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‘Internet Stamps’: ‘Sender Pays’ Is Back From The Dead

Jeremy Zawodny mentions that Tim Bray has proposed something he calls ‘Internet Stamps’ to solve the blog-spam problem; here’s Tim’s description of how it works:

An Internet Stamp is an assertion, signed by a Post Office, that some chunk of text was issued by someone who paid for the stamp. At least one major Post Office will be required by government statute to sell stamps to anyone in the world for either US$0.01 or EUR 0.01, and no stamp-selling organization will be recognized which sells stamps for less than this amount. For this to work, the number of stamp-selling organizations needs to be small and the organizations stable; another reason why Post Offices are plausible candidates.

It works like this: if you want to buy stamps, you sign up for an account with your Post Office; it works like paper stamps, you buy a bunch at a time in advance, in small amounts like $20 or EUR 10. Then the Post Office offers a Web Service where you connect to a port, authenticate yourself and send along some text; the Post Office decrements your account and sends back the stamp. There are a variety of digesting/signing/PKI techniques that could be applied to implement the stamps; a standard is required but should be easy.

Apparently himself and a few other guys chatted about it at the first Foo Camp, back in 2003. Funnily enough, in the anti-spam community, we were having our own chats about it, but it sounds like our paths didn’t cross for some reason…

We call this idea ‘sender pays’. Earlier in 2003, in June, John Levine published what I’d consider the canonical wrap-up of why it will not work, in ‘An Overview of e-Postage’.

That report demolishes the use of ‘sender pays’ for e-mail anti-spam, on three main counts:

  • Creating a transaction system large enough for e-postage would be prohibitively expensive. The nearest parallel is the credit card transaction system, which deals with 1% of the transaction volume per day, and with much larger profit margins to make it worth their while.

  • The true financial, administrative, and social costs of e-postage are completely unknown. What do you do when a ‘bad guy’ steals the e-postage stamps off Aunt Millie’s hard disk, without her knowledge? How much is the Fraud Handling Department going to cost? Is she just going to be out of luck when this happens? Will you need to use whitelisting and a content-based anti-spam filter as well, to filter out the messages sent using valid, but stolen, stamps?

  • Users hate micropayments. In short, see Andrew Odlyzko’s research.

Now, using it on weblog spam is a little more practical than e-mail spam, for one because it has a lower daily volume of transactions; but these objections still stand, in my opinion.

John Levine is one of the foremost authorities in anti-spam, and this report has been a mainstay of the anti-spam canon for two years. Anyone discussing a new anti-spam concept really ought to know this report backwards and forwards by this stage, and go into some detail as to how their proposal deals with the issues raised, if it’s to be taken seriously.