Re: little request :)

Hi all, On Fri, Feb 7, 2014 at 9:32 AM, Tjerk Meesters <tjerk.meesters@gmail.com>wrote: > > Hi all, > > > > On 6 February 2014 23:18, Lester Caine <lester@lsces.co.uk> wrote: > > > Yasuo Ohgaki wrote: > > >> > > >> Timing attack can be used to guess hash itself, one by one. > > >> There are many use cases that may be attacked by timing. e.g. API key > > >> This way, unbreakable random hash may be broken relatively easy. > > > > > > > > > What I am missing Yasuo is a practical example of how this can be > > actioned > > > as my normal methods would simply delay any following attempt to use a > > hash > > > after a few failed attempts. That should be normal practice to block a > > hack > > > attempt? > > > > I can run a server indefinitely. So can an attacker. What you're > > saying is that a time delay is added to lock an account. If you > > compare that to a timing attack requiring 1000 requests (assumed) with > > a 3 second inter-request delay from your measure, you end up with a > > total execution time of one hour (approx). > > > I think he meant that the server responds immediately, but the login will > fail when attempted before the imposed time-out has run its course. If the > server actually sleeps for a few seconds it becomes a DoS target. iptables is our friend. hashlimit is useful. Regards, P.S. I mixed up something with xxhash in previous mail. Google provides 32bit version now. https://code.google.com/p/xxhash/ P.S2. I've update compare sample. https://github.com/yohgaki/php-src/compare/PHP-5.6-rfc-hash-compare There are functions to play with. bool str_siphash_compare(str, str) - siphash(64bit) bool str_xxhash32_compare(str, str) - xxhash(32bit) bool str_md5_compare(str, str) - md5 hash(128bit) bool str_byte_compare(str, str) - timing safe bool str_compare(str, str) - normal strncmp -- Yasuo Ohgaki yohgaki@ohgaki.netHi