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RPOW - Reusable Proofs of Work
mitd writes "Hal Finney is inviting folks to test drive his new hashcash-based server rpow.net.
" The RPOW system provides for proof of work (POW) tokens to be reused. A POW token is something that takes a relatively long time to compute but which can be checked quickly."
Hal's security model paper is well worth the read and his proof of concept code is available for download.
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Spammers send millions of email a second, imagine if for every email they had to do some sums that took 2 seconds, before the server would accept the email...suddenly the rate of emails per second falls.....
Google Cache after slashdotting... http://www.google.ca/search?q=cache:YHGDB5MH4e0J:r pow.net/+&hl=en
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But seriously, the server went down after two replies, but not before I managed to get this:
[Read this instead adding a load to a battered server]
and this
-- "I'm not a religious man, but if you're up there, save me Superman..."
It is essentially a computer algorithm that is time consuming to calculate but fast to verify. It can be used to mitigate denial of service attacks for example. When a connection is made, the server will make a challenge which the client must compute. The server can quickly verify the response and reject the client if it is wrong. The extra computation means the client cannot succeed in an attempt to connect without doing the challenge thus slowing them down.
Can someone explain the concept behind this in a little uhh easier terms.
Here's how I understand it:
Imagine you have to do a research paper. Though it takes a long time to write this research paper, what you turn in to your professor is (relatively) quickly checked. The paper itself is like a POW token -- It proves that you did the work without you having to redo the work while the teacher is watching.
-nova20
All this means is that, as well as the net connection being slow, the processor will be running overtime calculating the checksums. The spammers will send as many emails as ever.
SPF has to be one of the easiest measures we can take to reduce spam. Spamassassin is about to hit 3.0 RC1 and many more of us will be able to easily associate scores with SPF records. As soon as mail has to originate from the correct domain we get better spam checking and a paper trail for the authorities to follow. If you don't have SPF records for your domain, head on over here or here and set them up.
As I read through the comments on this article, there are a few that seem to indicate that the poster was completely clueless. And then, when I look more closely, I see that all of them were posted by the same person.
Yes, I know that I shouldn't post replies like this, but this is getting annoying. Quite a few people have posted explanations about what this technology could be useful for. Make an effort to understand it, instead of continuing to post "I don't understand" comments.
You said: "Noone's going to install dedicated IBM crypto hardware in their mailservers. No company is going to invest big bucks in a mailserver just so it can run 100% CPU utilization all the time for no good reason. That costs actual real world money, and continues to cost in power usage."
That's absolutely right, and that's the whole POINT of POW tokens. If you are going to send one or two emails, it won't bother you all that much that your computer has to perform a few seconds of computation before your email gets accepted. If you are a spammer and you want to send a MILLION emails, then your computer would have to perform a few million seconds of computation, which would either slow you down tremendously OR force you to pay real money to buy lots of fast computers and power them.
The problem with the CURRENT model of email is that the sender does not have to pay anything to send spam, so they can send millions of them, and it's still worthwhile if they get one reply in ten thousand attempts. But if they had to pay something to send each spam, they would send less.
Junk snail mail senders have to pay for postage, and so, even though they may be annoying, they are not the same kind of problem as spammers are. They tend to send out flyers only for things that they expect to get SOME response for.
You also said "So spammers spam each other (or themselves from a different host) and have an endless supply of RPOW tokens." Again, you've missed the point. If they spam each other, then yes, the recipient now has the ability to send out the same amount of spam, but the sender has used up his tokens by transferring them to the sender. No new POW tokens are created by this process. If I give you $10 and you give me $10, we're NOT both $10 dollars richer -- what I gave you, I no longer have. And if we pass the $10 bill back and forth 100 times, we haven't somehow created $1000 for each of us to spend; we still have the same amount of money that we started with.
And your point about us not wanting secure hardware on our machines is irrelevant. Nothing in this idea implies that you should have secure hardware on your machine. It can all be done in software, open source software (or any other kind).
The RPOW website is really easier to understand if you first read the hashcash website it point to. So let's talk first about hashcash, since RPOW is mostly an extension.
With hashcash, I take a datestamp, the recipient's address, and some garbage characters, and put them in an X-hashcash header as part of the email. The garbage characters have been precalculated to give some number of '0's at the front of an SHA1 hash of the header. It's computationally expensive to force those '0's, the more '0's, the higher the expense. (The hashcash site mentioned 4 hours to produce 32 '0's on his system.) But it's cheap to verify that those '0's are there in the hash of the header. That's what makes the system work.
There is no challenge-response in hashcash. You publish a 'price', some number of hashcash '0's, to receive email. If the email is in you whitelist (and presumably has a good SPF) call it good. Call other mail without an X-hashcash header spam. You can then validate the X-hashcash headers on your system. Valid headers are stored, and since they contain a datestamp in cleartext, you can purge them after some interval. Note that you only store valid headers, and only for a limited time, so the database doesn't grow forever.
Hashcash requires no central server or database.
RPOW works off of hashcash. You make a hashcash 'stamp' and trade it in for a RPOW token. Since the RPOW lets that original computational effort be reused, it lets you up the 'price'. ie - require more '0's in the hash.
I haven't read the documentation thoroughly, but I suspect that RPOW is validated at the server, not by challenge/response. But remember that each RPOW ticket is used only once, and once shown secure, there wouldn't be a lot of attempts at spoofing. So the traffic volume (and server requirements) should remain reasonable. In other words, the server traffic would be related to the level of legitimate email, not the level of spam. Oh, when you check the RPOW with the server, it hands back a new RPOW that you can use to send email. As far as I can tell, there is no theoretical (only practical) lifetime limit to the tokens.
I'm less enthusiastic about RPOW than hashcash, simply because of the central server requirement. I also wonder/fear about the feasibility of building an SHA1 engine out of FPGAs that could precalculate stamps faster than any regular PC, and then distribute them to spambots for mailing.
The living have better things to do than to continue hating the dead.