Railgun

Railgun is a set of smart contracts providing shielded transfers and private DeFi interactions on Ethereum and other EVM-compatible chains. It uses zkSNARKs to maintain a UTXO-like note system (commitments and nullifiers) that allows users to send, receive, and interact with DeFi protocols while hiding wallet balances and transaction details.

Railgun - Privacy System for Ethereum and EVM Chains

Fits with patterns (names only)

  • Pattern: Private ISO 20022 Messaging & Settlement
  • Pattern: Shielded-Pool Atomic Swap (ZK-HTLC)
  • Pattern: ZK Shielded Balances for Derivatives
  • Pattern: Confidential ERC-20 (FHE/L2 ERC-7573)

Not a substitute for

  • Not a cross-chain settlement mechanism (no native atomicity across L1/L2s).
  • Not an institutional compliance layer (no built-in regulator viewing keys or scoped audit paths).
  • Not a programmable privacy rollup (functions only as contracts on existing L1/L2).

Architecture

  • Execution model: UTXO-style commitments (note commitments, nullifiers) stored in smart contracts.
  • Proof system: zkSNARKs (Groth16) validate note creation and spending.
  • Settlement: ERC-20/ERC-721/ERC-1155 tokens are deposited into Railgun contracts, converted to private notes, then spent/withdrawn.
  • Integration: Railgun “Adapt Modules” allow private interactions with existing DeFi protocols by wrapping function calls.
  • Data availability: all commitments stored publicly on-chain; privacy relies on zk proofs, not off-chain DA.

Privacy domains

  • Shielded transfers: hide sender, receiver, token, and amount within the anonymity set.
  • Private DeFi calls: interact with external contracts (e.g. Uniswap) without linking wallet identity.
  • No regulator view keys: users can self-disclose by sharing spending keys, but no scoped/threshold key system is natively supported.

Enterprise demand and use cases

  • Retail privacy: primary adoption among individual users seeking shielded ERC-20 transfers.
  • DeFi traders: private swaps and interactions with DEXs to prevent MEV or front-running.
  • Institutions: occasionally cited in research as a shielded pool candidate, but lacks regulator access features required for enterprise settlement.

Technical details

  • zkSNARK proving via Groth16, circuit for note validity and nullifier uniqueness.
  • Smart contract architecture deployed on Ethereum mainnet, BNB Chain, Polygon, and others.
  • UTXO model: each note represents a claim on deposited tokens; nullifiers prevent double spends.
  • Adapt Modules: special contracts that wrap DeFi calls (e.g. swaps, lending) to preserve privacy of user identity.

Strengths

  • Mature, deployed contracts live on multiple EVM chains.
  • Large existing anonymity set (user-driven shielded pool).
  • Supports many ERC standards (ERC-20, ERC-721, ERC-1155).
  • Extensible via Adapt Modules for DeFi interoperability.

Risks and open questions

  • No regulator-oriented audit path: may limit institutional adoption.
  • Prover costs & UX: Groth16 proofs are relatively heavy for end-users, requiring wallet integration, high gas operations (~2m).
  • On-chain DA: all commitments are public; long-term scalability may be constrained.
  • Trust assumptions: requires careful ceremony setup for zkSNARK parameters (trusted setup).

Links