c++ - determinisitic random number generator giving different random number for same seed -

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i want use deterministic random bit generator application. i' m using openssl random number generator apis. i'm using rand_pseuso_bytes() api generating pseudo random numbers. , i'm giving seed through rand_add(). if called random generator function 2 times, i'm getting 2 different random values @ these 2 calls. if seed same, should give me same values, have gone wrong ?

the code have written is

int nsize = 8;    /* 64 bit random number required */  int nentropy = 5; /* 40 bit entropy required */ /* generate random nonce making seed */ rand_bytes(cseed_64, nsize); rand_add(cseed_64, nsize, nentropy); /* random nonce cseed_64, seedin 64 bit                                       *  40 bit entropy */ /* calling random byte function generate random number function 10 times same seed*/ int j = 10; while( j--) {     rand_pseudo_bytes(crandbytes_64, 8);     printf("generated 64 bit random number \n");     for(i = 0 ; < nsize; i++)         printf("%x ",crandbytes_64[i]);     printf("\n"); }

but you're not calling rand_psuedo_bytes() same seed, you're making successive calls it, should produce different outputs. that's whole point of "generator" function--it produces different value on each call based on internal state.

when "seed" , random number generator, fix internal state, after generate random numbers evolving state. each seed, generate unique , reproducible sequence of numbers repeated calls, won't generate same numbers on each call, pointless.

the line:

rand_bytes(cseed_64, nsize);

creates random see value based on system entropy. should check errors here, may fail if not enough entropy available.

the line

rand_add(cseed_64, nsize, nentropy);

does not seed prng, adds seed existing prng state. if want set prng state fixed value, have use rand_seed(). if call rand_seed() given value, rand_pseudo_bytes() thereafter generate given sequence of random numbers. if call rand_seed() again same value, repeat same sequence.


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