Wireless Authentication and Encryption

What it is

Wireless authentication decides who may join a network, and encryption protects the data once they have joined.

Radio waves travel through walls, so anyone nearby can capture the frames. Without encryption, the data is readable by everyone in range.

Wi-Fi security has changed over the years. Older methods are broken, and a modern network should use WPA2 or WPA3.

How it works

A security method defines how a client proves its identity and how keys are made for encryption.

Security methods compared

Open networks need no key, and WEP can be cracked in minutes. WPA was a temporary fix for WEP hardware, and WPA2 brought AES.

TKIP versus AES

TKIP is built on the RC4 cipher so that old WEP hardware could run it. It needs extra work for every packet, and on many devices that work falls on the processor. AES with CCMP is accelerated in the radio chip on modern hardware, so it costs little processing.

TKIP also limits the speed. The 802.11n standard does not allow its high throughput rates with TKIP or WEP, so an n or ac client that uses TKIP falls back to legacy rates, 54 Mbps at most. To get n and ac speeds, use WPA2 with AES.

Personal and enterprise

Each method has two modes.

• Personal uses a pre-shared key (PSK). Every user knows the same passphrase.
• Enterprise uses 802.1X and EAP. Each user has their own credentials checked by a RADIUS server. The next page covers it.

A PSK is simple, but if one person leaks the passphrase, you must change it for everyone. A weak passphrase can be guessed offline from a captured handshake.

How keys are made

After authentication, the client and the access point run a four way handshake. It proves that both sides know the key and creates fresh keys for the session.

These keys encrypt unicast traffic for that one client. A separate group key protects broadcast and multicast traffic.

The session keys are different for each client and each session.

WPA3 and SAE

WPA3 personal replaces the PSK handshake with SAE (simultaneous authentication of equals). An attacker who captures the exchange cannot run offline guesses against it the way they can with WPA2.

WPA3 also requires protected management frames. Many networks run a mixed mode so that WPA2 only clients can still connect while newer clients use WPA3.

Protected management frames

Normal management frames, such as deauthentication, are not encrypted. An attacker can forge them and kick clients off.

Protected management frames (PMF, defined by 802.11w) add protection to these frames. On the legacy wireless package the setting is management-protection with the values disabled, allowed and required.

Configuring security

On the legacy wireless package, security lives in a security profile that you attach to the interface.

/interface wireless security-profiles add name=sec1 mode=dynamic-keys authentication-types=wpa2-psk unicast-ciphers=aes-ccm group-ciphers=aes-ccm wpa2-pre-shared-key=StrongPassphrase1
/interface wireless set wlan1 security-profile=sec1

• mode=dynamic-keys gives each client its own keys.
• authentication-types lists the allowed methods.
• unicast-ciphers and group-ciphers choose the encryption, and aes-ccm is the strong option.

On the wifi driver the security is a separate security profile and it can allow WPA2 and WPA3 together.

/interface wifi security add name=sec1 authentication-types=wpa2-psk,wpa3-psk passphrase=StrongPassphrase1

Choosing the right option