Chapter 11 looked in detail at TKIP, one of the options for implementing encryption and message authentication under RSN. TKIP, which is mandatory to implement for WPA, will be widely used for Wi-Fi LAN security due to its ability to be used on older WEP cards. However, it is not the default mode for IEEE 802.11i. The default mode is based on a block ciphersuite called the Advanced Encryption Standard or AES. AES-based security can generally be considered as stronger than TKIP-based security. This is not to say that TKIP is inadequate. In reality, TKIP is extremely strong and quite suitable for commercial applications. So why was an AES-based solution defined? And what does it mean to say that it is more secure? The answers to these questions and a detailed look at how AES CCMP works are provided in this chapter.
First, let's clarify what we mean when we talk about RSN using AES. AES is not a security protocol; it is a block cipher. In RSN the security protocol built around AES is called Counter Mode CBC MAC Protocol, or CCMP. CCMP defines a set of rules that use the AES block cipher to enable the encryption and protection of IEEE 802.11 frames of data. AES is to CCMP what RC4 is to TKIP.
One reason that CCMP is considered stronger than TKIP is that it was designed from the ground up to provide security for IEEE 802.11. The designers took a clean sheet of paper and created CCMP using the best-known techniques. By contrast, TKIP is a compromise, designed to accommodate existing WEP hardware and some aspects of TKIP, notably the Michael integrity protocol, are known to be vulnerable.