CODEWITHSUNDEEP
ccryptographyentropy
PsySc0rpi0n
PsySc0rpi0n

Reputation: 31

Use "/dev/urandom" with GMP library to generate a very big random number

I'm using Debian Bookworm and GMP library version 60201. I need to generate a random number with GMP library but I have 2 requirements, if possible, of course!

1 - Generate a number between 0 and a specific max value.

2 - Have some kind of entropy, preferrably from "/dev/urandom/" or anything better, but not too much complciated.

I have never worked with this library and I don't have any experience working with big numbers or cryptography, so, I've been trying to look at the docs, examples in the internet and even AI tools, but so far, I couldn't understand at least about the second point. I don't know if it is possible to use "/dev/urandom/" to get entropy or even if it is possible to add entropy using GMP library!

For the 1st point, I may have a solution, which is to generate random numbers while the generated number is not below the target max value. Not sure if this is the most efficient way, but seems to be a way!

Something like this:

do{
    /* 
     code to generate a random number
    */
}while(randNumber > max_target_val);

For the second point, I see this in the docs: https://gmplib.org/manual/Random-State-Seeding

On some systems there’s a special device /dev/random which provides random data better suited for use as a seed.

But I can't find any suitable example on how to use "/dev/urandom/" with GMP library. Any help would be appreciated!

Upvotes: 1

Views: 160

Answers (1)

hibiki
hibiki

Reputation: 9

If you need to generate numbers as seeds using /dev/urandom, the following code can assist you.

uint64_t random_num() {
    FILE *fp = fopen("/dev/urandom", "rb");
    uint64_t num = 0;
    fread(&num, sizeof(uint64_t), 1, fp);
    fclose(fp);
    return num;
}

Upvotes: 0

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