Not Ethereum, but smart contracts have been demonstrated in Bitcoin to guarantee delivery of certain immaterial goods for which you can build specialized zero-k

Not Ethereum, but smart contracts have been demonstrated in Bitcoin to guarantee delivery of certain immaterial goods for which you can build specialized zero-knowledge proofs. You could for example buy cryptographic keys this way. The idea has been around some time and was used to buy a Sudoku solution for a demonstration last year: https://bitcoincore.org/en/2016/02/26/zero-knowledge-contingent-payments-announcement/ https://bitcoincore.org/en/2016/02/26/zero-knowledge-conting...