Yifan Lu with help from H of UkakNEH made available PSVIMGTools for backing up and restoring data on the PS Vita handheld console similar to the PS3 backup tool.
Download: psvimgtools-master.zip / psvimgtools-master.zip (Mirror) / PSVIMGTools Master / GIT
To quote from Wiki.Henkaku.xyz: PSVIMG
PSVIMG files are encrypted files generated by CMA in backing up and restoring data from the Vita.
When CMA is used to backup system, game, or savedata from the Vita to a PC or PS3, the following algorithm is used:
- Using a tar-like structure, stream all of the file data into a file.
- If making a PSVMD file, use the deflate algorithm to compress.
- Generate a random nonce for the first 0x10 bytes using the RndNumber syscall.
- Generate a unique session AES256 key using a secret phrase and the PSN account id of the PSVita.
- Generate a SHA256 hash of the plaintext every 0x8000 bytes and insert the hash into the filestream.
- Encrypt the stream data using EncDecKeygen syscall from SceSblDmac5Mgr with the nonce as the header and the AES256 session key.
- Transmit to PC or PS3.
If you look at the 16 character hex directory name included in part of the backup path, that is your PSN account id. The AES256 session key is calculated by doing a SHA256 hash of the 8 byte hex binary representation of the PSN account id followed by the secret phrase: Sri Jayewardenepura Kotte
SHA256 of this buffer generates the AES256 session key of:Code:01 23 45 67 89 AB CD EF 53 72 69 20 4A 61 79 65 77 61 72 64 65 6E 65 70 75 72 61 20 4B 6F 74 74 65
Unfortunately, this is dependent on the PSVita for executing using the EncDecKeygen function. The AES256 key is altered inside the F00D Processor (Octopus Exploit) in some way currently unknown. Upon decryption, the session key is sent to F00D and an assigned slot.Code:02EAAB5A00EC9D4207E8B1F53F8A2F3F91F1A73AAFDD2A81CCFEE3E83E5B101A
When the HW crypto engine is invoked to perform the decryption, it is given the slot number. Presumably, the crypto engine talks directly with F00D to use the derived key.
Thanks to @CelesteBlue for the post on this news!