You're not going to get the ENCRYPTION key by brute force. It's not stored anywhere on the PSP. The best you can hope for is the DECRYPTION key, which is a totally different key.

The only incident of cracking an AES key I've ever heard of was when someone generated a key on a PC, then immediately ran a program that scanned the RAM for such keys. On the same PC.

Since there's so much false information in this thread, I'm closing it. Please, if you don't know what you're talking about, don't just make something up.