Re: [Asrg] 3. Proof-of-work analysis

> I'm in the Security Group of the Computer Laboratory at the University
> of Cambridge. Ben Laurie (yes, that Ben Laurie) and I have recently
> been doing some sums on proof-of-work / client puzzles / hashcash
> methods of imposing economic constraints upon the sending of spam...
>
> Ben wanted to know how big a proof was needed for a practical scheme
> he was considering -- and I told him it wasn't going to work. We then
> carefully worked through all the calculations, using the best data
> that we could obtain -- and we did indeed come to the conclusion that
> proof-of-work is not a viable proposal :(

That's a very interesting paper, thank you.  I wonder, however, what 
the distribution curves are like when "regular correspondents" are 
exempted from proof-of-work, not just mailing lists.  Would it be 
possible to re-examine the MTA logs for this type of pattern?

By "regular correspondents" I mean people who know each other well 
enough to send mail regularly, not necessarily frequently - even once a 
week over a period of months.  I ask this because I expect that users 
with slow machines - who would otherwise be the group most 
inconvenienced by proof-of-work schemes - send mail that mostly falls 
into this category.  I don't know, however, how much of the overall 
picture is accounted for by these.

For future work, it might be instructive to identify various non-spam 
use-cases which appear to have a high proof-of-work load - ie. on the 
"long tail" of the distribution curves presented - and consider 
practical ways of relieving or accommodating it.

--------------------------------------------------------------
from:     Jonathan "Chromatix" Morton
mail:     chromi@chromatix.demon.co.uk
website:  http://www.chromatix.uklinux.net/
tagline:  The key to knowledge is not to rely on people to teach you it.

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