[fakespastic]

Would have to be a rolling-key, I'm guessing...but as I mentioned in another comment, the interval would be the kicker. Maybe it's simpler, now that I think of it. A rolling-key system with 2-way authentication, a one-time key becoming invalid after a transaction is made.

[richcollins]

Couldn't you just type in a passphrase on your phone and have it sign the transaction?

[fakespastic]

Whatever solution is created, I don't want to have to manually verify every transaction.