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Good thing both sets of keys are theoretically only known by the owner of the associated account. Steemit Inc. probably doesn't have a secret database with private keys in it. Too much of a liability.

Still, I would make sense to change them for hive and store your private keys off-line

Yes, I eventually want to create some basic software that would allow anyone to use a Raspberry Pi to generate Graphene keys offline. You'd then broadcast them to the blockchain using a camera phone and QR code, which would make your keys pretty much unhackable via the Internet through the airgap.

Never heard about that, I like my ledger key.