Making the hashcash plugin more useful.

[Andrew Donkin <ar...@waikato.ac.nz>]

I think it is a crying shame that every SpamAssassin installation is a
tiny step away from taking advantage of hashcash headers, but nothing
is prompting mail admins to take that step.  We could do it for them.

I sent this to spamassassin-users a while ago, but I think it was the
wrong audience.  Please read on:



A while ago the hashcash list was lamenting the lack of support in
transfer agents.  They are stuck in a chicken and egg situation where
no user agents will add hashcash headers because no spam checkers are
looking for them.

I think we could bootstrap that process very easily with a simple
addition to SA.

Configuring my own SA setup to benefit from hashcash headers was as
simple as adding "hashcash_accept %u@waikato.ac.nz".  Voila, instant
potential benefit.  Zero actual benefit, since nobody is adding
hashcash headers to their outgoing email, but that's a whole new
crusade.

I think SA distributions should contain a comment block in
"rules/local.cf" along the lines of:

#   If you use the Hashcash plugin, uncomment this and change it
#   to suit your domain:
#
# hashcash_accept %u@YOUR_EMAIL_DOMAIN

Better still, the Hashcash plugin could determine the domain
algorithmically, and use it in the absence of any other
hashcash_accept configuration.  Schemes for doing that based on the
hostname are all half-baked and non-portable, involving trimming
components off the host's DNS domain, but just about anything is
better than nothing.

How about this: use the last three components of the DNS domain if the
last component has two letters, otherwise use the last two components.
Prefix that with %u@(?:.*\.)?

At worst, it will cause the plugin to accept hashcash payments
computed for an address with the correct username but at the wrong
domain.  Hashcash's double-spend protection will prevent the same
payment working twice, so I don't see this as much of a loophole.

What do you think?  At the very least, I would like to see a comment
in local.cf or init.pre.  I see no reason not to.  It is a shame to
see so many SA installations a tiny, tiny step away from taking
advantage of hashcash.


Here are some minor points for Perl programmers and pedants:

- I actually use ^%u@.*waikato.ac.nz$".  I think the hashcash plugin
  should anchor the pattern at both ends.

- More paranoid sites, or those inside .com which is easily polluted,
  should use "^%u@(?:.*\.)?theirdomain.com$" or just
  "^%u@theirdomain.com$"

-- 
_________________________________________________________________________
Andrew Donkin                  Waikato University, Hamilton,  New Zealand

Re: Making the hashcash plugin more useful.

[Tony Finch <do...@dotat.at>]

On Thu, 19 Jan 2006, Andrew Donkin wrote:
>
> I think it is a crying shame that every SpamAssassin installation is a
> tiny step away from taking advantage of hashcash headers, but nothing
> is prompting mail admins to take that step.

Hashcash is useless in the presence of large zombie armies.

Tony.
-- 
f.a.n.finch  <do...@dotat.at>  http://dotat.at/
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