These keys are symmetric, so they can be used for decryption. With these symmetric keys you might be able to decrypt games, videos, save files etc sitting on the disk. I don't believe signing will be possible, nobody uses symmetric keys for signing games.
What this does is increase the possibility of someone finding how to bypass the signature verification check and then running their own code.
What this does is increase the possibility of someone finding how to bypass the signature verification check and then running their own code.