android - What is the difference between pairing with a bluetooth device vs connecting to a bluetooth device?

Question

I am working on a Flutter app that connects to a bluetooth IOT device. I am using the flutter_blue library. This library allows for the scanning of nearby bluetooth devices. Based on that scan you can "connect" to a device. There is no concept of pairing to a device.

From my previous experience using bluetooth on my phone (when connecting to my car and my bluetooth speaker), I have to pair the device at the Android OS.

I am curious, from a high level, what are the differences between pairing a device vs connecting to a device. In addition, more specifically, what is the difference between pairing a device within the OS, vs scanning and connecting to the device from an app?

question from:https://stackoverflow.com/questions/65835536/what-is-the-difference-between-pairing-with-a-bluetooth-device-vs-connecting-to

Answer 1

According to the Bluetooth Core Specification Version 5.2 | Vol. 1, Part A, Chapter 5.1 pairing is defined as

the process for creating one or more shared secret keys

The keys demselfes are not shared but established using a procedure called Diffie-Hellman key exchange. This means that pairing is only necessary if a connection is encrypted. If you connect to a device that requires security measures on one of its characteristics Android will prompt the user of your app with a pairing request automatically.

Another term you might have heard is bonding, which is defined as:

the act of storing the keys created during pairing for use in subsequent connections in order to form a trusted device pair

Bonding allows a reconnection of your devices without another pairing process since the keys have been established before.

When using Bluetooth Low Energy (BLE) pairing a manually Device within the OS is not needed. You can always scan for a device that advertises its presence. As I said before: Pairing is handled by the OS automatically if needed.