nas: set NAS key set identifier to no key available when attaching with IMSI

lib/include/srslte/asn1/liblte_mme.h

@@ -1063,6 +1063,7 @@ LIBLTE_ERROR_ENUM liblte_mme_unpack_ms_network_capability_ie(uint8**
 // Defines
 // Enums
 // Structs
+#define LIBLTE_MME_NAS_KEY_SET_IDENTIFIER_NO_KEY_AVAILABLE (7)
 typedef struct {
   LIBLTE_MME_TYPE_OF_SECURITY_CONTEXT_FLAG_ENUM tsc_flag;
   uint8                                         nas_ksi;

srsue/src/stack/upper/nas.cc

@@ -1698,7 +1698,7 @@ void nas::gen_attach_request(srslte::unique_byte_buffer_t& msg)
   } else {
     attach_req.eps_mobile_id.type_of_id = LIBLTE_MME_EPS_MOBILE_ID_TYPE_IMSI;
     attach_req.nas_ksi.tsc_flag         = LIBLTE_MME_TYPE_OF_SECURITY_CONTEXT_FLAG_NATIVE;
-    attach_req.nas_ksi.nas_ksi          = 0;
+    attach_req.nas_ksi.nas_ksi          = LIBLTE_MME_NAS_KEY_SET_IDENTIFIER_NO_KEY_AVAILABLE;
     usim->get_imsi_vec(attach_req.eps_mobile_id.imsi, 15);
     nas_log->info("Requesting IMSI attach (IMSI=%s)\n", usim->get_imsi_str().c_str());
     liblte_mme_pack_attach_request_msg(&attach_req, (LIBLTE_BYTE_MSG_STRUCT*)msg.get());