Let us start here, from square one. No, from Zero!

reader/crypt.h

@@ -0,0 +1,17 @@
+#pragma once
+
+#include <cstdint>
+
+class Crypt {
+private:
+    uint32_t keys[4];
+
+public:
+    Crypt();
+
+    void set_keys(uint32_t reader_key, uint32_t game_key);
+
+    void crypt(uint8_t *data, size_t len);
+
+    uint16_t crc(const uint8_t *data, size_t len);
+};