Criticism of a proposed floating point (cs)prng requested.
in [Cryptography]
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From: unruh on 4 Jun 2010 20:54 On 2010-06-04, Phoenix <ribeiroalvo(a)gmail.com> wrote: > On 4 Jun, 23:21, Tom St Denis <t...(a)iahu.ca> wrote: >> On Jun 3, 2:24?pm, Phoenix <ribeiroa...(a)gmail.com> wrote: >> >> > The algorithm is: >> >> > x_n+1 = FRAC( x_n ( x_n + b_n ) +c ) >> >> > b=1,2,3?2048 >> > c=(0;1) >> >> > I ask criticism on the safety, randomness quality, speed performance, >> > non linearity, crypto >> > analisys, Discrete Logarithm Problem (DLP), etc. >> >> I have no idea what the DLP has to do with your scheme, and for fear >> of sounding like I'm an advocate, why don't you just write your >> algorithm to use fixed-point arithmetic and do away with any >> portability issues? >> >> Tom > > If we use fixed-point arithmetic, we have nothing. > Believe, I already try and test it. Then you have nothing since all floating point values are represented by fixed point arithmetic on any computer I know of.
From: Phoenix on 4 Jun 2010 21:03 On 5 Jun, 00:31, unruh <un...(a)wormhole.physics.ubc.ca> wrote: > Since floating point values are represented on the system as integers > (ie a finite number of bits) and since the representation can vary, why > in the world would anyone design a floating point crypto with all its > problems rather than the equivalent integer system. Ie, anything a > floating point algorithm can do, an integer one can as well-- maybe with > a bit more programming. Can you do that and after show us.
From: Scott Fluhrer on 4 Jun 2010 21:35 "Phoenix" <ribeiroalvo(a)gmail.com> wrote in message news:176b32bc-50cb-480e-a18a-56c7072883de(a)y12g2000vbg.googlegroups.com... > On 4 Jun, 22:20, Maaartin <grajc...(a)seznam.cz> wrote: > >> The question makes no sense, unless you use chemistry for securing >> your communication. >> >> > If answer is only for crypto, what is the solution to pass accurate >> > and compatible values in R from one system to another? >> >> This again makes no sense. Both communicating parties need the same >> PRNG for encrypting and decrypting their communication. The values >> generated by the PRNG are used as the keystream, so they mustn't be >> sent anywhere. > > No Maaartim, you don't undertand the question. > > Supose one do some calculation with Intel system: > > i.e. > I=LOG(SQR(2)*PI...a big expression) > > Another one make the same calculation with SUN system: > > S=LOG(SQR(2)*PI...a big expression) > > Acording to you, I is different form S. Why, yes, in general, they will differ. Generally not by a great deal (unless "a big expression" suffers from dreadful numerical stability problems), but in the last few bits, even if the two systems implement the same precision. There are quite a few ways of approximating logs (for example), and while they'll yield pretty close to the same answer, they won't be exact (and IEEE 754 does not mandate any particular algorithm). If the Intel and the SUN system selected different algorithms, then it's almost certain that they'll get slightly different results quite a lot of the time. -- poncho
From: unruh on 4 Jun 2010 21:39 On 2010-06-05, Phoenix <ribeiroalvo(a)gmail.com> wrote: > On 5 Jun, 00:31, unruh <un...(a)wormhole.physics.ubc.ca> wrote: > >> Since floating point values are represented on the system as integers >> (ie a finite number of bits) and since the representation can ?vary, why >> in the world would anyone design a floating point crypto with all its >> problems rather than the equivalent integer system. Ie, anything a >> floating point algorithm can do, an integer one can as well-- maybe with >> a bit more programming. > > Can you do that and after show us. I have no desire to do it, and better things to do with my time. It is you that wants to do it, and you that will have to do it. Just think about how floating point numbers are respresented in memory, and use that to think about how to program it yourself.
From: Tom St Denis on 4 Jun 2010 21:42
On Jun 4, 7:45 pm, Phoenix <ribeiroa...(a)gmail.com> wrote: > If we use fixed-point arithmetic, we have nothing. > Believe, I already try and test it. Care to elaborate? What fixed point system did you use? How many fractional bits? Also what problem is this trying to solve? What algorithms is it meant to be an improvement on? What analysis have you done [other than ENT stuff]? Have you considered the fact that since your state is basically one fractional value the key space is ridiculously small? Tom |