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In-Reply-To: <CAEKnhAHmmj+iySEPsuT9McJXKb9sR8MOTinvsxQYakDn2_hAMw@mail.gmail.com>
Date: Wed, 6 Nov 2019 19:44:22 +0000
Message-ID: <CAEKnhAFn1ivFPPNM0q6bsPRCekp2AaDNfUNkwrL8csaPgECcJA@mail.gmail.com>
To: Nikita Popov <nikita.ppv@gmail.com>
Cc: Christian Schneider <cschneid@cschneid.com>, PHP internals list <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="000000000000259ca20596b2c7d2"
Subject: Re: [PHP-DEV] PHP 7.4 BC break with openssl_random_pseudo_bytes()
From: bukka@php.net (Jakub Zelenka)

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On Wed, Oct 30, 2019 at 6:33 PM Jakub Zelenka <bukka@php.net> wrote:

>
>
> On Wed, 30 Oct 2019, 18:32 Jakub Zelenka, <bukka@php.net> wrote:
>
>>
>>
>> On Mon, 23 Sep 2019, 14:02 Nikita Popov, <nikita.ppv@gmail.com> wrote:
>>
>>> On Mon, Sep 23, 2019 at 2:52 PM Christian Schneider <
>>> cschneid@cschneid.com>
>>> wrote:
>>>
>>> > Hi,
>>> > I just noted (too late in the process, I know) that
>>> > openssl_random_pseudo_bytes(0) now throws an exception.
>>> >
>>> > This breaks code like
>>> >         $ivsize = openssl_cipher_iv_length($method);
>>> >         $iv = openssl_random_pseudo_bytes($ivsize);
>>> >         $data = openssl_encrypt($string, $method, $key,
>>> OPENSSL_RAW_DATA,
>>> > $iv);
>>> > if $method is 'aes-256-ecb' because $ivsize is 0.
>>> >
>>> > I do realize that ECB mode ciphers are deprecated but having them
>>> throw an
>>> > exception indirectly via openssl_random_pseudo_bytes() seems a bit
>>> strange,
>>> > even in the context of security.
>>> >
>>> > I checked the RFC
>>> > https://wiki.php.net/rfc/improve-openssl-random-pseudo-bytes and it
>>> > doesn't mention this BC break:
>>> > "False-checks on the return value of openssl_random_pseudo_bytes()
>>> will do
>>> > nothing since the function fails closed. Usage of $crypto_strongwill
>>> > generate errors."
>>> >
>>> > While I would have preferred the exception to be thrown only when
>>> $ivsize
>>> > is not an integer or less than 0 but I guess this cannot be changed at
>>> the
>>> > RC stage.
>>> >
>>> > I would recommend though that we aim to keep BC breaks to what's
>>> mentioned
>>> > in RFCs.
>>> >
>>>
>>> This was noted during the PR review in:
>>> https://github.com/php/php-src/pull/3649#discussion_r230598754
>>> Especially
>>> in conjunction with your example, I think we should revert this part an
>>> make openssl_random_pseudo_bytes(0) return "" without exception or
>>> warning.
>>> Ideally we'd adjust random_bytes() to do the same.
>>>
>>
>> I agree this should be reverted for 7.4 at least as it's a BC and wasn't
>> really in RFC. It really doesn't matter if it's a good thing or not as it's
>> a BC that we shouldn't do in minor release.
>>
>
> I mean BC break ofc... :)
>

I was thinking about the revert but after reading the RFC again, I don't
think it would be right thing to do. Although it's a bit generic and
doesn't mention when it can fail, it states that the exception is thrown on
fail. We always considered this case as a fail because it returned false so
it's kind of covered. It would be also quite late to do such changes in 7.4
and I guess RM wouldn't allow it anyway. It's basically BC break that went
through the RFC which is probably acceptable.

I have to say that the RFC wasn't really well done as the implementation
followed which caused this omission. We should really look properly to the
implementation when creating RFC so it's more detailed and doesn't cause
omission like this.

Cheers

Jakub

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