RE: set PASSKEY to 4 digits

Sigurd — Tue, 25 May 2021 07:36:00 GMT

Hi,

[quote user=""]

We are using a passkey in our application and by default is 6 digits long. I have found in other posts that this is mandatory a cannot be changed.

Is it real?

[/quote]

Yes.

From BLUETOOTH CORE SPECIFICATION Version 5.2 | Vol 3, Part C page 1289 , https://www.bluetooth.com/specifications/specs/core-specification/

For Secure Simple Pairing and Security Manager, the Bluetooth passkey is a 6-
digit numerical value.

In BR/EDR Legacy Pairing it was possible to use a 4-digit PIN, but this is not possible with Bluetooth Low Energy.

From BLUETOOTH CORE SPECIFICATION Version 5.2 | Vol 1, Part A page 271

Secure Simple Pairing has two security goals: protection against passive
eavesdropping and protection against man-in-the-middle (MITM) attacks
(active eavesdropping). It is a goal of Secure Simple Pairing to exceed the
maximum security level provided by the use of a 16 character, alphanumeric,
case-sensitive PIN with BR/EDR Legacy Pairing, which often used a 4-digit
PIN or a fixed PIN of commonly known values significantly limiting the security
on the link.