[Register or Login to view links]. That is to say, there's not supposed to be any good way to find the private key from the public key, short of searching through every possible number. And that's... not going to happen. See [Register or Login to view links]. Just counting up all 256-bit numbers would take more energy than the sun will put out in its lifetime.
Now, if someone found a flaw in RSA (the most common "public key" encryption algorithm), it might be possible to figure it out... but if they could do that, cracking the PS3 encryption would be way down on the list of what they'd do.
Nope, it's designed to be