Obfuscating Verifiable Random Functions for Proof-of-Stake Blockchains

Blockchain systems enable new applications, such as cryptocurrencies and smart contracts, using decentralized consensus without trusted authorities. A number of blockchain systems based on proof-of-stake techniques have been proposed, many of which use verifiable random functions (VRFs) as fundamental building blocks, such as Ouroboros, Algorand, and Dfinity, etc. The secret key of a VRF scheme is critical to the security of a VRF and the entire blockchain system built on it. To protect the secret keys of VRFs and maintain the efficiency of the proof-of-stake protocol, we extend the objective of cryptographic program obfuscation to VRFs and propose an obfuscatable VRF scheme. In particular, we propose an obfuscator that can transform the implementation of the scheme's random string generation algorithm and the given secret key into an unintelligible form. Obfuscated implementations of the random string generation algorithm are deployed on peers of a blockchain for supporting normal routines of the proof-of-stake protocol. Even if a hacker has controlled a peer's host, the owner's secret key will not be compromised because the key has been hardwired into the obfuscated implementation in an "encrypted manner". We formally prove the correctness and the security of the proposed VRF and obfuscator. Since the proposed scheme supports the general semantics of verifiable random functions, it can be used as a building block for all blockchain systems that adopt proof-of-stake protocols based on VRFs. The experimental result indicated that the scheme performs well on various platforms, such as cloud servers, workstations, smartphones, and embedded devices.