support A5/4 in Cipher Mode Command

Related: SYS#5324
Change-Id: I780a739b9bfbefd4f58be051794fe1a491823e67
changes/64/24764/2
Neels Hofmeyr 2 years ago
parent a7f8020bfa
commit 6ce2edcac1
  1. 2
      include/osmocom/msc/msc_common.h
  2. 10
      src/libmsc/msc_a.c
  3. 26
      src/libmsc/ran_msg_a.c

@ -32,6 +32,8 @@ struct geran_encr {
uint8_t alg_id;
uint8_t key_len;
uint8_t key[MAX_A5_KEY_LEN];
bool kc128_present;
uint8_t kc128[MAX_A5_KEY_LEN];
};
enum complete_layer3_type {

@ -292,6 +292,14 @@ int msc_a_vlr_set_cipher_mode(void *_msc_a, bool umts_aka, bool retrieve_imeisv)
return msc_a_ran_enc_ciphering(msc_a, umts_aka, retrieve_imeisv);
}
static uint8_t filter_a5(uint8_t a5_mask, bool umts_aka)
{
/* With GSM AKA: allow A5/0, 1, 3 = 0b00001011 = 0xb.
* UMTS aka: allow A5/0, 1, 3, 4 = 0b00011011 = 0x1b.
*/
return a5_mask & (umts_aka ? 0x1b : 0x0b);
}
static int msc_a_ran_enc_ciphering(struct msc_a *msc_a, bool umts_aka, bool retrieve_imeisv)
{
struct gsm_network *net;
@ -321,7 +329,7 @@ static int msc_a_ran_enc_ciphering(struct msc_a *msc_a, bool umts_aka, bool retr
.geran = {
.umts_aka = umts_aka,
.retrieve_imeisv = retrieve_imeisv,
.a5_encryption_mask = net->a5_encryption_mask,
.a5_encryption_mask = filter_a5(net->a5_encryption_mask, umts_aka),
/* for ran_a.c to store the GERAN key that is actually used */
.chosen_key = &msc_a->geran_encr,

@ -25,6 +25,7 @@
#include <osmocom/core/byteswap.h>
#include <osmocom/crypt/auth.h>
#include <osmocom/crypt/kdf.h>
#include <osmocom/gsm/tlv.h>
#include <osmocom/gsm/gsm0808.h>
@ -1019,6 +1020,9 @@ static int a5_n_to_gsm0808_chosen_enc_alg(uint8_t *dst, int a5_n)
case 3:
*dst = GSM0808_ALG_ID_A5_3;
return 0;
case 4:
*dst = GSM0808_ALG_ID_A5_4;
return 0;
default:
return -ENOTSUP;
}
@ -1078,21 +1082,39 @@ static struct msgb *ran_a_make_cipher_mode_command(struct osmo_fsm_inst *fi, con
/* In case of UMTS AKA, the Kc for ciphering must be derived from the 3G auth
* tokens. vec->kc was calculated from the GSM algorithm and is not
* necessarily a match for the UMTS AKA tokens. */
if (cm->geran.umts_aka)
if (cm->geran.umts_aka) {
int i;
osmo_auth_c3(ei->key, cm->vec->ck, cm->vec->ik);
else
for (i = 0; i < ei->perm_algo_len; i++) {
if (ei->perm_algo[i] != GSM0808_ALG_ID_A5_4)
continue;
/* A5/4 is included, so need to generate Kc128 */
osmo_kdf_kc128(cm->vec->ck, cm->vec->ik, cmc.kc128);
cmc.kc128_present = true;
break;
}
} else {
memcpy(ei->key, cm->vec->kc, sizeof(cm->vec->kc));
}
ei->key_len = sizeof(cm->vec->kc);
/* Store chosen GERAN key where the caller asked it to be stored.
* alg_id remains unknown until we receive a Cipher Mode Complete from the BSC */
if (cm->geran.chosen_key) {
*cm->geran.chosen_key = (struct geran_encr){0};
if (ei->key_len > sizeof(cm->geran.chosen_key->key)) {
LOG_RAN_A_ENC(fi, LOGL_ERROR, "Chosen key is larger than I can store\n");
return NULL;
}
memcpy(cm->geran.chosen_key->key, ei->key, ei->key_len);
cm->geran.chosen_key->key_len = ei->key_len;
if (cmc.kc128_present) {
memcpy(cm->geran.chosen_key->kc128, cmc.kc128, 16);
cm->geran.chosen_key->kc128_present = true;
}
}
LOG_RAN_A_ENC(fi, LOGL_DEBUG, "Tx BSSMAP CIPHER MODE COMMAND to BSC, %u ciphers (%s) key %s\n",

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