Linux Unwired

Chapter 4. Communicating Securely

In a wired network, physical security is complicated but manageable. You can restrict physical access to routers, switches, and network hardware. You can provide a complex authentication mechanism for proving that users are who they say they are. You can set up Virtual LANs or Virtual Private Networks for even more security. Even if an attacker were to plug into your wireless network, it would be difficult to penetrate further with these kinds of security measures in place.

The wireless network world is not nearly this secure. In fact, it’s not secure at all. Disassembling your network packets and transmitting them wirelessly means that anyone within reach can see them. A wily attacker could join or passively monitor your network from a mile away with a high-gain antenna, and you would never see him.

The Pitfalls of WEP

The IEEE specifications for 802.11a/b/g all provide a form of encryption called Wired Equivalent Privacy (WEP). WEP operates at the Media Access Control (MAC) layer, or the Data Link layer, between the Physical Layer (radio waves) and the Network Layer (TCP). WEP encryption is based on the RC4 algorithm from RSA Data Security and employs a 40-bit encryption key.

Anyone who knows the secret key (unless you’re the only user on the network, this key is shared, so it’s not all that secret) can participate in a WEP network. Secret keys are generally either plaintext words or somewhat longer combinations of hexadecimal numbers.

There are two ...