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Harald Welte gerrit-no-reply at lists.osmocom.org
Review at https://gerrit.osmocom.org/6812
trxcon/scheduler: implement A5/X ciphering support
This change implements the A5/X ciphering support transparently
for the logical channel handlers. In other words, a DL burst is
deciphered before being passed to a handler, and an UL burst is
ciphered before being sent to transceiver.
The implementation mostly relays on the libosmocore's A5 API.
Change-Id: Ib53418d8c0f394fdece09cf5cc240887cb0bb5af
---
M src/host/trxcon/l1ctl.c
M src/host/trxcon/sched_trx.c
M src/host/trxcon/sched_trx.h
3 files changed, 125 insertions(+), 3 deletions(-)
git pull ssh://gerrit.osmocom.org:29418/osmocom-bb refs/changes/12/6812/1
diff --git a/src/host/trxcon/l1ctl.c b/src/host/trxcon/l1ctl.c
index a11e792..070ee56 100644
--- a/src/host/trxcon/l1ctl.c
+++ b/src/host/trxcon/l1ctl.c
@@ -731,6 +731,49 @@
return 0;
}
+static int l1ctl_rx_crypto_req(struct l1ctl_link *l1l, struct msgb *msg)
+{
+ struct l1ctl_crypto_req *req;
+ struct l1ctl_info_ul *ul;
+ struct trx_ts *ts;
+ uint8_t tn;
+ int rc = 0;
+
+ ul = (struct l1ctl_info_ul *) msg->l1h;
+ req = (struct l1ctl_crypto_req *) ul->payload;
+
+ LOGP(DL1C, LOGL_NOTICE, "L1CTL_CRYPTO_REQ (algo=A5/%u, key_len=%u)\n",
+ req->algo, req->key_len);
+
+ /* Determine TS index */
+ tn = ul->chan_nr & 0x7;
+ if (tn > 7) {
+ LOGP(DL1C, LOGL_ERROR, "Incorrect TS index %u\n", tn);
+ rc = -EINVAL;
+ goto exit;
+ }
+
+ /* Make sure that required TS is allocated and configured */
+ ts = l1l->trx->ts_list[tn];
+ if (ts == NULL || ts->mf_layout == NULL) {
+ LOGP(DL1C, LOGL_ERROR, "TS %u is not configured\n", tn);
+ rc = -EINVAL;
+ goto exit;
+ }
+
+ /* Poke scheduler */
+ rc = sched_trx_start_ciphering(ts, req->algo, req->key, req->key_len);
+ if (rc) {
+ LOGP(DL1C, LOGL_ERROR, "Couldn't configure ciphering\n");
+ rc = -EINVAL;
+ goto exit;
+ }
+
+exit:
+ msgb_free(msg);
+ return rc;
+}
+
int l1ctl_rx_cb(struct l1ctl_link *l1l, struct msgb *msg)
{
struct l1ctl_hdr *l1h;
@@ -763,6 +806,8 @@
return l1ctl_rx_param_req(l1l, msg);
case L1CTL_TCH_MODE_REQ:
return l1ctl_rx_tch_mode_req(l1l, msg);
+ case L1CTL_CRYPTO_REQ:
+ return l1ctl_rx_crypto_req(l1l, msg);
default:
LOGP(DL1C, LOGL_ERROR, "Unknown MSG: %u\n", l1h->msg_type);
msgb_free(msg);
diff --git a/src/host/trxcon/sched_trx.c b/src/host/trxcon/sched_trx.c
index fba9ee4..120098b 100644
--- a/src/host/trxcon/sched_trx.c
+++ b/src/host/trxcon/sched_trx.c
@@ -27,6 +27,7 @@
#include <string.h>
#include <talloc.h>
+#include <osmocom/gsm/a5.h>
#include <osmocom/core/bits.h>
#include <osmocom/core/msgb.h>
#include <osmocom/core/logging.h>
@@ -292,6 +293,37 @@
return 0;
}
+int sched_trx_start_ciphering(struct trx_ts *ts, uint8_t algo,
+ uint8_t *key, uint8_t key_len)
+{
+ struct trx_lchan_state *state;
+ size_t len;
+ int i;
+
+ /* Prevent NULL-pointer deference */
+ if (!ts)
+ return -EINVAL;
+
+ /* Make sure we can store this key */
+ if (key_len > MAX_A5_KEY_LEN)
+ return -ERANGE;
+
+ /* Iterate over all allocated logical channels */
+ len = talloc_array_length(ts->lchans);
+ for (i = 0; i < len; i++) {
+ /* Set key length and algorithm */
+ state = ts->lchans + i;
+ state->a5.key_len = key_len;
+ state->a5.algo = algo;
+
+ /* Copy requested key */
+ if (key_len)
+ memcpy(state->a5.key, key, key_len);
+ }
+
+ return 0;
+}
+
struct trx_lchan_state *sched_trx_find_lchan(struct trx_ts *ts,
enum trx_lchan_type chan)
{
@@ -396,6 +428,9 @@
talloc_free(lchan->rx_bursts);
talloc_free(lchan->tx_bursts);
+ /* Reset ciphering state */
+ memset(&lchan->a5, 0x00, sizeof(lchan->a5));
+
/* Forget the current prim */
sched_prim_drop(lchan);
@@ -456,6 +491,40 @@
return TRXC_IDLE;
}
+static void sched_trx_a5_burst_dec(struct trx_lchan_state *lchan,
+ uint32_t fn, sbit_t *burst)
+{
+ ubit_t ks[114];
+ int i;
+
+ /* Generate keystream for a DL burst */
+ osmo_a5(lchan->a5.algo, lchan->a5.key, fn, ks, NULL);
+
+ /* Apply keystream over ciphertext */
+ for (i = 0; i < 57; i++) {
+ if (ks[i])
+ burst[i + 3] *= -1;
+ if (ks[i + 57])
+ burst[i + 88] *= -1;
+ }
+}
+
+static void sched_trx_a5_burst_enc(struct trx_lchan_state *lchan,
+ uint32_t fn, ubit_t *burst)
+{
+ ubit_t ks[114];
+ int i;
+
+ /* Generate keystream for an UL burst */
+ osmo_a5(lchan->a5.algo, lchan->a5.key, fn, NULL, ks);
+
+ /* Apply keystream over plaintext */
+ for (i = 0; i < 57; i++) {
+ burst[i + 3] ^= ks[i];
+ burst[i + 88] ^= ks[i + 57];
+ }
+}
+
int sched_trx_handle_rx_burst(struct trx_instance *trx, uint8_t tn,
uint32_t burst_fn, sbit_t *bits, uint16_t nbits, int8_t rssi, float toa)
{
@@ -512,9 +581,13 @@
if (!lchan->active)
goto next_frame;
- /* Put burst to handler */
+ /* Reached current fn */
if (fn == burst_fn) {
- /* TODO: decrypt if required */
+ /* Perform A5/X decryption if required */
+ if (lchan->a5.algo)
+ sched_trx_a5_burst_dec(lchan, fn, bits);
+
+ /* Put burst to handler */
handler(trx, ts, lchan, fn, bid, bits, rssi, toa);
}
@@ -538,7 +611,9 @@
{
int rc;
- /* TODO: perform A5/X burst encryption if required */
+ /* Perform A5/X burst encryption if required */
+ if (lchan->a5.algo)
+ sched_trx_a5_burst_enc(lchan, fn, bits);
/* Forward burst to transceiver */
rc = trx_if_tx_burst(trx, ts->index, fn, trx->tx_power, bits);
diff --git a/src/host/trxcon/sched_trx.h b/src/host/trxcon/sched_trx.h
index 54dbc85..504054a 100644
--- a/src/host/trxcon/sched_trx.h
+++ b/src/host/trxcon/sched_trx.h
@@ -253,6 +253,8 @@
int sched_trx_reset_ts(struct trx_instance *trx, int tn);
int sched_trx_configure_ts(struct trx_instance *trx, int tn,
enum gsm_phys_chan_config config);
+int sched_trx_start_ciphering(struct trx_ts *ts, uint8_t algo,
+ uint8_t *key, uint8_t key_len);
/* Logical channel management functions */
enum gsm_phys_chan_config sched_trx_chan_nr2pchan_config(uint8_t chan_nr);
--
To view, visit https://gerrit.osmocom.org/6812
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Gerrit-MessageType: newchange
Gerrit-Change-Id: Ib53418d8c0f394fdece09cf5cc240887cb0bb5af
Gerrit-PatchSet: 1
Gerrit-Project: osmocom-bb
Gerrit-Branch: master
Gerrit-Owner: Harald Welte <laforge at gnumonks.org>