Vita Developer @Yifan Lu has released Psvimgtools v0.1 via Github for Windows/OSX/Linux and is used for decrypting CMA Vita Backups (Info below)
Heres a quote from Yifan’s website
psvimgtools: Decrypt Vita Backups
The Vita’s Content Manager allows you to backup and restore games, saves, and system settings. These backups are encrypted (but not signed!) using a key derived in the F00D processor. While researching into F00D, xyz and Proxima stumbled upon a neat trick (proposed originally by plutoo) that lets you obtain this secret key and that has inspired me to write a set of tools to manipulate CMA backups. The upshot is that with these tools, you can modify backups for any Vita system including 3.63 and likely all future firmware. This does not mean you can run homebrew, but does enable certain tricks like disabling the PSTV whitelist or swapping X/O buttons.
Because my friends who discovered this are pretty busy with other stuff at the time, I will attempt to document their findings here. The backup encryption process is documented in detail on the wiki, but the short version is that your AID (unique to a PSN account) is used to generate a key seed. This key seed is used by the F00D processor (the security coprocessor) to generate a AES256 key, which is passed directly to the hardware crypto device. The ARM (application) processor can access this crypto hardware but cannot read any keys out of it. This means that ARM can use the hardware as a black-box to encrypt backups without knowing the key. Of course you can try to brute force the key since you know both the plaintext and ciphertext thanks to the HENkaku kernel hack, but that would take 22562256 time, which is physically impossible. However, since we can hack any Vita on 3.60, it is possible to use the Vita itself as a black box for extracting and modifying backups for other devices on unhackable firmwares, but since the process requires access to a hacked Vita, it is not very useful.
Here’s a quote form the Section Hacking Backups
What I did is completely reverse how CMA generates and parses the backup format. I have documented extensively how these formats work. I also wrote tools to dump and repack CMA backups and all this works with backups generated from the latest firmware.
Hacking backups isn’t as fun as having a hacked system. So, don’t update from 3.60 if you have it! You cannot run unsigned code with this, so you are only limited to tricks that can be done on the registry, app.db, and other places. This includes:
- Enabling almost any games to run on the PSTV
- Swap X/O buttons for out-of-region consoles
- Run PSP homebrew with custom bubbles
- and maybe more as people make new discoveries
My hope is that other people will take my tools as building blocks for a user-friendly way of enabling some of the tricks above as currently the processes are pretty involved. This also increases the attack surface for people looking to find Vita exploits as parsing of files that users normally aren’t allowed to modify are common weak points.
Additionally, because of how Sony implemented CMA backups and that the key-erase procedure is a hardware vulnerability, this is pretty much impossible to patch in future firmware updates. Unless Sony decides to break all compatibility with backups generated on all firmware up until the current firmware. And that would mean that any backup people made up until this theoretical update comes out would be unusable. Sony is known for pulling stunts like removing Linux from PS3, but I think this is beyond even what they would do.