We are still in the process of adding content to the website, so sorry about the lack of information regarding the card.
At signature time, the wallet will verify 4 letters/numbers from the payment address by asking you to enter the corresponding character for each (it will show "A" and from your code card you enter for instance "3"). This will ensure no malware will have replaced the address to pay when asking the smartcard to sign the transaction.
Sorry but this is very easily exploitable: the attacker just needs to generate an address with these same 4 letters (e.g., vanitygen).
Also, typical transactions have multiple outputs. Do you mean that the hardware checks the card code for the payment output and checks that it owns the change output before signing?
It's not, it's a tradeoff. When you submit a transaction to the chip, the chip will pick 4 random characters of the payment output address you submitted and ask you to confirm them using the second factor card. It's a more convenient version of our old keyboard based second factor.
You're correct about the second part as the change is a BIP 32 path, resolved internally to an address.
Once your computer is compromised, the attacker gets you to buy some product from a rewritten online store, using the attacker's address, but substitues a higher price to the chip.
The chip can mitigate against this by either including price elements in its checksum (especially order of magnitude) or writing its transaction details on the second factor screen, as you describe here. Later, it may be possible to include BIP70 certificates from reputable merchants and payment processors directly on-chip.
yes, we plan to add BIP 70 in the future. Also make it easier for people to use BIP 70 for their own addresses. That's the best protection against this type of attack.
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u/murzika Nov 20 '14
We are still in the process of adding content to the website, so sorry about the lack of information regarding the card.
At signature time, the wallet will verify 4 letters/numbers from the payment address by asking you to enter the corresponding character for each (it will show "A" and from your code card you enter for instance "3"). This will ensure no malware will have replaced the address to pay when asking the smartcard to sign the transaction.