I want to make a proof-of-concept about privacy-preserving smart contracts. I know it's uneconomical to use encryption with Ethereum smart contracts. Are there best practices about how to do that? Could I use some kind of off-chain approach for that purpose, such as Enigma or truebit? Some sample projects or tutorials would be a great help.
To give you more background: I aim to store encrypted data in a smart contract and allow parties that fulfill certain criteria, e.g. who made a payment to the smart contract, to retrieve the decrypted data.