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Message-ID: <A91E718E-B023-42DC-AC8D-BC989F5A80E4@cschneid.com>
Date: Mon, 23 Sep 2019 14:51:37 +0200
To: PHP internals <internals@lists.php.net>
Subject: PHP 7.4 BC break with openssl_random_pseudo_bytes()
From: cschneid@cschneid.com (Christian Schneider)

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
	$ivsize =3D openssl_cipher_iv_length($method);
	$iv =3D openssl_random_pseudo_bytes($ivsize);
	$data =3D openssl_encrypt($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.

- Chris