Game request: [Type-Moon]Fate/Hollow Ataraxia

[rr-]

My discoveries so far:

• FHA is protected with CXDEC algorithm.
• CXDEC uses following:
  • LSFR-based randomization
  • complex key derivation that uses ADLR chunk.
  • the decryption process is mostly linear and simple - just xor input in a few predictable ranges with values derived from the key.
• Each game using CXDEC protection uses very little customization. These are as follows:
  • Substitution table - used to derive the key. It lies unencrypted in cxdec.tpm file.
  • Configurable order of code blocks used in key derivation algorithm.
  • 32-bit private key.

In the case of FHA the 32-bit private key seems to be 008F0313.

The main difficulty lies in reversing the key derivation algorithm.

[rr-]

After this is done, this repository can be renamed to xp3_unpacker, and other games can be added.