ok On 23/01/14 23:38, "Krisztián Pintér" <[email protected]> wrote:
> >Michael Hammer (at Thursday, January 23, 2014, 9:49:32 PM): >> This may get off-topic, but are there good software tools for testing >> entropy, >> that could help applications determine if the underlying system is >>giving >> them good input? > >disclaimer: i'm no expert, it is just what i gathered. (i'm pretty >much interested in randomness.) > >short answer: no > >long answer: in some situations yes. if you are handed a bunch of >data, all you can do is to try different techniques to put an upper >limit on the entropy. for example you can calculate the shannon >entropy assuming independent bits. then you can hypothesize some >interdependence, and see if you can compress the data. you can apply >different lossless compression methods. the better compression you >find puts an upper limit on the entropy. but never a lower limit. > >you can only do better if you have an idea about the process that >created the data. for example you might assume that it is mostly >thermal noise. you can assume that thermal noise has some frequency >distribution, or energy or whatever, etc. within this assumption, you >can determine the entropy content by measurements. but at this point, >you are pretty much prone to two errors: 1, what if your assumption is >wrong and 2, what if your physical model overestimates the >unpredictability of the given system. example for the former: the >signal might be largely controllable by an external EM interference, >and then you measure not noise, but attacker controlled data. example >for the latter: a smartass scientist might come up with a better >physical model for thermal noise. > >it is also important to note that entropy is observer dependent. we >actually talk about the entropy as seen by the attacker. but it is not >straightforward to assess what is actually visible to an attacker and >what is not. observation methods improve with time. > >_______________________________________________ >dsfjdssdfsd mailing list >[email protected] >https://www.ietf.org/mailman/listinfo/dsfjdssdfsd _______________________________________________ dsfjdssdfsd mailing list [email protected] https://www.ietf.org/mailman/listinfo/dsfjdssdfsd
