Announcing the first SHA-1 collision
One practical attack using this: create a torrent of some highly desirable content- the latest hot TV show in high def or whatever. Make two copies, one that is malware free, another that isn't.Release the clean one and let it spread for a day or two. Then join the torrent, but spread the malware-hosting version. Checksums would all check out, other users would be reporting that it's the real thing, but now you've got 1000 people purposely downloading ransomware from you- and sharing it with others.Apparently it costs around $100,000 to compute the collisions, but so what? If I've got 10,000 installing my 1BTC-to-unlock ransomware, I'll get a return on investment.This will mess up torrent sharing websites in a hurry.Edit: some people have pointed out some totally legitimate potential flaws in this idea. And they're probably right, those may sink the entire scheme. But keep in mind that this is one idea off the top of my head, and I'm not any security expert. There's plenty of actors out there who have more reasons and time to think up scarier ideas.The reality is, we need to very quickly stop trusting SHA1 for anything. And a lot of software is not ready to make that change overnight.