Sankha, If I needed to use a PRNG for AES key (128 bits) and i called rand() 4 times, I still have a entropy of only 32 bits instead of 128 bits.
which means i just weakened the algorithm! what do I do? -Shailesh --- Sankha Subhra Som <[EMAIL PROTECTED]> wrote: > Nikhil, the term RNG is actually a misnormer the numbers > that a RNG generates > are actually pseudo random numbers, meaning they are > reproducible and the > generating function is known(hence they can be > reproduced). > Most of the RNG's we know of are LCG's(Linear > Congruential Generators) > They work on a simple recurrence relation > r(i+1) = (A * r(i) ) MOD m > MOD is the modulus operator. > In ur case > Considering that r(i), A and m are constant r(i+1) will > also be the same each > time u execute the program. > A clever workaround will be calling srand() with the seed > as the current > system time. > The ideal generators are those that have a period equal > to 'm'. > The period is the longest possible non-overlapping > sequence of numbers > generated by a LCG. > the greater the period the more desirable is the > generator(but the sequence > of numbers generated is also important). > The 'seed' is nothing but r(0) ie the first r on the RHS > of the recurrence > relation. > The C library RNG is not that good in the sense that it > has failed many > theoretical and empirical tests. > there are a lot of RNG'S that are much better than this > generator and have > whopping periods.They also provide the user with the > ability to generate > disjoint substreams of numbers using the same generator. > Random number generation is a tricky process and needs a > lot of mathematical > intuition. > And finally if you are looking for truly random numbers > try weather data from > internet weather stations.These are truly random. > For a more thorough understanding read Knuth:Art of > computer programming. > Enjoy!! > Sankha > -- > SANKHA SUBHRA SOM > ATC - BIOINFORMATICS > TCS > KLK BUILDING. > HYDERABAD-1 > Ph:(040)6787980-1024 > > ******************************************************** > An anonymous digitoid > ******************************************************** > The world is populated in the main by people who should > not exist. > > _______________________________________________ > http://mm.ilug-bom.org.in/mailman/listinfo/linuxers > __________________________________________________ Do you Yahoo!? New DSL Internet Access from SBC & Yahoo! http://sbc.yahoo.com _______________________________________________ http://mm.ilug-bom.org.in/mailman/listinfo/linuxers
