Converts .stc tables into .csv files.

Data versioning

During login sequence, game client queries Index/version endpoint to check if client is up-to-date.

If data_version in response differs from the version in client preferences, update is initiated.

The following function is used to get the URL:

from hashlib import md5

def get_data_file_full_url(version: str) -> str:
    return f'http://dkn3dfwjnmzcj.cloudfront.net/data/stc_{version}{md5(version.encode()).hexdigest()}.zip'

After completing the download, the archive is placed at <internal storage>/Android/data/com.sunborn.girlsfrontline.en/files/stc_data.dat and then contents extracted in <internal storage>/Android/data/com.sunborn.girlsfrontline.en/files/stc directory.

※ Game client preferences location is /data/data/com.sunborn.girlsfrontline.en/shared_prefs/com.sunborn.girlsfrontline.en.v2.playerprefs.xml

.stc

Format overview

    +---+---+---+---+---+---+
    |  id   |  lbs  |  rows |
    +---+---+---+---+---+---+
    +---+===================+
    | c |    column types   |
    +---+===================+
    +=======================+
    |       jump table      |
    +=======================+
    +=======================+
    |          data         |
    +=======================+

where:

• id is a u16 integer representing ID of this table, usually matches the file name, e.g. 5000.stc will have ID of 5000
• lbs, is a u16 length of the last 65536 byte block, not counting id and itself
• rows is a u16 number of rows in this table
• c is a u8 number of columns in a row
• column types is a sequence of u8 integers with c length, each value represents column type in a row as follows:
  • 1 => i8
  • 2 => u8
  • 3 => i16
  • 4 => u16
  • 5 => i32
  • 6 => u32
  • 7 => i64
  • 8 => u64
  • 9 => f32
  • 10 => f64
  • 11 => string with the structure as follows:

    +---+---+---+======+
    | a |  len  |  str |
    +---+---+---+======|
    

    where a is is_ascii flag, str is ASCII or UTF-8 encoded
• jump table is a sequence of two i32 and u32 integers (row_id and absolute offset) of every 100th row starting with first row (with 0-based indexing: 0th, 100th, 200th, etc)
• data is a sequence of rows, each row have c columns

※ Little-endian ordering is used

Table definitions

STC tables themselves don't define their name or column names, a way to acquire them is to dump headers using il2cpp dumper.

il2cpp metadata is encrypted, method unknown, use GameGuardian to dump memory and acquire decrypted file.

※ Do this on an offline virtual device in case some security measure gets tripped

※ Enable Hide GameGuardian from the game option before dumping memory

After dumping headers:

• look for CmdDef enum to find table names
• look for classes starting with Stc in the name to find column names

catchdata.dat

Essentially is a .jsonl file that is gzip compressed and XOR encrypted.

The decryption function is as follows:

key = b'c88d016d261eb80ce4d6e41a510d4048'

def xor(buffer: bytearray, key: bytes):
    for i in range(len(buffer)):
        buffer[i] ^= key[i % len(key)]