I do not remember being asked for a passphrase when I installed Bitocoin-Qt (0.8.2 - Beta) (though it was a couple months ago, I could be mistaken) and now am being asked for a passphrase. I have no idea what it is. Can this passphrase be reset? If it cannot, are there restrictions on what can be used for the passphrase (i.e. only letters and numbers) ?