From 5e01039d79674171d20c5ea40266635a576eee56 Mon Sep 17 00:00:00 2001 From: Harald Welte Date: Mon, 25 Jan 2021 17:59:06 +0100 Subject: select_best_cipher(): Prefer A5/1 over A5/2 We cannot simply use the highest 'x' in A5/x codecs. For A5/7 through A5/3, larger 'x' means better. But: A5/1 is better than A5/2, so we need to prefer the former over the latter. Change-Id: I399fff8d07d1bfcbc6b385e90914ff6d9e00eb73 Closes: OS#4975 --- src/osmo-bsc/osmo_bsc_bssap.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/src/osmo-bsc/osmo_bsc_bssap.c b/src/osmo-bsc/osmo_bsc_bssap.c index 63dee9e3d..9d7815314 100644 --- a/src/osmo-bsc/osmo_bsc_bssap.c +++ b/src/osmo-bsc/osmo_bsc_bssap.c @@ -402,12 +402,16 @@ int bsc_paging_start(struct bsc_paging_params *params) /* select the best cipher permitted by the intersection of both masks */ static int select_best_cipher(uint8_t msc_mask, uint8_t bsc_mask) { + /* A5/7 ... A5/3: We assume higher is better, + * but: A5/1 is better than A5/2, which is better than A5/0 */ + const uint8_t codec_strength[8] = { 7, 6, 5, 4, 3, 1, 2, 0 }; uint8_t intersection = msc_mask & bsc_mask; int i; - for (i = 7; i >= 0; i--) { - if (intersection & (1 << i)) - return i; + for (i = 0; i < ARRAY_SIZE(codec_strength); i++) { + uint8_t codec = codec_strength[i]; + if (intersection & (1 << codec)) + return codec; } return -1; } -- cgit v1.2.3