On 4 Mar 2000, Secret Squirrel wrote:
> Good point. In fact if a fixed-order mix chain is used (everyone uses
> the same order), then the aggregated amount is just passed as one chunk
> from one remailer to the next. However, when it gets to the final
> remailer it must then be broken up again into its constituent pieces.
> If one person is paying $10.25, another $51.49, another $3.99, etc., then
> when the last remailer disburses exactly these amounts to the recipients,
> everything will be revealed.
Pretty much puts a kibash on Hettinga's ideas if implemented this way...
> This seems to be a serious problem which must be addressed. Some of the
> ideas from mixmaster don't work here, like padding messages to a standard
> length. That would be analogous to "padding" all payments up to a
> standard value, but that just won't work for most financial transactions.
Sure it will provided the transactions have adequate book-keeping.
> This is the model of the almost omniscient but still strictly passive
> attacker. It was always unrealistic for the remailers (how hard for
> the NSA to steal keys?). But for the payment mix, this is actually a
> very good model for what the bank knows. It sees every payment in the
> system, it knows exactly who is paying whom. But it knows nothing about
> how payments are combined and disbursed within any one node of the system.
So how does one check the remailers to make sure they/re aggregating
correctly? Somebody has to have access to those logs which makes them
vulnerable to exposure to the banks. Further the banks could look at the
traffic going in and that coming out w/ respect to time and get a good
picture of what got combined where.
What this gives us is a system that is exposed at the two ends and audited
in the middle.
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