Dark DAOs: Vitalik Buterin explores ways to mitigate bribery threats

Proof of Complete Knowledge (PoCK) aims to prevent bribery attacks by ensuring real control over voting keys.

A group of researchers from Cornell University is investigating potential threats that could turn into “dark” voting systems in decentralized autonomous organizations (DAOs). 

This group is formed by Ethereum co-founder Vitalik Buterin and PhD students Mahimna Kelkar, Kushal Babel, Philip Daian and James Austgen. Their work revolves around how to mitigate an imminent threat to decentralization as DAOs go mainstream: unified attacks against protocols through smart contracts bribery.

During the Science of Blockchain Conference held at Columbia University in early August, Cointelegraph spoke with Mahimna Kelkar about the group’s research on proofs of complete knowledge (CK) — a new cryptographic notion they introduced in 2023.

Proof of knowledge is a cryptography concept that allows one party (the prover) to convince another party (the verifier) that they possess some secret information, like a secret key, without actually revealing that information.

The concept has been widely used in the crypto industry to improve privacy on transactions, but a “subtle gap” still allows scenarios where this secret information could be held by some external mechanism, like trusted hardware, rather than directly by the prover. According to Kelkar:

“When the secret key is held inside a trusted hardware, in what we call encumbrance of the secret key, you can still complete this proof of knowledge without actually having knowledge of the underlying secret key.”

Bribery attacks

This limitation in the way standard proofs of knowledge are defined could turn voting protocols vulnerable to bribery attacks, Kelkar explained. 

The lack of a central authority is a key concept behind DAOs’ governance. Members of a DAO are usually tokenholders with voting power on rules and decisions. In a bribery attack, however, a malicious actor could offer tokenholders financial incentives through smart contracts, bribing participants to vote for a particular proposal or outcome.

“[..] A voting platform may be vulnerable to bribery attacks […], where users can sort of sell their votes to bribers in a dark marketplace,” explained Kelkar. “What our work tries to do is establish an individual, real person kind of ownership of data.”

Proof of Complete Knowledge

An attacker could use a trusted execution environment (TEE) to ensure that tokenholders who accepted a bribe can’t vote freely. In this environment, the attacker controls when and how the keys can be used. 

The researchers identified two ways of enforcing proof of complete knowledge. One includes using TEE to prove that a voter owns a key and can use it. The tokenholder can also remove the key of this environment to use it freely whenever they want.

In this way, tokenholders still keep complete control over their key. Even if an attacker wants to lock the key away to control the voter, the key is already managed by the voting system’s own TEE.

A second approach involves restricting keys using application-specific integrated circuits (ASICS), which are usually machines used in Bitcoin mining. By sending a key to the ASIC — which lacks a TEE environment — the key remains accessible to the user, ensuring they have complete control over it, while still demonstrating that the key was used by the ASIC and preventing its use in a TEE.

The research is still in the prototype stage, according to Kelkar. “We show that this is a realistic threat to DAOs, and we show this by demonstrating a practically deployable dark DAO, which can facilitate vote buying in existing DAOs. It’s not something that you can deploy tomorrow, but it’s like practically instantiable as a research prototype today,” Kelkar added.