diff --git a/src/auc.h b/src/auc.h
index eba9843..6560dde 100644
--- a/src/auc.h
+++ b/src/auc.h
@@ -28,6 +28,7 @@ struct auc_rec {
 	struct llist_head list;
 	struct llist_head hash_list;
 	uint8_t imsi[15+1];
+	long offset_sqn;
 	struct osmo_sub_auth_data auth;
 };
 
diff --git a/src/auc_rec_csv.c b/src/auc_rec_csv.c
index 21a87a8..c5e257b 100644
--- a/src/auc_rec_csv.c
+++ b/src/auc_rec_csv.c
@@ -32,8 +32,8 @@
 2620301,1,000102030405060708090a0b0c0d0e0f,0f0e0d0c0b0a09080706050403020100,0001,32,0
 */
 
-static struct auc_rec *auc_rec_from_csv(void *ctx,
-					     const char *line_orig)
+static struct auc_rec *
+auc_rec_from_csv(void *ctx, const char *line_orig, long offset_nextline)
 {
 	char *line = talloc_strdup(ctx, line_orig);
 	char *tok;
@@ -99,6 +99,13 @@ static struct auc_rec *auc_rec_from_csv(void *ctx,
 		if (!tok)
 			goto ret_free;
 		rec->auth.u.umts.sqn = strtoull(tok, NULL, 10);
+		if (strlen(tok) != 8)
+			printf("SQN must be 8 digits wide in order to support updates\n");
+		else {
+			/* save file offfset for SQN so we can update it */
+			rec->offset_sqn = offset_nextline - (strlen(line_orig) - (tok - line));
+		}
+
 		/* IS_OP */
 		tok = strtok(NULL, ",");
 		if (!tok)
@@ -191,11 +198,14 @@ int auc_storage_read(void *ctx, const char *fname)
 
 	while ((line = fgets(line, 256, file))) {
 		struct auc_rec *rec;
+		long offset_nextline;
 
 		if (line[0] == '#')
 			continue;
 
-		rec = auc_rec_from_csv(ctx, line);
+		offset_nextline = ftell(file);
+
+		rec = auc_rec_from_csv(ctx, line, offset_nextline);
 		if (!rec)
 			continue;
 
diff --git a/src/gen_auc_txt.pl b/src/gen_auc_txt.pl
index 14cae39..62b259a 100755
--- a/src/gen_auc_txt.pl
+++ b/src/gen_auc_txt.pl
@@ -9,5 +9,5 @@ my $COUNT = $ARGV[0];
 my $i;
 
 for ($i = 0; $i < $COUNT; $i++) {
-	printf("90170%010u,5,%032u,%032u,0000,%u,0\n", $i, $i, $i, $i);
+	printf("90170%010u,5,%032u,%032u,0000,%08u,0\n", $i, $i, $i, $i);
 }