Obfuscating Verifiable Random Functions for Proof-of-Stake Blockchains

Blockchain systems, such as Bitcoin and Ethereum, enable new applications, such as cryptocurrencies and smart contracts, using decentralized consensus without trusted authorities. Since the most widely used technique, proof-of-work, suffers from the costs of high latency and huge energy consumption, a number of blockchain systems based on proof-of-stake techniques have been proposed in recent years, many of which use verifiable random functions as fundamental building blocks, such as Ouroboros, Algorand, and Dfinity, etc. The secret key of a verifiable random function scheme, similar to that of a digital signature scheme, is critical to the security of a verifiable random function and the entire blockchain system built on it. To protect the secret keys of verifiable random functions and maintain the efficiency of the proof-of-stake protocol, we extend the objective of cryptographic program obfuscation to verifiable random functions and propose a novel obfuscatable verifiable random function 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 verifiable random function 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 Verifiable Random Functions (VRFs). The extensive experimental result indicated that the scheme performs well on various platforms, such as cloud servers, workstations, PCs, smartphones, and embedded devices.