I'm sort of bearish on most things blockchain but this seems like one of a very small number of things that zero-trust auto-executing contracts could be useful for. Someone could probably work out a mathematical proof of "if you transfer this much etherium the private key will be decoded." Heh.

That's a lot of work for little reward, I think. Most of the time the idea is that the hackers have every incentive to decrypt or else word will spread that it doesn't work even if you pay so people will stop paying.

Brown hat hackers have an incentive to create non-functional ransomware, to spread FUD on the legitimate ransomware. If news spreads that some ransomware does not actually decrypt the files after payment, then potential victims would have a stronger incentive to secure their systems, and a weaker incentive to stockpile ransom funds (wt actual f!)

Then, the onus would once again be on the legitimate ransomware developers to prove their ability to do business, and some sort of Ethereum based automated contract might be an ideal tool for that.

If the context is widespread ransomware infection, provable decryption is unlikely to make a difference. Attackers are unlikely to make money from people who know what Ethereum, or a smart contract is. Even taking those who know the meaning, very few could actually verify the application.

The attacks work on those who didn't have protection and lost valuable data. Just sticking a "decryption guaranteed by Ethereum contract" will likely have the same effect on them.