Use OpenSSL instead of Mcrypt in the examples

[javiereguiluz]

This fixes #7925. Some comments:

• openssl_*() functions are not documented on php.net (see http://php.net/manual/en/function.openssl-decrypt.php) so I used this article as a reference: http://thefsb.tumblr.com/post/110749271235/using-opensslendecrypt-in-php-instead-of
• I think we don't need to use the OPENSSL_RAW_DATA or OPENSSL_ZERO_PADDING options ... but I'd like someone to verify this.
• I can't find an equivalent of \MCRYPT_3DES so I used \OPENSSL_ALGO_SHA1. I'm not sure if that's correct.

[jderusse]

SHA1 is a Hash algorithm, you cannont use it to encrypt/decrypt purpose

[javiereguiluz]

Which algo should we use instead?

[sstok]

I would actually recommend to use LibSodium instead of OpenSSL, encryption is a specialty that is hard to get right, LibSodium makes this as easy as possible. Alternatively you can use https://github.com/defuse/php-encryption which provide a developer friendly (and very secure) API on-top of OpenSSL.

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

[javiereguiluz]

@sstok I'm not sure we can do that, because this should work out-of-the-box in all/mosts PHP versions, so we can't use external libs.

[sstok]

If you can't use LibSodium I would recommend https://github.com/defuse/php-encryption (uses OpenSSL internally), yes it's PHP 5.4, and Symfony 2.7 still supports PHP 5.3, but from the point of security using an old unmaintained PHP version is already a horrible idea (TM).

It all depends on the level of security you want to provide, 3DES is horrible insecure (for many years). Using OpenSSL without proper padding, authentication (crypto authentication) or IV generating, your data is still encrypted. But it becomes easier to break the encryption and leaking sensitive information, and potentially making it possible change the underlying data https://paragonie.com/blog/2015/05/using-encryption-and-authentication-correctly#title.2.1 and thus compromising the trust level of your security.

As this is only used for session data (server-side) the risk smaller, but still existent.
Not to mention using this example and assuming it's safe 🙀.

---

For the purpose of an example I think it's best to provide a simple example (using OpenSSL) with a big warning that this is only meant as an example and it should not be used for an actual implementation, and providing links with information on how to do this safely 👍

[weaverryan]

@sstok Thanks for navigating this with us :). So PHP deprecated mcrypt "in favour of OpenSSL"... but there's really no simple way to actually use OpenSSL? If so, that sucks!

If https://github.com/defuse/php-encryption is "just as good" as LibSodium, I'd rather show it being used. I don't think we need to cover its installation, just show how the end-code would look and link to it (and say it's one encryption example). After all, if you're trying to secure your session data, you obviously care about security and are ok with doing some work to get things setup properly. As long as we show a secure example (even if it takes some setup), we're on solid ground.

[javiereguiluz]

Don't we really have a choice to solve this problem using pure PHP code (no libraries)? Let's remember that we're "just" encrypting some "silly" session data, not the nuclear launch codes. Thanks!

[mvrhov]

Just an example.

$iv = openssl_random_pseudo_bytes(openssl_cipher_iv_length('AES-256-CFB'), true);
return [
    'iv' => $iv,
    'encrypted' => openssl_encrypt($data, 'AES-256-CFB', $key, true, $iv)
];

[sstok]

Good enough as an example or session.

But not failure proof for corruption. Because "changing" the iv could produce a garbage/altered result and you would never notice, that's why authenticated encryption is so important, even if the risk is minimal here. You would still want to have a simple MAC to prevent (file-system) corruptions from breaking the application.

[javiereguiluz]

I finally updated the example to use the https://github.com/defuse/php-encryption library as suggested by Ryan. Thanks!

[xabbuh]

Thank you @javiereguiluz.