Beta
×

Welcome to the Slashdot Beta site -- learn more here. Use the link in the footer or click here to return to the Classic version of Slashdot.

Thank you!

Before you choose to head back to the Classic look of the site, we'd appreciate it if you share your thoughts on the Beta; your feedback is what drives our ongoing development.

Beta is different and we value you taking the time to try it out. Please take a look at the changes we've made in Beta and  learn more about it. Thanks for reading, and for making the site better!

RPOW - Reusable Proofs of Work

CmdrTaco posted more than 10 years ago | from the interesting-projects dept.

Encryption 191

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. "

cancel ×

191 comments

Sorry! There are no comments related to the filter you selected.

Umm (4, Insightful)

Anonymous Coward | more than 10 years ago | (#10001783)

Can someone explain the concept behind this in a little uhh easier terms. I read parts on the website, but I think I need a bit of background before I can really understand what is going on. Thanks

Re:Umm (4, Informative)

Anonymous Coward | more than 10 years ago | (#10001854)

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.....

Re:Umm (1)

stratjakt (596332) | more than 10 years ago | (#10002234)

Except that spammers have legions of pwned windows machines that can do the sums for 'em, or under this system, collect RPOW tokens for the spammers use.

Frankly, few companies would be willing to piss away the cash on the extra hardware for this system, and the idea of wasting all that power on all these computations, just for the sake of doing the computations, makes me cringe a bit.

Re:Umm (1)

nkh (750837) | more than 10 years ago | (#10002282)

Does that mean that legitimate mailing-lists servers will have to wait 2 seconds for each e-mails they send? I read a few of these lists and I'm sure there are other solutions to solve spam problems, like killing SMTP once and for all.

If RPOW is trying to slow down spammers, it won't work as it has been already told thousands of times: Windows 0wned machines computing hashes like a cluster...

Re:Umm (3, Informative)

aardvarkjoe (156801) | more than 10 years ago | (#10002651)

Does that mean that legitimate mailing-lists servers will have to wait 2 seconds for each e-mails they send?
This comes up every single time that someone talks about technical means of stopping spam. And every time, we have to remind you that whitelists can solve the problem trivially. (In this case, you have a system where the receiver [you] accept mail without proof of work from mailing lists.)

Windows 0wned machines computing hashes like a cluster...
Right now, cracked boxes are used for sending spam. If you slow down the rate that it's possible to send spam by 1000, then you get a thousandfold decrease in spam.

Re:Umm (1)

speaker4thedead (193887) | more than 10 years ago | (#10002646)

How would this effect valid email lists, like the gentoo newsletter, which people actually want to receive?

Re:Umm (4, Informative)

baywulf (214371) | more than 10 years ago | (#10001921)

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.

Re:Umm (0)

Anonymous Coward | more than 10 years ago | (#10001952)

Sounds like Amercian Gladiator

Re:Umm (0)

Anonymous Coward | more than 10 years ago | (#10002521)

"amercian"

Hmmmm... that word has possibilities. I just know there's a joke in there that's just "dieing" to get out.

Re:Umm (2, Insightful)

MenTaLguY (5483) | more than 10 years ago | (#10002218)

I don't really see how that helps much with distributed DOS attacks, which are the most common variety these days. The number of zombie machines involved is quite mind-boggling.

Re:Umm (1)

Quixote (154172) | more than 10 years ago | (#10002266)

Why not just tell the client to sleep for (int(rand(10)) seconds? In any case: keep in mind that HTTP is stateless (since you mentioned DoS, I'll bring up HTTP, a common DoS target). Each web page you load initiates 10s of connections. Imagine having to wait a couple of seconds for each connection to go through. Suddenly, the 1.2sec it takes to load a page like /. now will take 30sec; probably worse than dialup. Now this doesn't seem to hot anymore, does it? If this (RPOW/HashCash) is a form of electronic currency, then I can see a potential; using it to thwart DoS or SPAM is pointless, since we all know that technological solutions to these problems don't exist.

Re:Umm (5, Informative)

nova20 (524082) | more than 10 years ago | (#10001989)

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

Re:Umm (1, Funny)

LoudMusic (199347) | more than 10 years ago | (#10002219)

It proves that you did the work without you having to redo the work while the teacher is watching.

So in other words we'll have a site in a couple years that has a bunch of POW tokens we can download, change the name, and turn it in as our own? (:

Re:Umm (4, Insightful)

masoncooper (443243) | more than 10 years ago | (#10002555)

I know you meant to be funny but in a sense, you're right. These reusable tokens can be, well, reused. So if someone were to send you an email with a token, you could use that token(or token based on the previous token) to send an email out without having to create a new token. Since spammers are primarily outbound senders they wouldn't accumulate the tokens that a normal corporation would with frequent two-way communication. In effect, this is a lot like currency.

Re:Umm (0, Flamebait)

knodi (93913) | more than 10 years ago | (#10002674)

So this is a cache of term papers? Or a site where you can watch people type term papers? Just kidding, of course. But okay, so I understand it's hard to make tokens, but easy to verify them. What good is that?

Genaric (1)

Morphix84 (797143) | more than 10 years ago | (#10002074)

One of the reasons it's very ambiguous, is that it has multiple applications. The major ones are authentication of things like emails, where you would have to calculate the token for each user, or in the distant future, a form of digital currency that would actually reside on a hard drive as opposed to a server on a bank somewhere.

Huh? (1)

stratjakt (596332) | more than 10 years ago | (#10001786)

A hashcach POW token?

What does this server "serve" exactly?

I'm not sure submitters know quite what "article summary" means.

Re:Huh? (0)

Anonymous Coward | more than 10 years ago | (#10001844)

Hows about RTFA?

"[his] security model paper is well worth the read"

Re:Huh? (1)

stratjakt (596332) | more than 10 years ago | (#10001901)

What FA?

The link to the email? Ok, he has a box with some fancy IBM crypto co-proc in it. That clears things up.

Or his actual server, the one that's completely inaccessable?

20 bucks says the article submitter doesn't even know what this is. He just came across it and figured "bet thats tech sounding enough to get me some slashdot karma".

What problem does this solve? Spam? Hacking? Windows vulnerabilities? Will this put Linux on the desktop? Does this even have anything to do with linux? /. editors don't even know what this is. That's why the story has regular /. colors and wasn't crammed into one of the "sections". Is it a game? Something to do with IT? Anything about how much MSFT sucks and how awesome Apple is in the article? This the new dual screen gameboy from Nintendo? Will I get faster Doom 3 frame rates?

Isn't it obvious? (5, Informative)

BubbaThePirate (805480) | more than 10 years ago | (#10001916)

A POW token is something that takes a relatively long time to compute but which can be slashdotted quickly.

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]

"Overview

The RPOW server is designed to provide security and reliability through an unprecedented degree of visibility and transparency in its operations. For the first time it will be possible for any user of the system, anywhere in the world, to know what code is running on the server and to inspect that code for loopholes or back doors. I have done my best to make this system secure even against my efforts as the owner, operator and designer of the system to compromise its operations. I welcome public scrutiny of the code and of the design.

The RPOW system represents a new kind of security model, and is therefore unusually challenging to present and to review. RPOW combines an exceptional degree of physical security with an unprecedented level of transparency and visibility into the workings of the RPOW server. This combination implements the design goal of RPOW as a "Transparent Server", a system whose security properties can be analyzed and evaluated from any system on the internet.

In operation, the RPOW system consists of three parts: the server, the host process, and the client library with its associated demo driver. We will consider each part in turn. "

and this

"RPOW FAQs

Questions

1. What is the RPOW system?
2. How is RPOW pronounced?
3. How do I know the RPOW system is secure?
4. What is the difference between RPOW and Hashcash?
5. What is the difference between RPOW and Ecash?
6. What are some possible applications of the RPOW system?
7. How fast is the server?
8. If RPOW becomes popular, how could one server handle all the users?
9. Won't Moore's Law mean that tokens lose their value over time?
10. Why can't users pass RPOW tokens to each other without using a server?
11. Won't the RPOW server run out of disk space if it keeps track of all tokens it has ever seen?
12. Are you going to make changes to the RPOW system?
13. Why did you choose the IBM4758 Secure Cryptographic Coprocessor as the platform for the RPOW server?
14. Wasn't the IBM 4758 security broken a few years ago?

Answers

1. The RPOW system has three parts: client, host, and server. The client is a software library (plus a simple command-line driver for demonstration purposes) to allow generation and exchange of RPOW tokens. The host software runs on the PC which has the IBM 4758 cryptographic coprocessor card plugged into it. It acts as an intermediary, listening for connections from the net and passing data between client and server. It also assists the server with certain operations. The server runs on the IBM 4758 card and performs the secure cryptographic operations which implement the RPOW system.

2. RPOW is pronounced are-pow.

3. The security of the RPOW system ultimately depends on its design and its implementation. For the design, see the theory and security pages. For the implementation, see the source code available from the download page. The unique properties of the RPOW system design allow you to remotely verify that the program generated from the source code you download here is what is actually running on the RPOW server. If the design and implementation are sound, and that program is what is running on the server, you have a foundation for trust in the security of the system.

4. RPOW uses hashcash for its proof of work (POW) tokens. Hashcash tokens are evidence that a certain substantial amount of computer effort was expended to create them. RPOW allows hashcash tokens to be exchanged for RPOW tokens of an equivalent value, which can then be further exchanged for new RPOW tokens. The effect is similar to being able to pass hashcash tokens from hand to hand while they retained their value, as if they were real physical objects that had an inherent rarity.

5. Ecash, or electronic cash, is a proposal to create tokens that would be a form of money. A number of ecash systems have been fielded over the years, although so far none have been commercially successful. RPOW uses some of the same technology as certain ecash systems, such as a central server which uses digital signatures to create tokens. However, RPOW tokens do not carry monetary value. And the RPOW system does not require the use of blinding technology in order to protect user privacy. Without blinding, conventional ecash systems would offer users little privacy. RPOW's unique transparency features allow end users to verify that the system will not record the details of their transactions and will protect their privacy, even without cryptographic blinding. See the security page for more information on privacy.

6. Possible uses for RPOW include anti-spam tokens, "play money" for use in online games and fun bets, an aid to load balancing in P2P and file-exchange systems, and more. Any system which would benefit from a form of token which can be cheaply passed from user to user, but which is expensive to create, might want to look into RPOW.

7. The RPOW server can currently perform about 8 exchanges per second. The slowest steps are the RSA decryption of the incoming message, and the RSA signature of the outgoing RPOW tokens.

8. RPOW at present is a proof of concept intended for experimental, non-commercial use. Nevertheless I intend to keep it running for an extended period if possible, in order to let people experiment with the system, and to have some confidence that the RPOW tokens they receive will retain their value. If the concept proves successful it will be possible to expand the system to allow multiple RPOW servers to exist and to share the load of performing the exchanges. See the World of RPOW page for information on expanding RPOW to include multiple servers in a cluster or around the world.

9. If Moore's Law continues to hold true, the cost of creating a POW token will drop at a steady, exponential rate. This will mean that RPOW tokens will in fact lose value, in that an N bit token will be faster to compute today than it was in the past. However, the RPOW system is designed to handle tokens with a wide range of sizes, such that the most expensive token (50 bits) will take about a billion times longer to create than the least expensive one (20 bits). Further, many experts expect computer performance increases to begin falling off the Moore's Law curve (some say it has happened already). These factors should allow RPOW tokens to continue to be useful many years in the future. Keep in mind that this is not money and is not intended to be a stable store of value, but rather an easy-to-exchange representation of computer effort.

10. The RPOW server may appear to be a bottleneck in the design, but actually it is a crucial element. The problem with any digital datum as a representation of value is that it can be reproduced effortlessly. If users could pass RPOW tokens without going through the server, someone could create a single high-value token and then pass it around as many times as he wanted. The RPOW server keeps a record of all tokens which it has ever seen, and uses this to ensure that any created token is only exchanged once. Of course, after an exchange the new token can be exchanged again, and so on, but this is limited to sequential reuse. The result is similar to a physical object which is passed from person to person.

11. Given the size of disks available today, it would take many years before the seen-RPOW database would begin to fill a multi-gigabyte disk drive. And by then, bigger disks will be available. Nevertheless, in case it becomes necessary, the RPOW system does include a plan for rollover. The RPOW server can be commanded to create a new set of keys and start a new database. Old RPOW tokens can still be exchanged, but only new tokens will be created. The old database will still be used for the old tokens. Eventually there will be so few old tokens out there, tokens which their owners have not bothered to exchange in many months or years, that the old database can be erased and old tokens no longer honored. See the World of RPOW page for more information on the key rollover design.

12. Due to the nature of the security of the IBM 4758 board, and the architecture of the RPOW system, any changes to the RPOW server software will wipe the keys on the board. That would mean that all RPOW tokens out in the field would become worthless. Hence, I do not intend ever to change the RPOW server source code. I will attempt to keep the server running and unchanged for an indefinite period. The only exception will be if, through public review, someone finds a security weakness in the RPOW implementation which would defeat the security goals of the system. In that case it will be necessary to start over from scratch with new code, and new RPOW tokens will have to be created. I hope it won't be necessary. The RPOW server code is not all that complicated, so there is reason to expect that it does not have flaws sufficient to defeat its security.

13. The IBM 4758 coprocessor card has a number of desirable features for an RPOW server. For one, it is highly secure against physical attack, making it extremely unlikely that an RPOW operator could manipulate his server and make it misbehave, or steal the keys or other private information. But the most important feature of the IBM 4758 for this project is its support for what IBM calls Outbound Authentication. This capability, also known as Remote Attestation, allows the board to issue a signed certificate chain, using a private crypto key that never leaves the board, which attests to a cryptographic hash or fingerprint of the software running on the board. This certificate chain ultimately goes back to an IBM root key which is published on IBM's web servers and in the 4758 documentation. It is this capability which is the foundation for RPOW's security, the ability of remote users to validate that the published RPOW source code is actually running on the RPOW server that they are communicating with. No other secure hardware that I am aware of presently supports remote attestation based on a published key, as IBM does. This makes the IBM 4758 the only possible platform for RPOW servers.

14. In 2001, two Cambridge University researchers, Mike Bond and Richard Clayton, discovered an attack on the IBM 4758 which allowed them to extract a 3DES secret key held on the processor. However, this was not an attack on the 4758 itself, but rather a weakness in the application which was running on the IBM 4758, IBM's CCA (Common Cryptographic Architecture) support code. CCA failed to properly protect its keys in certain operations, and the researchers found a way to bypass the protections. RPOW does not use CCA in any way, so the attack is not relevant to RPOW. (IBM fixed their CCA software a few months later, so the attack no longer works against CCA, either.)"

Mod parent UP (0, Informative)

Anonymous Coward | more than 10 years ago | (#10001967)

informative.

Re:Isn't it obvious? (1)

stratjakt (596332) | more than 10 years ago | (#10002006)

So basically, this serves up encrypted blobs of crap that have no meaning other than you can assume the server spent a little time encrypting up the blobs of crap..

And a few mentions of what it "could" be used for, but of course it wont be.

So basically we have another neat solution out in search of a problem. That explains the lack of any "what the fuck is it?" verbage in the article summary. It really isn't anything.

Article Troll! (0)

Anonymous Coward | more than 10 years ago | (#10002423)

using a private crapto key

craptographic hash or fingerprint

and will protect their privacy, even without cryptographic blinding

What exactly is craptology there buddy.

taking bets on it's slashdoting (0, Redundant)

thexdane (148152) | more than 10 years ago | (#10001800)

story just went up and the site is slow, so it won't take long before it's not there anymore :|

Turkey lock. (-1, Troll)

Anonymous Coward | more than 10 years ago | (#10001806)

Lock the turkey! Glue it away.

My shoes speak to them, but we must refinance our broccoli.

More info on Hal can be found.... (2, Funny)

zegebbers (751020) | more than 10 years ago | (#10001836)

There is some excellent info on Hal here [tripod.com] , here [cnn.com] and here. [stat-junkie.com]

Re: RPOW - Reusable Proofs of Work (5, Funny)

Anonymous Coward | more than 10 years ago | (#10001839)

Hal's security model paper is well worth the read and his proof of concept code is available for download.

"I'm sorry Dave, but I can't let you download that..."

Re: RPOW - Reusable Proofs of Work (0)

Anonymous Coward | more than 10 years ago | (#10001972)

Hal's security model was excellent. Dave had to resort to direct hardware access to defeat it.

Cracked in 5..4..3... (0)

Anonymous Coward | more than 10 years ago | (#10001842)

I hope he doesn't use MD5 Hashes [slashdot.org] .

Verify (1)

Davak (526912) | more than 10 years ago | (#10001847)

Whoa...

I need some ubergeek translation on this one. Is this a complicated, better method for verifying against known published source code?

Davak

Re:Verify (4, Interesting)

3-State Bit (225583) | more than 10 years ago | (#10002103)

No, I don't think so. The idea of proving you've done some work is that you have made an investment and so are not doing 100,000 such investments per second.

However this probably doesn't work [cam.ac.uk] (PDF) [or as html [66.102.9.104] ].

Background (from that paper):
It is often suggested that unsolicited bulk email ("spam") is such a problem on the Internet because the current economic framework for email handling does little to discourage it. If only, it is suggested, the senders of email could be made to pay for their messages. Spammers would then cease their indiscriminate distribution of messages and email volumes would reduce as the senders targeted more carefully or just gave up altogether. Nevertheless, almost no one (other than those hoping for a handling fee) thinks that using actual money is a good way to achieve this economic utopia and even the holders of patents for "e-money" systems have failed to generate any significant enthusiasm for their wares.

However, there is an alternative to real-world money, which was first proposed by Dwork and Naor in 1992 [8]. Their idea was to have the sender of an email perform a complex computation as evidence that they believe that an email is worth receiving. The sender then proves to the recipient that this processing work has been completed and the email will then be accepted. The processing time is "free", so there is a minimal burden upon legitimate senders, but it is a finite resource, so that the spammers will not have unlimited amounts of processing time at their disposal and so cannot continue to send in bulk.

/.ed (5, Funny)

Dibblah (645750) | more than 10 years ago | (#10001848)

Okaaay... So it's a server that's *meant* to serve computationally expensive 'tokens'. And you post it on ./ . Niiice.

Re:/.ed (1)

FooAtWFU (699187) | more than 10 years ago | (#10002164)

Yes, to *serve* the tokens. Not to compute the tokens- other people do that. It'll just give you work and check the incoming result, which is *not* computationally expensive.

Re:/.ed (1)

jovlinger (55075) | more than 10 years ago | (#10002609)

sounds like the job for any problem in NP.

Proofs Of Work are few and far between (4, Funny)

Anonymous Coward | more than 10 years ago | (#10001853)

How about Proofs Of Not Working? Got plenty of those.

Huh? (0)

julesh (229690) | more than 10 years ago | (#10001868)

I don't get it. I understand the concept of what you would use one of these 'POW' tokens for (although the name is clearly ridiculous... acronym clash should be avoided whenever possible) -- e.g. to bypass a junk e-mail filter. But why would you want to be able to reuse them?

Re:Huh? (3, Informative)

teemu.s (677447) | more than 10 years ago | (#10002005)

my guess: cause its unfair if they would not be reuseable. you spent time/money/cputime for getting such a token - so if you spend them - you loose this. but if they are reuseable - and because its about pow tokens, where it can be proven, that you did that work - you just exchange your once made pow token against another and use it for e.g. outgoing email:

form the website:
"Using RPOW tokens for email would have advantages, as people could then reuse tokens from incoming email in outgoing email. Spammers will have no such advantages since almost all of their email is outgoing. Reuse allows the cost of the POW token to be much higher since most people won't have to generate them, making the system more effective as an anti spam measure."

Re:Huh? (1)

stratjakt (596332) | more than 10 years ago | (#10002144)

So spammers spam each other (or themselves from a different host) and have an endless supply of RPOW tokens. No problems solved.

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.

Besides, I thought we didn't want that kind of "secure" hardware in our machines. We don't want it when it's called Palladium or TCPA, at least.

The only use the article gives that makes sense to me is that of "play money for internet games". That'd work. An imaginary solution to an imaginary problem.

Re:Huh? (1)

It'sYerMam (762418) | more than 10 years ago | (#10002265)

If those who programmed mailservers would build in a delay between a person's outgoing emails, then we could do away with this.
The spammer could send as many as he wished, but they'd get caught up in the server, giving the same effect as a POW system but without the possibility of cracking.
Of course the spammers could set up their own little server, but that'd be DoSable/Legally Take Down-able.

Re:Huh? (2, Insightful)

stratjakt (596332) | more than 10 years ago | (#10002406)

Build in a delay? You mean in all the open source mail software thats used?

Surely noone would be smart enough to open the sendmail sourcecode and comment out the wait() lines.

All these schemes that rely on your computer "wasting time" to stop spam are silly.

I know, we can stop the spread of warez by making all file serving protocols automagically cap themselves at 2kbit or so. HTTP, FTP, P2P apps.. It's an awesome plan!

Wait I got a better one! We all go back to 300 baud dial-up modems. The ones you hand-dial on an old-timey rotary phone and then stick the handset onto the acoustic coupler. That's the ticket! What an awesome anti-spam plan. If you make the internet utterly fucking useless, all the spammers and bad guys will stop using it!

All ethernet technologies will be banned, computers will be networked with multiplexed RS-232 cards, with a hardware limit of 19,200 baud. Think about it, if a machine got infected on your "network", it wouldnt be a big deal, since your network couldn't possible contain more than a dozen nodes anyways. And it would take 20 minutes to "spread" to the next machine.

Actually all my sarcastic schmes are more pallatable to me than letting IBM jam their "trusted" hardware into my case. I dont want TCPA, not from Microsoft, and not from "our benevolent friends" at Apple or IBM.

Re:Huh? (1)

teemu.s (677447) | more than 10 years ago | (#10002338)

this "spammer spam each other/themselves" scenario would need the fact, that a normal spammer has the ressources (MTAs) doing so - do you think, they run their own MTAs in .tw?

Re:Huh? (4, Informative)

ifdef (450739) | more than 10 years ago | (#10002592)

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).

Re:Huh? (1)

armando_wall (714879) | more than 10 years ago | (#10002299)

I don't get it...

ObviousGuy?

Re:Huh? (1)

sk8king (573108) | more than 10 years ago | (#10002643)

That's funny. No mod points though.

Obligatory Pun (3, Funny)

grunt107 (739510) | more than 10 years ago | (#10001890)

Given the inaccessibility of the site:
RPOW/rMIA (break out the black flags w/web server silhouette)...

Re:Obligatory Pun (3, Funny)

trb (8509) | more than 10 years ago | (#10002068)

I was thinking, hashcrash-based server.

Re:Obligatory Pun (1)

shadowcabbit (466253) | more than 10 years ago | (#10002329)

Yeah, funny how appropriate the onomatopoeia/acronym "POW" is in this case...

Well, here it comes: (-1, Redundant)

WhatAmIDoingHere (742870) | more than 10 years ago | (#10001891)

Can't test drive a car after it's hit a tree head-on.

Can't test a site that's been /.'ed

Anon posting, ARTICLE TEXT (3, Informative)

Anonymous Coward | more than 10 years ago | (#10001907)

Reusable Proofs of Work
by Hal Finney
(hal at finney dot org)
What Is This? Theory Security Try It Out! FAQs Download

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. RPOW uses hashcash, which are values whose SHA-1 hashes have many high bits of zeros.

Normally POW tokens can't be reused because that would allow them to be double-spent. But RPOW allows for a limited form of reuse: sequential reuse. This lets a POW token be used once, then exchanged for a new one, which can again be used once, then once more exchanged, etc. This approach makes POW tokens more practical for many purposes and allows the effective cost of a POW token to be raised while still allowing systems to use them effectively.
Security

This is useful functionality, but the unique feature of the RPOW system is its approach to security. RPOW is the first public implementation of a server designed to allow users throughout the world to verify its correctness and integrity in real time.

Based on principles similar to those proposed for so-called "Trusted Computing", RPOW allows third parties to dynamically and remotely verify what program is running on the RPOW server. The RPOW server is implemented on a high-quality secure processor, the IBM 4758 PCI Cryptographic Coprocessor, which has been validated to the highest level of security publicly available, FIPS-140 level 4. The 4758 is a self-contained single-board computer which has its own device key, generated on-board, which never leaves the card. That key can issue cryptographically signed attestations which describe the software configuration running on the card, including the SHA-1 hash of the application program.

The source code to the RPOW server is available from the download page. Using publicly available tools, anyone can build from this source code a memory image identical to that running on the RPOW server. If the SHA-1 hash of this file matches that being reported by the 4758 device key, the user can conclude that the supplied source code is what is actually running on the 4758. By inspecting the source code he can then make sure there are no "back doors" or loopholes that would allow the owner/operator or designer of the system to defeat its security, for example by creating RPOW tokens without doing the required work.

Allowing clients to dynamically validate the security of a server turns the concept of Trusted Computing on its head. Rather than a threat to individual privacy, the technology becomes a boon to privacy and an empowering force for end users on the net.
Applications

Security researcher Nick Szabo has coined the term bit gold for information objects which are provably costly to create. He suggests that these could even serve as the foundation for a sort of payment system, playing the role in the informational world of gold in the physical world. RPOW would facilitate the use of POW tokens as a form of bit gold by allowing the tokens to be passed and exchanged from person to person.

POW tokens have been proposed as a form of pseudo-payment in several applications. One example is email. An email message containing a POW token would be relatively costly to send in terms of computing power. A POW token could then be a sign that the message was not spam.

Using RPOW tokens for email would have advantages, as people could then reuse tokens from incoming email in outgoing email. Spammers will have no such advantages since almost all of their email is outgoing. Reuse allows the cost of the POW token to be much higher since most people won't have to generate them, making the system more effective as an anti spam measure.
Transparent Servers
The RPOW system is just the first of what are planned as a series of systems which use this approach, which I call Transparent Servers. Such systems publish their source code for review and inspection, and use Trusted Computing-like features to prove that they are running the program generated by that code. This will provide an unprecedented level of transparency and visibility into the workings of network servers.

Perhaps most importantly, the use of transparency can actually increase end-user privacy. For the first time, users will be able to verify how network servers will handle sensitive information they provide. In the case of the RPOW server, users can see that the program makes no record of transactions and creates no linkage between the RPOW issued in one exchange with the same RPOW when it is later deposited, thereby protecting privacy. In addition, the basic security goal of the system, that it will never issue RPOWs without receiving a POW or RPOW of equal value, can be independently verified. Not even the owner of the RPOW server can break these rules.

For more information on the techniques used to provide these new and previously unavailable assurances, see the security page.

Digital Money (-1)

Anonymous Coward | more than 10 years ago | (#10001910)

It's an attempt a a digital money system. The primary problem with digital money is that it's too easy to duplicate, so you can't really trust someone who gives you digital money as they could also give it to someone else.

This system attempts to prevent that by modifying the digital money every time it changes hands.

Fragile Mirror (1)

Viral Fly-by (662186) | more than 10 years ago | (#10001914)

RPOW.net Home [truman.edu]

FAQ and "What is this?" links also included...

RPOW (0, Redundant)

rhs98 (513802) | more than 10 years ago | (#10001917)

This is the most useless website for a simple explaination of what this is for, or even what it is! Even the faq [rpow.net] page doesn't make much sense.

Looks like his server has been tested slashdot style though!

Mirror of article/download (1)

chrisopherpace (756918) | more than 10 years ago | (#10001935)

HERE [hnsg.net] .


NOTE: Only the source code is mirrored, site is way too slow to mirror the rest!

Re:Mirror of article/download (1)

chrisopherpace (756918) | more than 10 years ago | (#10001979)

Shoot, forgot the download link: HERE [hnsg.net] .

The file is downloading as I type this, hopefully it will finish so I can mirror it.

Defeating the purpose? (2, Insightful)

Anonymous Coward | more than 10 years ago | (#10001966)

Doesn't this really defeat the purpose of computationally expensive tokens? Couldn't a hacker break into the cache and steal a large number of pre-calculated POW tokens which would otherwise be impossible?

Easier Explanation of RPOW & RPOW Uses (3, Interesting)

diagnosis (38691) | more than 10 years ago | (#10001992)

From the web sites:

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. RPOW uses hashcash, which are values whose SHA-1 hashes have many high bits of zeros.

Possible uses for RPOW include anti-spam tokens, "play money" for use in online games and fun bets, an aid to load balancing in P2P and file-exchange systems, and more. Any system which would benefit from a form of token which can be cheaply passed from user to user, but which is expensive to create, might want to look into RPOW.


It's not clear to me that there is an obvious and immediate equivalent for RPOWs in existence. I'd be interested in hearing what people think this would be good for. It generally seems useful for making sure people do x amount of work before they are allowed to perform a task, but what can that be used for?

---------------------
Freedom or Evil: Freevil.net [freevil.net]
G. W. Bush says, "You decide!"

Re:Easier Explanation of RPOW & RPOW Uses (1)

pkhuong (686673) | more than 10 years ago | (#10002238)

Virtual money. If we agree that time*computing power=value, then we can assign a value to each token so that there is no gain to be made by creating a new token. While it may seem wasteful - GroupA use x h*flops to get y h*flops back, and x can't be too much smaller than y -, one must keep in mind that the token may be reused, so that GroupA only has to waste x*[number of tokens in circulation] h*flops to receive n h*flops. IE, for the system to work, there must be an incentive to not stockpile tokens. Fortunately, Moore provides us with built in inflation!

Re:Easier Explanation of RPOW & RPOW Uses (1)

pkhuong (686673) | more than 10 years ago | (#10002570)

yes, h*flops is n flaoting point ops. But who'd understand me if i said flo? (**** anal friend, yes i should have said floationg point ops :)

equivalent for RPOWs in existence (2, Insightful)

2nd Post! (213333) | more than 10 years ago | (#10002347)

Money. Difficult to make, easy to verify.
Goods. Like a car.
Trust. Extremely difficult to make, easy to verify.

Re:Easier Explanation of RPOW & RPOW Uses (1)

Pendersempai (625351) | more than 10 years ago | (#10002811)

The dollar. Currency, at its simplest form, is proof of value to society: work.

Proof-of-work tokens as an anti-spam measure? (4, Interesting)

JaredOfEuropa (526365) | more than 10 years ago | (#10002024)

For those asking what on earth (R)POW tokens are, here's one possible application (from rpow.com):
POW tokens have been proposed as a form of pseudo-payment in several applications. One example is email. An email message containing a POW token would be relatively costly to send in terms of computing power. A POW token could then be a sign that the message was not spam.


Using RPOW tokens for email would have advantages, as people could then reuse tokens from incoming email in outgoing email. Spammers will have no such advantages since almost all of their email is outgoing. Reuse allows the cost of the POW token to be much higher since most people won't have to generate them, making the system more effective as an anti spam measure.
An interesting scheme...

One potential problem I see with such an anti-spam measure is that I keep hearing about spam runs being done from many regular users' computers by means of a spamming worm infrection. Such a worm could also be adapted to generate the POW tokens... or even steal them from the users' incoming email and re-use them under this scheme! That'll be just great, having your computer not only hijacked to send out spam, but loaded down with the heavy burden of generating POW tokens.

Re:Proof-of-work tokens as an anti-spam measure? (2, Informative)

4of11 (714557) | more than 10 years ago | (#10002242)

Although if spammers did use zombied computers, maybe the owners of the infected PCs would know something was wrong when their computer was runnning so slow they couldn't do anything. Right now, these computers can send out tons of emails without significantly hitting its performance. This is key, because if the computer becomes unusable, it will soon not be available for spamming when the user takes it to the shop. Maybe the central server could even put a limit to new keys per hour per IP to limit RPOW factories like this. In any event, spam would certainly be reduced by this, as each zombie could not send out nearly as many emails.

Re:Proof-of-work tokens as an anti-spam measure? (0)

Quixote (154172) | more than 10 years ago | (#10002314)

as people could then reuse tokens from incoming email in outgoing email.

What's to prevent me from sending the same token to 1 million people? Aha, you say: there'll be a central database of tokens to make sure that they are not being rused en masse. And that, then, becomes your bottleneck, making this useless.

Re:Proof-of-work tokens as an anti-spam measure? (1)

dpilot (134227) | more than 10 years ago | (#10002358)

It's worth linking through to the hashcash site, too. It's fast to validate tokens, and you only store valid ones. That keeps the size within reason. Don't know how RPOW handles it, but the date is part of the hashcash token, and you can set the expiry as part of the validation, also trimming your database.

Re:Proof-of-work tokens as an anti-spam measure? (1)

Rich0 (548339) | more than 10 years ago | (#10002568)

Yes, but how do you reuse them?

Suppose I'm a spammer, I generate one token and use it to send out 1 million emails to hundreds of thousands of different servers. How do the recipient servers figure out that they're being duped?

With non-reusable POW it is simple. The recipient generates a challenge, and the sender calculates the response, which the recipient verifies. A given challenge is only used once, and the recipient can guarantee that by simply using a random number generator - no storage or communication necessary.

On the other hand, if you reuse the POWs there has to be some mechanism for recipients to find out if the sender has used the POW more than once. The only way I can think of is by using a central DB. Now the central DB becomes a bottleneck, since it has to handle a request for every email sent between any two parties on the internet. Sure, you could distribute the load (put a server ID in the RPOW), but now you have thousands of these servers - who pays for them?

Re:Proof-of-work tokens as an anti-spam measure? (1, Informative)

Anonymous Coward | more than 10 years ago | (#10002539)

What's to prevent me from sending the same token to 1 million people?

You can't re-use tokens if the mail server you are connecting to issues a different challenge each time, and you must compute a POW based on the challenge issued by the server.

Re:Proof-of-work tokens as an anti-spam measure? (1)

Rasta Prefect (250915) | more than 10 years ago | (#10002547)

What's to prevent me from sending the same token to 1 million people? Aha, you say: there'll be a central database of tokens to make sure that they are not being rused en masse. And that, then, becomes your bottleneck, making this useless.

No, not really. Generally these schemes involve the token being in some way tied to the specific message. A hash containing the to and from addresses for instance.

Re:Proof-of-work tokens as an anti-spam measure? (1)

DM9290 (797337) | more than 10 years ago | (#10002491)

But at least if your computer is loaded down with the heavy burden of generating POW tokens, the rate at which it can send spam and harm others is reduced. And thus RPOW would have accomplished something beneficial.

Uhhhhhh... (1)

sirGullible (750869) | more than 10 years ago | (#10002033)

"Hal Finney is inviting folks to test drive his new hashcash-based server rpow.net. "
Sure, if by "test drive" you mean /.

Trusted computing? I think not. (1)

42forty-two42 (532340) | more than 10 years ago | (#10002043)

Based on principles similar to those proposed for so-called "Trusted Computing", RPOW allows third parties to dynamically and remotely verify what program is running on the RPOW server. The RPOW server is implemented on a high-quality secure processor, the IBM 4758 PCI Cryptographic Coprocessor, which has been validated to the highest level of security publicly available, FIPS-140 level 4. The 4758 is a self-contained single-board computer which has its own device key, generated on-board, which never leaves the card. That key can issue cryptographically signed attestations which describe the software configuration running on the card, including the SHA-1 hash of the application program.

How do we know it's actually signing the running image? For all we know it's just an ordinary computer programmed to claim it's a 4758.

Re:Trusted computing? I think not. (0)

Anonymous Coward | more than 10 years ago | (#10002202)

Well, yes... I suppose that you could always fly over and visit Hal to convince yourself. Alternatively, I guess you could form/find a web of trust amongst people who have done so.

I really don't see how this isn't trusted computing - I only see that you are paranoid and lazy. (It's a dangerous combo.)

Re:Trusted computing? I think not. (2, Informative)

SpootFinallyRegister (787720) | more than 10 years ago | (#10002401)

Easy.

IBM releases the public key that corresponds to a private key stored on the card, the so called device key. The usual encode message with pub key, give to device, get decoded message back. Nothing will be able to perform this validation without the private key.

The only snag in this is if the hardware can be fooled with to extract the key, and though I really dont know anything about hacking hardare, I can't imagine that a high level security validation is given to a piece of hardware that easily gives up its secure information.

In other words, your xbox is not validated to FIPS-140 l4.

Too bad... (1, Funny)

HawkingMattress (588824) | more than 10 years ago | (#10002070)

I thought it was about providing my boss reusable proofs that i'm working while I'm in fact reading slashdot ;) That would be waaaaay more usefull than this stupid error 500 thing...

Site down? Don't think so... (0)

Anonymous Coward | more than 10 years ago | (#10002087)

I'm not having any trouble connecting, but I still can't figure out WTF a POW is. The site only explains how it is turned into an RPOW.

dude, that's so excellent...who's hungry? (3, Funny)

eufreka (793009) | more than 10 years ago | (#10002127)

Until now, I always thought that "hashcash" was only related to Repeated Puffs of Weed (RPOWs).

And although the process of exchanging "toke'ns" was highly "cryptographic", ultimately not a lot of work got done...

Anyway, I got confused there for a minute, but I am better now. This might help others:

From http://www.hashcash.org/ [hashcash.org]

Hashcash is a denial-of-service counter measure tool. Its main current use is to help hashcash users avoid losing email due to content based and blacklist based anti-spam systems. A hashcash stamp constitutes a proof-of-work which takes a parameterizable amount of work to compute for the sender. The recipient can verify received hashcash stamps efficiently.
Rock on!

Zombie farms (4, Interesting)

Bronster (13157) | more than 10 years ago | (#10002130)

What a crock of a system. Let's see:

a) to be useful for anything involving third parties where you don't already have a trust relationship, this would need to be common/easy enough to get that other people already have software to support these things. That's not going to happen any time soon - it's a big enough change you may as well come up with an already secure email infrastructure [insert boilerplate "why your solution to spam is stupid" here].

b) 8 tokens per second? Puhleaze. I get that many emails through just one small server with 5 domains on it.

c) as the subject says. Zombies. In a world where thousands of low TC0 machines are sitting around running malware, it's piss-easy for the blackhat spammers to collect their 8 tokens/second by running POWer@home on their zombie farm.

BZZZZt. Strike three and you're out. Nice idea, but not practical.

Re:Zombie farms (1)

mzwaterski (802371) | more than 10 years ago | (#10002194)

As a general user I would only accept emails that have "paid" there time using a system such as this. It would be a quick and easy way for the system to become univerally used as people would migrate to using the system if they wanted their emails read.

Re:Zombie farms (1)

stratjakt (596332) | more than 10 years ago | (#10002274)

So you want industry controlled crypto hardware in your machine that you have no conrol over? That is TCPA/Palladium?

Because thats exactly what that IBM board in the box is.

Guess that's how you sell Palladium to the slashdot crowd. Tell them it will "stop spam" by having your computer to a whole lot of calculatin'.

This doesn't even solve the real spam problem, all that wasted bandwidth. This is just another method of filtering, one that wastes a lot of electricity computing the hell out of things that dont need to be computed. The spam still clogs up my pipe.

Re:Zombie farms (1)

mzwaterski (802371) | more than 10 years ago | (#10002422)

I agree that wasting computing power doesn't seem to be the most logical thing to do, but the cost to send email is too low. The amount of junk snail mail that one gets is limited by the cost of paper and postage. I fully believe that the cost to send email needs to be increased. In that regard, I'd prefer a system that wastes my CPU time to send an email to a system that requires me to pay a postage to send an email. Part of that reasoning is that I don't believe anyone should be able to profit from my sending of an email, I prefer the monthly fee to access the internet. Those who use the internet less might disagree with me, but for now that is my opinion.

Re:Zombie farms (1)

nkh (750837) | more than 10 years ago | (#10002466)

I know you're joking with POWer@home but does anyone know if BOINC [berkeley.edu] has already been used by spammers or crackers to write tools?

Calibration issues (3, Insightful)

markh1967 (315861) | more than 10 years ago | (#10002166)

I'm not sure how well this technique would work in the real world when you have a huge range of systems trying to connect to you. If you set the number of bits in the token so a fast Pentium 4 based system will take two seconds to compute it how many hours would it take a 386, palm-pilot, or Internet enabled phone? Conversely, if you set the number of bits low so that slow systems can compute them in reasonable time then someone with a much faster computer will not be slowed by any noticeable rate and the system becomes useless. If this system is taken up surely it will do more to discriminate against people without state-of-the-art hardware. Surfing is annoying enough on a very slow machine without having to wait for 30 minutes to compute the RPOW before the site will let you connct.

SHA-1 (0)

Anonymous Coward | more than 10 years ago | (#10002170)

It uses SHA-1, which has just been broken for 36 out of 80 cycles by a new technique, which is drawing into question how long it will be cryptographically viable.

What i dont understand about hashcash? (1)

VC (89143) | more than 10 years ago | (#10002172)

Why have the server send a challenge to sign at all? Surely the MUA (mail client) could just add an x-header-expensive-hash-of-this-mail

to *every* mail that goes out, which would be wildly different for each mail beacuse the email address would change.

Same concept, but would work with current mail clients/servers and could tell the server/mail client at the other end that the server really wants you to get this..

Anyone know why this wouldn't work?

Re:What i dont understand about hashcash? (1)

Some guy named Chris (9720) | more than 10 years ago | (#10002362)

Because it would be computationally expensive to check the validity of the hash on the receiving end.

It's a one way proof of work, not bi-directional make-work. What do you think this is, a government job? :D

Re:What i dont understand about hashcash? (1)

zaphod.nu (100500) | more than 10 years ago | (#10002445)

Because then the email server has to compute the hash as well to verify it, which means that server would quickly get swamped.
The point of this is to force the client to compute an expensive hash, not a problem for sending an email to mom, but a much larger problem for people sending out 10000 viagra mails.

oh I thought this was for creditors! (0)

Anonymous Coward | more than 10 years ago | (#10002190)

Like he would print me out a fake check stub that I can use to get a low interest rate loan or something...heh.

"official" mirror, one application (0)

Anonymous Coward | more than 10 years ago | (#10002254)

An official cryptome mirror carries the story [quintessenz.at] cryptome doesn`t have ads to pay the bandwith bill. Few want their ads there [quintessenz.org] apparantly and it would mess with the "cryptome keeps no logs" policy. Dont take this policy to seriously though, Neil young mentioned the increase in NYPD and fbi visits in the run up to the republican convention and how hard it is to find a host that allows for wiping of logs.

please be gentle with this valuable site...

The first proof of work application I learned about was in anonymous remailers. To avoid spammers using sending their messages though remailers some remailers require a proof of work token. So to send an e-mail you have to run a program that slurps some CPU power. It then genarates a token you include in your mail. The remailer can quickly verify you spend some CPU power (thus time) on your message and relay the mail. That way spamming would require insane amounts of CPU (or time).

Keeping honest folks honest (3, Funny)

vile8 (796820) | more than 10 years ago | (#10002293)

Great, I was just complaining the other day that my computer is a lazy, good for nothing document editor. Here I sit with 3ghz and a gig of ram and nothing to actually process other than ps streams.

Since its based on working your computers resources perhaps other names could possibly be "RPOW by Jake"? Or "RPOW's of steel"?

Seriously, what happens next year when its not computationally expensive to compute the tokens? Ew, or what if you are a clever spammer with a degree in electrical engineering and the time to make your own token generating card to sell to all the other spammers on ebay for a small fortune (or you could prove it works by spamming them with advertisements...)?

Well, its always good to have another device to keep honest folks honest I guess.

Simple summary and questions (1)

CommieLib (468883) | more than 10 years ago | (#10002330)

Apparently, RPOWs are a way of throttling down incoming requests by forcing them to solve a time-consuming puzzle. You would want to do this to mitigate DOS attacks.

Here's the question for those who know more, i.e., anyone who knows anything about this. Won't this necessarily and dramatically increase request time? It should impose no (significant) additional load on the server, but won't this mean that requests take x*response time to begin?

Russian Black Market (2, Informative)

Sv-Manowar (772313) | more than 10 years ago | (#10002385)

so when will a black market pop up for cracked ones ;)

Let's make it do something useful (3, Insightful)

kanweg (771128) | more than 10 years ago | (#10002432)

Now, if this concept of having the sender do something is changed into having the sender do useful (Folding at home or another distributed computing project), it would be a nice twist.

Bert

Re:Let's make it do something useful (0)

Anonymous Coward | more than 10 years ago | (#10002739)

Ok, Lets think about this...

How about a "signed" dataset with provable verification servers located at the distributed computation project sites. Only to be fair to the distributed project the tokens should *not* be reusable, or at least provide a lesser degree of "postage" with each reuse (e.g. $.50,$.20,$.10,$.05,..).

Then the problem would be that the spammers would just invest in HUGE computer farms and ultimately find a cure for "medical cancer" (that doesn't soud too bad so far..), but then we'd still be left with the scourage of "spam cancer"!

On the bright side, think of all the "postage" you'd collect for free via spam! You would never have to lick another foul tasting e-stamp again. ;-)~ [$]

Spammers don't send their spam (4, Informative)

Albanach (527650) | more than 10 years ago | (#10002441)

Spammers don't send spam, unpatched windows boxes do. Loads of folk here must be getting calls form folk saying "my net connection's slow" you take a look and the machine is infested.

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 [pobox.com] or here [infinitepenguins.net] and set them up.

Re:Spammers don't send their spam (1)

kindbud (90044) | more than 10 years ago | (#10002624)

SPF has to be one of the easiest measures we can take to reduce spam.

Yeah, except that it was never intended for that purpose, and doesn't have any features to do anything to prevent spam. But other than those two minor points, it's perfect.

cure for spam? (1)

cyclobotomy (681303) | more than 10 years ago | (#10002556)

would spam be feasible on an email-like system that uses RPOW tokens? Making the spammer give up computation time for each email sent seems like the perfect solution.

Re:cure for spam? (1)

BarryNorton (778694) | more than 10 years ago | (#10002640)

Everybody look - I've just invented the wheel!

I have a better idea (1)

drinkypoo (153816) | more than 10 years ago | (#10002560)

Instead, require that someone complete a seti@home, folding@home, distributed encryption cracking, or similar work unit before they can send you an email. That way at least the CPU power is going somewhere worthy instead of just being a waste of electricity.

But if they are reusable, ... (1)

James Turpin (789479) | more than 10 years ago | (#10002578)

... can't the spammer just keep copies of old RPOW tokens and reuse them himself later? How is this prevented?

mailing lists (0)

Anonymous Coward | more than 10 years ago | (#10002692)

If this was implemented how would it affect mailing lists? I personally subscribe to a couple, one of which generates 100-200+ emails a day sometimes.
Load More Comments
Slashdot Login

Need an Account?

Forgot your password?