fix(bluetooth): Passkey pairing improvements.

* Capture the last 6 entered digits, and then require pressing
   Enter/Return to submit the entered digits. This matches the
   messaging shown on hosts regarding how to complete pairing.
* Fix the wording on the Kconfig menu item to accurately describe
  the feature.

app/Kconfig

@@ -160,8 +160,9 @@ config BT_DEVICE_APPEARANCE
     default 961
 
 config ZMK_BLE_PASSKEY_ENTRY
-    bool "Experimental: Requiring typing passkey from host to pair BLE connection"
+    bool "Require passkey entry on the keyboard to complete pairing"
     default n
+    select RING_BUFFER
 
 config BT_PERIPHERAL_PREF_MIN_INT
     default 6

app/src/ble.c

@@ -13,6 +13,7 @@
 #include <stdio.h>
 
 #include <zephyr/settings/settings.h>
+#include <zephyr/sys/ring_buffer.h>
 #include <zephyr/bluetooth/bluetooth.h>
 #include <zephyr/bluetooth/conn.h>
 #include <zephyr/bluetooth/hci.h>
@@ -42,8 +43,7 @@ LOG_MODULE_DECLARE(zmk, CONFIG_ZMK_LOG_LEVEL);
 #define PASSKEY_DIGITS 6
 
 static struct bt_conn *auth_passkey_entry_conn;
-static uint8_t passkey_entries[PASSKEY_DIGITS] = {};
+RING_BUF_DECLARE(passkey_entries, PASSKEY_DIGITS);
-static uint8_t passkey_digit = 0;
 
 #endif /* IS_ENABLED(CONFIG_ZMK_BLE_PASSKEY_ENTRY) */
 
@@ -469,7 +469,7 @@ static void auth_passkey_entry(struct bt_conn *conn) {
     bt_addr_le_to_str(bt_conn_get_dst(conn), addr, sizeof(addr));
 
     LOG_DBG("Passkey entry requested for %s", addr);
-    passkey_digit = 0;
+    ring_buf_reset(&passkey_entries);
     auth_passkey_entry_conn = bt_conn_ref(conn);
 }
 
@@ -486,7 +486,7 @@ static void auth_cancel(struct bt_conn *conn) {
         auth_passkey_entry_conn = NULL;
     }
 
-    passkey_digit = 0;
+    ring_buf_reset(&passkey_entries);
 #endif
 
     LOG_DBG("Pairing cancelled: %s", addr);
@@ -605,7 +605,7 @@ static int zmk_ble_init(const struct device *_arg) {
 #if IS_ENABLED(CONFIG_ZMK_BLE_PASSKEY_ENTRY)
 
 static bool zmk_ble_numeric_usage_to_value(const zmk_key_t key, const zmk_key_t one,
-                                           const zmk_key_t zero, uint32_t *value) {
+                                           const zmk_key_t zero, uint8_t *value) {
     if (key < one || key > zero) {
         return false;
     }
@@ -634,7 +634,23 @@ static int zmk_ble_handle_key_user(struct zmk_keycode_state_changed *event) {
         return ZMK_EV_EVENT_HANDLED;
     }
 
-    uint32_t val;
+    if (key == HID_USAGE_KEY_KEYBOARD_RETURN || key == HID_USAGE_KEY_KEYBOARD_RETURN_ENTER) {
+        uint8_t digits[PASSKEY_DIGITS];
+        uint32_t count = ring_buf_get(&passkey_entries, digits, PASSKEY_DIGITS);
+
+        uint32_t passkey = 0;
+        for (int i = 0; i < count; i++) {
+            passkey = (passkey * 10) + digits[i];
+        }
+
+        LOG_DBG("Final passkey: %d", passkey);
+        bt_conn_auth_passkey_entry(auth_passkey_entry_conn, passkey);
+        bt_conn_unref(auth_passkey_entry_conn);
+        auth_passkey_entry_conn = NULL;
+        return ZMK_EV_EVENT_HANDLED;
+    }
+
+    uint8_t val;
     if (!(zmk_ble_numeric_usage_to_value(key, HID_USAGE_KEY_KEYBOARD_1_AND_EXCLAMATION,
                                          HID_USAGE_KEY_KEYBOARD_0_AND_RIGHT_PARENTHESIS, &val) ||
           zmk_ble_numeric_usage_to_value(key, HID_USAGE_KEY_KEYPAD_1_AND_END,
@@ -643,20 +659,13 @@ static int zmk_ble_handle_key_user(struct zmk_keycode_state_changed *event) {
         return ZMK_EV_EVENT_BUBBLE;
     }
 
-    passkey_entries[passkey_digit++] = val;
+    if (ring_buf_space_get(&passkey_entries) <= 0) {
-    LOG_DBG("value entered: %d, digits collected so far: %d", val, passkey_digit);
+        uint8_t discard_val;
-
+        ring_buf_get(&passkey_entries, &discard_val, 1);
-    if (passkey_digit == PASSKEY_DIGITS) {
-        uint32_t passkey = 0;
-        for (int i = 0; i < PASSKEY_DIGITS; i++) {
-            passkey = (passkey * 10) + passkey_entries[i];
-        }
-
-        LOG_DBG("Final passkey: %d", passkey);
-        bt_conn_auth_passkey_entry(auth_passkey_entry_conn, passkey);
-        bt_conn_unref(auth_passkey_entry_conn);
-        auth_passkey_entry_conn = NULL;
     }
+    ring_buf_put(&passkey_entries, &val, 1);
+    LOG_DBG("value entered: %d, digits collected so far: %d", val,
+            ring_buf_size_get(&passkey_entries));
 
     return ZMK_EV_EVENT_HANDLED;
 }

docs/docs/config/bluetooth.md

@@ -10,5 +10,6 @@ See [Configuration Overview](index.md) for instructions on how to change these s
 ## Kconfig
 
 | Option                                | Type | Description                                                                                                                                  | Default |
-| ------------------------------------- | ---- | ----------------------------------------------------------------------------------------------------------------------- | ------- |
+| ------------------------------------- | ---- | -------------------------------------------------------------------------------------------------------------------------------------------- | ------- |
+| `CONFIG_ZMK_BLE_PASSKEY_ENTRY`        | bool | Enable passkey entry during pairing for enhanced security. (Note: After enabling this, you will need to re-pair all previously paired hosts) | n       |
 | `CONFIG_BT_GATT_ENFORCE_SUBSCRIPTION` | bool | Low level setting for GATT subscriptions. Set to `n` to work around an annoying Windows bug with battery notifications.                      | y       |