DLC Decryption

[Hykem]

I have a question regarding the encryption/decryption of SAVEDATA.
Thanks to Hykems option "Disable SAVEDATA encryption", my old savegames still work, even tough they are not encrypted. However, since encryption seems to work now, I've been trying to convert that unencrypted SAVEDATA to encyrpted savedata. So far without success.
Is there a way to use jpcsp or another program to manually encrypt/decrypt SAVEDATA?

Unfortunately, those old save games had many missing data portions, so they were never compatible with a real PSP.
You can try to disable "Disable SAVEDATA encryption" and let JPCSP auto detect the SAVEDATA as unencrypted (this is now possible, JPCSP detects if the SAVEDATA is encrypted or not). If this succeeds (it may not work, because the old PARAM.SFO files were terribly corrupted) then JPCSP will load your unencrypted SAVEDATA and the next time you save your game it will output it as encrypted.
By the way, I suggest you also take a look at the standalone program SED for PC (http://wololo.net/downloads/index.php/download/8122 ) which uses the same algorithms used by PPSSPP/JPCSP without having to use an emulator.

Thanks for the reply Hykem.
Whenever "Disable SAVEDATA encryption" is disabeled, the SAVEDATA show up as corrupted(probably because of the PARAM.SFO as you said).
I did take a look at SED for PC as you suggested but couldn't get it to work. Probably because I don't know much about how the PSP encrypts/decrypts savegames. I have absolutely no clue what the game-key-file is supposed to contain or where I could find that file. I don't even know what the game-key itself is supposed to be.
If you find the time please explain it to me.

The game key is an internal key supplied by the game itself to process SAVEDATA encryption/decryption.
You can use JPCSP to dump this key too. Just check the option "Extract SAVEDATA key to TMP folder" and the key will be saved in binary form under the folder TMP. You can then use this binary file with SED for PC.
Nonetheless, if you wish, just post the corrupted SAVEDATA files here and I'll try to manually fix them for you.