For over 40 years, one problem has defined the entire field of secure multi-party computation.
In 1982, computer scientist Andrew Yao posed a deceptively simple question: how can two parties figure out who is wealthier, without either one revealing how much they actually have? The answer must be provably correct. But neither side learns anything beyond the result.
This became known as Yao’s Millionaires’ Problem, and it laid the theoretical foundation for the entire field of secure multi-party computation (MPC). For decades, it stood as the benchmark: if your system can solve this problem with full privacy guarantees, it can handle real-world confidential computation.
In February 2025, COTI demonstrated a live solution to the Millionaires’ Problem on the COTI Network using Garbled Circuits. Encrypted inputs, private computation, verified results. Neither party revealed a single data point.
Now, COTI has taken that same capability and deployed it on Ethereum Sepolia testnet. The Millionaires’ Problem, solved with 100% end-to-end cryptography, directly on Ethereum’s infrastructure. No trusted intermediary. No data exposure. Just math.
How the Demo Works
The demonstration follows the classic MPC setup:
Two parties each hold a private value representing their wealth.
Neither party reveals their actual input to the other or to the network.
The computation runs on encrypted data, producing a verifiable result: who is wealthier.
The answer is provably correct, without any plaintext values ever being exposed on-chain.
The entire process is powered by COTI’s Garbled Circuits implementation, a cryptographic protocol purpose-built for secure multi-party computation on-chain. Inputs are encrypted, computed collaboratively, and resolved, all without a centralized party or trusted setup.
Think of it this way: two people walk into a room, whisper their numbers into separate locked boxes, and walk out knowing who had the bigger number. Neither one ever opened the other’s box. That’s what Garbled Circuits make possible, except the room is Ethereum, and the boxes are pure cryptography.
Why This Matters
The Millionaires’ Problem isn’t just an academic exercise. It is the original MPC challenge. The foundational test case that proves whether a system can perform meaningful computation on private data without exposing it.
COTI first proved this on its own network. Now, solving it on Ethereum’s testnet using pure cryptography and no trusted intermediaries demonstrates that Garbled Circuits can deliver practical, verifiable privacy directly on the world’s largest smart contract platform.
The timing matters too. Ethereum co-founder Vitalik Buterin has been increasingly vocal about the need for privacy-preserving computation in decentralized systems. In a detailed thread on decentralized governance and AI, Buterin specifically called out Garbled Circuits as the path to pure-cryptographic security guarantees for multi-party computation.
“I would love to see at least the two-party case solved with garbled circuits so we can get pure-cryptographic security guarantees.” — Vitalik Buterin
This wasn’t the first signal either. At ETH Tokyo in 2025, Buterin stated publicly that Garbled Circuits are faster than more complicated forms of MPC and that many use cases exist where the technology is valuable.
COTI’s Garbled Circuits has solved this and the only project to answer Vitalik’s public challenge.
From COTI Network to Ethereum
COTI’s implementation of Garbled Circuits, built in partnership with Soda Labs, has been live on COTI’s mainnet since March 2025. The gcEVM is the first production-ready Garbled Circuits implementation for on-chain confidentiality, offering full EVM compatibility. Developers can write confidential smart contracts in Solidity using familiar tools like Hardhat, simply adding privacy parameters to unlock multi-party computation capabilities.
This Sepolia testnet deployment is a preview of Privacy-on-Demand, COTI’s initiative to bring Garbled Circuits natively to Ethereum and other major chains. The goal: highly-scalable programmable privacy, available to any app, dApp, or builder, all powered by $COTI.
What Privacy-on-Demand Means for Ethereum
Privacy-on-Demand extends COTI’s privacy infrastructure beyond its own Layer 2, making it accessible as a service layer across leading blockchains. For Ethereum, this unlocks real private use cases that aren’t possible on a fully transparent chain:
Builders can integrate confidential computation directly into Ethereum-native dApps without migrating to a separate chain.
DeFi protocols can protect sensitive execution parameters, such as thresholds, order sizes, or strategy logic, from front-running and observation-based extraction.
Enterprise and institutional applications can handle private data on-chain while maintaining compliance and auditability.
Governance systems can enable private voting and decision-making without exposing individual inputs, the exact use case Buterin described.
What Comes Next
This testnet deployment is not the finish line. It’s a milestone on COTI’s path to making Garbled Circuits available natively on Ethereum and other major blockchains, extending the same privacy capabilities that are already live and in production on COTI’s own network.
The Millionaires’ Problem has stood as the benchmark for MPC systems for over 40 years. Solving it first on COTI, and now on Ethereum’s testnet with full end-to-end encryption and no trusted intermediaries, is a clear signal: practical, scalable privacy on public blockchains isn’t theoretical anymore.
Privacy-on-Demand is coming to Ethereum.
About COTI
COTI is the programmable privacy layer for Web3. Built for enterprises, builders, and agents. Powered by high-performance Garbled Circuits and enterprise-grade COTI Nightfall (ZK), COTI enables encrypted computation on any public blockchain. Fast, low-cost, and compliant privacy across DeFi, AI, and beyond.
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