1.Brute force sony's digital signiture (sony might give us the encryption key if we
ask them nicely )
2.Rip apart our psp and replace flash0 chip
3.Look into the "supposed" psp serial port.
For people who don't know what each one does:
1. We try to get sony encryption key with this we could make our own "legit" programs ones the psp think were made by sony authorised companies. This is right now the hardest method (unless we get galactically luckey) as it would take our computers 100's to 1000's of years to guess the right code. Another way for this theory to work is to buy a official sony software developers kit (SDK) for a few thousand dollars.
2. This method will void your warranty you literally replace the psp's flash0 chip with another one with the desired firmware on it. This has been allegedly
sucessfully done by a guy called Ookm using 32mb Samsung NAND chips. Right now this is another difficult method.
3. The psp's mp3 remote port can be turned into a serial port with a few modifications. then we can connect this port to our computer. Right now we have only been able to emulate the remote (play music) and turn off their psp using this technique but who knows? We might find a way to reflash the flash0 using this technique.
Right now these are the methods with the most potential in my opinion. There is also that allegedly "leaked official SDK" but these allegations haven't been confirmed by anyone.