diff --git a/openbsc/include/openbsc/gsm_data.h b/openbsc/include/openbsc/gsm_data.h
index e012079..3960bbe 100644
--- a/openbsc/include/openbsc/gsm_data.h
+++ b/openbsc/include/openbsc/gsm_data.h
@@ -65,6 +65,7 @@
 enum gsm_hooks {
 	GSM_HOOK_NM_SWLOAD,
 	GSM_HOOK_RR_PAGING,
+	GSM_HOOK_RR_SECURITY,
 };
 
 enum gsm_paging_event {
@@ -104,6 +105,12 @@
 #define msgb_bcid(__x)		OBSC_MSGB_CB(__x)->bssgp_cell_id
 #define msgb_llch(__x)		OBSC_MSGB_CB(__x)->llch
 
+enum gsm_security_event {
+	GSM_SECURITY_NOAVAIL,
+	GSM_SECURITY_AUTH_FAILED,
+	GSM_SECURITY_SUCCEEDED,
+};
+
 struct msgb;
 typedef int gsm_cbfn(unsigned int hooknum,
 		     unsigned int event,
@@ -179,6 +186,15 @@
 	unsigned int waiting_for_imei : 1;
 };
 
+/*
+ * AUTHENTICATION/CIPHERING state
+ */
+struct gsm_security_operation {
+	struct gsm_auth_tuple atuple;
+	gsm_cbfn *cb;
+	void *cb_data;
+};
+
 /* Maximum number of neighbor cells whose average we track */
 #define MAX_NEIGH_MEAS		10
 /* Maximum size of the averaging window for neighbor cells */
@@ -194,6 +210,7 @@
 };
 
 #define MAX_A5_KEY_LEN	(128/8)
+#define A38_COMP128_KEY_LEN	16
 #define RSL_ENC_ALG_A5(x)	(x+1)
 
 /* is the data link established? who established it? */
@@ -223,6 +240,7 @@
 	 * Operations that have a state and might be pending
 	 */
 	struct gsm_loc_updating_operation *loc_operation;
+	struct gsm_security_operation *sec_operation;
 
 	/* use count. how many users use this channel */
 	unsigned int use_count;
diff --git a/openbsc/src/Makefile.am b/openbsc/src/Makefile.am
index d5d0068..03f62ab 100644
--- a/openbsc/src/Makefile.am
+++ b/openbsc/src/Makefile.am
@@ -23,7 +23,7 @@
 libmsc_a_SOURCES = gsm_subscriber.c db.c \
 		mncc.c gsm_04_08.c gsm_04_11.c transaction.c \
 		token_auth.c rrlp.c gsm_04_80.c ussd.c silent_call.c \
-		handover_logic.c handover_decision.c meas_rep.c
+		handover_logic.c handover_decision.c meas_rep.c auth.c
 
 libvty_a_SOURCES = common_vty.c
 
diff --git a/openbsc/src/auth.c b/openbsc/src/auth.c
new file mode 100644
index 0000000..5a54da0
--- /dev/null
+++ b/openbsc/src/auth.c
@@ -0,0 +1,103 @@
+/* Authentication related functions */
+
+/*
+ * (C) 2010 by Sylvain Munaut <tnt@246tNt.com>
+ *
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include <openbsc/db.h>
+#include <openbsc/debug.h>
+#include <openbsc/gsm_data.h>
+
+#include <osmocore/comp128.h>
+
+#include <stdlib.h>
+
+
+static int
+_use_comp128_v1(struct gsm_auth_info *ainfo, struct gsm_auth_tuple *atuple)
+{
+	if (ainfo->a3a8_ki_len != A38_COMP128_KEY_LEN) {
+		DEBUGP(DMM, "Invalid COMP128v1 key (len=%d) %s",
+			ainfo->a3a8_ki_len,
+			hexdump(ainfo->a3a8_ki, ainfo->a3a8_ki_len));
+		return -1;
+	}
+
+	comp128(ainfo->a3a8_ki, atuple->rand, atuple->sres, atuple->kc);
+
+	return 0;
+}
+
+/* Return values 
+ *  -1 -> Internal error
+ *   0 -> Not available
+ *   1 -> Tuple returned, need to do auth, then enable cipher
+ *   2 -> Tuple returned, need to enable cipher
+ */
+int auth_get_tuple_for_subscr(struct gsm_auth_tuple *atuple,
+                              struct gsm_subscriber *subscr, int key_seq)
+{
+	struct gsm_auth_info ainfo;
+	int i, rc;
+
+	/* Get subscriber info (if any) */
+	rc = db_get_authinfo_for_subscr(&ainfo, subscr);
+	if (rc < 0) {
+		DEBUGP(DMM, "No retrievable Ki for subscriber, skipping auth");
+		return rc == -ENOENT ? 0 : -1;
+	}
+
+	/* If possible, re-use the last tuple and skip auth */
+	rc = db_get_lastauthtuple_for_subscr(atuple, subscr);
+	if ((rc == 0) &&
+	    (atuple->key_seq != GSM_KEY_SEQ_INVAL) &&
+	    (atuple->use_count < 3))
+	{
+		atuple->use_count++;
+		db_sync_lastauthtuple_for_subscr(atuple, subscr);
+		return 2;
+	}
+
+	/* Generate a new one */
+	atuple->use_count = 1;
+	atuple->key_seq = (atuple->key_seq + 1) % 7;
+        for (i=0; i<sizeof(atuple->rand); i++)
+                atuple->rand[i] = random() & 0xff;
+
+	switch (ainfo.auth_algo) {
+		case AUTH_ALGO_NONE:
+			return 0;
+
+		case AUTH_ALGO_COMP128v1:
+			if (_use_comp128_v1(&ainfo, atuple))
+				return 0;
+			break;
+
+		default:
+			DEBUGP(DMM, "Unsupported auth type algo_id=%d\n",
+				ainfo.auth_algo);
+			return 0;
+	}
+
+        db_sync_lastauthtuple_for_subscr(atuple, subscr);
+
+	return 1;
+}
+
diff --git a/openbsc/src/gsm_04_08.c b/openbsc/src/gsm_04_08.c
index ed2b4e5..2563158 100644
--- a/openbsc/src/gsm_04_08.c
+++ b/openbsc/src/gsm_04_08.c
@@ -30,6 +30,7 @@
 #include <time.h>
 #include <netinet/in.h>
 
+#include <openbsc/auth.h>
 #include <openbsc/db.h>
 #include <osmocore/msgb.h>
 #include <osmocore/bitvec.h>
@@ -54,6 +55,7 @@
 #include <openbsc/silent_call.h>
 
 void *tall_locop_ctx;
+void *tall_authciphop_ctx;
 
 int gsm0408_loc_upd_acc(struct gsm_lchan *lchan, u_int32_t tmsi);
 static int gsm48_tx_simple(struct gsm_lchan *lchan,
@@ -68,6 +70,91 @@
 
 static u_int32_t new_callref = 0x80000001;
 
+
+static void release_security_operation(struct gsm_subscriber_connection *conn)
+{
+	if (!conn->sec_operation)
+		return;
+
+	talloc_free(conn->sec_operation);
+	conn->sec_operation = NULL;
+	put_subscr_con(conn);
+}
+
+static void allocate_security_operation(struct gsm_subscriber_connection *conn)
+{
+	use_subscr_con(conn)
+
+	conn->sec_operation = talloc_zero(tall_authciphop_ctx,
+	                                  struct gsm_security_operation);
+}
+
+int gsm48_secure_channel(struct gsm_lchan *lchan, int key_seq,
+                         gsm_cbfn *cb, void *cb_data)
+{
+	struct gsm_network *net = lchan->ts->trx->bts->network;
+	struct gsm_subscriber *subscr = lchan->conn.subscr;
+	struct gsm_security_operation *op;
+	struct gsm_auth_tuple atuple;
+	int status = -1, rc;
+
+	/* Check if we _can_ enable encryption. Cases where we can't:
+	 *  - Encryption disabled in config
+	 *  - Channel already secured (nothing to do)
+	 *  - Subscriber equipment doesn't support configured encryption
+	 */
+	if (!net->a5_encryption) {
+		status = GSM_SECURITY_NOAVAIL;
+	} else if (lchan->encr.alg_id > RSL_ENC_ALG_A5(0)) {
+		DEBUGP(DMM, "Requesting to secure an already secure channel");
+		status = GSM_SECURITY_SUCCEEDED;
+	} else if (!ms_cm2_a5n_support(subscr->equipment.classmark2,
+	                               net->a5_encryption)) {
+		DEBUGP(DMM, "Subscriber equipment doesn't support requested encryption");
+		status = GSM_SECURITY_NOAVAIL;
+	}
+
+	/* If not done yet, try to get info for this user */
+	if (status < 0) {
+		rc = auth_get_tuple_for_subscr(&atuple, subscr, key_seq);
+		if (rc <= 0)
+			status = GSM_SECURITY_NOAVAIL;
+	}
+
+	/* Are we done yet ? */
+	if (status >= 0)
+		return cb ?
+			cb(GSM_HOOK_RR_SECURITY, status, NULL, lchan, cb_data) :
+			0;
+
+	/* Start an operation (can't have more than one pending !!!) */
+	if (lchan->conn.sec_operation)
+		return -EBUSY;
+
+	allocate_security_operation(&lchan->conn);
+	op = lchan->conn.sec_operation;
+	op->cb = cb;
+	op->cb_data = cb_data;
+	memcpy(&op->atuple, &atuple, sizeof(struct gsm_auth_tuple));
+
+		/* FIXME: Should start a timer for completion ... */
+
+	/* Then do whatever is needed ... */
+	if (rc == 1) {
+		/* Start authentication */
+		return gsm48_tx_mm_auth_req(lchan, op->atuple.rand, op->atuple.key_seq);
+	} else if (rc == 2) {
+		/* Start ciphering directly */
+		lchan->encr.alg_id = RSL_ENC_ALG_A5(net->a5_encryption);
+		lchan->encr.key_len = 8;
+		memcpy(lchan->encr.key, op->atuple.kc, 8);
+
+		return gsm48_send_rr_ciph_mode(lchan, 0);
+	}
+
+	return -EINVAL; /* not reached */
+}
+
 static int authorize_subscriber(struct gsm_loc_updating_operation *loc,
 				struct gsm_subscriber *subscriber)
 {
@@ -160,6 +247,7 @@
 		return 0;
 
 	release_loc_updating_req(&lchan->conn);
+	release_security_operation(&lchan->conn);
 
 	/* Free all transactions that are associated with the released lchan */
 	/* FIXME: this is not neccessarily the right thing to do, we should
@@ -735,6 +823,43 @@
 	return 0;
 }
 
+/* Chapter 9.2.3: Authentication Response */
+static int gsm48_rx_mm_auth_resp(struct msgb *msg)
+{
+	struct gsm48_hdr *gh = msgb_l3(msg);
+	struct gsm48_auth_resp *ar = (struct gsm48_auth_resp*) gh->data;
+	struct gsm_lchan *lchan = msg->lchan;
+	struct gsm_subscriber_connection *conn = &msg->lchan->conn;
+	struct gsm_network *net = lchan->ts->trx->bts->network;
+
+	DEBUGP(DMM, "MM AUTHENTICATION RESPONSE (sres = %s)\n",
+		hexdump(ar->sres, 4));
+
+	/* Safety check */
+	if (!conn->sec_operation) {
+		DEBUGP(DMM, "No authentication/cipher operation in progress !!!\n");
+		return -EIO;
+	}
+
+	/* Validate SRES */
+	if (memcmp(conn->sec_operation->atuple.sres, ar->sres,4)) {
+		gsm_cbfn *cb = conn->sec_operation->cb;
+		if (cb)
+			cb(GSM_HOOK_RR_SECURITY, GSM_SECURITY_AUTH_FAILED,
+			   NULL, lchan, conn->sec_operation->cb_data);
+
+		release_security_operation(conn);
+		return gsm48_tx_mm_auth_rej(lchan);
+	}
+
+	/* Start ciphering */
+	lchan->encr.alg_id = RSL_ENC_ALG_A5(net->a5_encryption);
+	lchan->encr.key_len = 8;
+	memcpy(msg->lchan->encr.key, conn->sec_operation->atuple.kc, 8);
+
+	return gsm48_send_rr_ciph_mode(msg->lchan, 0);
+}
+
 /* Receive a GSM 04.08 Mobility Management (MM) message */
 static int gsm0408_rcv_mm(struct msgb *msg)
 {
@@ -768,7 +893,7 @@
 		DEBUGP(DMM, "CM REESTABLISH REQUEST: Not implemented\n");
 		break;
 	case GSM48_MT_MM_AUTH_RESP:
-		DEBUGP(DMM, "AUTHENTICATION RESPONSE: Not implemented\n");
+		rc = gsm48_rx_mm_auth_resp(msg);
 		break;
 	default:
 		LOGP(DMM, LOGL_NOTICE, "Unknown GSM 04.08 MM msg type 0x%02x\n",
@@ -910,6 +1035,37 @@
 	return db_apdu_blob_store(msg->lchan->conn.subscr, apdu_id_flags, apdu_len, apdu_data);
 }
 
+/* Chapter 9.1.10 Ciphering Mode Complete */
+static int gsm48_rx_rr_ciph_m_compl(struct msgb *msg)
+{
+	struct gsm_lchan *lchan = msg->lchan;
+	struct gsm_subscriber_connection *conn = &lchan->conn;
+	gsm_cbfn *cb;
+	int rc = 0;
+
+	DEBUGP(DRR, "CIPHERING MODE COMPLETE\n");
+
+	/* Safety check */
+	if (!conn->sec_operation) {
+		DEBUGP(DRR, "No authentication/cipher operation in progress !!!\n");
+		return -EIO;
+	}
+
+	/* FIXME: check for MI (if any) */
+
+	/* Call back whatever was in progress (if anything) ... */
+	cb = conn->sec_operation->cb;
+	if (cb) {
+		rc = cb(GSM_HOOK_RR_SECURITY, GSM_SECURITY_SUCCEEDED,
+			NULL, lchan, conn->sec_operation->cb_data);
+	}
+
+	/* Complete the operation */
+	release_security_operation(conn);
+
+	return rc;
+}
+
 /* Chapter 9.1.16 Handover complete */
 static int gsm48_rx_rr_ho_compl(struct msgb *msg)
 {
@@ -967,8 +1123,7 @@
 		rc = gsm48_rx_rr_app_info(msg);
 		break;
 	case GSM48_MT_RR_CIPH_M_COMPL:
-		DEBUGP(DRR, "CIPHERING MODE COMPLETE\n");
-		/* FIXME: check for MI (if any) */
+		rc = gsm48_rx_rr_ciph_m_compl(msg);
 		break;
 	case GSM48_MT_RR_HANDO_COMPL:
 		rc = gsm48_rx_rr_ho_compl(msg);
diff --git a/openbsc/src/talloc_ctx.c b/openbsc/src/talloc_ctx.c
index 4b373b4..8e7ec23 100644
--- a/openbsc/src/talloc_ctx.c
+++ b/openbsc/src/talloc_ctx.c
@@ -4,6 +4,7 @@
 extern void *tall_msgb_ctx;
 extern void *tall_fle_ctx;
 extern void *tall_locop_ctx;
+extern void *tall_authciphop_ctx;
 extern void *tall_gsms_ctx;
 extern void *tall_subscr_ctx;
 extern void *tall_sub_req_ctx;
@@ -22,6 +23,7 @@
 	tall_fle_ctx = talloc_named_const(tall_bsc_ctx, 0,
 					  "bs11_file_list_entry");
 	tall_locop_ctx = talloc_named_const(tall_bsc_ctx, 0, "loc_updating_oper");
+	tall_authciphop_ctx = talloc_named_const(tall_bsc_ctx, 0, "auth_ciph_oper");
 	tall_gsms_ctx = talloc_named_const(tall_bsc_ctx, 0, "sms");
 	tall_subscr_ctx = talloc_named_const(tall_bsc_ctx, 0, "subscriber");
 	tall_sub_req_ctx = talloc_named_const(tall_bsc_ctx, 0, "subscr_request");