Question: GT4 Replay Crypto

[Silentwarior112]

I was trying to see if GT4O could have the demo replays re-enabled for license tests and eventually ended up here to check PDTools.Crypto/GT4ReplayCrypto.cs to see if custom replays could be put in the game files and read. Saved replays lack the little header that this method is targeting, which I think is the only bit that is missing to make them work.

1. If we put real PS2 aside, could the method generate the header around a saved replay file generated by PCSX2?

2. Is it possible to adapt the method into a PS2 homebrew application to generate that header around a saved replay file generated by real PS2?

[Nenkai]

Are custom replays already encrypted? If not, then you would need to encrypt it on a real console because of the float differences.

Either way, replays only either work on a real console, or on emulator depending on where it was encrypted, but never on both at once.

[Silentwarior112]

They both appear to be encrypted looking at the bytes
Which would lead me to think that only the 0x40 header needs to be generated (to get encode_param crucially) based on the already encrypted payload

I think this would need to be a ps2 homebrew tool for both console and emu, depending on where a replay was generated you would run the tool on the corresponding platform I guess.

[Silentwarior112]

Don't think this matters much but Gran Turismo 3 also uses the same format, what's interesting is that GT3 has the 0x40 header for both the demo replays on disc AND saved replays

[Silentwarior112]

Would a homebrew program made using the Enceladus project work?
I managed to get a file browser up and running with it, currently it just copies the selected file but the platform is there to implement the file processing

[Silentwarior112]

I tried it anyway, got a decoder program written up and I might have had success with it.
You can find the decoder at: https://github.com/Silentwarior112/GT4-Replay-Decoder
I recorded my own replay (no 0x40 header) and ran it through this, and got a successful output. The decoded bytes appear to be coherent but I've never seen a decoded one before so I wouldn't know for sure.

[Silentwarior112]

Managed to get a full tool working. Saved replays can be decrypted, and encrypted as either a saved replay or the demo type with the required header to work as license demos.

You and PDTools are credited in the repo's readme