xref: /nrf52832-nimble/packages/NimBLE-latest/docs/ble_sec.rst (revision 042d53a763ad75cb1465103098bb88c245d95138)
1NimBLE Security
2---------------
3
4The Bluetooth Low Energy security model includes five distinct security
5concepts as listed below. For detailed specifications, see BLUETOOTH
6SPECIFICATION Version 4.2 [Vol 1, Part A].
7
8-  **Pairing**: The process for creating one or more shared secret keys.
9   In LE a single link key is generated by combining contributions from
10   each device into a link key used during pairing.
11
12-  **Bonding**: The act of storing the keys created during pairing for
13   use in subsequent connections in order to form a trusted device pair.
14
15-  **Device authentication**: Verification that the two devices have the
16   same keys (verify device identity)
17
18-  **Encryption**: Keeps message confidential. Encryption in Bluetooth
19   LE uses AES-CCM cryptography and is performed in the *Controller*.
20
21-  **Message integrity**: Protects against message forgeries.
22
23Bluetooth LE uses four association models depending on the I/O
24capabilities of the devices.
25
26-  **Just Works**: designed for scenarios where at least one of the
27   devices does not have a display capable of displaying a six digit
28   number nor does it have a keyboard capable of entering six decimal
29   digits.
30
31-  **Numeric Comparison**: designed for scenarios where both devices are
32   capable of displaying a six digit number and both are capable of
33   having the user enter "yes" or "no". A good example of this model is
34   the cell phone / PC scenario.
35
36-  **Out of Band**: designed for scenarios where an Out of Band
37   mechanism is used to both discover the devices as well as to exchange
38   or transfer cryptographic numbers used in the pairing process.
39
40-  **Passkey Entry**: designed for the scenario where one device has
41   input capability but does not have the capability to display six
42   digits and the other device has output capabilities. A good example
43   of this model is the PC and keyboard scenario.
44
45Key Generation
46~~~~~~~~~~~~~~
47
48Key generation for all purposes in Bluetooth LE is performed by the
49*Host* on each LE device independent of any other LE device.
50
51Privacy Feature
52~~~~~~~~~~~~~~~
53
54Bluetooth LE supports an optional feature during connection mode and
55connection procedures that reduces the ability to track a LE device over
56a period of time by changing the Bluetooth device address on a frequent
57basis.
58
59There are two variants of the privacy feature.
60
61-  In the first variant, private addresses are resolved and generated by
62   the *Host*.
63-  In the second variant, private addresses are resolved and generated
64   by the *Controller* without involving the Host after the Host
65   provides the Controller device identity information. The Host may
66   provide the Controller with a complete resolving list or a subset of
67   the resolving list. Device filtering becomes possible in the second
68   variant when address resolution is performed in the Controller
69   because the peer’s device identity address can be resolved prior to
70   checking whether it is in the white list.
71
72**Note**: When address resolution is performed exclusively in the Host,
73a device may experience increased power consumption because device
74filtering must be disabled. For more details on the privacy feature,
75refer to BLUETOOTH SPECIFICATION Version 4.2 [Vol 3, Part C] (Published
7602 December 2014), Page 592.
77