xboxkrnl: Add a bunch of crypto functions

third_party/crypto/des/descbc.h

@@ -0,0 +1,34 @@
+#ifndef DESCBC_H
+#define DESCBC_H
+
+#include "des.h"
+
+class DESCBC
+{
+public:
+    DESCBC(ui64 key, ui64 iv) : des(key), iv(iv), last_block(iv) {}
+    inline ui64 encrypt(ui64 block)
+    {
+      last_block = des.encrypt(block ^ last_block);
+      return last_block;
+    }
+
+    inline ui64 decrypt(ui64 block)
+    {
+      ui64 result = des.decrypt(block) ^ last_block;
+      last_block = block;
+      return result;
+    }
+
+    inline void reset()
+    {
+      last_block = iv;
+    }
+
+private:
+    DES des;
+    ui64 iv;
+    ui64 last_block;
+};
+
+#endif // DESCBC_H