add: cryptohelper support

common/cardhelper.h

@@ -0,0 +1,21 @@
+//-----------------------------------------------------------------------------
+// Iceman, February 2020
+//
+// This code is licensed to you under the terms of the GNU GPL, version 2 or,
+// at your option, any later version. See the LICENSE.txt file for the text of
+// the license.
+//-----------------------------------------------------------------------------
+// Utility functions used in many places, not specific to any piece of code.
+//-----------------------------------------------------------------------------
+
+#ifndef __CARDHELPER_H
+#define __CARDHELPER_H
+
+#include <ctype.h>
+#include "common.h"
+
+bool IsCryptoHelperPresent(void);
+bool Encrypt(uint8_t *src, uint8_t *dest);
+bool Decrypt(uint8_t *src, uint8_t *dest);
+void DecodeBlock6(uint8_t *src);
+#endif