DRC communicates with DRH using 5GHz 802.11n. Pairing uses a slightly modified version of WPS, normal connection encryption uses a slight modified version of WPA2.
When the console is in GamePad pairing mode (press twice on the SYNC button), it exposes an open access point named WiiU<mac2><mac>_STA1 (where <mac> is the adapter MAC address and <mac2> almost the adapter MAC address). The GamePad connects to this access point (TODO: how does it choose the AP to connect to?) and initiates a WPS handshake to get the credentials for the normal communication mode.
Nintendo modified the WPS handshake slightly to obfuscate the protocol: a normal WPS implementation will not compute the same AuthKey and fail at stage M2. The standard specifies that the AuthKey is computed from KDF(KDK). In Nintendo’s implementation, AuthKey is computed from KDF(KDK_ROT) where KDK_ROT is KDK rotated 3 bytes to the left.
The WPS handhake uses a PIN code which must be the same on console and GamePad. When pairing, the console displays the first part of the code on the TV screen using symbols: ♠ = 0, ♥ = 1, ♦ = 2, ♣ = 3. The second part of the PIN is hardcoded to 5678. For example, if the console displays ♠♠♦♣, the PIN is 00235678. If you are trying to associate a gamepad to your computer (and not your computer to a Wii U), you get to choose the code, as long as you enter the same on the GamePad it should work.
After the WPS handshake is done, you should get the Wii U SSID, BSSID (AP MAC address) and PSK.
In normal operation mode (not pairing), the Wii U exposes a WPA2-PSK access point with an empty SSID. In the beacon frames it broadcasts, the AP advertises support for these ciphers:
Note that because these are not the standard RSN algorithms, you may have trouble getting your supplicant to associate with the AP: it needs to advertise the support for these algorithms or the Wii U will refuse your connection with error code 0x000c.
The only difference between the Nintendo Pairwise CCM and the standard pairwise CCM is a 3 bytes rotation of the PTK to the left after it’s computed.
After that, the GamePad sends a DHCP request and the console answers it with an IP (default: console=192.168.1.10 gamepad=192.168.1.11).
A patched version of Wireshark that has support for the modified Nintendo ciphers is available on memahaxx/drc-wireshark.