Re: New Emacs facilities from Gnus

[Reiner Steib]

On Sun, Nov 04 2007, Richard Stallman wrote:

>     ;;; hashcash.el --- Add hashcash payments to email
>     ;; Maintainer: Paul Foley <address@hidden>
>
> What does this do?  What are hashcash payments?

I have attached some explanatory text from wikipedia below (*).
In (info "(gnus)Hashcash"), there is also some information.

> Will this work with sendmail.el and rmail.el?

Probably it wouldn't be difficult to add it there (maybe in
`sendmail-send-it').

Bye, Reiner.

(*)
,----[ http://en.wikipedia.org/wiki/Hashcash ]
| Hashcash
| From Wikipedia, the free encyclopedia
| 
| Hashcash is a proof-of-work system designed to limit email spam and
| denial of service attacks. It was proposed in March 1997 by Adam
| Back [2].
| [...]
|
| How it works
| 
| Hashcash is a method of adding a textual stamp to the header of an
| email to prove the sender has expended a modest amount of CPU time
| calculating the stamp prior to sending the email. In other words, as
| the sender has taken a certain amount of time to generate the stamp
| and send the email, it is unlikely that they are a spammer. The
| receiver can, at negligible computational cost, verify that the stamp
| is valid. However, the only known way to find a header with the
| necessary properties is brute force, trying random values until the
| answer is found; though testing an individual string is easy, if
| satisfactory answers are rare enough it will require a substantial
| number of tries to find the answer.
| 
| The theory is that spammers, whose business model relies on their
| ability to send large numbers of emails with very little cost per
| message, cannot afford this investment into each individual piece of
| spam they send. Receivers can verify whether a sender made such an
| investment and use the results to help filter email.
| 
| Technical details
| 
| The header line looks something like [3]
| 
|    X-Hashcash: 1:20:060408:address@hidden::1QTjaYd7niiQA/sc:ePa
| 
| The header contains: the recipients email address, the date, and
| information proving the required computation has been performed. The
| presence of the recipients email address forces a new header be
| computed for each recipient, the date allows the recipient to record
| headers received recently and make sure the header is unique this
| email.
|
| [...]
`----