Changes

TrackMania '''.pak files''' are archives that contain a collection of other files, much like .zip archives. They are found in the "Packs" folder in the game installation directory. In ManiaPlanet, there are also '''.Pack.Gbx''' files with the same purpose.

TrackMania '''.pak files''' are archives that contain a collection of other files, much like .zip archives. They are found in the "Packs" folder in the game installation directory. In ManiaPlanet, there are also '''.Pack.Gbx''' files with the same purpose.

In older TM versions, .pak files are both zlib-compressed and encrypted (version 3); even the file index containing the file names and directory structure is encrypted. In ManiaPlanet, they include an uncompressed/uncrypted section as well (versions 6+). Since version 18+, compression has been switched to LZ4 with a specific dictionary.

In older TM versions, .pak files are both zlib-compressed and encrypted (version 3); even the file index containing the file names and directory structure is encrypted. In ManiaPlanet, they include an uncompressed/uncrypted section as well (versions 6+). Since version 18+, compression has been switched to {{wp|LZ4 (compression algorithm)|LZ4}} with a specific dictionary.

== Encryption ==

== Encryption ==

====GBX compression intricacies====

====GBX compression intricacies====

There are some not-so-obvious details about compressed .gbx files, which may not seem important at first sight but actually make a world of difference when extracting them. Not addressing these ''will'' result in corrupt data. (Note: this is about the deflate compression specific to .pak files, not the LZO compression specific to .gbx data sections. .gbx files in a .pak don't have LZO-compressed data sections (BUUR header)).

There are some not-so-obvious details about compressed .gbx files, which may not seem important at first sight but actually make a world of difference when extracting them. Not addressing these ''will'' result in corrupt data. (Note: this is about the deflate compression specific to .pak files, not the {{wp|Lempel–Ziv–Oberhumer|LZO}} compression specific to .gbx data sections. .gbx files in a .pak don't have LZO-compressed data sections (BUUR header)).

* Files from a .pak are not decrypted and then decompressed in their entirety before they are parsed. Instead, the parser requests data from the decompressor as it goes along, which in turn requests data from the decrypter. Whenever the decompressor's buffer is empty and new data is requested, it requests blocks of 0x100 bytes from the decrypter and decompresses each block into its buffer of 0x400 bytes, until the buffer is full. Then, whenever the parser requests more data, it is simply copied over from the buffer – until the buffer is empty again.

* Files from a .pak are not decrypted and then decompressed in their entirety before they are parsed. Instead, the parser requests data from the decompressor as it goes along, which in turn requests data from the decrypter. Whenever the decompressor's buffer is empty and new data is requested, it requests blocks of 0x100 bytes from the decrypter and decompresses each block into its buffer of 0x400 bytes, until the buffer is full. Then, whenever the parser requests more data, it is simply copied over from the buffer – until the buffer is empty again.

* You ''must'' use the [http://www.zlib.net zlib library]. Don't use a different zlib-compatible implementation, and also don't skip over the zlib header and decompress the data with a deflate implementation. TrackMania very much depends on zlib's behaviour: how soon it starts returning decompressed data after compressed data has been put into it, and how much decompressed data it returns on every iteration.

* You ''must'' use the [http://www.zlib.net zlib library]. Don't use a different zlib-compatible implementation, and also don't skip over the zlib header and decompress the data with a deflate implementation. TrackMania very much depends on zlib's behaviour: how soon it starts returning decompressed data after compressed data has been put into it, and how much decompressed data it returns on every iteration.