errata-11838: validate encryption key size to emit GAP Security Level, gap_set_required_encryption_key_size allows to set the required key size

CHANGELOG.md

@@ -24,6 +24,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - L2CAP ERTM: handle invalid Information Response (assume no extended features supported)
 - POSIX: use monotonic clock as timebase if available
 - HCI Transport H4/H5/EM9304 SPI: ignore block read/sent from UART driver when closed
+- HCI: Read Encryption Key Size after encryption was enabled
+- Errata 11838:
+  - GAP: gap_set_required_encryption_key_size allows to set the required key size, default = 16 (max)
+  - GAP: validate encryption key size to emit GAP Security Levels
 
 ## Changes July 2019
 

src/gap.h

@@ -198,6 +198,12 @@ void gap_ssp_set_authentication_requirement(int authentication_requirement);
  */
 void gap_ssp_set_auto_accept(int auto_accept);
 
+/**
+ * @brief Set required encryption key size for GAP Levels 1-3 on ccassic connections. Default: 16 bytes
+ * @param encryption_key_size in bytes. Valid 7..16
+ */
+void gap_set_required_encryption_key_size(uint8_t encryption_key_size);
+
 /**
  * @brief Start dedicated bonding with device. Disconnect after bonding.
  * @param device

src/hci.c

@@ -2017,6 +2017,9 @@ static void event_handler(uint8_t *packet, int size){
                     uint8_t key_size = packet[OFFSET_OF_DATA_IN_COMMAND_COMPLETE+3];
                     log_info("Handle %x04x key Size: %u", handle, key_size);
                     conn->encryption_key_size = key_size;
+                } else {
+                    log_info("Read Encryption Key Size failed -> assuming insecure connection with key size of 1");
+                    conn->encryption_key_size = 1;
                 }
                 conn->authentication_flags |= CONNECTION_ENCRYPTED;
                 hci_emit_security_level(handle, gap_security_level_for_connection(conn));
@@ -2797,6 +2800,9 @@ void hci_init(const hci_transport_t *transport, const void *config){
 
     // Master slave policy
     hci_stack->master_slave_policy = 1;
+
+    // Errata-11838 mandates 7 bytes for GAP Security Level 1-3, we use 16 as default
+    hci_stack->gap_required_encyrption_key_size = 16;
 #endif
 
     // Secure Simple Pairing default: enable, no I/O capabilities, general bonding, mitm not required, auto accept 
@@ -2884,6 +2890,15 @@ void hci_close(void){
     hci_stack = NULL;
 }
 
+#ifdef ENABLE_CLASSIC
+void gap_set_required_encryption_key_size(uint8_t encryption_key_size){
+    // validate ranage and set
+    if (encryption_key_size < 7)  return;
+    if (encryption_key_size > 16) return;
+    hci_stack->gap_required_encyrption_key_size = encryption_key_size;
+}
+#endif
+
 #ifdef ENABLE_CLASSIC
 void gap_set_class_of_device(uint32_t class_of_device){
     hci_stack->class_of_device = class_of_device;
@@ -4275,7 +4290,13 @@ static void hci_emit_security_level(hci_con_handle_t con_handle, gap_security_le
 static gap_security_level_t gap_security_level_for_connection(hci_connection_t * connection){
     if (!connection) return LEVEL_0;
     if ((connection->authentication_flags & CONNECTION_ENCRYPTED) == 0) return LEVEL_0;
-    return gap_security_level_for_link_key_type(connection->link_key_type);
+    if (connection->encryption_key_size < hci_stack->gap_required_encyrption_key_size) return LEVEL_0;
+    gap_security_level_t level_for_key_type = gap_security_level_for_link_key_type(connection->link_key_type);
+    // LEVEL 4 always requires 128 bit encrytion key size
+    if (security_level == LEVEL_4 && connection->encryption_key_size < 16){
+        security_level = LEVEL_3;
+    }
+    return security_level;
 }    
 
 static void hci_emit_discoverable_enabled(uint8_t enabled){

src/hci.h

@@ -747,6 +747,10 @@ typedef struct {
     uint8_t            ssp_authentication_requirement;
     uint8_t            ssp_auto_accept;
     inquiry_mode_t     inquiry_mode;
+#ifdef ENABLE_CLASSIC
+    // Errata-11838 mandates 7 bytes for GAP Security Level 1-3, we use 16 as default
+    uint8_t             gap_required_encyrption_key_size;
+#endif
 
     // single buffer for HCI packet assembly + additional prebuffer for H4 drivers
     uint8_t   * hci_packet_buffer;