Short answer: You can't. The whole reason for exploits is so that we can load unsigned programs (a.k.a. Homebrew). If we knew the key, and if we knew how to sign eboots, then we wouldn't have to constently look for new exploits.

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This question was answered in your other thread: You don't. The encryption key cannot be found anywhere but in Sony's possession. Any code we run on the PSP is unsigned.

Since this thread is essentially a duplicate, I'll close it.