1 files changed, 73 insertions, 0 deletions
diff --git a/src/crypto.c b/src/crypto.c
new file mode 100644
index 0000000..1189882
--- /dev/null
+++ b/src/crypto.c
@@ -0,0 +1,73 @@
+/* crypto.c -- Code for deriving encryption keys.
+
+   Copyright (C) 2017 Jakob Tsar-Fox, All Rights Reserved.
+
+   This file is part of Nekopack.
+
+   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 <stdbool.h>
+#include <stdint.h>
+
+#include "crypto.h"
+
+
+/* Returns the game_key structure for a given game identifier, as
+   defined in crypto.h */
+struct game_key get_key(int game) {
+    struct game_key k = {0};
+    switch (game) {
+        case NEKOPARA_VOLUME_0:
+            k.master = 0x1548e29c;
+            k.fallback_initial = 0x9c;
+            k.fallback_primary = 0xd7;
+            k.uses_initial = true;
+            break;
+        case NEKOPARA_VOLUME_0_STEAM:
+            k.master = 0x44528b87;
+            k.fallback_initial = 0x87;
+            k.fallback_primary = 0x23;
+            k.uses_initial = true;
+            break;
+        case NEKOPARA_VOLUME_1:
+            k.master = 0x1548e29c;
+            k.fallback_initial = 0x00;
+            k.fallback_primary = 0xd7;
+            k.uses_initial = false;
+            break;
+        case NEKOPARA_VOLUME_1_STEAM:
+            k.master = 0x44528b87;
+            k.fallback_initial = 0x00;
+            k.fallback_primary = 0x23;
+            k.uses_initial = false;
+            break;
+    }
+    return k;
+}
+
+
+/* Generates an initial key for the given key structure and file key. */
+uint8_t derive_initial(struct game_key k, uint64_t file_key) {
+    if (!k.uses_initial) return 0x00;
+    uint8_t initial = (k.master ^ file_key) & 0xff;
+    return initial == 0 ? k.fallback_initial : initial;
+}
+
+
+/* Generates a primary key for the given key structure and file key. */
+uint8_t derive_primary(struct game_key k, uint64_t file_key) {
+    uint32_t tmp = k.master ^ file_key;
+    uint8_t primary = (tmp >> 24 ^ tmp >> 16 ^ tmp >> 8 ^ tmp) & 0xff;
+    return primary == 0 ? k.fallback_primary : primary;
+}