Re: PHP 7.4 BC break with openssl_random_pseudo_bytes()

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. Nikita