support A5/4 in Cipher Mode Command
Related: SYS#5324 Change-Id: I780a739b9bfbefd4f58be051794fe1a491823e67
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@ -32,6 +32,8 @@ struct geran_encr {
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uint8_t alg_id;
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uint8_t key_len;
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uint8_t key[MAX_A5_KEY_LEN];
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bool kc128_present;
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uint8_t kc128[MAX_A5_KEY_LEN];
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};
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enum complete_layer3_type {
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@ -292,6 +292,14 @@ int msc_a_vlr_set_cipher_mode(void *_msc_a, bool umts_aka, bool retrieve_imeisv)
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return msc_a_ran_enc_ciphering(msc_a, umts_aka, retrieve_imeisv);
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}
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static uint8_t filter_a5(uint8_t a5_mask, bool umts_aka)
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{
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/* With GSM AKA: allow A5/0, 1, 3 = 0b00001011 = 0xb.
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* UMTS aka: allow A5/0, 1, 3, 4 = 0b00011011 = 0x1b.
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*/
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return a5_mask & (umts_aka ? 0x1b : 0x0b);
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}
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static int msc_a_ran_enc_ciphering(struct msc_a *msc_a, bool umts_aka, bool retrieve_imeisv)
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{
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struct gsm_network *net;
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@ -321,7 +329,7 @@ static int msc_a_ran_enc_ciphering(struct msc_a *msc_a, bool umts_aka, bool retr
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.geran = {
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.umts_aka = umts_aka,
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.retrieve_imeisv = retrieve_imeisv,
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.a5_encryption_mask = net->a5_encryption_mask,
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.a5_encryption_mask = filter_a5(net->a5_encryption_mask, umts_aka),
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/* for ran_a.c to store the GERAN key that is actually used */
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.chosen_key = &msc_a->geran_encr,
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@ -25,6 +25,7 @@
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#include <osmocom/core/byteswap.h>
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#include <osmocom/crypt/auth.h>
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#include <osmocom/crypt/kdf.h>
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#include <osmocom/gsm/tlv.h>
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#include <osmocom/gsm/gsm0808.h>
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@ -1019,6 +1020,9 @@ static int a5_n_to_gsm0808_chosen_enc_alg(uint8_t *dst, int a5_n)
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case 3:
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*dst = GSM0808_ALG_ID_A5_3;
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return 0;
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case 4:
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*dst = GSM0808_ALG_ID_A5_4;
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return 0;
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default:
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return -ENOTSUP;
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}
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@ -1078,21 +1082,39 @@ static struct msgb *ran_a_make_cipher_mode_command(struct osmo_fsm_inst *fi, con
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/* In case of UMTS AKA, the Kc for ciphering must be derived from the 3G auth
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* tokens. vec->kc was calculated from the GSM algorithm and is not
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* necessarily a match for the UMTS AKA tokens. */
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if (cm->geran.umts_aka)
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if (cm->geran.umts_aka) {
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int i;
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osmo_auth_c3(ei->key, cm->vec->ck, cm->vec->ik);
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else
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for (i = 0; i < ei->perm_algo_len; i++) {
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if (ei->perm_algo[i] != GSM0808_ALG_ID_A5_4)
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continue;
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/* A5/4 is included, so need to generate Kc128 */
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osmo_kdf_kc128(cm->vec->ck, cm->vec->ik, cmc.kc128);
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cmc.kc128_present = true;
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break;
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}
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} else {
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memcpy(ei->key, cm->vec->kc, sizeof(cm->vec->kc));
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}
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ei->key_len = sizeof(cm->vec->kc);
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/* Store chosen GERAN key where the caller asked it to be stored.
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* alg_id remains unknown until we receive a Cipher Mode Complete from the BSC */
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if (cm->geran.chosen_key) {
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*cm->geran.chosen_key = (struct geran_encr){0};
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if (ei->key_len > sizeof(cm->geran.chosen_key->key)) {
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LOG_RAN_A_ENC(fi, LOGL_ERROR, "Chosen key is larger than I can store\n");
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return NULL;
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}
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memcpy(cm->geran.chosen_key->key, ei->key, ei->key_len);
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cm->geran.chosen_key->key_len = ei->key_len;
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if (cmc.kc128_present) {
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memcpy(cm->geran.chosen_key->kc128, cmc.kc128, 16);
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cm->geran.chosen_key->kc128_present = true;
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}
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}
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LOG_RAN_A_ENC(fi, LOGL_DEBUG, "Tx BSSMAP CIPHER MODE COMMAND to BSC, %u ciphers (%s) key %s\n",
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