ciphering: Handle ciphering support for A5/3 correctly

This was found and debugged by Sylvain. The BTS will always support
A5/0 so we do not keep track of that, the first bit of the flags is
used for A5/1, second for A5/2... but for RSL there is an offset to
go from RSL to A5(x). Add a testcase and change the code.

1 files changed, 15 insertions, 0 deletions

diff --git a/src/common/bts.c b/src/common/bts.c
index 1375f4a5..8f6dc694 100644
--- a/src/common/bts.c
+++ b/src/common/bts.c
@@ -213,3 +213,18 @@ struct msgb *bts_agch_dequeue(struct gsm_bts *bts)
 
 	return msgb_dequeue(&btsb->agch_queue);
 }
+
+int bts_supports_cipher(struct gsm_bts_role_bts *bts, int rsl_cipher)
+{
+	int sup;
+
+	if (rsl_cipher < 1 || rsl_cipher > 8)
+		return -ENOTSUP;
+
+	/* No encryption is always supported */
+	if (rsl_cipher == 1)
+		return 1;
+
+	sup =  (1 << (rsl_cipher - 2)) & bts->support.ciphers;
+	return sup > 0;
+}