MRTD add helper functions:

- Check digit
- KMRZ

lib/nfc/protocols/mrtd_helpers.h

@@ -0,0 +1,37 @@
+#pragma once
+
+#include <stdint.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <string.h>
+
+typedef struct {
+    uint8_t year;
+    uint8_t month;
+    uint8_t day;
+} MrtdDate;
+
+// NULL terminated document ID
+#define MRTD_DOCNR_MAX_LENGTH 21
+
+typedef enum {
+    MrtdAuthMethodBac,
+    MrtdAuthMethodPace,
+} MrtdAuthMethod;
+
+typedef struct {
+    MrtdAuthMethod method;
+
+    // BAC input fields
+    MrtdDate birth_date;
+    MrtdDate expiry_date;
+    char doc_number[MRTD_DOCNR_MAX_LENGTH];
+
+    //TODO: PACE
+} MrtdAuthData;
+
+uint8_t mrtd_bac_check_digit(const uint8_t* input, const size_t length);
+
+void mrtd_print_date(uint8_t* output, MrtdDate* date);
+
+bool mrtd_bac_get_kmrz(MrtdAuthData* auth, uint8_t* output, size_t output_size);