Once the passkey is provided, the AP is accessible from the client, as shown in the figure below. When I connect my Blackberry Wi-Fi client to the AP, it asks for a passkey, here is the display: The cipher text will again be prepended with the same IV, chosen non-uniquely. This WEP key will perform an XOR operation with the data and CRC integrity and generate the cipher text. The 24bit IVs prefixed by the AP take the total to 64/128 bits. Note that the actual WEP key is 40/104 bits. The three-byte IVs use two bits to define the encryption key in use. Here, my AP has the option to generate four keys based on a given passphrase.

The data is prepended with an initialization vector (IV) field, which contains information about the encryption key in use. Since it uses RC4 symmetric encryption, both client and AP use identical data encryption keys. WEP is defined in the 802.11 standards as a protocol for protecting authorized WLAN users from casual eavesdropping. Unfortunately, it isn’t, but is instead a mandatory field for any legitimate client to connect to an AP. It is commonly believed that disabling SSID broadcasts is a security measure. This aircrack tutorial will take you through the steps involved in cracking a WEP key using aircrack-ng.

A WEP encryption key can be easily cracked using aircrack-ng.

How to use aircrack for windows