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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
2025-11-19 15:27:17 +01:00
parent 91e7030cf8
commit 4db49a8767
4 changed files with 177 additions and 50 deletions
Download Patch File Download Diff File Expand all files Collapse all files

19
openair3/SECU/key_nas_deriver.c
View File

@@ -150,8 +150,23 @@ void nr_derive_key(algorithm_type_dist_t alg_type, uint8_t alg_id, const uint8_t
* NOTE: knas is dynamically allocated by the KDF function
*/
/** @brief KgNB derivation (A.9 3GPP TS 33.501) */
void derive_kgnb(uint8_t kamf[32], uint32_t count, uint8_t *kgnb)
/** @brief KgNB derivation function (Annex A.9 3GPP TS 33.501)
*
* Derives KgNB from K_AMF and the uplink NAS COUNT.
* This function is applied when cryptographically protected 5G radio bearers are
* established and when a key change on-the-fly is performed.
*
* KDF input S structure (per Annex A.9):
* - FC = 0x6E
* - P0 = Uplink NAS COUNT (count parameter)
* - L0 = length of uplink NAS COUNT (0x00 0x04)
* - P1 = Access type distinguisher (0x01 for 3GPP access)
* - L1 = length of Access type distinguisher (0x00 0x01)
*
* @param[in] kamf 256-bit K_AMF key (input key KEY to KDF)
* @param[in] count Uplink NAS COUNT value (P0 in KDF input S)
* @param[out] kgnb Derived 256-bit KgNB key */
void derive_kgnb(const uint8_t kamf[32], const uint32_t count, uint8_t *kgnb)
{
/* Compute the KDF input parameter
* S = FC(0x6E) || UL NAS Count || 0x00 0x04 || 0x01 || 0x00 0x01

2
openair3/SECU/key_nas_deriver.h
View File

@@ -16,7 +16,7 @@ typedef enum {
UP_INT_ALG = 0x06
} algorithm_type_dist_t;
void derive_kgnb(uint8_t kamf[32], uint32_t count, uint8_t *kgnb);
void derive_kgnb(const uint8_t kamf[32], const uint32_t count, uint8_t *kgnb);
void derive_keNB(const uint8_t kasme[32], const uint32_t nas_count, uint8_t *keNB);