Re: unify entropy source for all php related functions

On Sat, Feb 15, 2014 at 11:59 AM, Pádraic Brady <padraic.brady@gmail.com>wrote: > Hi, > > On 14 February 2014 15:30, Jakub Zelenka <bukka@php.net> wrote: > > It uses /dev/urandom for seeding PRNG. It means that it reads only 32 > bytes > > (256 bits) from it. If you call openssl_random_pseudo_bytes you will get > > bytes generated by PRNG > > > > > >> - $crypto_strong will always be true on Linux (UNIX-whatever) > >> > > > > Yes. The reason is that /dev/urandom is non-blocking and you will always > > get enough entropy from it. You don't have to check the flag on Linux > > because it will be always true! > > > > The point is that OpenSSL considers /dev/urandom strong enough for > seeding > > CSPRNG. > > > > Jakub > > There are the three categories: > > 1. Non-Cryptographically Deterministic PRNG > 2. Entropy Input PRNG > 3. Cryptographically Secure PRNG > > OpenSSL is the second. /dev/urandom is also the second. /dev/random is > the third (after a warmup period!). Something like rand() would be in > the first under the assumption that time is predictable. > > Those are the technical categories anyway... In reality, you can use a > non-CSPRNG for cryptographic needs over the short term. If you can't, > it means the damn thing is broken ;). If you have something like a > long term or high value cryptographic product, you wont want to stint > on entropy and you won't want to run afoul of any future issue with > the entropy collection or mixing, and you're probably not going to > even use a machine remotely susceptible in inactivity (which may limit > the entropy sources). > > Be careful of taking claims at face value where definitions are in doubt. > > Paddy > > > Thanks for the explanation. It makes sense. I thought that they considers the PRNG as Cryptographically Secure because the documentation states that it produces cryptographically strong pseudo-random bytes http://www.openssl.org/docs/crypto/RAND_bytes.html (RAND_bytes is equal to RAND_pseudo_bytes on Linux) Jakub