Forwarded from Extropians: First off, before I discuss schemes for tagging data, let me say that I'm completely opposed to copyrights, patents, and all forms of intellectual property law. They're unhip and anti-extropian. I realize that a majority of Extropians will come out in favor of copyright law, given that they're knowledge workers, but they're misguided: there are plenty of ways to turn information into cash without making the free exchange of information illegal. Use your originality rather than a big stick. (For more, see my article "Free the Bits", article #94-9-488) <falls off of soapbox> That said, let me describe the ways I've worked out to be Big Brother. I've done some work on methods of tagging data in such a way that the tags can't be removed without destroying the information. This is what we really want if we're trying to trace where our data goes. I'm interested in cryptographically strong methods of tagging data, so putting tags in the noise bits of an image, or in the whitespace of text, is not good enough. Such tags can be easily ripped out. The old mapmaker's trick -- inserting a small nonexistent street into each map -- is more like what I'm getting at. The idea is to do a small amount of damage at a chosen site, in such a way that if the thieves try to cover up the damage without detecting the target site, they will have to destroy the information they set out to steal. Mainly I've thought about the case of tagging a piece of ASCII text, with a different set of tags for each copy of the text, enabling me to enforce a contract with a buyer of the information not to redistribute it. I'm going to choose to make small content changes, like exchanging a word for its synonym, as my means of inserting tags into the text which can't be smoothed away. The meat of what I'm interested in is when, say, 10 thieves get together and compare their (distinctly tagged) copies of a newswire article. Can they succeed in removing the tags and distributing a clean copy? They do a "diff" of their copies and discover that the 100'th word is sometimes "but" and sometimes "however", and similarly for 20 other words throughout the document. The thieves now have to decide which word to include in their output document (say, by flipping a coin), in order to scramble any information the tagger hoped to insert. So who wins? Tagger or thieves? The short answer is, my kind of tagging is effective in most cases, but not against a large group of sophisticated thieves (more than about 20 or so of them). This is because the number of tag bits required, according to my calculations, is exponential in the number of thieves. To see some stuff I wrote last year as part of a discussion on the sci.crypt newsgroup, and code for a simulator I wrote to test out an interesting case, retrieve article #94-9-497... -- Marc Ringuette (mnr@cs.cmu.edu). Freely forward/archive this. End of forwarded message Brian D Williams Extropian Cypherpatriot "A country that wants to be unarmed and free, wants what never has been and never will be." --- Thomas Jefferson