What is the difference between Bluetooth LE Secure Connections LE security mode 1 and level 3 and 4?

Stackoverflow Link

Question

I would like to know what are the differences between Secure Simple Pairing and Secure Connections in Bluetooth v4.2.

Between BR/EDR legacy, BR/EDR, LE, LE legacy, I don't get it.

Answer

Most answers to your questions are given in the spec Bluetooth Core, VOL1.PartA.5

---

Timeline

The following suites exist:

BR/EDR

• Prior to version 2.1 => BR/EDR legacy
• Version 2.1 => BR/EDR (uses Secure Simple Pairing)
• Version 4.2 => BR/EDR (uses Secure Connections)

LE

• Version 4.0 and 4.1 => LE legacy (uses Secure Simple Pairing)
• Version 4.2 => LE (uses Secure Connections)

---

Legacy

It all started with the initial security algorithms (BR/EDR legacy) for the following security features:

• pairing
• bonding
• device authentication
• message encryption
• message integrity

The algorithms used in BR/EDR legacy were not FIPS approved.

Secure Simple Pairing

This was introduced in version 2.1. Secure Simple Pairing uses FIPS-approved algorithms for pairing and message integrity and so in essence it upgraded the security of BR/EDR legacy, which is why we call this new one BR/EDR security.

Version 4.0 ported the exact same security model as BR/EDR to Low Energy (LE), with the following exceptions:

• no Numeric Comparison equivalent
• Just Works and Passkey Entry do not provide passive eavesdropping protection, because ECDH is not used in LE 4.0.

Secure Connections

In version 4.1, the Secure Connections feature was added to BR/EDR. This was an upgrade to the existing Secure Simple Pairing algorithms for pairing, device authentication, and message integrity. See table for a comparison with the Simple Pairing method for BR/EDR (not LE!):

BR/EDR Algorithms; Vol 2, Part H

Version 4.2 then upgraded LE as well. One of the main improvements was the adoption of ECDH for pairing. It also modified the Numeric Comparison association model to be used on Bluetooth LE. LE pairing used in 4.0 and 4.1 is since then referred to as LE Legacy. LE Secure Connections and BR/EDR Secure Connections are functionally equal.

One last word on the association methods

• Numeric Comparison protects against passive and active attacks;
• Just works protects against passive attacks IF ECDH is used, and never protects against active attacks;
• Passkey entry protects against passive attacks IF ECDH is used, and should protect against an active MITM attack (although there are some doubts about that, e.g. Padovan .
• Out Of Band security depends on the OOB method that is used.