Laravel Crypt value changing on each reload - php

Question

I'm trying to use Laravel's Crypt functionality, to simply store a value in a database and grab it later on to use. However I noticed that I was unable to decrypt this value.
My application key is a random, 32 character string. My cipher is MCRYPT_RIJNDAEL_128.
From the PHP info, MCRYPT is installed, and RIJNDAEL_128 is supported.
To test, I do the following on a GET rou:
$t = "123456789";
var_dump(Crypt::encrypt($t));
See: http://laravel.io/bin/2e9Xr#
On each page refresh, the output is a different value, which is obviously incorrect - however I have no idea why.
I'm using an EasyPHP as my dev server. However one thing I have noticed is that the application requests are significantly slow on this environment as compared to the production, Apache web server.
This makes me wonder if there is some sort of environment refresh going on each time, potentially resetting the "resources" MCRYPT is using to encrypt, and thus is different each time.
Any clues?

Answer 1

That is normal behavior. Every Crypt::encrypt call should produce a different output for security reasons.
Crypt is incredibly inefficient for small strings. For example, Crypt::encrypt("Hello World") outputs something like the following: eyJpdiI6Imhnb2hRazVabUNZUnVRVzFBSEExVkE9PSIsInZhbHVlIjoiTHJ4c05zcjdJZkZwWU1vRVVRMEcwZE5nTUdjQnhyM2RKWTMzSW04b1cxYz0iLCJtYWMiOiIyZjRmNDc3NGEyNGQyOGJjZGQ4MWQxYWViYzI1MjNjZTU0MmY4YTIxYTEyNWVjNDVlZDc4ZWEzNzRmN2QwM2ZiIn0=
Immediately recognizable as a base 64 string. When decoded, it becomes {"iv":"hgohQk5ZmCYRuQW1AHA1VA==","value":"LrxsNsr7IfFpYMoEUQ0G0dNgMGcBxr3dJY33Im8oW1c=","mac":"2f4f4774a24d28bcdd81d1aebc2523ce542f8a21a125ec45ed78ea374f7d03fb"}
Using Crypt, you can encrypt and decrypt large plaintexts easily without worrying about the details. But if you want to store or transmit a lot of separately encrypted entities, then you might want to consider a different approach.
So why is it like this?
(Note: the directory structures are valid for Laravel 4.2).
For one, most secure block cipher modes of operation require an IV (initialization vector), which is a bunch of random bytes with length matching the block size. Using a different IV for every ciphertext is important for thwarting cryptanalysis and replay attacks. But let's look a bit at the actual Crypt code.
Starting with the config/app.php aliases array, we see 'Crypt' => 'Illuminate\Support\Facades\Crypt'
So we check the vendor/laravel/framework/src/Support/Facades directory, and we find Crypt.php which says the module accessor name is actually "encrypter". Checking the config/app.php providers array shows 'Illuminate\Encryption\EncryptionServiceProvider'.
vendor/laravel/framework/src/Illuminate/Encryption has several files of interest: Encrypter.php and EncryptionServiceProvider.php. The service provider binds the accessor with a function that creates, configures, and returns an instance of Encrypter.
In the Encrypter class, we find the encrypt method:
public function encrypt($value)
{
$iv = mcrypt_create_iv($this->getIvSize(), $this->getRandomizer());
$value = base64_encode($this->padAndMcrypt($value, $iv));
// Once we have the encrypted value we will go ahead base64_encode the input
// vector and create the MAC for the encrypted value so we can verify its
// authenticity. Then, we'll JSON encode the data in a "payload" array.
$mac = $this->hash($iv = base64_encode($iv), $value);
return base64_encode(json_encode(compact('iv', 'value', 'mac')));
}
And there you have it. Each time you call Crypt::encrypt, it generates a new IV, encrypts the value, creates a MAC of the IV and ciphertext, and then returns a base 64 encoded JSON string of an associative array of the IV, MAC, and ciphertext. Each IV will be different, which means every ciphertext and MAC will also be different--even for the same value. Really smart if all plaintexts are large, but pretty impractical for a lot of smaller plaintexts where MACs are unnecessary overhead.
tl;dr version:
16 bytes of randomness is generated for every encrypt call, and it cascades into the ciphertext and MAC, all of which is returned in a base 64 encoded JSON associative array. Thus, every Crypt::encrypt call produces different output.

Answer 2

That's how mcrypt works - http://mnshankar.wordpress.com/2014/03/29/laravel-hash-make-explained/
$test = 'test';
$crypted = Crypt::encrypt($test);
echo $crypted.'<br />'; // encrypted string
echo Crypt::decrypt($crypted); // "test"