Merge pull request #40 from skx/38-encryption

Generate encrypted versions of the ZX Spectrum game

Author: skx

.gitignore

@@ -1,6 +1,4 @@
-game.com
-lihouse.com
-lihouse2.com
 lighthouse
 encrypt
 *.tap
+*.com

Makefile

@@ -5,6 +5,7 @@ VERSION := $(or ${GITHUB_REF},${GITHUB_REF},"unreleased-git")
 
 all: lighthouse game-cpm game-spectrum
 
+
 # Build the C version
 lighthouse: handlers.c  inventory.c  items.c  main.c  world.c util.c
 	gcc  -o lighthouse -Os -Wall -Wextra -Werror handlers.c  inventory.c  items.c  main.c  world.c util.c
@@ -14,6 +15,12 @@ lighthouse: handlers.c  inventory.c  items.c  main.c  world.c util.c
 clean:
 	rm -f lighthouse *.com *.tap encrypt || true
 
+
+# Build the encryption helper
+encrypt: encrypt.c
+	gcc -o encrypt -Wall -Werror encrypt.c
+
+
 # Format our C-code
 format:
 	astyle --style=allman -A1 --indent=spaces=4   --break-blocks --pad-oper --pad-header --unpad-paren --max-code-length=200 *.c *.h
@@ -23,28 +30,51 @@ format:
 version:
 	echo "DB \"$$(echo ${VERSION} | awk -F/ '{print $$NF}' )\"" >  version.z80
 
+
+
 # build the game for CP/M
 game-cpm: game.z80 bios.z80 version Makefile
 	pasmo --equ ENTRYPOINT=100h --equ ENCRYPT_STRINGS=0 --equ SPECTRUM=0 game.z80 lihouse.com
 
+# build the game for CP/M with encrypted strings/code
+game-cpm-encrypted: game.z80 bios.z80 version Makefile encrypt
+	pasmo --equ ENTRYPOINT=100h --equ ENCRYPT_STRINGS=1 --equ SPECTRUM=0 game.z80 lihouse.com
+	./encrypt lihouse.com lihousex.com
+	rm lihouse.com
+
+
+
 # build the game for the ZX Spectrum
 game-spectrum: game.z80 bios.z80 version Makefile
 	pasmo --tapbas --equ ENTRYPOINT=32768 --equ ENCRYPT_STRINGS=0 --equ SPECTRUM=1 game.z80 lihouse.tap
 
-# Build the encryption helper
-encrypt: encrypt.c
-	gcc -o encrypt -Wall -Werror encrypt.c
+# build the game for the ZX Spectrum with encrypted strings
+game-spectrum-encrypted: game.z80 bios.z80 version Makefile encrypt
+	pasmo --tapbas --equ ENTRYPOINT=32768 --equ ENCRYPT_STRINGS=1 --equ SPECTRUM=1 game.z80 lihouse.tap
+	./encrypt -crc lihouse.tap lihousex.tap
+	rm lihouse.tap
+
 
 # Build the game for release - with strings encrypted
-release: game.z80 encrypt version
-	pasmo --equ ENTRYPOINT=100h --equ ENCRYPT_STRINGS=1 --equ SPECTRUM=0 game.z80 lihouse.com
-	./encrypt
-	mv lihouse2.com lihouse.com
+release: version
+	make game-cpm-encrypted
+	make game-cpm
+	make game-spectrum-encrypted
+	make game-spectrum
 
 
-# Run for CP/M
-run-cpm: game
+# Run the CP/M version via runcpm
+run-cpm: game-cpm
 	~/cpm/cpm lihouse
 
-run-spectrum:
-	xspect -quick-load -load-immed -tap *.tap
+# Run the CP/M version via runcpm, with the encrypted version of the code
+run-cpm-encrypted: game-cpm-encrypted
+	~/cpm/cpm lihouseX
+
+# Run the spectrum version
+run-spectrum: game-spectrum
+	xspect -quick-load -load-immed -tap lihouse.tap
+
+# Run the spectrum version, with strings encrypted
+run-spectrum-encrypted: game-spectrum-encrypted
+	xspect -quick-load -load-immed -tap lihousex.tap

README.md

@@ -19,6 +19,7 @@ Quick links within this README file:
 * [Bugs?](#bugs)
 
 
+
 ## Play Online
 
 Thanks to the excellent [jsspeccy](https://github.com/gasman/jsspeccy3) ZX Spectrum emulator you can play this game with your browser here:</p>
@@ -88,27 +89,25 @@ defining `SPECTRUM`, and `ENTRYPOINT` as appropriate.
 * Along the way I realized that having fixed inventory slots made the coding more of a challenge, so I made the location of each object a property of the object itself.
 * The Z80 version has more easter-eggs (Try typing "`xyzzy`" a few times).
 * There are __two__ victory conditions.
-* The CP/M version of the game can be built with the text-strings, and game code, protected by simple XOR encryption:
+* The game can be built with the text-strings, and game code, protected by simple XOR encryption:
   * This stops users from looking through the binary for hints.
-  * Run `make release` to build the _protected_ CP/M version.
+  * Run `make release` to build both "normal" and "protected" versions of the release.
+  * The encrypted versions of the games have an X suffix in their filenames.
+
 
 
 ## Compiling & Running It
 
 Ensure you have the `pasmo` assembler installed, and then use the supplied Makefile to compile the game.
 
-Running `make` will generate the default targets:
-
-* `make lighthouse`  -> Build the game for linux.
-* `make lihouse.com` -> Build the game for CP/M, without the XOR encryption.
-* `make lihouse.tap` -> Build the game for the 48k ZX Spectrum.
-
-If you wish to build only individual things then :
+Running `make` will generate the default targets, if you wish to build only individual things then :
 
 * `make game-cpm` to build a normal CP/M version.
+  * `make game-cpm-encrypted` to build an encrypted CP/M version.
 * `make game-spectrum` to build the ZX Spectrum version.
+  * `make game-spectrum-encrypted` to build the encrypted ZX Spectrum version.
 * `make lighthouse` will build the C-game for Linux
-* `make release` will build the _protected_ CP/M version.
+* `make release` will build both versions of the CP/M and ZX Spectrum release.
 
 
 
@@ -117,7 +116,10 @@ If you wish to build only individual things then :
 If you look on our [release page](https://github.com/skx/lighthouse-of-doom/releases/) you can find the latest stable build.
 
 * For CP/M download `lihouse.com` to your system, and then run `LIHOUSE` to launch it.
+  * `lihousex.com` is the encrypted version.
 * For the ZX Spectrum download `lihouse.tap` to your system, and then launch in your favourite emulator.
+  * `lihousex.tap` is the encrypted version.
+
 
 
 ## Bugs?

encrypt.c

@@ -1,47 +1,130 @@
 /*
- * Load `lihouse.com` and scramble the strings, saving to `lihouse2.com`.
+ * Generate an encrypted version of the specified input file.
+ *
+ * Optionally update the CRC check of the file - this is necessary
+ * for the .TAP version we generate for the ZX Spectrum.
  */
 
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <malloc.h>
 
+typedef unsigned char byte;
+
+
+// calculate the checksum for the given region
+byte crc(byte *start, int length)
+{
+    byte tcrc = 0;
+
+    for (int i = 0; i < length; i++)
+        tcrc = tcrc ^ start[i];
+
+    return tcrc;
+}
+
 int main(int argc, char *argv[])
 {
-    FILE *f = fopen("lihouse.com", "r");
+    // check argument count
+    if (argc != 3 && argc != 4)
+    {
+        printf("Usage: encrypt [-crc] input output\n");
+        return 1;
+    }
+
+    // flags / arguments
+    int do_crc = 0;
+    char *input = NULL;
+    char *output = NULL;
+
+    // look for flags
+    if (argc == 4)
+    {
+        // Should we run a CRC update?
+        for (int i = 1; i < argc ; i++)
+        {
+            if (strcmp(argv[i], "-crc") == 0)
+            {
+                do_crc = 1;
+            }
+        }
+    }
+
+    // look for input/output names.
+    for (int i = 1; i < argc ; i++)
+    {
+        // Ignore flags
+        if (strcmp(argv[i], "-crc") == 0)
+        {
+            continue;
+        }
+
+        // input file goes first
+        if (input == NULL)
+        {
+            input = argv[i];
+            continue;
+        }
+
+        // output file goes second.
+        if (output == NULL)
+        {
+            output = argv[i];
+            continue;
+        }
+    }
+
+    printf("Input file: %s\n", input);
+    printf("Output file: %s\n", output);
+
+    if (do_crc)
+    {
+        printf("CRC will be updated\n");
+    }
+    else
+    {
+        printf("No CRC update\n");
+    }
+
+    // Open the file for reading
+    FILE *f = fopen(input, "r");
 
     if (f == NULL)
     {
-        printf("Failed to open file\n");
-        return 0;
+        printf("Failed to open input file: %s\n", input);
+        return 1;
     }
 
     // get file size
     fseek(f, 0L, SEEK_END);
     size_t sz = ftell(f);
 
+    printf("File size is %ld bytes\n", sz);
+
     // get back to start
     fseek(f, 0L, SEEK_SET);
 
     // allocate memory
-    char *buf = malloc(sz);
+    unsigned char *buf = malloc(sz);
 
     if (buf == NULL)
     {
         printf("failed to allocate memory\n");
-        return 0;
+        return 1;
     }
 
     // read the file
-    int n = fread(buf, sizeof(char), sz, f);
+    int n = fread(buf, sizeof(unsigned char), sz, f);
 
     if (ferror(f) != 0)
     {
         printf("error reading\n");
         return 1;
     }
-    if ( n != sz ) {
+
+    if (n != sz)
+    {
         printf("short read\n");
         return 1;
     }
@@ -68,12 +151,40 @@ int main(int argc, char *argv[])
                 k++;
             }
 
+            if (do_crc)
+            {
+                // Now we have to fixup the CRC
+                unsigned char *pos = buf;
+
+                for (int i = 1; i < sz; i++)
+                {
+                    size_t blocksize = pos[0] | (pos[1] << 8);
+
+                    if ((pos + blocksize + 1) < (buf + sz))
+                    {
+                        if (blocksize > 1)
+                        {
+                            char ccrc = crc(&pos[2], blocksize - 1);
+
+                            if (pos[blocksize + 1] != ccrc)
+                            {
+                                printf("Updated CRC\n");
+                                pos[blocksize + 1] = ccrc;
+                            }
+                        }
+                    }
+
+
+                    pos += blocksize + 2;
+                }
+            }
+
             // Write
-            FILE *nw = fopen("lihouse2.com", "w");
+            FILE *nw = fopen(output, "w");
 
             if (nw == NULL)
             {
-                printf("Failed to open file for writing\n");
+                printf("Failed to open file for writing: %s\n", output);
             }
 
             fwrite(buf, sz, 1, nw);