WiFi - Arduino Sketches: Tools and Techniques for Programming Wizardry - page 173

articles you want, you go to pay, entering in your debit card details. Wireless
information can, theoretically, be seen by anyone. Just like a regular conversation,
if the person is close enough to hear, then he can get access to that information.
To avoid this, infrastructure wireless communications are normally encrypted.
Anyone can listen in to your conversation with your favorite Internet site but
will not be able to understand because that conversation is encrypted with a
special key that others do not know.
There are two forms of encryption: WEP and WPA2. WEP (short for Wireless
Equivalent Privacy) is an early form of wireless encryption. Today, the standard is
outdated, and Wi-Fi networks are encouraged to use the newer WPA2 encryption.
WPA2 (short for Wi-Fi Protected Access 2) is a solution to the weaknesses
found in WEP and is a stronger version of the previous WPA encryption. It
enables strong 256-bit AES encryption, using either 64 hexadecimal characters
or 8 to 63 printable ASCII characters as a passkey. Again, several versions exist,
but two main versions are used: WPA2 Personal and WPA2 Enterprise. WPA2
Personal requires a passkey and is perfect for home or small ofi ce environ-
ments. WPA2 Enterprise requires a specialized server and protects against
more advanced attacks.
Not only does the encryption secure communications, it also secures the
network. A wireless device that does not have the password cannot connect.
SSID
The network SSID, short for Service Set ID, is essentially the “network name,”
as it is known. This is the name that displays when you refresh your wireless
network list, and is the name that devices attempt to connect to. SSIDs are
sometimes hidden but are always present. A hidden SSID works in exactly the
same way, only the name is not broadcast to devices; devices can still attempt
to connect to a hidden SSID.
RSSI
RSSI is short for Received Signal Strength Indication and is an indication of
signal strength. The units are arbitrary; some devices report signal strength as
a percentage, others as a unit called dBm, or decibels per milliwatt of power.
Reading this value gives an indication of signal strength and not distance
because signal strength can be altered by physical obstructions (like walls) or
electromagnetic interference.
Arduino WiFi
The Arduino WiFi library is designed to work with a large amount of network
controllers through a simple system. The WiFi library “talks” to the Wi-Fi shield