HUGE denial of service attack against any ecash customer!!!

[Ian Goldberg <iang@cs.berkeley.edu>]

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(Again Cc:'d to ecash-feedback, hoping for a security prize.  I wonder
 who's keeping track...  Also Cc:'d to cypherpunks, for fun...)

So I had some more free time... (Dave cringes when I say that.)

Here's a cute one:

Give me an account number, and I can prevent it from being used until
an arbitrary time in the future (of my choosing).

How?  Simple.

Send a deposit message with 0 coins (well, any message will work, I think, but
this is one of the simplest messages there is) with a timestamp of some future
time.

Messages stamped prior to that (such as everything coming from the
actual user for that account, until the time comes) will be politely
discarded.  (Actually, I think the last reply to a withdrawal request
is continually resent, but I'm not exactly sure of this.)  In any case,
the actual user will be unable to withdraw money from his mint until
the time sent in the denial-of-service message.  (Unless he forward-dates
his computer's clock, or something...)

I've tested this against myself and Sameer (with his cooperation, of course).
Anyone else want to be locked out for an hour?  (Actually, I could pretty
effectively lock out _everyone_ for an arbitrarily long time, it seems...)

   - Ian "Right.  I want the sources to the client and the server
          released.  Now."  :-)

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