Re: Idea for alternative hashcash/antispam implementation.

Jesper Krogh wrote:
...
> Greylisting is currently an exstremely effective way to stop spam at the
> moment since most spammers use broken MTA's and thereby don't redeliver the
> message. But as greylisting becomes more and more used, this picture is
> likely to change.
> 
...

> The only negative thing I can come up with at the moment is that it
> requires an SMTP-protocol update in order to work.

I created a variant called Brown listing.  It uses existing blacklists 
but if the message has a hashcash stamp in it, it passes.  The cost of 
postage for passing a blacklists is approximately three times that of 
e-mail from a non blacklists a source.  no need to modify SMTP, uses 
existing data sources and builds on ordinary hashcash embedded within 
e-mail.

additionally, with information gathered via camram, one could build a 
group filter mostly automatically and any errors could be handled by 
feedback created through white listing and large initial stamps. (i.e. 
spam sources identified by corrected content filter data and corrections 
applied by white listing sources)

I also suggested a method for propagating postage requirements via DNS. 
  One could use that to propagate the brown list value or one could 
stick the brown list value into the 500 response message.  The initial 
weakness would be that with a small number of users, it could be 
overwhelmed by the resources of the spamming community but as the user 
population grows those resources would be quickly overwhelmed.  In the 
beginning, one could make the multiplier five or 10 times.  A 10 minute 
stamp for someone on a blacklist is not too horrible (unless it's me ;-))

---eric



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