
Stored Hashcash - trevmckendrick
http://www.cdixon.org/2014/03/15/stored-hashcash/
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spindritf
_In order to send an email, the sender first has to solve a math problem.
Legitimate activities suffer an indiscernible delay, but illegitimate
activities that require massive volume are hobbled._

Illegitimate activities are often carried out in a parasitic manner using
infected and hijacked equipment for which the spammer and attacker don't have
to pay. This will do little to hinder those tactics.

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patio11
It's worth mentioning that hashcash has never been widely deployed for email
spam prevention, and never will be. (As far as I'm aware its widest success
was getting a modest reduction in scores in the default SpamAssassin ruleset
at one point, which -- AFAIK -- was eventually rolled back because, while
people are attracted to the philosophy of hashcash, nobody actually uses it.)

Why?

1) The supermajority of spam is sent through systems which can be operated by
an attacker but which are not actually owned by them. This includes, most
prominently, botted-up residential PCs. Prior to wide availability of always-
on high speed Internet it included email servers which were insufficiently
locked-down. Hashcash does not meaningfully affected the economics of botnets.

2) The most successful anti-spam measure in history makes direct use of a
consequence of #1: since mail servers do not move in nature that much, and
legitimate mail systems do not frequently mix outgoing spam and outgoing ham,
you can make IP-based reputational systems. If a residential IP starts sending
email in large amounts, assume spam. If a novel IP starts sending email, treat
as suspiciously smelling ham until they've demonstrated sufficient history,
but flip the spam bit if/when they get aggressive. If a new MSA springs up,
ensure their industry veterans at the helm understand the importance of their
anti-abuse team, and tell them explicitly that their IPs are dead if they
don't.

This worked fantastically well. It's the primary anti-spam measure which
protects your inbox. (No. I know you think Bayesian filters are. They're more
expensive to operate at scale, are virtually unusable by the common-
denominator email user, and don't solve any problem better than IP reputation
does.)

3) Hashcash never caught on in part because the people who care most about
spam also care most about sending billions of emails. "We make it economically
unattractive to send billions of emails" is a non-starter for them. You can
guess who I'm talking about by taking a look at any user database and
observing what percentage of email addresses in it terminate with the top, oh,
five domain names. (Interestingly, email is a P2P protocol at the server level
which is best described as "All peers are equal, in that they will be equally
squashed beneath the boots of our governing oligopoly if they misbehave.")

Note that none of hashcash's problems are solved by "And now it can be stored
for later."

Source: My first engineering job was as an anti-spam researcher.

~~~
dennisgorelik
> My first engineering job was as an anti-spam researcher.

Was it at Japanese megacorp?

~~~
patio11
That was the 2nd one. The first one was as the Coordinator of International
Relations at a prefectural technology incubator. We didn't have many
International Relations to Coordinate and I was theoretically getting paid out
of the R&D division's budget, so I got myself assigned to the anti-spam group
so that I didn't spend 3 hours a month translating and 157 hours a month
reading Slashdot.

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wmf
_How valuable would stored Hashcash be?_

It depends on the rules of the system. If the system arbitrarily limits the
creation of hashcash to 2.5 per minute and limits the total in circulation to
21 M then it could be worth a lot (although with high volatility). Without
such limits each unit of hashcash would be worth almost nothing, but the
overall system might be more efficient and thus worth more.

Also, if the system limits itself to 7 transactions per second it may not be
useful for anti-spam or bandwidth accounting.

~~~
stuhood
But if this theoretical (but somehow very well defined) system supported
offchain transactions, whereby a sender could attach a signed transaction for
the appropriate amount to the sent message (rather than submitting it via a
theoretical "peer-to-peer" network), then the throughput would be effectively
unlimited.

EDIT: or micropayments:
[https://en.bitcoin.it/wiki/Contracts#Example_7:_Rapidly-
adju...](https://en.bitcoin.it/wiki/Contracts#Example_7:_Rapidly-
adjusted_.28micro.29payments_to_a_pre-determined_party)

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rdl
How is that not bitcoin?

I've long been a fan of a "bounty" system -- you attach digital coins to a
message, with the recipient specifying how many coins must be attached (maybe
higher for voice, lower for email, mid level for SMS). If the message was
unwanted (not merely spam, but even just a stupid request), the recipient
collects the coins; otherwise, the sender gets them back.

This nicely aligns incentives. If the recipient takes coins improperly, you
stop sending him mail.

~~~
cdixon
It is Bitcoin. I was just trying to present some of the ideas behind Bitcoin
without all the baggage of the word.

~~~
rdl
You really should have a beer w Adam Back sometime; he's one of my favorite
people from the cypherpunks golden age.

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meowface
I'm not sure how stored hashcash makes sense for preventing spam and DDoS.
Won't services pop up that mine away, accumulate successful computation
tokens, then sell them cheaply to spammers and flooders? Or spammers and
flooders can simply leave their computer running a week in advance of planned
attacks, and acquire a bunch of tokens all on their own.

We already see this kind of thing in CAPTCHA farms.

~~~
danieldk
_Won 't services pop up that mine away, accumulate successful computation
tokens, then sell them cheaply to spammers and flooders?_

Not as long as the cost of mining per e-mail is higher than the average
revenue per e-mail.

~~~
meowface
True, but then you could have potential issues like people running old
computers who send 100 or more legitimate emails per day. They won't want to
wait 1 - 10 minutes for their computer to spin away every time. They also
probably don't want to leave their computer running all night just to get
enough tokens for the next day.

CAPTCHA is not a nice option, but compared to the alternatives it's probably
the best we're going to get.

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crdoconnor
Your post advocates a

(X) technical ( ) legislative (X) market-based ( ) vigilante

approach to fighting spam. Your idea will not work. Here is why it won't work.
(One or more of the following may apply to your particular idea, and it may
have other flaws which used to vary from state to state before a bad federal
law was passed.)

( ) Spammers can easily use it to harvest email addresses

(X) Mailing lists and other legitimate email uses would be affected

( ) No one will be able to find the guy or collect the money

( ) It is defenseless against brute force attacks

( ) It will stop spam for two weeks and then we'll be stuck with it

( ) Users of email will not put up with it

( ) Microsoft will not put up with it

( ) The police will not put up with it

( ) Requires too much cooperation from spammers

(X) Requires immediate total cooperation from everybody at once

(X) Many email users cannot afford to lose business or alienate potential
employers

( ) Spammers don't care about invalid addresses in their lists

( ) Anyone could anonymously destroy anyone else's career or business

Specifically, your plan fails to account for

( ) Laws expressly prohibiting it

( ) Lack of centrally controlling authority for email

( ) Open relays in foreign countries

( ) Ease of searching tiny alphanumeric address space of all email addresses

(X) Asshats

( ) Jurisdictional problems

(X) Unpopularity of weird new taxes

(X) Public reluctance to accept weird new forms of money

(X) Huge existing software investment in SMTP

( ) Susceptibility of protocols other than SMTP to attack

(X) Willingness of users to install OS patches received by email

(X) Armies of worm riddled broadband-connected Windows boxes

(X) Eternal arms race involved in all filtering approaches

(X) Extreme profitability of spam

( ) Joe jobs and/or identity theft

( ) Technically illiterate politicians

( ) Extreme stupidity on the part of people who do business with spammers

( ) Dishonesty on the part of spammers themselves

( ) Bandwidth costs that are unaffected by client filtering

(X) Outlook

and the following philosophical objections may also apply:

(X) Ideas similar to yours are easy to come up with, yet none have ever been
shown practical

( ) Any scheme based on opt-out is unacceptable

( ) SMTP headers should not be the subject of legislation

( ) Blacklists suck

( ) Whitelists suck

( ) We should be able to talk about Viagra without being censored

( ) Countermeasures should not involve wire fraud or credit card fraud

( ) Countermeasures should not involve sabotage of public networks

( ) Countermeasures must work if phased in gradually

(X) Sending email should be free

( ) Why should we have to trust you and your servers?

( ) Incompatiblity with open source or open source licenses

( ) Feel-good measures do nothing to solve the problem

( ) Temporary/one-time email addresses are cumbersome

( ) I don't want the government reading my email

(X) Killing them that way is not slow and painful enough

Furthermore, this is what I think about you:

(X) Sorry dude, but I don't think it would work.

( ) This is a stupid idea, and you're a stupid person for suggesting it.

( ) Nice try, assh0le! I'm going to find out where you live and burn your
house down!

~~~
anon4
Thank you, I was about to look up the form and post it myself. I'd also check

(X) Microsoft will not put up with it

(X) Countermeasures must work if phased in gradually

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hayksaakian
Instead of hash cash, could you charge 10 dogecoin?

We abstract out the computational requirements into a sub-penny but not
insignificant payment.

Then again, how much would spammers be willing to pay?

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wyager
Is this supposed to be an explanation of the value of Bitcoin, or am I to take
this at face value?

~~~
kapitalx
The proof of work concepts behind bitcoin are based on hashcash (originally
proposed in 1997)

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plaxis
How about we increase energy costs? Huh guys?

~~~
oscilloscope
Storing, transmitting and reading spam consumes energy as well.

