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With airdecap-ng you can decrypt WEP/WPA/WPA2 capture files. As well, it can be used to strip the wireless headers from an unencrypted wireless capture.
airdecap-ng [options] <pcap file>
|-l||don't remove the 802.11 header|
|-b||bssid||access point MAC address filter|
|-k||pmk||WPA/WPA2 Pairwise Master Key in hex|
|-e||essid||target network ascii identifier|
|-p||pass||target network WPA/WPA2 passphrase|
|-w||key||target network WEP key in hexadecimal|
The following removes the wireless headers from an open network (no WEP) capture:
airdecap-ng -b 00:09:5B:10:BC:5A open-network.cap
The following decrypts a WEP-encrypted capture using a hexadecimal WEP key:
airdecap-ng -w 11A3E229084349BC25D97E2939 wep.cap
The following decrypts a WPA/WPA2 encrypted capture using the passphrase:
airdecap-ng -e 'the ssid' -p passphrase tkip.cap
The capture file must contain a valid four-way handshake. For this purpose having (packets 2 and 3) or (packets 3 and 4) will work correctly. You in fact don't truly need all four handshake packets.
As well, only data packets following the handshake will be decrypted. This is because information is required from the handshake in order to decrypt the data packets.
See thisFAQ entry
None at this time.