Perry E. Metzger wrote:
Ben Laurie <[EMAIL PROTECTED]> writes:

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.

Tedium is something that computers do very well. They don't care about
how much work they have to do. The only issue is whether we induce too
many serialized public key operations, and thus too much delay.

Sure, but multiple physical devices aren't my computer's problem, they're my problem.

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?

Yup. I want that for a variety of reasons.

In which case, you're adding complexity - a relying party has to let
the issuing bank come between it and you to get anywhere.

That's the case already. Only the issuing bank knows if the account
has any credit left in it, after all.

This would preclude, for example, offline transactions.

We used to live in an era where offline transactions were
important. Now that you can get online literally anywhere, and now
that merchants pretty much are required to check card validity and
funds availability online anyway, that's no longer an interesting
concern. I can't think of the last time I was involved in an offline
transaction -- even folks at street fairs can now afford GPRS and
similar communications for their veriphone (and similar) units.

There are reasons to want to do offline transactions and to not have intermediaries that go beyond mere connectivity. Anonymity being the one of most concern to me, but I'll wager there are others.



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