Re: [ANNOUNCE] contrib/hashcash.el spam fighter

[Simon Josefsson <jas@extundo.com>]

Stainless Steel Rat <ratinox@peorth.gweep.net> writes:

> | This is not how X-Hashcash works.  The sender must generate a X-Hashcash
> | specific for each recipient.  The recipient keeps a database of received
> | coins to prevent double spendings.  There are some descriptions and links
> | at http://www.cypherspace.org/~adam/hashcash/.
>
> So, the recipient must keep a list of -all- hashes he has received?  And
> must search that ever-increasing database for every message he receives?
> This puts more work on the recipient than on the sender.  

No, it does not work like that.  Each coin has a limited life length
(e.g., 28 days), the receiver only has to keep track of valid ones
within the time window.  This is explained on the web page...

> And what happens when a legitimate sender accidentally generates a
> hash that has been used already?

If you have good random number generator, this won't happen in practice.

> The more I learn about X-Hashcash, the more I see that it is doomed to
> fail.

Do you have a better idea?