- Create a deterministic wallet and a larger number of private keys and associated bitcoin addresses on a safe (e.g. offline) computer.
- Backup the seed securely. Store the private keys securely (e.g. on a piece of paper).
- Note addresses and send Bitcoins to a number of different addresses. (They are now in cold storage.)
- When needed, take one of the private keys and import it from an online wallet (e-wallet, cellphone, etc.) (This includes the risk of the private key getting stolen by malware or the e-wallet operator. However, such a theft would only apply to a small amount, not your total fortune.)
If one private key of a deterministic wallet gets compromised (known to an advisory), are the other keys (and the seed) still secure?
By design, this is not the case for the electrum deterministic wallet and the developers are aware of this. How about other deterministic wallets, e.g. Armory?