Beat Spam Using Hashcash

Shell writes "If they want to send spam, make them pay a price. 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." If you're specifically interested in hashcash for your mail server, Camram has some interesting ideas -- their Frequently Raised Objections page may be illuminating.

Hashcash got me arrested...

[Anonymous Coward]

Those damn police dogs can smell through plastic pretty well!

HashCash?

[Hatta]

And remember, you can't spell "Budget" without "Get Bud".

now what?

[Scythr0x0rs]

You make me pay precious CPU time to e-mail my mother-in-law? you insensitive clods!

I had to quit smoking...

[RandoX]

...because I was out of hash cash.

Re:Again?

[AndroidCat]

Yeah, it's not even a new Final Ultimate Solution to the Spam Problem (FUSSP). [bouthors.org]

As an anonymous coward

[Anonymous Coward]

I think it would be great if /. implemented this. If posting took 200 sec of computation then only people with something interesting to say would bother. Much less spam and karma-whoring.

Flamewars would be restricted to people at work posting from supercomputers :)

-J

How many numbers would that be?

[Skapare]

However, verifying a stamp requires just one SHA-1 computation. For use in e-mail, a 20-bit value is currently the recommended price: Senders need to perform about a million trials to find a valid stamp, which takes less than a second on the most recent CPUs and compiled applications. And it still takes only a few seconds on relatively old machines.

Fur sail 2 u nou: 5 mil-leeun facter numberz

Yuz cun b-u-l-k f4ster wit dis CD uv all-ready calcoolated leest uf numbors. Fer onlee $99.95, u getz ohver fiv milyun numz ant wee tos in freeee a miliun fresh A-O-L addys. Vizut us @ hotprimefactors.biz to ordur.

It's easily solved

[Skapare]

It's easily solved. Just buy the CD of pre-calculated prime factors from the spammers.

Re:Hashcash got me arrested...

[Infinityis]

Maybe Winzip and Ziplock should merge. I think it'd be nice to have encrypted, password protected sandwich bags, but at 90% compression, I think the bread might not taste so good afterwards.

People at Best Buy

[Renraku]

Wow, they can see the future!

They've been telling people for YEARS that anything under the top-of-the-line computer won't be able to send email or brose the internet!

Hashcash....hmmmm....

[Shant3030]

reminds of what I used to call my student loans while in college...

Re:hashcash.org is down..?

[Tablizer]

Funny this story should appear today.. I have been trying to find a mirror of hashcash.org for the last few days...

Oh, they've got mirrors, but you needa hashcode to read 'em

Re:Slashdot Spam Form Response

[TekPolitik]

Your post advocates a _____ approach to fighting spam.

Leave the poor misguided fools alone. Seriously, if they're putting in the effort to do this anyway, just let them try. They can even start demanding HashCash if they want - and it's their problem when the rest of us just decide it's not worth the additional effort to send them email.

Your idea will not work. Here is why it won't work.

There is one foolproof approach to ensure you never, ever receive another spam email again. Shut down your mail server and stop using email. Or insist senders provide HashCash tokens - it amounts to the same thing.

Re:Hashcash got me arrested...

[zexxxx]

Winzip is lossless. The bread should taste the same...