A bank safe deposit box, securely stored in a vault behind several feet of concrete on five sides with a virtually impenetrable combination-and-time-lock-protected door on the sixth side, is about as safe a storage place as you can get for your cash, gold, jewels, important documents, and other valuables. You rarely hear of anyone losing valuables from a safe deposit box, but there’s an almost daily news story about sensitive data being lost or stolen. This makes for an interesting thought experiment.
While it’s not possible to provide the physical security of a bank vault on a laptop or other portable storage device, it is possible to protect the information itself with encryption so that only authorized persons can access it. Take the bank’s physical security out of the mix for a moment, making it possible for someone to walk right into the vault; they still can’t unlock your box without access to the bank’s key and your key. Similarly, encryption requires two keys: the encryption key and a passphrase; without both, the encrypted volume won’t open.
One could say, therefore, that an encrypted volume is a virtual safe deposit box for your valuable data.