The Missing PHP AES Encryption Example |

Posted October 1, 2014 4:28 pm by tim & filed under Crypto, PHP.

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PHP has a lot of available documentation. So much that Googling just about any PHP function provides a php.net result on the first page and a good majority of the content is accurate. And when it’s not, the public comments usually fill in the holes. The OpenSSL cryptography extension is one part of php.net that is very lacking, so much that you’ll even be greeted with Warning: this function is currently not documented; only its argument list is available for both openssl_encrypt and openssl_decrypt — perhaps the two most commonly looked up OpenSSL functions.

Environr

The future of environment configuration is here.

Here’s the full example. We’ll jump into the details below.

<?php // DEFINE our cipher define('AES_256_CBC', 'aes-256-cbc'); // Generate a 256-bit encryption key // This should be stored somewhere instead of recreating it each time $encryption_key = openssl_random_pseudo_bytes(32); // Generate an initialization vector // This *MUST* be available for decryption as well $iv = openssl_random_pseudo_bytes(openssl_cipher_iv_length(AES_256_CBC)); // Create some data to encrypt $data = "Encrypt me, please!"; echo "Before encryption: $data\n"; // Encrypt $data using aes-256-cbc cipher with the given encryption key and // our initialization vector. The 0 gives us the default options, but can // be changed to OPENSSL_RAW_DATA or OPENSSL_ZERO_PADDING $encrypted = openssl_encrypt($data, AES_256_CBC, $encryption_key, 0, $iv); echo "Encrypted: $encrypted\n"; // If we lose the $iv variable, we can't decrypt this, so: // - $encrypted is already base64-encoded from openssl_encrypt // - Append a separator that we know won't exist in base64, ":" // - And then append a base64-encoded $iv $encrypted = $encrypted . ':' . base64_encode($iv); // To decrypt, separate the encrypted data from the initialization vector ($iv). $parts = explode(':', $encrypted); // $parts[0] = encrypted data // $parts[1] = base-64 encoded initialization vector // Don't forget to base64-decode the $iv before feeding it back to //openssl_decrypt $decrypted = openssl_decrypt($parts[0], AES_256_CBC, $encryption_key, 0, base64_decode($parts[1])); echo "Decrypted: $decrypted\n"; ?>

Update — 4/3/2017 — Thanks to those commenters who pointed out the issue with the initialization vector clashing. The gist has been updated to base64 encode $iv to mitigate.

This example regenerates the encryption key each time it runs. This is most likely not what you want. Ideally, the encryption key or password should be kept somewhere safe and only readable by the process that’s responsible for encrypting/decrypting.

After defineing our cipher, we generate the encryption key / password using openssl_random_pseudo_bytes. Here we’re creating a 32-byte or 256-bit key (the largest supported by AES).

Next, we create an initialization vector required by the openssl_encrypt function (well, technically it’s not required but you should use it). We use the same openssl_random_pseudo_bytes function used to generate the key, but this time we provide it with openssl_cipher_iv_length to generate the appropriately sized initialization vector for our cipher.

After creating some data to encrypt we use openssl_encrypt to create our ciphertext. If an initialization vector was used, we must be able to access it again for decryption so the simplest way to do this is to append it to our ciphertext with a separator. Because the initialization vector is not confidential, there’s no need to further encrypt it.

The decryption process starts by splitting the ciphertext into the original ciphertext and the initialization vector. We can then call openssl_decrypt, providing the original ciphertext, cipher, encryption key, and the initialization vector. The resulting value should match our unencrypted with which we started.

23 Responses to “The Missing PHP AES Encryption Example”

Anonymous

Great work. It really helped me a lot! Previously I was using an algorithm called rijndael but openssl one seems much neater. Kudos to you! 😀
July 1st, 2015 Reply
- Fred
  
  Actually Rijndael is the cipher algorithm used by AES. And OpenSSL is not an algorithm, it’s a library.
  September 18th, 2015 Reply
P. Dantic

Thanks for this. Your example could be made slightly clearer by using:

list($encrypted, $iv) = explode(‘:’, $encrypted);
August 26th, 2015 Reply
Jos

Great article! Probably good to tell that if you want to store the encrypted info in a (MySQL) database you need to use the VARBINARY type for that field
September 29th, 2015 Reply
josh

This does not always decrypt the data!!!! if the iv has a : in it everything blows up!
November 7th, 2015 Reply
Marat

You would probably need to bin2hex $encrypted and $iv before sending in through HTTP GET or POST
January 12th, 2016 Reply
chadwalt

I have aes and it does encrypt but when I use it to decrypt I don’t get the original file.
January 15th, 2016 Reply
Twodee

Hey! This post seems great, and it has proved to be so helpful. But there’s one question, I have seen the openssl autogenerated iv and key, and it returns some characters my browser can’t recognize. Should I use something like base64 encode or hash them maybe so that I can get them when I require in plain text?
January 19th, 2016 Reply
/dev/random

Good article, thank you.

Sometimes the decryption function does not work because the initialization vector (IV) contains another “:” so the explode function does not split correctly the encrypted data and the IV. To fix it you just need to add another parameter to the explode function to split at the first occurence of “:”:

explode(‘:’, $encrypted, 2);
February 4th, 2016 Reply
Mark

You’re missing a critical step. When you use openssl_random_pseudo_bytes you should be passing in a second argument. The function populates this argument with true/false indicating whether or not strong cryptography was used. If it is not then your IV may not meet standards and should not be used.
February 5th, 2016 Reply
Josh

Thanks for the article!

Sometimes the decryption function does not work because the initialization vector (IV) contains another “:”

Replace line 29 with this:
$parts = explode(‘:’, $encrypted,(mb_substr_count($encrypted, “:”))+1);
February 21st, 2016 Reply
Mike Harris

I think its also worth noting that picking a character such as : which *wont* be present in your base64-ed string gives a pretty big clue to anyone who gains illicit access to your data that the portion after the : is some sort of salt or iv.

Surely its safer to make your iv look exactly like base64 data and just append to the start or end. you always know the length of the iv so you can just substring it off before decrypting the remaining data.

I’m new to this stuff so apologies if I’m talking rubbish!
February 25th, 2016 Reply
Marcelo

Im geting this error: Constant AES_256_CBC already defined
March 23rd, 2016 Reply
Jonathan

@/dev/random
Exploding on the first occurrence of “:” will not allow you to have a “:” in your encryption data.
Using base64 encode on both the encryption data and the iv before combining will solve this:

base64_encode($encrypted) . ‘:’ . base64_encode($iv);
April 5th, 2016 Reply
Dale

As a possible workaround for the : issue mentioned above, perhaps a check of the generated hash for the : character and regenerating until one comes up without a : in it would work? Otherwise,

$parts = explode(‘:’, $encrypted_data);
$encrypted = array_shift($parts);
$iv = implode(‘:’, $parts);

might get you where you want to go even if there was a : in there.
April 29th, 2016 Reply
Emile Jobity

Thank looked all over could not find. this help
April 30th, 2016 Reply
Walturburk

Why not just write the encryption key and iv to a config.ini file on your server, since they always stay the same after being generated.

The config file is stored in a folder not accessible from the internet.

No need to re-save the iv for everything encrypted, right?
August 4th, 2016 Reply
harpej singh

we have AES encrypted code but i am unable to decrypt them.
i have also key for them.
encrypted code in java/jsp and i want to decrypt in PHP.
how it is possible.
i am using below code

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″);
}

it working fine if we encrypt our new string, but we have already encrypted code.
please help me

harpej singh
hs_2005@yahoo.co.in
9214311070
November 25th, 2016 Reply
clem

Great but I am encountering error below using the very same code above:

Warning: openssl_decrypt(): IV passed is only 8 bytes long, cipher expects an IV of precisely 16 bytes, padding with \0 in C:\xampp\htdocs\aes256cbc.php on line 26
Decrypted: Encrypt W�S�?��:se!
December 14th, 2016 Reply
Billy

About “:” problem >> use “separator” instead of “:”. That’s it.

$separator = “separator”;
$encrypted = $encrypted . $separator . $iv;
explode($separator, $encrypted);
December 17th, 2016 Reply
- Cocksworth McJohnson
  
  The reason for the “:” is that u wont notice that its a separator when looking at the encrypted text. The word “separator” makes this whole dealio kinda obvious.
  January 12th, 2017 Reply
  - Billy
    
    It is not a problem IMHO, because the iv itself can be public.
    June 24th, 2017 Reply
Taylor Morgan

Thanks for this great example, Tim. I used the flow you describe to create encrypted permalink tokens.(http://www.tmdesigned.com/passing-immutable-data-with-encrypted-tokens/) Data is encrypted and sent as part of the URL, then decrypted when the user visits to prepopulate the page.
July 4th, 2017 Reply