GTS protocol

The following is wild conjecture based on LordLandon's sendpkm.py.

Communication with the GTS is done over regular HTTP with http://gamestats2.gs.nintendowifi.net/. The same protocol is used for all five Gen IV games.

HTTP headers

The games don't seem to care about these at all. The GTS sends back a bunch of boilerplate response headers, but the game happily accepts a response with only a Content-Length.

Protocol

All requests to the server are GET requests of the form page.asp?pid=pid&hash=hash&data=data.

pid

The pid is an unsigned 32-bit integer that appears to uniquely identify a game cartridge. When the pid is obtained and whether the pid has any relation to the Pal Pad friend code are unknown.

For the mathematically inclined: Eevee's Platinum pid is 192615460 (0x0b7b1424) and his Pal Pad code is 0904 2026 4621.

Challenge/response

Before each "real" request, the game sends a request of the form page.asp?pid=pid and the server responds with a 32-byte challenge token. The game computes sha1("sAdeqWo3voLeC5r16DYv" + token) and uses that as the hash value which it sends to the server. The data parameter is encrypted, as explained further down.

That is, each request looks like the following:

1. Game requests GET /pokemondpds/page.asp?pid=pid
2. Server responds with token
3. Game requests GET /pokemondpds/page.asp?pid=pid&hash=sha1(...)&data=data
4. Server responds with payload

The exact details of the game's requests are not currently known, but we are working on it!

Checksum

A 32-bit checksum of the data is used as the key for the encryption. The checksum is simply the sum of every byte of the data.

The first 4 bytes of the sent data are the checksum, xored with 0x4a3b2c1d, and sent in network byte order (big-endian).

Encryption

The data sent to the server is encrypted with a stream cipher, and urlsafe-base64-encoded.

This encryption algorithm, like others used in the game, uses a Linear Congruential Generator (not a very strong choice). The multiplicative constant is 0x45, and the additive constant is 0x1111. It appears that the game uses a signed dword to store the seed, which doesn't really matter; it shouldn't affect anything. (It means that the modulus is effectively 0x80000000.)

GRNG[n+1] = (GRNG[n] * 0x45 + 0x1111) & 0x7fffffff

The GRNG is seeded with the checksum, like so:

GRNG[0] = checksum | (checksum << 16)

The keystream is composed of the lower byte of the high word of successive GRNG values.

keystream[n] = (GRNG[n] >> 16) & 0xff

Xor the keystream with the plaintext to get the ciphertext. Xor the keystream with the ciphertext to get the plaintext.

Conversation

The first request the game makes is to /pokemondpds/worldexchange/info.asp. The server responds with 0x0001.

Platinum, Heart Gold, and Soul Silver will then make a request to /pokemondpds/common/setProfile.asp. The server responds with eight NULs (0x00000000 0x00000000).

After the above step(s) or performing any of the tasks below other than searching, the game makes a request to /pokemondpds/worldexchange/result.asp. If the game has had a Pokémon sent to it (via a successful trade?), the server responds with the entire encrypted Pokémon save struct. If there is a Pokémon deposited in the GTS, it responds with 0x0004. Otherwise, it responds with 0x0005.

Receiving a Pokémon

If the game receives a Pokémon from a successful trade as a response from result.asp, it next requests /pokemondpds/worldexchange/delete.asp. The server responds with 0x0001.

A note on sendpkm.py

After doing the above, some Platinum, Heart Gold, and Soul Silver games will report a communication error and dump the player back to the title screen. The Pokémon is still successfully received. At least one person with HG/SS has received a Pokémon from a fake server without getting the error, and Diamond/Pearl have never been reported to have the problem. It's possible that the server should respond with something other than 0x0001.

Depositing a Pokémon

Pokémon are offered on the GTS by requesting /pokemondpds/worldexchange/post.asp. The sent data is 300 bytes long, and includes the Pokémon struct.

The game then saves. After the save is complete, it issues a request to /pokemondpds/worldexchange/post_finish.asp.

Retrieving the deposited Pokémon

Checking on the deposited Pokémon is apparently done by /pokemondpds/worldexchange/get.asp. The response appears to be a Pokémon save struct.

Retrieving the deposited Pokémon is done by /pokemondpds/worldexchange/return.asp. The response is merely 0x0001; the actual Pokémon data is taken from the get.asp request.

Searching

Searching is done through /pokemondpds/worldexchange/search.asp. The sent data is either 15 or 16 bytes long.

The server responds with a full 292-byte Pokémon struct for each result. If there are n results, the response will be 292 * n bytes long. If there are no results, the server will give an empty response (0 bytes).

Pokémon struct

The Pokémon data for the GTS is 292 bytes—56 bytes larger than a party Pokémon struct. The extra 56 bytes are GTS-specific data, such as the player's name & country, and what Pokémon they are requesting.

They are as follows:

0x00-0x01 Current Pokémon
0x02      Gender          1=male; 2=female; 3=either/neither
0x03      Level
0x04-0x05 Requested Pokémon
0x06      Gender
0x07      Min level
0x08      Max level
0x09      always 0?
0x10      sometimes 1, sometimes 0
0x0B      always 0?
0x0C-0x0D Year deposited
0x0E      Month dep'd
0x0F      Day dep'd
0x10      Hour dep'd
0x11      Minute dep'd
0x12      Second depd'd
0x13      always 0?
0x14-0x1a Another timestamp. Time traded away?
0x1b      always 0?
0x1c-0x1f pid - also 0x4c in the sav
0x20-0x2F OT Name
0x30-0x31 OT ID
0x32      Country
0x33      City
0x34-0x37 Unknown