Messages in this thread Patch in this message | | | Date | Wed, 13 Feb 2019 23:48:59 +0100 | From | Pavel Machek <> | Subject | [PATCH] pre-shared passcode: secure pairing for "no keyboard, no display" devices |
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Hi!
Currently, "no keyboard, no display" devices can be paired, but pairing is not secure against active attacker.
Can we do better? Not for the first pairing; but for the next ones -- yes, I believe we can.
BLE device in this case has internal storage, and Linux running there. From factory, random 6-digit number is stored in the flash. Legitimate user knows the number, and system is manipulated so that pairing passkey will be this pre-shared passkey. After pairing, user is allowed to change it.
[Or maybe passkey is 000000 from the factory; this is still win for the user, as long as he can change the key to something random in a secure cave.]
Fortunately, kernel support for this is rather easy; patch is attached below.
Does someone see a security issue with proposal above?
What would be suitable interface for setting pre-shared passkey? Module parameter is really easy.
Signed-off-by: Pavel Machek <pavel@denx.de>
diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c index 621146d..7a2b06595 100644 --- a/net/bluetooth/smp.c +++ b/net/bluetooth/smp.c @@ -2674,6 +2674,11 @@ static u8 sc_select_method(struct smp_chan *smp) return method; } +static int preshared_passkey = -1; + +module_param(preshared_passkey, int, 0600); +MODULE_PARM_DESC(preshared_passkey, "Preshared passkey for device w/o keyboard or display"); + static int smp_cmd_public_key(struct l2cap_conn *conn, struct sk_buff *skb) { struct smp_cmd_public_key *key = (void *) skb->data; @@ -2752,9 +2757,11 @@ static int smp_cmd_public_key(struct l2cap_conn *conn, struct sk_buff *skb) set_bit(SMP_FLAG_DEBUG_KEY, &smp->flags); if (smp->method == DSP_PASSKEY) { get_random_bytes(&hcon->passkey_notify, sizeof(hcon->passkey_notify)); + if (preshared_passkey != -1) + hcon->passkey_notify = preshared_passkey; hcon->passkey_notify %= 1000000; hcon->passkey_entered = 0; smp->passkey_round = 0; if (mgmt_user_passkey_notify(hdev, &hcon->dst, hcon->type,
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