Vitalik Buterin created an anonymous billboard instead of promoting ETH

Ethereum co-founder Vitalik Buterin put together a small prototype of an anonymous billboard using zero-knowledge proofs. In a joke, he noted that he’s choosing interesting side projects again instead of promoting ETH.

Buterin described the approach with the term “vibe coding”: he explained the problem in simple terms, while AI tools wrote most of the code for him. The project runs on Aztec— a privacy-focused blockchain built on Ethereum’s cryptographic foundation.
Return of the privacy idea

Buterin described the concept of an anonymous billboard with moderation back in 2022—in an essay about zero-knowledge proofs and privacy. There, he presented a message board where everyone can publish posts anonymously. Moderators could remove posts for violations without knowing the authors’ identities.

Buterin regularly returns to the topic of privacy protection. Earlier this month, he warned that the revived EU initiative Chat Control threatens everyday cybersecurity. A new draft law would require checks of private messages for prohibited content.

Buterin is convinced that privacy tools need to be protected more strongly, because any concessions will turn into a loss of security. His large-scale roadmap Lean Ethereum is also built on similar cryptographic principles.
How the billboard works

In the aztec_experiments repository on GitHub, there are three working prototypes: a token contract, a voting oracle, and the billboard itself. The billboard relies on cryptographic “nullifiers” based on the Poseidon2 hash function. They confirm a user’s right to post and, at the same time, prevent duplicate posts without revealing the author.

Before sending data to the blockchain, a private function checks against the associated token contract whether the user has permission to write. Buterin broke down the entire process in detail in the first post of the thread.