Adds mediocre crack protection

- Added a simple checksum calculation lib
- Validates the hardcoded "lib file" checksum against the calculated
    checksum.

By looking at instructions for the cracked version of BreakHack on
various sites that show up on google it seems that the common theme is
to replace the steamlib dll/so with a modified version. Now the Steam
version of the game will validate a hardcoded checksum against a live
validated version to see if everything seems ok before boot.

It's not a major hinderance but it should eliminate the more basic
sites modus operandi.

Honestly I don't really care if people steal the game. IT'S OPEN SOURCE
FFS!

And the above exclamation confirms why I did this. Also, I wanted to se
if it was possible. Game on Crackers! :D

.vimrc

@@ -5,5 +5,5 @@ nnoremap <F4> :ter ++close env LD_LIBRARY_PATH=$LD_LIBRARY_PATH:./ ./_build/debu
 
 packadd termdebug
 let g:termdebug_wide = 1
-let g:syntastic_c_include_dirs = [ '_build/debug', '/usr/include/SDL2', 'steamworks_c_wrapper/src', 'physfs-3.0/src', 'bh_random/src' ]
+let g:syntastic_c_include_dirs = [ '_build/debug', '/usr/include/SDL2', 'steamworks_c_wrapper/src', 'physfs-3.0/src', 'bh_random/src', 'checksum/src' ]
 let g:syntastic_cpp_include_dirs = [ 'steamworks_c_wrapper/sdk/public/steam', 'bh_random/src' ]

CMakeLists.txt

@@ -40,6 +40,7 @@ if (STEAM)
 	add_subdirectory(steamworks_c_wrapper)
 endif()
 add_subdirectory(bh_random)
+add_subdirectory(checksum)
 
 if ("${CMAKE_C_COMPILER_ID}" STREQUAL "Clang")
 	set(CLANG 1)
@@ -130,6 +131,7 @@ include_directories(
 	${LUA_INCLUDE_DIR}
 	sqlite3
 	bh_random/src
+	checksum/src
 	)
 
 if (CMOCKA_FOUND)
@@ -249,6 +251,7 @@ target_link_libraries(breakhack
 	${LUA_LIBRARIES}
 	${PHYSFS_LIBRARY}
 	bh_random
+	checksum
 	)
 
 if (STEAM)

checksum/CMakeLists.txt

@@ -0,0 +1,33 @@
+cmake_minimum_required(VERSION 3.1)
+project(checksum C)
+
+if (NOT CMAKE_BUILD_TYPE)
+	set(CMAKE_BUILD_TYPE Release)
+endif ()
+
+
+add_executable(checksumtool
+	src/checksum
+	)
+target_compile_definitions(checksumtool PUBLIC EXECUTABLE=1)
+
+add_library(checksum
+	src/checksum
+	)
+
+IF ( MSVC )
+    MESSAGE ( STATUS "Setting MSVC MT switches")
+		string (REPLACE
+			"/MDd"
+			"/MTd"
+			CMAKE_C_FLAGS_DEBUG
+			${CMAKE_C_FLAGS_DEBUG}
+    )
+		string (REPLACE
+			"/MDd"
+			"/MTd"
+			CMAKE_C_FLAGS_RELEASE
+			${CMAKE_C_FLAGS_RELEASE}
+    )
+endif ()
+

checksum/src/checksum.c

@@ -0,0 +1,61 @@
+/*
+**  CHECKSUM.C - Compute the checksum of a file
+**
+**  public somain demo by Bob Stout
+*/
+
+#include <stdlib.h>
+#include "checksum.h"
+
+unsigned
+checksum(void *buffer, size_t len, unsigned int seed)
+{
+      unsigned char *buf = (unsigned char *)buffer;
+      size_t i;
+
+      for (i = 0; i < len; ++i)
+            seed += (unsigned int)(*buf++);
+      return seed;
+}
+
+unsigned
+checksum_fp(FILE *fp)
+{
+      unsigned int seed = 0;
+      char buf[4096];
+
+      size_t len;
+      do {
+	      len = fread(buf, sizeof(char), sizeof(buf), fp);
+	      seed = checksum(buf, len, seed);
+      } while (len > 0);
+
+      return seed;
+}
+
+#ifdef EXECUTABLE
+#include <stdio.h>
+
+int main(int argc, char *argv[])
+{
+      FILE *fp;
+      const char *file;
+
+      if (argc < 2) {
+	      printf("You need to provide an input file\n");
+	      printf("Example: %s <file>", argv[0]);
+      }
+      file = argv[1];
+
+      if (NULL == (fp = fopen(file, "rb")))
+      {
+            printf("Unable to open %s for reading\n", file);
+            return -1;
+      }
+
+      printf("The checksum of %s is %#x\n", file, checksum_fp(fp));
+
+      return 0;
+}
+
+#endif

checksum/src/checksum.h

@@ -0,0 +1,27 @@
+/*
+ * BreakHack - A dungeone crawler RPG
+ * Copyright (C) 2018  Linus Probert <linus.probert@gmail.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <stdio.h>
+
+unsigned
+checksum(void *buffer, size_t len, unsigned int seed);
+
+unsigned
+checksum_fp(FILE *fp);

src/defines.h

@@ -22,6 +22,10 @@
 #include <stdint.h>
 #include "config.h"
 
+/* Checksums */
+#define SO_LIBSTEAM_CHECKSUM 	0x19ba253
+#define DLL_LIBSTEAM_CHECKSUM 	0x19ba253
+
 /* Room/Map dimensions */
 #define MAP_ROOM_WIDTH		16
 #define MAP_ROOM_HEIGHT		12

src/main.c

@@ -57,6 +57,7 @@
 #include "time.h"
 #include "sprite_util.h"
 #include "event.h"
+#include "checksum.h"
 
 #ifdef STEAM_BUILD
 #include "steam/steamworks_api_wrapper.h"
@@ -1361,10 +1362,39 @@ void close(void)
 	SDL_Quit();
 }
 
+static void
+validate_lib_checksum(void)
+{
+	FILE *fp;
+#ifdef WIN32
+	const char *file = "./libsteam_api.dll";
+	unsigned int expected = DLL_LIBSTEAM_CHECKSUM;
+#else
+	const char *file = "./libsteam_api.so";
+	unsigned int expected = SO_LIBSTEAM_CHECKSUM;
+#endif
+
+	if (NULL == (fp = fopen(file, "rb")))
+	{
+		fatal("Unable to open %s for reading\n", file);
+	}
+	unsigned calculated = checksum_fp(fp);	
+
+	if (calculated != expected) {
+		fatal("Checksum validation failiure: %#x != %#x", calculated, expected);
+	} else {
+		info("Checksum validated: %#x", calculated);
+	}
+}
+
 int main(int argc, char *argv[])
 {
 	UNUSED(argc);
 
+#ifdef STEAM_BUILD
+	validate_lib_checksum();
+#endif // STEAM_BUILD
+
 	PHYSFS_init(argv[0]);
 #ifndef DEBUG
 	PHYSFS_mount("assets.pack", NULL, 0);