Private PSK (PPSK) Overview

Private Pre Shared Key (PPSK) is a function that allows multiple WiFi keys to be used for a single SSID.
It can be compared to a door that can be unlocked by people with different keys to gain access to a building.
This is in contrast to a door where everyone has the same key to unlock it and gain access to a building.
The advantage of using different keys is the ease of management.
Suppose you have a small office setup where an employee leave the company on a bad foot and you want to make sure they do not get access to the WiFi network.
Without the support of PPSK you need to:
- Change the shared key on the access point(s).
- Inform all employees that the WiFi key has changed and hopefully they will be smart enough to update any devices that are configured to connect to the office WiFi network.
- Another place where you need to update the WiFi key is any peripherals that are connected to the network, including printers, scanners and cameras.
With PPSK support, you simply revoke the PPSK of employees.
Also using one SSID with multiple keys improves bandwidth utilisation and provides a simplified user experience.

History

The PPSK function has been around for a long time.
Aerohive (now Extreme Networks) was probably the first vendor to come up with this feature more than 8 years ago.
Most enterprise vendors have caught up and added the feature, but some have ignored the request for this feature for years. (Here you can see a post where the Ubiquity community asked for this feature 7 years ago)
Ubiquity finally implemented the feature in Unifi in 2023.
This was probably because TP-Link's Omada already included the feature and some of the Ubiquity customers who wanted the feature then opted for Omada.
However, the Ubiquity implementation does not include a RADIUS option, whereas the Omada implementation does.
Some people think Omada is a copy of Unifi. With PPSK, we can definitely say that Omada took the initiative before Unifi.
Each vendor has its own unique implementation and sometimes its own terminology.
- Cisco calls it Identity PSK.
- Aruba calls it Multiple Pre-Shared Key (MPSK).
- Ruckus calls it Dynamic PSK.
Some of the names and technologies are trademarked and protected.
Under the hood, however, most providers that have recently added the PPSK function use the hostapd programme.
hostapd is an open source authenticator for WiFi APs.
This feature offers two main functions.
- The ability for each device that connects to a single SSID to have a unique WPA2 shared key.
- The ability for each device to be assigned to a predefined VLAN after authentication.

WPA2 Enterprise is definitely more secure, but there are two problems that prevent most people from implementing it.
The certificate management. The Certificate Authority (CA) certificate must be installed on the client that is connecting.
Not all WiFi devices support this.
- Many IOT devices do not support WPA2-Enterprise
- Many printers and WiFi cameras do not support WPA2-Enterprise.