WPA

Introduction

WPA is the second generation of wireless encryption, after WEP. WPA and WPA2 are similar and either/both of them will be referred to just as WPA in the discussion here.

At first blush, WPA is just an alphabet soup of options. They describe two basic aspects of encryption: what encryption method to use, and what key management method to use. One of the key management methods, EAP, has several options.

WEP is easy to deploy but has been widely known for many years to be easily broken. Many of your customers will know that WEP is breakable. There are plug-and-play kits for doing so, accompanied by online reviews, tutorials, CDs, and so on. See [1], [2], or [3].

The simplest way to fully secure a wireless link is to use PSK, CCMP, and a strong password, as described below.

Encryption

WPA supports two methods for encrypting transmitted data: TKIP and CCMP. CCMP is based on the AES standard and is sometimes referred to as AES-CCMP or just AES.

TKIP was included in the WPA standard mainly due to backward compatibility considerations with WEP. It has been shown to have a weakness when used with PSK key management (see below) that allows an attacker to spoof small packets with well-known contents such as ARP or QoS packets. There is no known TKIP vulnerability that leads to key compromise.

CCMP is the method of choice with WPA. Is it built around the AES methods which have been declared suitable for protecting U.S. Government classified information. CCMP is considered fully secure, with no known vulnerabilities. Most laptops now support WPA, but some support only TKIP, so if you are serving the general public, you may need to use TKIP.

Key management

WPA supports two approaches to key management: PSK and EAP. EAP has numerous variations.

PSK (pre-shared key) follows the familiar practice of statically configuring partners with matching passwords. PSK should ideally not be used with TKIP encryption due to the above-described weakness. There are various opinions about how strong a password to use with PSK+CCMP to be safe from brute force attacks. Some recommend a randomly chosen sequence of at least 10 characters. For passphrases comprising words found in a dictionary, some recommend at least 20 characters. Longer is better, and the inclusion of punctuation, mixed case, and outright randomness all help. Over time, the recommended minimum lengths tend to creep upwards.

EAP has six versions under WPA. EAP-TLS requires a certificate to be installed on both AP and client, and as a result is especially secure. The other EAP methods require certificates only on the server. They are EAP-TTLS, three variations of PEAP, and EAP-SIM which is oriented toward mobile devices.