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Date: Wed, 6 Jan 2016 16:09:10 +0000
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To: bishop@php.net
Cc: Scott Arciszewski <scott@paragonie.com>, PHP internals list <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [RFC] OpenSSL AEAD support
From: bukka@php.net (Jakub Zelenka)

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Hi,

On Wed, Jan 6, 2016 at 3:35 PM, Bishop Bettini <bishop@php.net> wrote:

> Hi Jakub,
>
> On Wed, Jan 6, 2016 at 10:01 AM, Jakub Zelenka <bukka@php.net> wrote:
>>
>> https://wiki.php.net/rfc/openssl_aead
>
>
> I think the API might need to be more generic so that any future cipher
> modes with different parameters could also be passed in.
>
> The reference model I'd suggest is the "context" parameter passed to
> stream related-functions.  Userland creates a context, then passes the
> context to the encrypt/decrypt functions. The context is specific to the
> wrapper and drives specific behavior. Encrypt can add to the context any
> specific cipher state that needs to be passed along to decrypt.
>
> Using this model, the openssl API might look like:
>
> $context = openssl_context_create([ 'aead' => [ 'aad' => '...',
> 'tag_length' => '...' ]]);
> $ciphertext = openssl_encrypt(
>     $data, $method, $password, $options, $iv,
>     $context // here is the new parameter, encapsulating all cipher
> specifics
> );
>
> echo $context['aead']['tag']; // populated by openssl_encrypt
>
> $plaintext = openssl_decrypt(
>     $ciphertext, $method, $password, $options, $iv,
>     $context // fully-reversible, because all necessary data are in context
> );
>
>
Please see note in https://wiki.php.net/rfc/openssl_aead#rejected_features
. Any context related features will add a lot to the size of the
implementation. In this case it would also mean introducing an object with
dimension handler to the openssl ext which doesn't really match with the
rest of the extension API. The proposed API is more conformant to the rest
and the code addition is also limited which is very important from the
maintenance point of view.

I have got already an extension where you can do all of this context
related stuff ( see https://github.com/bukka/php-crypto ) but I don't think
that anything like this should be part of the openssl ext. I think we
should concentrate on adding just the most important features with minimal
code addition to openssl ext and also concentrate on the fixing the actual
bugs. Bare in mind that all of this has to be maintained for very long time
and when you look to the regular contributors to openssl ext, you won't see
too many people...

To sum it up this is a minimal proposal to add AEAD support to openssl ext.
Anything context related is out of scope of this RFC.

Cheers

Jakub

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