Use BCrypt for get byte on windows (#86)

* Use BCrypt for get byte on windows

* Revert "Use BCrypt for get byte on windows"

This reverts commit e664b927f2.

* Revert changes to method signature, move assert. remove mod operation

src/electionguard/random_source.c

@@ -5,6 +5,7 @@
 
 #ifdef HAVE_BCRYPTGENRANDOM
 #include <windows.h>
+#include <assert.h>
 #include <ntstatus.h>
 #include <bcrypt.h>
 #endif
@@ -63,9 +64,9 @@ uint8_t RandomSource_get_byte(RandomSource source)
     size_t item_count;
     uint8_t ret;
 #ifdef HAVE_BCRYPTGENRANDOM
-    //NTSTATUS ntstatus =
-        //BCryptGenRandom(NULL, &ret, 1, BCRYPT_USE_SYSTEM_PREFERRED_RNG);
-        ret = 1;
+    NTSTATUS ntstatus =
+        BCryptGenRandom(NULL, &ret, 1, BCRYPT_USE_SYSTEM_PREFERRED_RNG);
+    assert(ntstatus == STATUS_SUCCESS);
 #else
     fread(&ret, 1, 1, source->dev_random);
 #endif

src/electionguard/rsa.c

@@ -37,7 +37,7 @@ void generate_keys(rsa_private_key* priv_key, rsa_public_key* pub_key)
     /* Select p */
     for(int i = 0; i < BUFFER_SIZE; i++)
     {
-        buffer[i] = RandomSource_get_byte(source) % 0xFF;
+        buffer[i] = RandomSource_get_byte(source);
     }
 
     buffer[0] |= 0xC0;                                  // Set the top two bits to 1 to ensure int(tmp) is relatively large