The 3DS dlplay title has two dlplay modes: 3DS and DS. DS dlplay is just regular dsmode dlplay, same interface and protocol as before. Like DS gamecards, holding down start+select while starting the dsmode dlplay client will disable stretching the screens.
Download Play protocol
The Download Play protocol for 3DS is completely different from the DS Wireless Multiboot (WMB) protocol. While the DS WMB protocol used to send program code in plaintext over wireless, the Download Play protocol is now using WPA2 encryption with 128-bit AES CTR to broadcast the application.
Cleartext beacons have static Nintendo tag data, broadcasted at a rate of 0.102400/s. WPA2 data frames are broadcasted as well, the size of these varies. After a client authenticates to the host, the host sends an association response, with a random ASCII hex SSID, like: "EB6FAB77". After that the systems communicate and transfer the binary with WPA2 encrypted data frames.
This is a dump of the Nintendo tag of the cleartext beacon from Monkey ball 3D, with vendor 001f32:
000: 18 05 9f ae 17 c8 a5 1d 0b 81 28 be 74 0f d4 af 010: 97 30 04 60 fd 2d f3 d9 8d bc 22 80 51 60 3c 75 020: d9 89 6d 16 c4 f3 aa 89 26 d4 14 25 67 75 8e 4b 030: 3c 97 85 c9 83 15 d4 96 06 b1 29 b6 f5 51 57 71 040: cc b6 1f 4a c8 bd 4f c0 57 43 cb ab fa 37 74 b0 050: 64 6b 87 69 a1 de a4 05 7c 7c 49 5d f5 21 25 83 060: 4c f2 d0 70 38 14 7b 0f f4 97 f7 ff f3 ff 36 cd 070: c2 e2 c0 78 98 d1 d5 4d 3d d4 9b 57 84 6c e2 4f 080: 25 f2 56 c4 19 88 64 13 78 68 e2
Broadcasted application data
The Download Play protocol broadcasts 3DS application data in a format similar to the WAD format for the Nintendo Wii. ( this is also the .CIA format internally. ) The broadcasted application data is an archive file format, which contains a certificate chain, a ticket, a TMD, and the actual application itself, in CXI format. The broadcasted archive data is temporarily stored as a file on the internal NAND Flash storage, and is kept there until new archive data from a different game is received through the Download Play protocol.
The CXI application content is again encrypted, this time using 128-bit AES CBC. The encryption uses the decrypted titlekey of the ticket, and the titleid padded with zeros as the IV. To get the decrypted titlekey, the titlekey stored in the ticket must be decrypted using 128-bit AES-CBC with the 3DS common key, and the same IV as mentioned previously.
So in actuality, the 3DS application code, as it is being transmitted wirelessly has been encrypted 3 times:
- The first time is using 128-bit AES CTR encryption for the ExeFS of the CXI format,
- the second time is using 128-bit AES CBC encryption in the archive data,
- and the third time is using 128-bit AES CTR for the WPA2 encryption.