Re: [Dev-C++] true random numbers.

Aloha from Honolulu,
   My browser (Mozilla) reports that it can't find that web site.  I 
also tried pasting http// ahead of the www, but got the same 
non-result.  Having followed this debate I'm curious.  I hope you can 
post a better URL.
Mahalo (Thank You),
Roger Furer

Rob Lawless wrote:

>  I am completely niave to this science of randomness but my college 
> lecturer
> designed a program to generate true random numbers i am not aware of 
> the ins
> & outs of how its done basically something to do with atmospheric noise
> everything is explained on his website
> www.random.org <http://www.random.org>
> just thought i would mentions this seeing as you are getting into a pretty
> heated debate :)
> & as always have fun!
> rob
> ----- Original Message -----
> From: "Per Westermark" <pw...@ia... 
> <mailto:pw...@ia...>>
> To: "Aitor Moreno" <ait...@gm... <mailto:ait...@gm...>>
> Cc: <dev...@li... 
> <mailto:dev...@li...>>
> Sent: Tuesday, November 09, 2004 8:09 PM
> Subject: Re: [Dev-C++] true random numbers.
>
>
> > There are already good random number generators with immensely much 
> better
> > randomnes and immensely much longer sequences making them evilishly hard
> > to follow.
> >
> > With a good entrophy to seed them - some of which I discussed in my
> > previous mail - even a quite simle application can use good 
> cryptographic
> > strength random numbers.
> >
> > Why invent an octagonal wheel when there are already true round wheels
> > available out there on the net?
> >
> > Let's play a bit with the time() function - even if repeated a large
> > number of times - doesn't create hardly any entrophy. Let's say you 
> get 10
> > bits of entrophy for the first call (i.e. a random time within a start
> > window of 15 minutes). Each following call add an entrophy close to 
> zero.
> > Let's say that you call time() on average every 60 seconds (2^6
> > alternatives), which might give you 6 bits of entrophy. To get 256 
> bits of
> > entrophy (a very lousy entrophy for encryption seed), you then need 40
> > calls within a 40 minute interval... For real entrophy, you should
> > probably have at least 1024 or 2048 bits, which in this case 
> translates to
> > a smapling interval of 150 to 300 minutes.
> >
> > Let's then look a bit closer at the above alternative. You have 
> still not
> > specified how you should manage to make the individual "random" delays
> > between each time() sample. If this isn't true random (which it can't be
> > since you haven't even managed to get a real seed yet) and instead
> > generated by calls to rand() (which is using a known algorithm and 
> have a
> > very short sequence) then your 6 bits of entrophy for each 60 second
> > window actually gets multiplied by 0, i.e. you are still at your initial
> > 10 bits of entrophy from the 15-minute uncertainty of when the first 
> call
> > was made.
> >
> > A large number of people have tried your approach in a number of 
> variants.
> > Every one of them who have had their results stressed have fallen 
> through,
> > i.e. the "randomnes" has been quickly shot to pieces.
> >
> > We are not talking about world-class cryptographic analysis to pick the
> > above methods to pieces. More like a suitable programming exercise for
> > project Euler:
> >   http://www.mathschallenge.net/index.php?section=project
> > or maybe a home exercise for some courses at the university.
> >
> > - There are no ways to just algorithmically create randomnes.
> > - There are good random number generators available freely.
> > - For most environments, entrophy can be picked up from the system.
> >
> > Why then bother to try and do something that can't be done? Instead fix
> > good random generator from the net. Fix reasonably good entrophy 
> from the
> > system. Mix together and use. Takes less time than even thinking about
> > inventing some smart methods for "garbling" the rand() sequence.
> >
> > time(), srand(), rand() etc are _only_ for selecting which attack a 
> moster
> > should use, what color a screen saver should display etc. They can 
> not be
> > used for anything where random quality or preditability (or actually 
> lack
> > of) is important.
> >
> > With time() you get a few bits, but you have to look somewhere else to
> > collect the rest of the bits to use. In an interactive environment, the
> > user is a great source of entrophy. Else, you really have to dig in and
> > look under every stone there is. Only remember that repeating the same
> > operation twice doesn't double the entrophy. Most of the time it doesn't
> > give a single bit extra...
> >
> > I don't write this to be difficult. It's just that there must be
> > absolutely no misconception that rand() and time() may be used for
> > cryptography or other fields where good random numbers and entrophy
> > are needed.
> >
> > Note: more comments inlined below.
> >
> > /Per W
> >
> > On Tue, 9 Nov 2004, Aitor Moreno wrote:
> >
> > > Yes.. I agree with you. Since time() doesn't generate true random
> > > numbers, with this EASY approach, better results are achieved... do
> > > you agree with me?
> >
> > See comments above - no extra entrophy added.
> >
> > > >
> > > Yes, of course this can happen.... but this introduces a noise in the
> > > resulting sequence.
> >
> > Not noise - as in randomnes. It only adds predictability, i.e. "hooks"
> > that may be used to figure out what extra code you are using to 
> garble the
> > rand() function.
> >
> > > >
> > > Obviously... it is like trying to encrypt a java applet.... it is
> > > impossible, but with all the known techniques, you can make the attack
> > > more difficult, only for those attacks that know how to do it....
> > >
> > > With this easy approach, you can add a real noise to the resulting
> > > sequence that makes the analysis more difficult... or isn't it??
> >
> > As I mentioned above: A lot of people have tried obfuscation. I 
> don't know
> > about anyone who have managed to survive a real hack attempt.
> >
> > > >
> > > And if it is small set of random numbers, with the proposed function,
> > > reseeding the sequence, and the interval between successive numbers is
> > > not trivial....
> > > do you think that is harder or easier to perform the analysis?
> >
> > You need a random generator to make this strategy work. Then, you still
> > receive entrophy in a real slow way. And in the end, rand() in itself is
> > too bad to be helped by good entrophy
> >
> > > >
> > > and if it is used only for choose a random color for my background ?
> > >
> > > I know what you are comment... and all it is true... the true random
> > > numbers are difficult to obtain...  And, like the topic was "true
> > > random numbers", I have to agree with that, because I think in the
> > > same way .
> > >
> > > But, a good approach for easy applications can be the proposed one in
> > > the first post or in the second one....
> > >
> > > In all cryptographic books it is used to appear a chapter about 
> this ...
> >
> > A good approach for easy applications that are not limited to selecting
> > the background color of a window is to pick the code available in these
> > chapters of the cryptographic books, or to just google for a download
> > site. Any other design decision either fails or requires extensive
> > statistics and cryptographics knowledge and may still backfire.
> >
> >
> >
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