Reaver implements a brute force attack against Wifi Protected Setup (WPS) registrar PINs in order to recover WPA/WPA2 passphrases, as described in http://sviehb.files.wordpress.com/2011/12/viehboeck_wps.pdf.
Reaver has been designed to be a robust and practical attack against WPS, and has been tested against a wide variety of access points and WPS implementations.
On average Reaver will recover the target AP’s plain text WPA/WPA2 passphrase in 4-10 hours, depending on the AP. In practice, it will generally take half this time to guess the correct WPS pin and recover the passphrase.
While Reaver does not support reconfiguring the AP, this can be accomplished with wpa_supplicant once the WPS pin is known.
Reaver targets the external registrar functionality mandated by the WiFi Protected Setup specification. Access points will provide authenticated registrars with their current wireless configuration (including the WPA PSK), and also accept a new configuration from the registrar.
In order to authenticate as a registrar, the registrar must prove its knowledge of the AP’s 8-digit pin number. Registrars may authenticate themselves to an AP at any time without any user interaction. Because the WPS protocol is conducted over EAP, the registrar need only be associated with the AP and does not need any prior knowledge of the wireless encryption or configuration.
Reaver performs a brute force attack against the AP, attempting every possible combination in order to guess the AP’s 8 digit pin number. Since the pin numbers are all numeric, there are 10^8 (100,000,000) possible values for any given pin number. However, because the last digit of the pin is a checksum value which can be calculated based on the previous 7 digits, that key space is reduced to 10^7 (10,000,000) possible values.
The key space is reduced even further due to the fact that the WPS authentication protocol cuts the pin in half and validates each half individually. That means that there are 10^4 (10,000) possible values for the first half of the pin and 10^3 (1,000) possible values for the second half of the pin, with the last digit of the pin being a checksum.
Reaver brute forces the first half of the pin and then the second half of the pin, meaning that the entire key space for the WPS pin number can be exhausted in 11,000 attempts. The speed at which Reaver can test pin numbers is entirely limited by the speed at which the AP can process WPS requests. Some APs are fast enough that one pin can be tested every second; others are slower and only allow one pin every ten seconds. Statistically, it will only take half of that time in order to guess the correct pin number.
Reaver is only supported on the Linux platform, requires the libpcap and libsqlite3 libraries, and can be built and installed by running:
# make install
To remove everything installed/created by Reaver:
# make distclean
Usually, the only required arguments to Reaver are the interface name and the BSSID of the target AP:
# reaver -i mon0 -b 00:01:02:03:04:05
Reaver Home: http://code.google.com/p/reaver-wps/