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sm: move sm_ctkd_from_le up

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Matthias Ringwald 2021-05-06 16:06:24 +02:00
parent 79b2612de5
commit bbd73538bb
1 changed files with 31 additions and 30 deletions
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61
src/ble/sm.c
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@ -2389,6 +2389,37 @@ static void sm_run_distribute_keys(sm_connection_t * connection){
btstack_assert(false);
}
static bool sm_ctkd_from_le(sm_connection_t *sm_connection) {
#ifdef ENABLE_CROSS_TRANSPORT_KEY_DERIVATION
// requirements to derive link key from LE:
// - use secure connections
if (setup->sm_use_secure_connections == 0) return false;
// - bonding needs to be enabled:
bool bonding_enabled = (sm_pairing_packet_get_auth_req(setup->sm_m_preq) & sm_pairing_packet_get_auth_req(setup->sm_s_pres) & SM_AUTHREQ_BONDING ) != 0u;
if (!bonding_enabled) return false;
// - need identity address / public addr
bool have_identity_address_info = ((setup->sm_key_distribution_received_set & SM_KEYDIST_FLAG_IDENTITY_ADDRESS_INFORMATION) != 0) || (setup->sm_peer_addr_type == 0);
if (!have_identity_address_info) return false;
// - there is no stored BR/EDR link key or the derived key has at least the same level of authentication (bail if stored key has higher authentication)
// this requirement is motivated by BLURtooth paper. The paper recommends to not overwrite keys at all.
// If SC is authenticated, we consider it safe to overwrite a stored key.
// If stored link key is not authenticated, it could already be compromised by a MITM attack. Allowing overwrite by unauthenticated derived key does not make it worse.
uint8_t link_key[16];
link_key_type_t link_key_type;
bool have_link_key = gap_get_link_key_for_bd_addr(setup->sm_peer_address, link_key, &link_key_type);
bool link_key_authenticated = gap_authenticated_for_link_key_type(link_key_type) != 0;
bool derived_key_authenticated = sm_connection->sm_connection_authenticated != 0;
if (have_link_key && link_key_authenticated && !derived_key_authenticated) {
return false;
}
// get started (all of the above are true)
return true;
#else
UNUSED(sm_connection);
return false;
#endif
}
static void sm_run(void){
// assert that stack has already bootet
@ -3128,36 +3159,6 @@ static void sm_handle_encryption_result_enc_ph3_ltk(void *arg){
sm_aes128_state = SM_AES128_ACTIVE;
btstack_crypto_aes128_encrypt(&sm_crypto_aes128_request, sm_persistent_er, sm_aes128_plaintext, setup->sm_local_csrk, sm_handle_encryption_result_enc_csrk, (void *)(uintptr_t) connection->sm_handle);
}
static bool sm_ctkd_from_le(sm_connection_t *sm_connection) {
#ifdef ENABLE_CROSS_TRANSPORT_KEY_DERIVATION
// requirements to derive link key from LE:
// - use secure connections
if (setup->sm_use_secure_connections == 0) return false;
// - bonding needs to be enabled:
bool bonding_enabled = (sm_pairing_packet_get_auth_req(setup->sm_m_preq) & sm_pairing_packet_get_auth_req(setup->sm_s_pres) & SM_AUTHREQ_BONDING ) != 0u;
if (!bonding_enabled) return false;
// - need identity address / public addr
bool have_identity_address_info = ((setup->sm_key_distribution_received_set & SM_KEYDIST_FLAG_IDENTITY_ADDRESS_INFORMATION) != 0) || (setup->sm_peer_addr_type == 0);
if (!have_identity_address_info) return false;
// - there is no stored BR/EDR link key or the derived key has at least the same level of authentication (bail if stored key has higher authentication)
// this requirement is motivated by BLURtooth paper. The paper recommends to not overwrite keys at all.
// If SC is authenticated, we consider it safe to overwrite a stored key.
// If stored link key is not authenticated, it could already be compromised by a MITM attack. Allowing overwrite by unauthenticated derived key does not make it worse.
uint8_t link_key[16];
link_key_type_t link_key_type;
bool have_link_key = gap_get_link_key_for_bd_addr(setup->sm_peer_address, link_key, &link_key_type);
bool link_key_authenticated = gap_authenticated_for_link_key_type(link_key_type) != 0;
bool derived_key_authenticated = sm_connection->sm_connection_authenticated != 0;
if (have_link_key && link_key_authenticated && !derived_key_authenticated) {
return false;
}
// get started (all of the above are true)
return true;
#else
UNUSED(sm_connection);
return false;
#endif
}
static void sm_handle_encryption_result_enc_csrk(void *arg){
hci_con_handle_t con_handle = (hci_con_handle_t) (uintptr_t) arg;