Gasless Transaction

A paymaster is a smart contract that sponsors transaction fees on behalf of users. This is a core mechanism in Account Abstraction (ERC-4337) and networks like zkSync. The paymaster can be funded by dApps, wallet providers, or other entities to cover gas costs.

• ERC-4337 Bundlers: Submit and pay for user operations.
• Gas Policies: Sponsors can set rules (e.g., only for specific contracts).

A precursor to modern paymasters, meta-transactions allow users to sign messages off-chain. A relayer (a separate server) then submits the signed message as an on-chain transaction, paying the gas fee. This decouples the signer from the fee payer.

• Gas Relay Networks: Services like GSN (Gas Station Network) pioneered this model.
• Signature Verification: The target contract must implement logic to validate the off-chain signature.

For applications requiring multiple interactions (e.g., gaming), session keys enable temporary, limited-authority keys. A user pre-approves a session, and the dApp can submit transactions from that key without further signatures, with gas sponsored by the dApp.

• Time or Usage Limits: Sessions expire after a set time or number of actions.
• Reduced Friction: Eliminates pop-up wallet confirmations for each action.

Some L2s and sidechains implement native fee abstraction. For example, Starknet and zkSync Era have system-level support for paying fees in ERC-20 tokens instead of the native chain token (ETH). This simplifies the user experience, as they don't need to hold the base asset for gas.

• Token Sponsorship: dApps can pay fees in stablecoins like USDC.
• Protocol-Level: Built into the chain's protocol, not just smart contracts.

Shifting fee payment introduces new economic considerations. Sponsors must manage gas price volatility and prevent Denial-of-Service (DoS) attacks where malicious users spam sponsored transactions.

• Rate Limiting & Whitelists: Common anti-abuse measures.
• Deposit Models: Paymasters often require a prepaid deposit for gas.
• Trust Assumptions: Users must trust the sponsor not to censor or front-run their transactions.

The primary goal is to remove a major UX hurdle: requiring users to acquire and manage native tokens for gas before using a dApp. This enables:

• Frictionless Onboarding: New users can interact immediately.
• Predictable Pricing: Costs can be baked into service fees or subscriptions.
• Batch Transactions: Sponsors can bundle multiple actions into one gas-paid transaction.

The application itself covers gas costs as a customer acquisition or usability cost. This is often implemented via a subscription model or is funded by the dApp's treasury. It's a business-layer solution rather than a protocol-level one.

• Implementation: Direct integration with a relayer or paymaster.
• Trade-off: Centralizes cost burden on the dApp operator.

Gasless transactions are not a single protocol but an abstraction layer built on top of existing blockchain infrastructure. They separate the act of signing a transaction from the act of paying for its execution. This is typically implemented via meta-transactions, where a user signs a message that is later submitted and paid for by a relayer, or account abstraction (ERC-4337), which uses a Paymaster contract to sponsor fees.

Before standardized account abstraction, gasless systems often used a relayer network. The flow was:

1. User signs a meta-transaction message off-chain.
2. Message is sent to a trusted relayer server.
3. Relayer wraps the message in a real transaction, pays the gas, and broadcasts it. This model required trust in the relayer's availability and honesty, and the logic for fee sponsorship was managed off-chain. Protocols like GSN (Gas Station Network) popularized this approach.

The entity paying the gas (sponsor) does so under specific conditions, creating distinct business models:

• dApp Pays: The application sponsors user fees to reduce onboarding friction, treating gas as a customer acquisition cost.
• Pay in ERC-20: A Paymaster allows users to pay fees in a stablecoin or app token, abstracting away ETH.
• Sponsored Sessions: Fees are covered for a user's first transaction, a specific action, or for a limited time period.
• Fee Delegation: Another user (e.g., a project) pre-funds a Paymaster to cover fees for a community.

Gasless systems must implement safeguards to prevent economic attacks:

• Rate Limiting: Capping sponsored transactions per user or contract to prevent spam.
• Whitelists: Restricting sponsorship to specific dApp functions or verified users.
• Staked Deposits: Requiring dApps or paymasters to stake funds, which can be slashed for malicious behavior.
• Reputation Systems: For bundlers and paymasters in ERC-4337, to ensure reliable service. Without these, systems are vulnerable to transaction spam that drains the sponsor's funds.

Several protocols and tools enable gasless transactions:

• Stackup, Biconomy, Candide: ERC-4337 Bundler and Paymaster infrastructure providers.
• OpenGSN: The original Gas Station Network for relayed meta-transactions.
• Safe{Wallet}: Smart account infrastructure with native fee delegation support.
• Polygon PoS: Offers native gasless transaction APIs for developers. These services provide SDKs and APIs that allow dApps to integrate gasless features without managing underlying infrastructure.

A gasless transaction is a blockchain operation where a third party, known as a sponsor or paymaster, covers the network gas fees on behalf of the end user. This is a core feature of account abstraction, which decouples fee payment from transaction initiation. The sponsor is typically the dApp developer or a dedicated service, enabling a seamless user experience similar to web2 applications.

• Key Mechanism: The user signs a meta-transaction, which is then relayed and paid for by the sponsor's smart contract.
• Primary Benefit: Removes the requirement for users to hold the network's native token (e.g., ETH, MATIC) to interact with dApps.

The security model shifts from the user securing their gas funds to trusting the sponsor's infrastructure and intentions. Critical considerations include:

• Sponsor Integrity: The sponsor must not censor, front-run, or maliciously modify the user's signed transaction intent.
• Relayer Security: The service relaying the transaction must be reliable and resistant to DoS attacks.
• Smart Contract Risk: Bugs in the sponsor's paymaster contract could lead to lost funds or failed transactions. Users delegate significant trust to this code.
• Nonce Management: Sponsorship systems must correctly handle transaction nonces to prevent replay attacks and ensure execution order.

Sponsors absorb gas costs to drive user adoption and capture value elsewhere in their application's ecosystem. Common economic models include:

• Customer Acquisition Cost: Treating gas fees as a marketing expense to onboard users.
• Subscription Models: Offering gasless transactions as a premium feature for paying subscribers.
• Tokenomics: Using a project's native token to subsidize fees, creating utility and demand.
• Sponsored Sessions: Paying for a user's first transactions or specific actions (e.g., a game's first 10 moves).

Sustainability requires careful calculation of customer lifetime value (LTV) versus the cost of gas sponsorship.

While gasless transactions dramatically improve UX, they introduce centralization vectors that contradict core blockchain principles.

• Single Point of Failure: If the sponsor's relayer goes offline, users cannot submit transactions.
• Censorship Risk: A sponsor could refuse to process transactions from certain addresses or for certain dApp functions.
• Regulatory Exposure: Sponsors may be compelled to implement KYC/AML checks on users, creating a gated experience.

Hybrid models, like allowing users to pay their own gas as a fallback, can mitigate these risks.

The ERC-4337 standard for Account Abstraction provides a decentralized, permissionless framework for gasless transactions without requiring consensus-layer changes. Its key component for gas sponsorship is the Paymaster.

• Paymaster Contract: A smart contract that validates conditions and pays for a UserOperation. It can implement rules like:
  • Paying for specific users or dApps.
  • Accepting payment in ERC-20 tokens.
  • Sponsoring transactions up to a certain gas limit.
• Bundler Network: A decentralized network of nodes that bundle UserOperations and submit them to the blockchain, competing on efficiency.

This standard aims to preserve decentralization while enabling sponsor-based UX.

Gasless systems introduce unique attack surfaces that must be defended.

• Gas Griefing: A malicious user could spam the sponsor with computationally heavy transactions to drain its funds. Mitigated by setting strict gas limits and requiring reputation or staking.
• Economic Exploitation: Arbitrage bots could exploit sponsorship rules for profit. Mitigated with whitelists, rate limits, and complex validation logic in the paymaster.
• Front-running the Paymaster: An attacker could see a paymaster's transaction in the mempool and submit a similar, more expensive one to drain its balance. Mitigated using private transaction relays or commit-reveal schemes.
• Sybil Attacks: Creating many fake accounts to abuse a sponsorship program. Often mitigated with social proof or attestation requirements.

A smart contract that acts as a gas sponsor in an ERC-4337 UserOperation. It can pay for a user's transaction fees under predefined conditions, enabling true gasless experiences. Paymasters can implement various business models:

• Sponsored by dApp: The application covers fees to reduce user friction.
• Pay in ERC-20 tokens: Users pay fees in a token other than the network's native currency.
• Subscription-based: Users have fees covered as part of a service plan.

A decentralized network of nodes that broadcast and pay for meta-transactions on behalf of users. These networks manage the economic layer of gasless transactions, often using a system of staking and reputation to ensure reliability. Examples include:

• GSN (Gas Station Network): An open-source infrastructure for relaying meta-transactions.
• Biconomy: A commercial platform providing relayer services and paymaster infrastructure.

A security mechanism, often enabled by account abstraction, that grants a temporary, limited authority to a dApp or service. This allows for a series of pre-approved transactions (like in a gaming session) without requiring a signature for each one, while the user's main private key remains secure. Key characteristics:

• Time-bound or usage-bound permissions.
• Limited scope to specific contract functions or value amounts.
• Can be revoked by the user at any time.

Critical backend processes that make gasless transactions economically viable. This involves predicting transaction costs and finding the most efficient execution paths to minimize the sponsor's expense. Techniques include:

• Static analysis of smart contract bytecode to estimate gas.
• Transaction bundling to amortize fixed costs across multiple operations.
• Layer 2 integration, where gasless models are often more sustainable due to significantly lower base fees.