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RRC: Implement proper NH chain synchronization for RRC Reestablishment

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Refactor key derivation logic to properly handle Next Hop (NH) chain
synchronization according to 3GPP TS 33.501 specifications for both
RRC Reestablishment and Master Key Update procedures.

Changes in rrc_gNB.c:
- Clarify key derivation in rrc_gNB_generate_RRCReestablishment by
  explicitly selecting base key (NH or KgNB) based on nh_ncc value
- Add comment explaining vertical vs horizontal derivation logic

Changes in rrc_UE.c:
- Add nr_sync_nh_chain(): Common helper to synchronize NH parameter
  chain per TS 33.501 Annex A.10, supporting both Master Key Update
  and RRC Reestablishment procedures
- Add nr_derive_kgnb_horizontal(): Derive KNG-RAN* from current KgNB
  when NCC values match (horizontal derivation per TS 33.501 A.11/A.12)
- Add nr_derive_kgnb_vertical(): Derive KNG-RAN* from synchronized NH
  after NH chain sync (vertical derivation per TS 33.501 A.11/A.12)
- Add nr_update_kgnb_from_ncc(): Unified function implementing TS 33.501
  6.9.2.3.4 logic for updating KgNB based on received nextHopChainingCount
- Refactor as_security_key_update(): Use new nr_update_kgnb_from_ncc()
  helper function for cleaner, more maintainable code
- Fix nr_rrc_ue_process_rrcReestablishment(): Properly handle received
  nextHopChainingCount and update KgNB using unified helper function
- Add debug logging for key derivation process

Key NAS deriver utils:
- update derive_kgnb documentation and protect input keys with const attribute
This commit is contained in:
Guido Casati
2025-12-19 17:14:23 +01:00
parent 91e7030cf8
commit 4db49a8767
4 changed files with 177 additions and 50 deletions
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openair2/RRC/NR/rrc_gNB.c
+4 -1
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@@ -1092,7 +1092,10 @@ static void rrc_gNB_generate_RRCReestablishment(rrc_gNB_ue_context_t *ue_context
const f1ap_served_cell_info_t *cell_info = &du->setup_req->cell[0].info;
uint32_t ssb_arfcn = get_ssb_arfcn(du);
LOG_I(NR_RRC, "Reestablishment update key pci=%d, earfcn_dl=%u\n", cell_info->nr_pci, ssb_arfcn);
nr_derive_key_ng_ran_star(cell_info->nr_pci, ssb_arfcn, ue_p->nh_ncc > 0 ? ue_p->nh : ue_p->kgnb, ue_p->kgnb);
/* Derive KgNB* using NH if nh_ncc > 0 (vertical derivation), else use KgNB (horizontal derivation) */
const uint8_t *base_key = ue_p->nh_ncc > 0 ? ue_p->nh : ue_p->kgnb;
nr_derive_key_ng_ran_star(cell_info->nr_pci, ssb_arfcn, base_key, ue_p->kgnb);
int size = do_RRCReestablishment(ue_context_pP->ue_context.nh_ncc, buffer, NR_RRC_BUF_SIZE, xid);
LOG_A(NR_RRC, "Send RRCReestablishment [%d bytes] to RNTI %04x\n", size, ue_p->rnti);