diff --git a/CMakeLists.txt b/CMakeLists.txt
index e8f37d3..a9c64ff 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -30,6 +30,7 @@ add_executable(pico_fido)
 
 target_sources(pico_fido PUBLIC
         ${CMAKE_CURRENT_LIST_DIR}/src/fido/fido.c
+        ${CMAKE_CURRENT_LIST_DIR}/src/fido/cmd_register.c
         )
 set(HSM_DRIVER "hid")
 include(pico-hsm-sdk/pico_hsm_sdk_import.cmake)
diff --git a/src/fido/cmd_register.c b/src/fido/cmd_register.c
new file mode 100644
index 0000000..28e3189
--- /dev/null
+++ b/src/fido/cmd_register.c
@@ -0,0 +1,24 @@
+/*
+ * This file is part of the Pico FIDO distribution (https://github.com/polhenarejos/pico-fido).
+ * Copyright (c) 2022 Pol Henarejos.
+ *
+ * This program 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, version 3.
+ *
+ * This program 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 this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "fido.h"
+#include "hsm.h"
+#include "apdu.h"
+
+int cmd_register() {
+    return SW_OK();
+}
diff --git a/src/fido/fido.c b/src/fido/fido.c
index 00f2135..7836e0d 100644
--- a/src/fido/fido.c
+++ b/src/fido/fido.c
@@ -18,6 +18,7 @@
 #include "fido.h"
 #include "hsm.h"
 #include "apdu.h"
+#include "u2f.h"
 #include <stdio.h>
 
 void init_fido();
@@ -56,8 +57,11 @@ typedef struct cmd
   int (*cmd_handler)();
 } cmd_t;
 
+extern int cmd_register();
+
 static const cmd_t cmds[] = {
-      { 0x00, 0x0}
+    { U2F_REGISTER, cmd_register },
+    { 0x00, 0x0}
 };
 
 int fido_process_apdu() {
diff --git a/src/fido/fido.h b/src/fido/fido.h
index e69de29..cd484f2 100644
--- a/src/fido/fido.h
+++ b/src/fido/fido.h
@@ -0,0 +1,25 @@
+/*
+ * This file is part of the Pico FIDO distribution (https://github.com/polhenarejos/pico-fido).
+ * Copyright (c) 2022 Pol Henarejos.
+ *
+ * This program 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, version 3.
+ *
+ * This program 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 this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef _FIDO_H_
+#define _FIDO_H_
+
+#define U2F_PUBKEY_LEN 65
+#define KEY_PATH_LEN 32
+#define KEY_HANDLE_LEN (KEY_PATH_LEN + SHA256_DIGEST_LENGTH)
+
+#endif //_FIDO_H