There is also good discussion on concept of probably fair here in this thread https://bitcointalksearch.org/topic/concept-of-provably-fair-and-if-its-possible-1431468
Thanks for the link for the thread here. It is almost flooded by the old thread, I already see that thread from past but i didn't find it again when i search it.
How can we know that this site are telling the truth about the verification of the roll result. what I mean is who is behind this site, are they legit. but anyway, i will study it on my own, i will open this thread so that anyone who was interested will saw this infos.