Aztec and Railway — Ethereum Privacy Layers

Privacy on Ethereum's Public Chain

Ethereum is fully transparent by default — every transaction, balance, and interaction is public. This transparency is core to Ethereum's audit-and-verify security model but hostile to privacy needs (business confidentiality, personal safety, tax planning). Multiple projects are building privacy layers on top of Ethereum. Aztec provides shielded transactions in a dedicated privacy rollup. Railway (formerly Railgun) provides privacy for existing L1 ETH and tokens via stealth addresses. Each represents a different architectural bet on Ethereum privacy.

Aztec's Rollup Approach

Aztec is a ZK rollup dedicated to private smart contracts and transactions. Users deposit assets from L1 into Aztec; within Aztec, they can conduct private transactions using ZK proofs. Withdrawal back to L1 reveals the withdrawn amount but not the intermediate history. Aztec's ZK proof system (based on PLONK derivatives) is optimised for privacy applications. The trade-off vs generic rollups: less general-purpose, more privacy-optimised. Aztec has pivoted several times through its history; current architecture is the third major iteration.

Railway's Stealth Approach

Railway takes a different approach — smart contracts on Ethereum L1 that enable shielded transfers of existing tokens. Users deposit into Railway's shielded pool; transfers within the pool are private (like Tornado Cash mechanics but for arbitrary tokens); withdrawals reveal recipient and amount. Railway's advantage: works with existing tokens without requiring bridge. Disadvantage: privacy is only within the pool, exit reveals information. Both models have legitimate uses; users choose based on specific privacy needs.

• Aztec: dedicated ZK rollup with private smart contracts
• Railway: privacy layer for existing tokens via shielded pool
• Different architectural bets on how to add privacy to Ethereum
• Multiple production deployments emerging post-Tornado Cash