Can Smart Contracts Generate Digital Signatures?

Abstract

Smart contracts are commonly used for automated processing on blockchains, and research related to smart contracts is actively conducted. However, smart contracts are constrained by the fact that they cannot hold secret information due to transparency requirements, and thus smart contracts cannot perform calculations using secret information. In particular, they generally cannot generate digital signatures, which are computations using a secret key. This limits the potential of smart contracts. In this study, we propose a new scheme that enables smart contracts to generate signatures even if the smart contract does not hold a secret key. The proposed scheme allows smart contracts to securely delegate signature generation to off-chain servers that hold the signing key and do not support TEE. Even if the off-chain server is compromised by an attacker and the secret key (signing key) is stolen, the smart contract still generates a valid signature. We provide a new secure and effective signature generation approach using smart contracts and incentive mechanisms, even if the signing key is publicly available.