Re: [Boost-users] Seeding boost::mt19937 with bytes from CryptoGenRandom

11 Feb 2010

      Thank you Steven. While I do not have boost installed on this computer, the
code below compiles and runs as I would expect. Upon each execution, the
value of seed changes. I expect boost::mt19937 rng(seed); will work. And now
I have a very good random seed thanks to your advice.

Your friend,

Ed

#include <iostream>
#include 
#include 

int main()
{

    HCRYPTPROV hProvider = 0;
    BYTE randomBytes[8];
    CryptAcquireContext(&hProvider, 0, 0, PROV_RSA_FULL,
CRYPT_VERIFYCONTEXT);
    CryptGenRandom(hProvider, sizeof(randomBytes), randomBytes);
    CryptReleaseContext(hProvider, 0);

    uint64_t seed;
    memcpy(&seed, &randomBytes[0], sizeof(seed));

    std::cout << seed << std::endl;

    return 0;

}

On Wed, Feb 10, 2010 at 11:58 PM, Steven Watanabe wrote:
...
AMDG
e m wrote:
...
I have a C++ program that uses /dev/urandom on Unix systems to seed
boost::mt19937. I'm porting the program to Windows. I can get good, random
seed data on Windows similar to random seed data produced from /dev/urandom
on Unix systems like so:
HCRYPTPROV hProvider = 0;
BYTE randomBytes[8];
CryptAcquireContext(&hProvider, 0, 0, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT);
CryptGenRandom(hProvider, sizeof(randomBytes), randomBytes);
CryptReleaseContext(hProvider, 0);
However, I'm running into trouble attempting to pass these randomBytes to
boost::mt19937. On Unix I do something similar to this:
uint64_t GetSeed()
{
uint64_t seed;
std::ifstream urandom;
urandom.open("/dev/urandom");
urandom.read(reinterpret_cast (&seed), sizeof(seed));
urandom.close();
return seed;
}
boost::mt19937 rng(GetSeed());
That works OK on Unix I think. Could anyone suggest how to get the random
data from the Windows CryptoAPI passed to boost::mt19937 as seed data? I
don't normally program Windows systems, so this has been a bit of a
challenge for me.
Try
uint64_t seed;
memcpy(&seed, &randomBytes[0], sizeof(seed));
In Christ,
Steven Watanabe
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