1 files changed, 76 insertions, 0 deletions
diff --git a/src/crypto.c b/src/crypto.c
new file mode 100644
index 0000000..2d527c7
--- /dev/null
+++ b/src/crypto.c
@@ -0,0 +1,76 @@
+/* This file is part of Nekopack.
+
+   Copyright (C) 2017 Jakob Tsar-Fox, All Rights Reserved.
+
+   Nekopack 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.
+
+   Nekopack 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 Nekopack. If not, see <http://www.gnu.org/licenses/>. */
+
+#include "cli.h"
+#include "crypto.h"
+
+
+/* Returns the encryption keys for a given game value. */
+key get_encryption_key(game current_game) {
+    key encryption_key;
+    switch (current_game) {
+        case NEKOPARA_VOLUME_0:
+            encryption_key.master_key = 0x1548e29c;
+            encryption_key.initial_fallback_key = 0x9c;
+            encryption_key.primary_fallback_key = 0xd7;
+            encryption_key.uses_initial_key = 1;
+            break;
+        case NEKOPARA_VOLUME_0_STEAM:
+            encryption_key.master_key = 0x44528b87;
+            encryption_key.initial_fallback_key = 0x87;
+            encryption_key.primary_fallback_key = 0x23;
+            encryption_key.uses_initial_key = 1;
+            break;
+        case NEKOPARA_VOLUME_1:
+            encryption_key.master_key = 0x1548e29c;
+            encryption_key.initial_fallback_key = 0x00;
+            encryption_key.primary_fallback_key = 0xd7;
+            encryption_key.uses_initial_key = 0;
+            break;
+        case NEKOPARA_VOLUME_1_STEAM:
+            encryption_key.master_key = 0x44528b87;
+            encryption_key.initial_fallback_key = 0x00;
+            encryption_key.primary_fallback_key = 0x23;
+            encryption_key.uses_initial_key = 0;
+            break;
+        default:
+            encryption_key.master_key = 0x00000000;
+            encryption_key.initial_fallback_key = 0x00;
+            encryption_key.primary_fallback_key = 0x00;
+            encryption_key.uses_initial_key = 0;
+    }
+    return encryption_key;
+}
+
+
+/* Decrypts the contents of a buffer according to a file key. */
+void decrypt_buffer(Bytef *encrypted_buffer, uint64_t buffer_length,
+                    key encryption_key, uint32_t file_key) {
+    uint32_t xor_key = file_key ^ encryption_key.master_key;
+    uint8_t initial_key = xor_key & 0xff;
+    uint8_t primary_key = (xor_key >> 24 ^ xor_key >> 16 ^ \
+                           xor_key >> 8 ^ xor_key) & 0xff;
+    if (xor_key == 1 && initial_key == 0)
+        initial_key = encryption_key.initial_fallback_key;
+    else if (primary_key == 0)
+        primary_key = encryption_key.primary_fallback_key;
+    if (encryption_key.uses_initial_key)
+        encrypted_buffer[0] ^= initial_key;
+    for (uint64_t i = 0; i < buffer_length; i++) {
+        encrypted_buffer[i] ^= primary_key;
+    }
+}