CryptGenRandom is giving same value while calling in loop - c++

Question

Sorry, I cant use separate class for this and I tried to build following code and getting same output when calling from out side in loop.
unsigned int crypt_rand()
{
HCRYPTPROV hProvider = 0;
const DWORD dwLength = sizeof(unsigned int);
unsigned int pbBuffer[dwLength] = {};
if (!::CryptAcquireContext(&hProvider, 0, 0, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT | CRYPT_SILENT))
return 1;
if (!::CryptGenRandom(hProvider, sizeof(unsigned int), reinterpret_cast<PBYTE>(&pbBuffer)))
{
::CryptReleaseContext(hProvider, 0);
return 1;
}
if (!::CryptReleaseContext(hProvider, 0))
return 1;
return (unsigned int)pbBuffer;
}
If I am calling this function from loop getting same output every time.Is it anything I can give like input as time in this method.Can you plz help me on this?
for (DWORD i = 0; i < 5; ++i)
{
rand_no = crypt_rand();
std::cout << "windows::"<<i<<"::"<<rand_no<< std::endl;
}
Output is
windows::0::4519964
windows::1::4519964
windows::2::4519964
windows::3::4519964
windows::4::4519964

Answer 1

The use of casts (the reinterpret_cast and the one in the return statement) is hiding some important compiler errors that would have allowed you to write this code correctly in the first place.
Avoid the casts as much as you can, fix the types instead.
CryptGenRandom expects a
BYTE *pbBuffer
parameter. Pass it a pointer to an array of BYTE not anything else (you are passing a pointer to an array of int).
In your return statement you are casting an address to unsigned int. You need to take the BYTE array and convert the values it contains to an int (you can find examples of that online or you can make one yourself via sit shifts and additions). What you are doing now is probably outputting the same address (or part of it) over and over again.
To clarify, define your array as
BYTE pbBuffer[dwLength] = {};
and call your function as
::CryptGenRandom(hProvider, dwLength, pbBuffer)
Avoid casts, especially the C style casts, and read about arrays. In C++, when passed to a function an array decays to a pointer to the first element of the array. If you have an array of BYTE it will decay to a BYTE*, the expected type of your function.

Answer 2

The problem is in return (unsigned int)pbBuffer; here you are just getting address of pbBUffer everytime.If pbBuffer is an array and function crypt_rand is returning unsigned int then it should be elements of array at return.
You need to enable warnings during your compilation.These kind of possible errors must be there as warning.

Answer 3

You want a random number that is an unsigned int?
Just cast the contents of the BYTE buffer to an unsigned int
How about:
unsigned int crypt_rand()
{
HCRYPTPROV hProvider = 0;
const DWORD dwLength = sizeof(unsigned int);
BYTE buffer[dwLength];
if (!::CryptAcquireContext(&hProvider, 0, 0, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT | CRYPT_SILENT))
return 1;
if (!::CryptGenRandom(hProvider, sizeof(buffer), &buffer))
{
::CryptReleaseContext(hProvider, 0);
return 1;
}
if (!::CryptReleaseContext(hProvider, 0))
return 1;
return *(unsigned int*)buffer;
}