class Encryption
{
    protected $key;
    protected $eot;
    protected $ivs;
    protected $iv;

    public function __construct($key='quay', $eot='___EOT')
    {
        // SET KEY, DELIMITER, INITIALIZATION VECTOR - MUST BE KNOWN TO BOTH PARTS OF THE ALGORITHM
        $this->key = $key;
        $this->eot = $eot;
        $this->ivs = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_ECB);
        $this->iv  = mcrypt_create_iv($this->ivs);
    }

    public function encrypt($text)
    {
        // APPEND END OF TEXT DELIMITER
        $text .= $this->eot;

        // ENCRYPT THE DATA
        $data = mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $this->key, $text, MCRYPT_MODE_ECB, $this->iv);

        // MAKE IT base64() STRING SAFE FOR STORAGE AND TRANSMISSION
        return base64_encode($data);
    }

    public function decrypt($text)
    {
        // DECODE THE DATA INTO THE BINARY ENCRYPTED STRING
        $text = base64_decode($text);

        // DECRYPT THE STRING
        $data = mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $this->key, $text, MCRYPT_MODE_ECB, $this->iv);

        // REMOVE END OF TEXT DELIMITER
        $data = explode($this->eot, $data);
        return $data[0];
    }
}

// INSTANTIATE THE CLASS
$c = new Encryption();

// INITIALIZE VARS FOR LATER USE IN THE HTML FORM
$encoded = '';
$decoded = '';

// IF ANYTHING WAS POSTED SHOW THE DATA
if (!empty($_POST["clearstring"]))
{
    $encoded = $c->encrypt($_POST["clearstring"]);
    echo "<br/>{$_POST["clearstring"]} YIELDS ENCODED ";
    var_dump($encoded);
}

if (!empty($_POST["cryptstring"]))
{
    $decoded = $c->decrypt($_POST["cryptstring"]);
    echo "<br/>{$_POST["cryptstring"]} YIELDS DECODED ";
    var_dump($decoded);
}

$form = <<<FORM
<form method="post">
<input name="clearstring" value="$decoded" />
<input type="submit" value="ENCRYPT" />
<br/>
<input name="cryptstring" value="$encoded" />
<input type="submit" value="DECRYPT" />
</form>
FORM;

echo $form;