StreetPass is a feature that allow your 3DS to connect with other 3DS using WiFi in standby mode. It can be used to share Mii(s) on Mii Plaza for example. Games' StreetPass data is stored on SD card under extdata, while Mii Plaza StreetPass data is stored on NAND. Not all StreetPass data is stored on SD card: "StreetPass Management" can still be used without a SD card inserted. Wifi infrastructure with APs are used to communicate, like WMB and multi-player. StreetPass in sleepmode can work without SD card inserted. Games' Streetpass data are temporarily stored in NAND, and when the games process the StreetPass data they move that data to extdata on SD card.
WiFi Probe Request Frame
Whenever the 3DS is woken from sleep (or turned on), and WiFi is enabled, it sends out a 802.11 Probe Request which include all saved access points, as well a probe to an SSID containing an arbitrary string of data, such as "ic[kSvm9s@*cYD>/~IEVj\(fGG;qDo8j". The probe may be related to the 3DS looking for Nintendo Zone APs. This string changes at least daily, and most likely every time the device is woken up.
The MAC address used for these probes is the static MAC address found in the Settings application. Unlike the StreetPass MAC address, it will not change over time. This MAC address OUI also differs from the one used in StreetPass.
StreetPass Probe Frame
Using Wireshark tool with a WiFi card in monitor mode allow you to see the data used to scan for other 3DS in the range. The below is a broadcast probe request from an 3DS while in standby mode, with SSID "Nintendo_3DS_continuous_scan_000". This frame also contains a custom Nintendo tag, the contents of this tag from different 3ds captures don't match. Probe responses contain the same Nintendo tag data as the probe requests from the same 3DS. The MAC address used in sleepmode seems to change every time there's a streetpass hit, as well as the last 8-bytes of the Nintendo tag data? The MAC address + 8 byte ID for StreetPass is seen to change every time the user enters and exits and Settings application.
0000 00 00 1a 00 2f 48 00 00 19 7d 19 de 2a 00 00 00 ..../H...}..*... 0010 12 16 9e 09 a0 00 c9 02 00 00 40 00 00 00 ff ff ..........@..... 0020 ff ff ff ff da 6b f7 22 f3 77 ff ff ff ff ff ff .....k.".w...... 0030 40 77 00 20 4e 69 6e 74 65 6e 64 6f 5f 33 44 53 @w. Nintendo_3DS 0040 5f 63 6f 6e 74 69 6e 75 6f 75 73 5f 73 63 61 6e _continuous_scan 0050 5f 30 30 30 01 08 82 84 8b 0c 12 96 18 24 32 04 _000.........$2. 0060 30 48 60 6c dd 15 00 1f 32 01 11 05 00 02 08 00 0H`l....2....... 0070 00 f0 08 c8 34 6e 05 0f c9 c6 80 5b 6f bc 5a ....4n.....[o.Z
It is uncertain how the 3DS determines when it can do a StreetPass again with another 3DS, or what information is actually used to track that. It may be related to how long that 3DS was in range constantly/out of range. 3DSes that are constantly in range of each other in sleepmode, usually do StreetPass every <12 hours?
When in standby mode the old DS WiFi is used, which includes SpotPass and StreetPass, but in "active" mode the regular DSi WiFi bus is used.
Nintendo Tag Format
The offsets, in bytes, mentioned in the table below start at the beginning of the Nintendo tag ID, which is variable in length, and can be found right after the Vendor Specific OUI type of the 802.11 frame, which is often seen as a byte of "01". Each one of the elements are discussed in more detail after the table. Note that this table represents a current theory on what each of the fields represent, with the argument stated in the corresponding sections.
| Offset | Length | Purpose | Description | Example |
|---|---|---|---|---|
| 0x00 | 0x01 | Protocol identification | May be for protocol identification. All captures thus far show this value at 17, hexadecimal 11. | 11 |
| 0x01 | 0x01 | Unknown | Seems to vary by device, but stays consistent and doesn't change between Street Passes. May be a length or counter field in relation to the next set of fields. | 05 |
| 0x02 | 0x05 | StreetPass Services | Starting at the 0x02 offset, it appears to be a list of StreetPass services, each in length of 5 bytes. This continues on depending on the number of services the user has enabled at the time. | 00 02 08 00 00 |
| -0x08 | 0x08 | StreetPass ID | Seen to change after every time the Settings app is used. Also may change after each StreetPass hit and system power-off? | 0f c9 c6 80 5b 6f bc 5a |
Protocol Version
Appears to represent a protocol version, or device identification. This field remains consistent on all devices, despite variable enabled StreetPass services or length of the tag. Could also represent region.
Unknown Field
As mentioned, possibly a length field for the StreetPass services.
StreetPass Services
The third field in the protocol header appears to be an arbitrary length list of StreetPass services enabled on the device. Each StreetPass service seems to be identified by a 5 byte ID. Observed service IDs include, Mii Plaza: 00 02 08 00 00.
Some services have a 6-byte field preceding or succeeding the StreetPass service that is just FF bytes (e.g. FF FF FF FF FF FF). The purpose of these is unknown, although may be used as data for a service, or as separator of some sort for different types of StreetPass services.
StreetPass ID
When there's a StreetPass hit, and no StreetPass data changed on either of the 3DSes, no data is transferred besides probes? Perhaps there's some ID in the Nintendo tag that gets updated every-time the 3DS' StreetPass data changes? After turning off power, then powering on and entering sleepmode, the MAC doesn't change from prior to power off but the last 8-bytes of the Nintendo tag changes. This tag has been seen to not be sequential over time. After one of the new StreetPass content is handled, (running one of the StreetPass titles etc) the 8bytes in the Nintendo tag changes?
StreetPass spoofing
A streetpass "AP" was spoofed on a laptop with hostapd by setting the SSID to "Nintendo_3DS_continuous_scan_000", with the extra Nintendo tag from another 3DS' probe request. The SSID and AP can't be easily spoofed with hostapd for streetpass when 3DS is "active", for the random "ic[kSvm9s@*cYD>/~IEVj\(fGG;qDo8j" strings. The 3DS didn't seem to authenticate or associate with the "AP". Streetpass "AP" comms use WPA2 encryption. Eventually the 3DS stops communicating with the fake "AP" since the AP doesn't understand the sent data,(especially since it's encrypted) and sends a 802.11 "Action" frame, with category ID 0x7f and Nintendo's vendor ID: 00 1f 32.(However the 3DS keeps communicating with the above process repeatedly) Communication with two 3DSes are the same as above except there's encrypted data sent to/from both consoles, unlike the fake "AP".