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;
+}
+