Beat spam using hashcash (IBM developerWorks) [LWN.net]

David Mertz discusses hashcash as a spam prevention method on IBM developerWorks. "Built on the widely available SHA-1 algorithm, hashcash is a clever system that requires a parameterizable amount of work on the part of a requester while staying "cheap" for an evaluator to check. In other words, the sender has to do real work to put something into your inbox. You can certainly use hashcash in preventing spam, but it has other applications as well, including keeping spam off of Wikis and speeding the work of distributed parallel applications. In this article, you'll meet David's own Python-based hashcash implementation."

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Beat spam using hashcash (IBM developerWorks)

Posted Nov 11, 2004 21:00 UTC (Thu) by ballombe (subscriber, #9523) [Link]

hashcash is based on the assumption that CPU time is scarce to
spammers. However spammers use hundred of thousands of trojaned box
nowadays so it is not clear whether this will have any effects on spam.

However, this is completely unpractical for mailing-lists.

Beyond that, I question the ethic of forcing people to waste resource
to send an email.

Beat spam using hashcash (IBM developerWorks)

Posted Nov 12, 2004 22:19 UTC (Fri) by giraffedata (subscriber, #1954) [Link]

There are lots of different ways spamming happens. It will probably take lots of separate solutions to get rid of it completely. The trojaned spambot problem will probably be addressed with some kind of security solution, whereas no amount of security will stop someone from sending spam from his own machine in his own name. A resource burn might be effective there, though.

However, this is completely unpractical for mailing-lists.

These solutions usually have a feature where you can excuse expected email from the payment. Maybe by password or authenticated source.

The resource burn is particularly effective for those emails you aren't expecting and come from strangers but that are nonetheless valuable to you. For example, an advertisement for a new product you actually want. If the advertiser takes care to selectively send the ad to people who might actually be interested, he can afford the resource burn.

I question the ethic of forcing people to waste resource to send an email

Yeah, me too. It would be much better if we could find a way to make this expenditure by the sender go somewhere besides into thin air. Like to the recipient to compensate him for reading the email. Or to charity.

But this kind of payment is prevalent in our society. Think of all the resources that are allocated according to how long a person is willing to stand in line. Standing in line for 6 hours is the way you prove you want it more than the guy behind you, but it's a total waste of resources.