der Mouse <mouse(_at_)Rodents(_dot_)Montreal(_dot_)QC(_dot_)CA> wrote:
Why? Simply because all the hashcash protocols I've seen outlined, or
that I've thought of, involve some kind of challenge by the recipient
which must be answered by the "payer". A simple example might be "find
a data blob whose SHA-1 hash has these 20 bits set to these values".
Simple attempt (which probably won't work, but would take me a few
hours to figure out why): "The message, including the timestamp
(which must be accurate to 10 seconds and only one is accepted per 10
seconds) and including From and Envelope-To (same as To) must have the
first 20 bits of its MD5 equal to 10101010101010101010; you may insert
an X-HashCash-Munger: header to make it work"
You can't do the work once for many recipients because the recipient
is included in the hash; and you can't re-use it because of the
timestamp.
Seth
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