Perry E. Metzger wrote:
Florian Weimer <[EMAIL PROTECTED]> writes:

* Perry E. Metzger:

Nick Owen <[EMAIL PROTECTED]> writes:

It would seem simple to thwart such a trojan with strong authentication
simply by requiring a second one-time passcode to validate the
transaction itself in addition to the session.

Far better would be to have a token with a display attached to the
PC. The token will display a requested transaction to the user and
only sign it if the user agrees. Because the token is a trusted piece
of hardware that the user cannot install software on, it provides a
trusted communications path to the user that the PC itself cannot.

On the surface, we already have such technology in Germany (it's
optional for bank customers), but there's a drawback: The external
device doesn't know anything about the structure of banking
transactions, so it relies on the (potentially compromised) host
system to send the correct message to display before generating the
signature.  Ouch.

That could be fixed. I think the right design for such a device has it
only respond to signed and encrypted requests from the issuing bank
directed at the specific device, and only make signed and encrypted
replies directed only at the specific issuing bank. If anything in
between can tamper with the communications channel you don't have the
properties you want out of this.

Not entirely clear what you mean by the "issuing bank" here, but I'm hoping you don't mean that the bank issues the device - that would be very tedious.

I also find "directed only at the specific issuing bank" unclear - I presume you mean encrypted s.t. only the issuing bank can read it? In which case, you're adding complexity - a relying party has to let the issuing bank come between it and you to get anywhere. This would preclude, for example, offline transactions.

As I've said before, I totally agree that the only way to go is to have signatures made on such a device, but I do think its very important to design the thing right - and the above isn't sounding right to me.



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