Added some functions to save and restore AS keys for the case of failed handover in the USIM

lib/include/srslte/interfaces/ue_interfaces.h

@@ -78,6 +78,8 @@ class usim_interface_rrc
 public:
   virtual void generate_as_keys(uint8_t* k_asme, uint32_t count_ul, srslte::as_security_config_t* sec_cfg)        = 0;
   virtual void generate_as_keys_ho(uint32_t pci, uint32_t earfcn, int ncc, srslte::as_security_config_t* sec_cfg) = 0;
+  virtual void store_keys_before_ho(const srslte::as_security_config_t& as_cfg)                                   = 0;
+  virtual void restore_keys_from_failed_ho(srslte::as_security_config_t* as_cfg)                                  = 0;
 };
 
 // GW interface for NAS

srsue/hdr/stack/upper/pcsc_usim.h

@@ -84,6 +84,8 @@ public:
   // RRC interface
   void generate_as_keys(uint8_t* k_asme, uint32_t count_ul, srslte::as_security_config_t* sec_cfg);
   void generate_as_keys_ho(uint32_t pci, uint32_t earfcn, int ncc, srslte::as_security_config_t* sec_cfg);
+  void store_keys_before_ho(const srslte::as_security_config_t& as_ctx);
+  void restore_keys_from_failed_ho(srslte::as_security_config_t* as_ctx);
 
 private:
   srslte::log* log = nullptr;
@@ -108,6 +110,11 @@ private:
   uint8_t k_enb_star[KEY_LEN] = {};
   uint8_t auts[AKA_AUTS_LEN]  = {};
 
+  // Helpers to restore security context if HO fails
+  uint8_t                      old_k_enb[32] = {};
+  uint8_t                      old_ncc       = {};
+  srslte::as_security_config_t old_as_ctx    = {};
+
   uint32_t current_ncc = 0;
 
   bool initiated = false;

srsue/hdr/stack/upper/usim.h

@@ -63,6 +63,8 @@ public:
   // RRC interface
   void generate_as_keys(uint8_t* k_asme, uint32_t count_ul, srslte::as_security_config_t* sec_cfg);
   void generate_as_keys_ho(uint32_t pci, uint32_t earfcn, int ncc, srslte::as_security_config_t* sec_cfg);
+  void store_keys_before_ho(const srslte::as_security_config_t& as_ctx);
+  void restore_keys_from_failed_ho(srslte::as_security_config_t* as_ctx);
 
 private:
   auth_result_t gen_auth_res_milenage(uint8_t* rand,
@@ -107,6 +109,11 @@ private:
   uint8_t k_enb[32]         = {};
   uint8_t k_enb_star[32]    = {};
 
+  // Helpers to restore security context if HO fails
+  uint8_t                      old_k_enb[32] = {};
+  uint8_t                      old_ncc       = {};
+  srslte::as_security_config_t old_as_ctx    = {};
+
   uint32_t current_ncc  = 0;
   bool     is_first_ncc = false;
 

srsue/src/stack/rrc/rrc_procedures.cc

@@ -367,8 +367,7 @@ proc_outcome_t rrc::si_acquire_proc::react(si_acq_timer_expired ev)
  *************************************/
 
 rrc::serving_cell_config_proc::serving_cell_config_proc(rrc* parent_) :
-  rrc_ptr(parent_),
-  log_h(srslte::logmap::get("RRC"))
+  rrc_ptr(parent_), log_h(srslte::logmap::get("RRC"))
 {}
 
 /*
@@ -762,8 +761,7 @@ void rrc::plmn_search_proc::then(const srslte::proc_state_t& result) const
  *************************************/
 
 rrc::connection_request_proc::connection_request_proc(rrc* parent_) :
-  rrc_ptr(parent_),
-  log_h(srslte::logmap::get("RRC"))
+  rrc_ptr(parent_), log_h(srslte::logmap::get("RRC"))
 {}
 
 proc_outcome_t rrc::connection_request_proc::init(srslte::establishment_cause_t cause_,
@@ -1195,7 +1193,6 @@ proc_outcome_t rrc::connection_reest_proc::init(asn1::rrc::reest_cause_e cause)
   // configure lower layers to consider the SCell(s), if configured, to be in deactivated state;
   rrc_ptr->phy->set_activation_deactivation_scell(0);
 
-
   // 1> apply the default physical channel configuration as specified in 9.2.4;
   // Note: this is done by the MAC Reset procedure
 
@@ -1503,6 +1500,7 @@ srslte::proc_outcome_t rrc::ho_proc::init(const asn1::rrc::rrc_conn_recfg_s& rrc
     rrc_ptr->apply_rr_config_dedicated(&recfg_r8.rr_cfg_ded, true);
   }
 
+  rrc_ptr->usim->store_keys_before_ho(rrc_ptr->sec_cfg);
   // Security procedure
   int ncc = -1;
   if (recfg_r8.security_cfg_ho_present) {
@@ -1582,7 +1580,7 @@ srslte::proc_outcome_t rrc::ho_proc::react(t304_expiry ev)
   Info("HO preparation timed out. Reverting RRC security config from source cell.\n");
 
   // revert security settings from source cell for reestablishment according to Sec 5.3.7.4
-  rrc_ptr->generate_as_keys();
+  rrc_ptr->usim->restore_keys_from_failed_ho(&rrc_ptr->sec_cfg);
 
   rrc_ptr->pdcp->config_security_all(rrc_ptr->sec_cfg);
 

srsue/src/stack/upper/pcsc_usim.cc

@@ -263,9 +263,7 @@ void pcsc_usim::generate_nas_keys(uint8_t*                    k_asme,
   RRC interface
 *******************************************************************************/
 
-void pcsc_usim::generate_as_keys(uint8_t*                      k_asme,
-                                 uint32_t                      count_ul,
-                                 srslte::as_security_config_t* sec_cfg)
+void pcsc_usim::generate_as_keys(uint8_t* k_asme, uint32_t count_ul, srslte::as_security_config_t* sec_cfg)
 {
   if (!initiated) {
     ERROR("USIM not initiated!\n");
@@ -334,6 +332,24 @@ void pcsc_usim::generate_as_keys_ho(uint32_t pci, uint32_t earfcn, int ncc, srsl
       k_enb, sec_cfg->cipher_algo, sec_cfg->integ_algo, sec_cfg->k_up_enc.data(), sec_cfg->k_up_int.data());
 }
 
+void pcsc_usim::store_keys_before_ho(const srslte::as_security_config_t& as_ctx)
+{
+  INFO("Storing AS Keys pre-handover. NCC=%d\n", current_ncc);
+  old_as_ctx = as_ctx;
+  old_ncc    = current_ncc;
+  memcpy(old_k_enb, k_enb, 32);
+  return;
+}
+
+void pcsc_usim::restore_keys_from_failed_ho(srslte::as_security_config_t* as_ctx)
+{
+  INFO("Restoring Keys from failed handover. NCC=%d\n", old_ncc);
+  *as_ctx     = old_as_ctx;
+  current_ncc = old_ncc;
+  memcpy(k_enb, old_k_enb, 32);
+  return;
+}
+
 /*******************************************************************************
   Helpers
 *******************************************************************************/

srsue/src/stack/upper/usim.cc

@@ -284,6 +284,24 @@ void usim::generate_as_keys_ho(uint32_t pci, uint32_t earfcn, int ncc, srslte::a
   usim_log->info_hex(sec_cfg->k_rrc_int.data(), sec_cfg->k_rrc_int.size(), "HO K_RRC_int");
 }
 
+void usim::store_keys_before_ho(const srslte::as_security_config_t& as_ctx)
+{
+  usim_log->info("Storing AS Keys pre-handover. NCC=%d\n", current_ncc);
+  old_as_ctx = as_ctx;
+  old_ncc    = current_ncc;
+  memcpy(old_k_enb, k_enb, 32);
+  return;
+}
+
+void usim::restore_keys_from_failed_ho(srslte::as_security_config_t* as_ctx)
+{
+  usim_log->info("Restoring Keys from failed handover. NCC=%d\n", old_ncc);
+  *as_ctx     = old_as_ctx;
+  current_ncc = old_ncc;
+  memcpy(k_enb, old_k_enb, 32);
+  return;
+}
+
 /*******************************************************************************
   Helpers
 *******************************************************************************/