Gasless Swap

Gasless transactions rely on a relayer network to pay gas fees on the user's behalf. This creates a dependency on the relayer's availability and integrity.

• Single Point of Failure: If the primary relayer goes offline, transactions cannot be processed.
• Transaction Censorship: A malicious or compliant relayer can selectively choose which transactions to submit or delay, potentially front-running or blocking users.
• Solution: Decentralized relayer networks or permissionless meta-transaction protocols mitigate this risk.

Users sign EIP-712 structured messages instead of sending signed transactions, creating new attack surfaces.

• Replay Attacks: A signed message intended for one network (e.g., Polygon) could be maliciously submitted to another (e.g., Ethereum Mainnet) if not properly protected by a domain separator and chain ID.
• Phishing Signatures: Users must carefully verify the exact details (token amounts, recipient) in their wallet's signing prompt, as a malicious dApp could request a signature for unfavorable terms.

The entity sponsoring the gas fees (the dApp, a paymaster) assumes financial risk and must manage it sustainably.

• Sybil Attacks: An attacker could spam the network with low-value transactions, draining the sponsor's gas fund.
• Gas Price Volatility: Sudden network congestion can make sponsoring transactions economically unviable, causing service disruption.
• Fund Custody: Users must trust the sponsor's smart contract to securely hold funds earmarked for gas payment.

Gasless systems add layers of smart contract logic, increasing the attack surface area.

• Paymaster Logic: Flaws in the paymaster contract that validates and pays for transactions can lead to fund theft or drained subsidies.
• Signature Verification: Bugs in the signature verification logic (e.g., in a Gasless Forwarder contract) could allow unauthorized transactions to be executed.
• Upgradeability Risks: Many systems use upgradeable proxy contracts for relayer logic; a compromised admin key could upgrade to a malicious contract.

The 'gasless' abstraction can lead to dangerous misunderstandings about blockchain fundamentals.

• False Sense of Finality: Users may think a signed message is a confirmed transaction, but it still requires relay and on-chain confirmation.
• Hidden Costs: Fees may be abstracted but not absent; they can be bundled into worse exchange rates or taken from the swapped amount.
• Private Key Security: Signing a message uses the same private key as a transaction; a malicious site can still drain funds if a user signs a harmful message.

Gasless swaps interact with multiple protocols (DEX, aggregator, relayer), creating composite risk.

• Oracle Manipulation: If the swap uses a price oracle for validation, manipulation could cause incorrect execution.
• Deadline Enforcement: Users often set a transaction deadline in their signed message; a delayed relay could result in a trade executing at an unfavorable price.
• Dependency Risks: The system's security is now tied to all integrated protocols (e.g., the underlying DEX's router contract).

A meta-transaction is a signed message containing the intent of a transaction, which is then submitted and paid for by a separate entity called a relayer. This is the fundamental cryptographic primitive enabling gasless interactions. The user signs a message off-chain, and the relayer wraps it in an on-chain transaction, paying the gas fee.

• Key Components: User signature, relayer, and a smart contract that can verify the signature and execute the intent.
• Example: A user signs an order to swap tokens; a decentralized relayer network picks it up, pays the gas, and submits it to the blockchain.

ERC-4337 is an Ethereum standard that enables account abstraction without requiring consensus-layer changes. It allows users to have smart contract wallets with custom logic for transaction validation, sponsorship, and gas payment. This is a primary architectural foundation for sophisticated gasless experiences.

• UserOperation: A new transaction type representing a user's intent, bundled and executed by Bundlers.
• Paymasters: Smart contracts that can sponsor gas fees for users, enabling true gasless transactions or payment in ERC-20 tokens.

A paymaster is a smart contract (central to ERC-4337) that agrees to pay for a user's gas fees under specific conditions. It decouples the entity paying for gas from the entity initiating the transaction, enabling gasless or alternative-fee models.

• Sponsorship: A dApp or service can deploy a paymaster to cover fees for its users.
• Token Payment: Paymasters can allow users to pay fees in the ERC-20 token they are swapping, not just the native chain token (e.g., paying for an ETH swap with USDC).

A relayer network is a decentralized system of nodes that accept signed meta-transactions from users, pay the gas fees, and broadcast them to the blockchain. Relayers are compensated via fees or other incentives embedded in the transaction flow.

• Function: Provides the infrastructure and liquidity for gas fees required to execute user-signed messages.
• Examples: Networks like GSN (Gas Station Network) pioneered this model, and Bundlers in the ERC-4337 ecosystem serve a similar role.

Gas sponsorship is a business model where a third party (e.g., a dApp, wallet, or protocol) covers the network transaction costs for end-users. This removes a major UX barrier and is the commercial driver behind most gasless swap implementations.

• Implementation: Typically managed via a paymaster contract or a dedicated relayer service.
• Use Case: A decentralized exchange (DEX) aggregates fees from its treasury or a small surcharge on trades to sponsor the gas for its users' swaps.

Signature verification is the critical cryptographic process that allows a smart contract to validate that a gasless transaction request (a meta-transaction or UserOperation) was legitimately signed by the owner of the account. This ensures security and non-repudiation in a gasless flow.

• Process: The contract recovers the signer's address from the provided signature using the ecrecover function or other schemes like EIP-1271 for smart contract wallets.
• Security: The entire gasless system depends on this verification to prevent unauthorized transactions from being executed.