From 978f5845d6d21c37393cbd47bed3b1ee55760318 Mon Sep 17 00:00:00 2001
From: Marko Lindqvist <cazfi74@gmail.com>
Date: Mon, 29 Mar 2021 06:23:56 +0300
Subject: [PATCH 19/25] Support unpredictable random seed on Windows

See osdn #41842

Signed-off-by: Marko Lindqvist <cazfi74@gmail.com>
---
 configure.ac       |  8 +++++---
 utility/randseed.c | 31 +++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/configure.ac b/configure.ac
index dad6c94e28..e91f064293 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1434,11 +1434,13 @@ AC_CHECK_FUNCS([strerror strstr uname nanosleep usleep])
 AC_CHECK_FUNCS([getline _strcoll stricoll _stricoll strcasecoll])
 AC_CHECK_FUNCS([backtrace setenv putenv])
 
-dnl Possible random sources on Unixen
+dnl Possible random sources
+AC_CHECK_HEADERS([sys/random.h bcrypt.h])
+AC_CHECK_LIB([bcrypt], [BCryptGenRandom], [
+  AC_DEFINE([HAVE_BCRYPTGENRANDOM], [1], [BCryptGenRandom() available])
+  UTILITY_LIBS="${UTILITY_LIBS} -lbcrypt" ])
 AC_CHECK_FUNCS([getentropy clock_gettime])
 
-AC_CHECK_HEADERS([sys/random.h])
-
 dnl TODO: Reimplement this check, in a cross-compiling friendly way
 dnl AC_CHECK_FILES([/dev/urandom])
 
diff --git a/utility/randseed.c b/utility/randseed.c
index 5610b27270..523b3f9f5c 100644
--- a/utility/randseed.c
+++ b/utility/randseed.c
@@ -19,6 +19,9 @@
 
 #include "fc_prehdrs.h"
 
+#ifdef HAVE_BCRYPT_H
+#include <bcrypt.h>
+#endif
 #include <errno.h>
 #include <fcntl.h>
 #include <stdint.h>
@@ -31,6 +34,9 @@
 #ifdef HAVE_UNISTD_H
 #include <unistd.h>
 #endif
+#ifdef FREECIV_MSWINDOWS
+#include <ntdef.h>
+#endif
 
 /* utility */
 #include "fcintl.h"
@@ -63,6 +69,27 @@ static bool generate_seed_getentropy(uint32_t *ret)
   return FALSE;
 }
 
+/**********************************************************************//**
+  Read a 32-bit random value using BCryptGenRandom(), if available.
+  (Windows)
+  Return FALSE on error, otherwise return TRUE and store seed in *ret.
+**************************************************************************/
+static bool generate_seed_bcryptgenrandom(uint32_t *ret)
+{
+#ifdef HAVE_BCRYPTGENRANDOM
+  NTSTATUS Status;
+
+  Status = BCryptGenRandom(NULL, (PUCHAR)ret, sizeof(uint32_t),
+                           BCRYPT_USE_SYSTEM_PREFERRED_RNG);
+
+  if (NT_SUCCESS(Status)) {
+    return TRUE;
+  }
+#endif /* HAVE_BCRYPTGENRANDOM */
+
+  return FALSE;
+}
+
 /**********************************************************************//**
   Read a 32-bit random value using /dev/urandom, if available. 
   (Most Unix-like systems)
@@ -172,6 +199,10 @@ unsigned int generate_game_seed(void)
     log_debug("Got random seed from getentropy()");
     return seed;
   }
+  if (generate_seed_bcryptgenrandom(&seed)) {
+    log_debug("Got random seed from BCryptGenRandom()");
+    return seed;
+  }
   if (generate_seed_urandom(&seed)) {
     log_debug("Got random seed from urandom()");
     return seed;
-- 
2.30.2