I just got my tried to unpack the Twitter application for PS VITA and sadly I have to say that the AES key for PKG encryption and decryption changed.
The PKG's I used for my testings were pretty old and the key update was expected.
Nevertheless it's a bit disappointing but a new nice challange :)
The PS3 can decrypt the new packages on firmware 4.00 which contains the new PS VITA PKG AES key for the PS3 <--> PS VITA content exchange feature. This means we can decrypt and get the content of the PS VITA PKG files via a 4.00 PS3. Sadly there's no solution to re-encrypt it again, yet.
Let the games begin! (again...) :D