We implement ERC-4337 in mobile crypto wallets to remove barriers of seed phrases and mandatory ETH for gas. The ERC-4337 standard (described in EIP-4337) replaces EOA with smart contract wallets. The user gains gasless transactions, social recovery, and biometric signing—without storing a seed phrase. For developers, integration involves working with UserOperation, Bundler, and Paymaster. The result is a Web2-level UX: users log in with Face ID, and transactions are free for them. Contact us to discuss your project.
Traditional EOA wallets require managing private keys and having ETH for gas. This creates a barrier to mass DeFi adoption. ERC-4337 solves this through smart accounts that can sponsor gas and be recovered without a seed phrase. The mobile app becomes just a client that signs operations with biometrics.
Which ERC-4337 components are used in a mobile wallet?
Smart Account
Instead of an EOA, the user gets a smart contract wallet (SimpleAccount, SafeAccount, LightAccount by Alchemy, Kernel by ZeroDev). The contract address is deterministic via CREATE2—it can be computed before deployment. The mobile client stores the ownerPrivateKey (signer key) in Secure Enclave (iOS) / Android Keystore, not the wallet itself.
EntryPoint Contract
(0x5FF137D4b0FDCD49DcA30c7CF57E578a026d2789—same address on all EVM networks)—a global singleton that accepts UserOperation[] from Bundlers.
Bundler
A node that collects UserOperations from the mempool, simulates them, and packs them into a regular on-chain transaction. SDKs to use: @alchemy/aa-core, permissionless.js, viem/account-abstraction. In the mobile app, the Bundler is an HTTP endpoint where the client sends eth_sendUserOperation. Alchemy's bundler processes operations 2x faster than the public mempool.
Paymaster
An optional contract that sponsors gas. Verifying Paymaster signs a permission on the server; ERC-20 Paymaster allows payment in USDC. In the mobile client, before sending a UserOperation, we request pm_sponsorUserOperation from the Paymaster API (Alchemy, Pimlico, Biconomy). Gas savings for the user can reach 90%.
How does gas estimation work in ERC-4337?
The fields callGasLimit, verificationGasLimit, preVerificationGas need to be estimated before sending. The Bundler provides eth_estimateUserOperationGas—we call it before showing the user the gas amount. Pimlico, Alchemy Gas Manager automate this. Without correct estimation, the Bundler will reject the operation with AA21 didn't pay prefund. On L2 (Optimism/Base), the L1 data fee is accounted for.
How does ERC-4337 change mobile wallet UX?
Signing UserOperation. The smart account verifies the signature via isValidSignature (ERC-1271). The owner (owner EOA) signs. On iOS—SecKeyCreateSignature with kSecKeyAlgorithmECDSASignatureMessageX962SHA256 via Secure Enclave (key never leaves the chip). On Android—KeyPairGenerator with AndroidKeyStore provider, signature via Signature.getInstance("SHA256withECDSA").
Biometric authentication before signing—LocalAuthentication (iOS) / BiometricPrompt (Android). The private key is only accessible after biometric verification—the key is marked with kSecAccessControlBiometryCurrentSet (iOS) or setUserAuthenticationRequired(true) (Android Keystore).
Session Keys. ERC-4337 allows delegating limited signing rights. Example: a mobile game requests a session key with permission to spend up to 5 USDC per transaction—the user signs once, subsequent micro-transactions proceed without confirmation. Implementation via ISessionKeyPlugin (ERC-6900) or analogous in Kernel (ZeroDev).
Social Recovery. The smart account can support recovery through guardians—trusted addresses (e.g., email-recovery via ZeroDev Email Recovery or phone via social login through Web3Auth). The user loses their key → contacts guardians → after a timelock (usually 48 h) gets a new owner. For mobile UX: in the app—a "Recovery" section where guardians can be added and threshold configured.
Case Study: DeFi mobile wallet (our client)
Smart Account based on LightAccount v1.1, Bundler—Alchemy, Paymaster sponsors first 10 transactions for new users. Signing via Secure Enclave (iOS) and Android Keystore. Onboarding without a seed phrase: user creates an account via Apple Sign In → ECDSA keypair generated in Secure Enclave → smart account address computed via getCounterFactualAddress → on first deposit, account is deployed via initCode in UserOperation. The user never sees a private key or seed phrase. Smart Account reduces user confirmations by 3x compared to EOA wallets.
What challenges arise when implementing ERC-4337?
Frontrunning UserOperations. The ERC-4337 mempool is public—Bundlers see unconfirmed UserOperations. For confidential operations, use a private bundler (Flashbots, MEV Blocker) or a Paymaster with encrypted data.
Multi-chain. EntryPoint v0.6 and v0.7 have different addresses on different networks. The wallet must support both. SmartAccountClient from @alchemy/aa-core abstracts this, but configuration per network is separate.
Gas estimation on Optimism/Base. The L2 gas model differs: the L1 data fee is added to L2 gas. eth_estimateUserOperationGas from the Bundler accounts for this, but verification on different networks separately is recommended.
What stages does ERC-4337 wallet development involve?
| Stage | Result |
|---|---|
| Requirements analysis and stack selection | Technical specification with SDK and contract version justification |
| Architecture design | Client–Bundler–Paymaster interaction diagram |
| Smart account + client SDK development | Integration of signing, gas estimation, session keys |
| Testnet testing | UserOperation validation on 3+ EVM networks |
| Deployment and launch | Bundler/Paymaster access, documentation, team training |
Timelines and Costs
| Scope | Estimated Time |
|---|---|
| Basic ERC-4337 wallet, gasless, biometric | 10–16 weeks |
| Wallet with session keys and social recovery | 5–8 months |
| DeFi platform with multi-chain support | 8–14 months |
Cost is calculated individually after analyzing smart contract requirements, supported networks, and onboarding UX flow.
We have 10+ years of experience in mobile development and 50+ completed projects integrating blockchain technologies. Get a consultation on implementing ERC-4337 in your mobile app—contact us to discuss the project and create a RoadMap.