I've found the encryption key used by [insert random game name here]. I put the relevant info into the savedata samples in the PSP SDK, and decrypted the game's savedata OK.
I also plugged the same info into the encryption sample. However, when I run my encryption program, it just appends 16 bytes of value 0x00 to the beginning of the unencrypted file and places that in the savedata folder. Help! What have I done wrong? I simply cannot figure it out.