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. "

Comments

Umm

[Anonymous Coward]

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

[Anonymous Coward]

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

[baywulf]

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

[nova20]

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

[MenTaLguY]

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

[masoncooper]

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

[aardvarkjoe]

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

[ultranova]

A thousandfold slowdown of the rate of sending just means a larger part of all those zombies will be used to get the job done. The factor you talk about is very easy to manage considering the total number of compromised machines out there.

Then you just have to increase the cost. In a way, it's a very free-market system: people keep on getting spam, and thus upping the cost of sending it to them. Eventually, a balance is found between the amount of spam you have to put up with and the amount of legitimate contacts that give up contacting you.

Of course, a really smart system lets you cryptographically sign your messages, and lets the recipient to add the public key to his whitelist, so you typically only need to pay the hashing cost once, unless of course you are a spammer (in which case people will not mark you as trusted).

Re:Umm

[ultranova]

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.

That's why you'll use HTTP 1.1. It lets you request more than one item without closing connection inbetween (the so-called "keepalive" option in the HTTP request). AFAIK supported by every modern (and most not-so-modern) browser.

This is, after all, what the keepalive feature was designed for; to reduce the overhead of dozens of connections per page request in a graphics-heavy page, allowing you to "pipe" request after request over the same connection - and since connections are statefull, you can just verify the first request of each connection and bypass the verification on rest.

using it to thwart DoS or SPAM is pointless, since we all know that technological solutions to these problems don't exist.

The technological solution to SPAM is to require that all messages sent to you be crypted with your public key, and automatically blocking those that aren't, expect for whitelisted addresses. Having to crypt every e-mail sent once per recipient makes even the SPAM Grendel clusters choke; and, of course, nothing stops you from giving everyone a different public key and revoking (removing from your keyring) those that start returning spam - the good old multiple email address trick, but with less hassle, and no headaches over what to do when spammers happen to find your main address. Just have a program running in your System Tray / Gnome Panel / Whatever which lets you generate new keypairs with a single click (and adds them to your keyring automatically, and remembers where you gave the public key to).

This has the added benefit of giving you better privacy, and the government / mafia / telecomm packet sniffers something to choke on :).

As a side note, it might make sense to verify mailing list posts with cryptographic signatures than whitelists; after all, adress can always be forged.

It is true that there is no technical solution to the general brute force DDoS attack. If the attacker can generate enough requests for a webpage, the server gets slashdotted and becomes unreachable. However, even in this case better technology can keep the server from crashing, allowing it to come back online immediately when the attack stops.

More info on Hal can be found....

[zegebbers]

There is some excellent info on Hal here , here and here.

Re: RPOW - Reusable Proofs of Work

[Anonymous Coward]

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..."

/.ed

[Dibblah]

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

Proofs Of Work are few and far between

[Anonymous Coward]

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

Cache

[Klar]

Google Cache after slashdotting... http://www.google.ca/search?q=cache:YHGDB5MH4e0J:r pow.net/+&hl=en

Obligatory Pun

[grunt107]

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

Re:Obligatory Pun

[trb]

I was thinking, hashcrash-based server.

Anon posting, ARTICLE TEXT

[Anonymous Coward]

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 Trus

Isn't it obvious?

[BubbaThePirate]

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

Defeating the purpose?

[Anonymous Coward]

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

[diagnosis]

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
G. W. Bush says, "You decide!"

Re:Huh?

[teemu.s]

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."

Proof-of-work tokens as an anti-spam measure?

[JaredOfEuropa]

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?

[4of11]

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?

[dpilot]

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.

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

[ArsonSmith]

yea this actually seems rather easy to acomplish. just do something similar to an md5sum but much more intensive on the message + outgoing emails and attache it to the email. a PGP signiature would be a good idea for something to use as well.

Why isn't PGP/GPG setup and configured on installation of all OSS mail readers?

Re:Verify

[3-State Bit]

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 (PDF) [or as html].

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.

dude, that's so excellent...who's hungry?

[eufreka]

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 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

[Bronster]

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.

Calibration issues

[markh1967]

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.

Keeping honest folks honest

[vile8]

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.

equivalent for RPOWs in existence

[2nd Post!]

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

Russian Black Market

[Sv-Manowar]

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

Re:Trusted computing? I think not.

[SpootFinallyRegister]

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.

Re:Huh?

[stratjakt]

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.

Let's make it do something useful

[kanweg]

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

Spammers don't send their spam

[Albanach]

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 or here and set them up.

Re:Spammers don't send their spam

[Alsee]

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.

Wrong. The processor will certainlty be bogged down generating tokens, but the net connection will be wide open if it can only generate one token and send one spam every 4 or 5 minutes.

And no, even 10 minutes wouldn't be a problem for normal email users. The very first time you launch your mail program it can start generating a token, even before you've configured the mail host and you entered your name. It can work on tokens while you download your mail, while you sit there reading your mail, and while you address and type any mail you want to send.

And the tokens are reusable. If someone sends you mail through this system then they are giving you a token you can use yourself on the next mail you send out. Hell, so long as there are spammers generating tokens and mailing them out normal people will never need to generate their own tokens. Just save the tokens you get on spam and use them to send your own mail, So even 1-hour to generate a mail token wouldn't be any sort of problem.

-

Re:Huh?

[ifdef]

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).

Reusable Tokens

[cbr2702]

If I recieve a token from someone else, can I copy it and attach it to multiple messages? If so, what's to stop spammers from calculating one token and attaching it to a large number of messages?

Re:Reusable Tokens

[cbr2702]

I can't attach it to multiple messages? Whyever not? Imagine I get a token in a message from someone, I attach it to a new message, and send it on to someone else. That is the way reusable tokens are supposed to work, right? But let's say instead that I attach that reusable token to two outgoing messages. Without some central DB of token usage, the recipients can only determine that the tokens I have provided are valid, not that they have not been used for other messages. So this does not prevent spam.

What about server problems/attacks

[PetiePooo]

From the article:
The RPOW server is running on a high-security processor card, the IBM 4758 Secure Cryptographic Coprocessor, validated to FIPS-140 level 4. ... Please keep in mind that if there are problems I may need to reload the server code, which will invalidate any RPOW tokens which people have previously created.

So, in other words, it passes out little tokens that are worth something ... but just until the server is taken out.

Ok, so its running FIPS-certified code on FIPS-certified hardware. Still, how sure can you be that it will keep running 24/365 for years on end? If that private key is needed for proof of authenticity, and that key never leaves the board, that makes it, among other things, one heckuva terrorist target.

Re:What about server problems/attacks

[Paul Crowley]

The tokens it hands out aren't *that* valuable, so if the machine goes down you don't lose all that much.

Re:Out of Curiousity ...

[night tilda]

> ... how much does a IBM 4758 cost?

In the region of $2000-3000 when they were still being produced. I've seen them for sale for $800 or so more recently. So not that much for any kind of org.

Re:But if they are reusable, ...

[Anonymous Coward]

RTFP -- any transfer of tokens, or generation of new tokens from old ones (re-use), must happen through the central server.