Challenges for combining smart contracts with trusted computing

Modern Trusted Execution Environments (TEEs), such as Intel SGX, gain more and more popularity in the blockchain community and their adoption has already been started. Combining smart-contract execution with TEEs promises efficient solutions for protecting data privacy in distributed ledgers, as an alternative to much more costly cryptographic protocols. This paper describes practical challenges that arise from the combination of smart contracts with TEEs. In particular, we discuss existing solutions and their conceptional differences of on-chain and off-chain execution followed by technical challenges on attestation, key management, and non-deterministic execution.