Merge pull request #4 from tetsudaiga/FallbackRandomGeneration

Use RtlGenRandom if BCryptGenRandom fails

random/random.c

@@ -18,6 +18,14 @@
 	static int lock = -1;
 #endif
 
+#if defined(__WINDOWS__)
+
+#define RTL_GENRANDOM "SystemFunction036"
+
+NTSTATUS last_bcrypt_error = 0;
+
+#endif
+
 
 static __inline void delay(unsigned int count)
 {
@@ -29,7 +37,38 @@ int random_bytes(unsigned char* random_array, unsigned int nbytes)
 { // Generation of "nbytes" of random values
 
 #if defined(__WINDOWS__)	
-	if (!BCRYPT_SUCCESS(BCryptGenRandom(NULL, random_array, nbytes, BCRYPT_USE_SYSTEM_PREFERRED_RNG))) {
+	if (BCRYPT_SUCCESS(last_bcrypt_error))
+	{
+		NTSTATUS status = BCryptGenRandom(
+			NULL, random_array, nbytes, BCRYPT_USE_SYSTEM_PREFERRED_RNG);
+
+		if (BCRYPT_SUCCESS(status))
+		{
+			return true;
+		}
+
+		last_bcrypt_error = status;
+	}
+
+	HMODULE hAdvApi = LoadLibraryA("ADVAPI32.DLL");
+	if (!hAdvApi)
+	{
+		return false;
+	}
+
+	BOOLEAN(APIENTRY * RtlGenRandom)
+		(void*, ULONG) = (BOOLEAN(APIENTRY*)(void*, ULONG))GetProcAddress(hAdvApi, RTL_GENRANDOM);
+
+	BOOLEAN genrand_result = FALSE;
+	if (RtlGenRandom)
+	{
+		genrand_result = RtlGenRandom(random_array, nbytes);
+	}
+
+	FreeLibrary(hAdvApi);
+
+	if (!genrand_result)
+	{
 		return false;
 	}