Appendix D Wireless LANs
B222s User’s Guide
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called Rijndael. They both include a per-packet key mixing function, a Message Integrity Check
(MIC) named Michael, an extended initialization vector (IV) with sequencing rules, and a re-keying
mechanism.
WPA and WPA2 regularly change and rotate the encryption keys so that the same encryption key is
never used twice.
The RADIUS server distributes a Pairwise Master Key (PMK) key to the AP that then sets up a key
hierarchy and management system, using the PMK to dynamically generate unique data encryption
keys to encrypt every data packet that is wirelessly communicated between the AP and the wireless
clients. This all happens in the background automatically.
The Message Integrity Check (MIC) is designed to prevent an attacker from capturing data packets,
altering them and resending them. The MIC provides a strong mathematical function in which the
receiver and the transmitter each compute and then compare the MIC. If they do not match, it is
assumed that the data has been tampered with and the packet is dropped.
By generating unique data encryption keys for every data packet and by creating an integrity
checking mechanism (MIC), with TKIP and AES it is more difficult to decrypt data on a Wi-Fi
network than WEP and difficult for an intruder to break into the network.
The encryption mechanisms used for WPA(2) and WPA(2)-PSK are the same. The only difference
between the two is that WPA(2)-PSK uses a simple common password, instead of user-specific
credentials. The common-password approach makes WPA(2)-PSK susceptible to brute-force
password-guessing attacks but it’s still an improvement over WEP as it employs a consistent,
single, alphanumeric password to derive a PMK which is used to generate unique temporal
encryption keys. This prevent all wireless devices sharing the same encryption keys. (a weakness of
WEP)
User Authentication
WPA and WPA2 apply IEEE 802.1x and Extensible Authentication Protocol (EAP) to authenticate
wireless clients using an external RADIUS database. WPA2 reduces the number of key exchange
messages from six to four (CCMP 4-way handshake) and shortens the time required to connect to a
network. Other WPA2 authentication features that are different from WPA include key caching and
pre-authentication. These two features are optional and may not be supported in all wireless
devices.
Key caching allows a wireless client to store the PMK it derived through a successful authentication
with an AP. The wireless client uses the PMK when it tries to connect to the same AP and does not
need to go with the authentication process again.
Pre-authentication enables fast roaming by allowing the wireless client (already connecting to an
AP) to perform IEEE 802.1x authentication with another AP before connecting to it.
Wireless Client WPA Supplicants
A wireless client supplicant is the software that runs on an operating system instructing the wireless
client how to use WPA. At the time of writing, the most widely available supplicant is the WPA patch
for Windows XP, Funk Software's Odyssey client.
The Windows XP patch is a free download that adds WPA capability to Windows XP's built-in "Zero
Configuration" wireless client. However, you must run Windows XP to use it.
Summary of Contents for B222s
Page 4: ...Contents Overview B222s User s Guide 4 ...
Page 12: ...Table of Contents B222s User s Guide 12 ...
Page 13: ...13 PART I User s Guide ...
Page 14: ...14 ...
Page 28: ...28 ...
Page 78: ...Chapter 7 Routing B222s User s Guide 78 ...
Page 82: ...Chapter 8 DNS Route B222s User s Guide 82 ...
Page 102: ...Chapter 10 Network Address Translation NAT B222s User s Guide 102 ...
Page 114: ...Chapter 12 Firewall B222s User s Guide 114 ...
Page 120: ...Chapter 14 Parental Control B222s User s Guide 120 ...
Page 125: ...Chapter 15 VoIP B222s User s Guide 125 ...
Page 144: ...Chapter 15 VoIP B222s User s Guide 144 ...
Page 154: ...Chapter 17 Traffic Status B222s User s Guide 154 ...
Page 156: ...Chapter 18 User Account B222s User s Guide 156 ...
Page 170: ...Chapter 24 Backup Restore B222s User s Guide 170 ...
Page 172: ...Chapter 25 Diagnostic B222s User s Guide 172 ...
Page 218: ...Appendix B Setting Up Your Computer s IP Address B222s User s Guide 218 ...
Page 228: ...Appendix C Pop up Windows JavaScript and Java Permissions B222s User s Guide 228 ...
Page 252: ...Appendix E Common Services B222s User s Guide 252 ...