GTS protocol

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Revision as of 01:58, 16 March 2011 by Icehawk78 (talk | contribs) (→‎pid)
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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 followed by page.asp?pid=pid&hash=hash&data=data. The hash variable in the latter, is a hash of the string returned by the former, as described bellow.


pid

The pid is an unsigned 32-bit integer that appears to uniquely identify a game cartridge. Although this has not been confirmed entirely: Your PID is generated when you get your friendcode for the first time and is set to: friendcode & 0x7fffffff

When you change the device and are forced to change your friendcode with it, your PID doesn't change but you get a new friendcode. Your new Friend Code appears to be set by appending a random byte (likely sent from Nintendo's servers) to the end of your PID. For example, nicholas's Soul Silver PID is 258303618 (0x8266650f)and his Friend Code is 4297 5503 3218 (0xf8266650f64) taking endianness into account.

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.

For 5th gen GTS, the hash is instead, generated by sha1("HZEdGCzcGGLvguqUEKQN" + token)

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

Data

The data sent to the server consists of a checksum, your pid, and a payload. The 5th gen GTS also adds the length of the payload, after the pid.

Checksum

The checksum is a 32-bit integer, computed by simply taking the sum of every byte of the pid and payload.

It is the first four bytes of the data, xor-ed with 0x4a3b2c1d (0x2db842b2 for 5th gen) and packed in network byte order (big-endian).

Payload

The pid (, length) and payload are encrypted with a stream cipher in for the 4th gen protocol.

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.

The entire data string is then encoded with urlsafe-base64.

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 trade, the server responds with the entire encrypted Pokémon save struct. Otherwise, if there is a Pokémon deposited in the GTS, it responds with 0x0004; if not, it responds with 0x0005.

Receiving a traded 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.

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. If the Pokémon is rejected by the server, the response is 0x000c; otherwise, if the deposit is successful, 0x0001.

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 Generation IV 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. In Generation IV, the trainer name is encoded with the Pokémon character table, while in Generation V, the trainer name is Unicode encoded.

They are as follows:

Generation IV Encrypted Bytes

Offset Contents
0x00-0x01 Nat. Dex ID
0x02 Gender
0x03 Level
0x04-0x05 Requested Nat. Dex ID
0x06 Requested Gender
0x07 Requested Min Level
0x08 Requested Max Level
0x09 Unknown - always 0?
0x0A Trainer's Gender
0x0B Unknown - always 0?
0x0C-0x13 Timestamp - deposited time
0x14-0x1B Timestamp - time traded?
0x1C-0x1F PID
0x20-0x2F Trainer's Name
0x30-0x31 Trainer's OT ID
0x32 Country
0x33 City
0x34 Trainer's Sprite
0x35 Is Exchanged Flag
0x36 Game Version
0x37 Language


The data for the Generation V GTS is 296 bytes and adds the trainer's secret ID, an additional two unknown bytes at the end, and shifts the position of the trainer name to after the trainer and secret IDs.

Generation V Encrypted Bytes

Offset Contents
0x00-0x01 Nat. Dex ID
0x02 Gender
0x03 Level
0x04-0x05 Requested Nat. Dex ID
0x06 Requested Gender
0x07 Requested Min Level
0x08 Requested Max Level
0x09 Unknown - always 0?
0x0A Trainer's Gender
0x0B Unknown - always 0?
0x0C-0x13 Timestamp - deposited time
0x14-0x1B Timestamp - time traded?
0x1C-0x1F PID
0x20-0x21 Trainer's OT ID
0x22-0x23 Trainer's Secret ID
0x24-0x33 Trainer's Name
0x34 Country
0x35 City
0x36 Trainer's Sprite
0x37 Alternate Form
0x38 Game Version
0x39 Language
0x3A-0x3B Unknown - always 0?


Pokémon Gender

Value Type
0x01 Male
0x02 Female
0x03 Either/neither


Trainer Gender

Value Type
0x00 Male
0x01 Female


Timestamp Format

The timestamps are set by the server, and are always PST (UTC-8).

Offset Contents
0x00-0x01 Year
0x02 Month
0x03 Day
0x04 Hour
0x05 Minute
0x06 Second
0x07 Unknown - always 0?


Alternate Form

The normal/default form is 0x01; if it is another form, this byte will correspond to the appropriate Pokémon structure alternate form.


Game Version

Value Version
0x0A Diamond
0x0B Pearl
0x0C Platinum
0x07 HeartGold
0x08 SoulSilver
0x15 Black
0x14 White
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