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Re: [Dev-C++] true random numbers.
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From: Per W. <pw...@ia...> - 2004-11-10 10:35:32
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Try again. www.random.org is working! /Per W On Tue, 9 Nov 2004, Roger Furer wrote: > 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. > > > > > > > > > > > > ------------------------------------------------------- > > > This SF.Net email is sponsored by: > > > Sybase ASE Linux Express Edition - download now for FREE > > > LinuxWorld Reader's Choice Award Winner for best database on Linux. > > > http://ads.osdn.com/?ad_id=5588&alloc_id=12065&op=click > > <http://ads.osdn.com/?ad_id=5588&alloc_id=12065&op=click> > > > _______________________________________________ > > > Dev-cpp-users mailing list > > > Dev...@li... > > <mailto:Dev...@li...> > > > TO UNSUBSCRIBE: http://www23.brinkster.com/noicys/devcpp/ub.htm > > > https://lists.sourceforge.net/lists/listinfo/dev-cpp-users > > > > > > > > > ------------------------------------------------------- > This SF.Net email is sponsored by: > Sybase ASE Linux Express Edition - download now for FREE > LinuxWorld Reader's Choice Award Winner for best database on Linux. > http://ads.osdn.com/?ad_id=5588&alloc_id=12065&op=click > _______________________________________________ > Dev-cpp-users mailing list > Dev...@li... > TO UNSUBSCRIBE: http://www23.brinkster.com/noicys/devcpp/ub.htm > https://lists.sourceforge.net/lists/listinfo/dev-cpp-users > |
