Benjamindees:
Smartcards are an interesting suggestion. If there were an ECDSA card out there, it sounds like a private key could not be extracted from it, even for backup purposes. Is this correct?
If the implementation were done on a non-ECDSA javacard, something like a computer or smartphone would still have to interface with it, correct?
My concern is that a compromised machine could tamper with the input to the javacard, such that the destination address and/or amount is changed when a user wants to make a transfer.
On the other hand, the idea of using a smart card kept in a safe as a bitcoin savings account seems pretty sexy from a usability standpoint. For people like allinvain who want to keep around 25,000 BTC for a long period of time, is a smartcard something he'd want to keep it on?
(ben-abuya you posted right around when I was going to and it looks like we have similar concerns about the smart card as a savings account)
Wow, just found this:
http://www.gemalto.com/products/top_javacard/download/TOP_DL_v2_Sept10.pdfLooks like it's got everything baked in. I bet you could do some cool stuff with an app running on windows and mac that would handle all the administrative stuff, while leaving all the key generation and storage to these cards.
One idea I just had is for card A to generate a wallet and encrypt it with a random string. It splits the random string into two and encrypts half the random string with card B's public key. The host computer transfers the encrypted half to card B. Then you'd either have to securely delete the orignal wallet.dat and random string on card A, or copy the first half of the random string to card C and securely destroy card A. I don't know enough about how smart cards work to know if this is possible, but the possibilities seem endless.
Also, these would be great for small wallets, for using like a credit card.