This reminds me that I should really publish that blog post about using hashes to send documents "into the future" (really just to prove you wrote them at an earlier date) at some point.<p>>Hash matching, or hash scanning, compares certain pieces of content such as videos, pictures or text, to a database of illegal content. It is done by turning the content into “hashes”, a sample of the content a bit like a fingerprint. The hashes of content stored or shared by a specific user are then compared to the hashes of known illegal content in a database and result in a match if the software deems that the hashes are identical or similar enough.<p>Because one of the things I realized while writing it is that there's an interesting contrapositive to keeping your own public list of hashes online somewhere:<p>1. By putting a hash on your public hash list, you are making a claim that you have access to a particular document at a particular time.<p>2. If someone else posts a hash on your hash list, say to a well-known document like the HTML source of example.com, they have in effect proven that you are not the <i>sole person</i> who can edit that hash list, and<p>3. Therefore your claim to access of <i>anything</i> on that hash list is repudiable and hence the entire list must be thrown out.<p>So... Maybe there's a similar counterjamming method available here? E.g. stuff the hash of "Hello world" into one of these illegal databases, then show it's there, to call into question the idea that everything on these databases is illegal and thereby get them thrown out of court.<p>(P.S., I'm almost positive you can use keypair encryption to get around this, but I haven't taken a bus ride long enough to puzzle out the details of how yet.)