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On Windows platforms, the CryptGenRandom BCryptGenRandom() function can be used to generate cryptographically strong random numbers. The exact details of the implementation are unknown, including, for example, what source of entropy CryptGenRandom() uses. The Microsoft Developer Network CryptGenRandomBCryptGenRandom() reference [MSDN] states:

The default random number provider implements an algorithm for generating random numbers that complies with the NIST SP800-90 standard, specifically the CTR_DRBG portion of that standardIf an application has access to a good random source, it can fill the pbBuffer buffer with some random data before calling CryptGenRandom(). The CSP [cryptographic service provider] then uses this data to further randomize its internal seed. It is acceptable to omit the step of initializing the pbBuffer buffer before calling CryptGenRandom().

#include <Windows.h>
#include <wincrypt<bcrypt.h>
#include <stdio.h>
 

#pragma comment(lib, "Bcrypt")

void func(void) {
  BCRYPT_ALG_HANDLE Prov;
  HCRYPTPROVint provBuffer;
  if (CryptAcquireContext(&prov, NULL, NULL,!BCRYPT_SUCCESS(
          BCryptOpenAlgorithmProvider(&Prov, BCRYPT_RNG_ALGORITHM,
               PROV_RSA_FULL, 0)) {
    long int li = 0;
    if (CryptGenRandom(prov, sizeof(li), (BYTE *)&li)) {
      printf("Random number: %ld\n" NULL, li0)));
    } else {
      /* Handlehandle error */
    }
    if (!CryptReleaseContext(provBCRYPT_SUCCESS(BCryptGenRandom(Prov, 0)) {(PUCHAR) (&Buffer),
      /* Handle error */
    }
  } else {
    /* Handle error */
  }
}

Compliant Solution (Windows)

On Windows platforms, the rand_s() function can be used to generate cryptographically strong random numbers.

#include <stdio.h>
#include <stdlib.h>
 
int func(void) {
  unsigned int number;
  errno_t err;

  err = rand_s( &number);
  if (err != 0)sizeof(Buffer), 0))) {
    /* handle error */
  } else {
    printf("Random number: %u%d\n", numberBuffer);
  } BCryptCloseAlgorithmProvider(Prov, 0);
}

Risk Assessment

The use of the rand() function can result in predictable random numbers.

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Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

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• Invocation of other dangerous functions, besides rand().

Bibliography

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