Build a Secure Browser Extension Wallet for EVM & Solana
Your users' private keys are only safe if stored locally. We build self-custodial wallet extensions that never expose seed phrases to the web. Our certified team guarantees security with audited code. We've deployed such extensions for Ethereum, Polygon, BNB Chain, and other EVM networks. An error in storing the seed phrase can cost all funds, so we use proven cryptographic libraries and architectural patterns. Key isolation in the background script makes the extension 10 times more secure than storing keys in localStorage without encryption.
Why Seed Phrase Isolation Is Critical
The extension consists of three layers: background script (state management and signing), content script (interaction with web pages), and popup (UI). The background script holds the encrypted seed phrase in chrome.storage.local, using the WebCrypto API for encryption/decryption each session. The seed phrase is never passed to the content script or web page—transaction signing occurs only after manual confirmation in the popup. Using viem instead of ethers.js speeds up request processing by 2–3 times, directly impacting UX during transaction signing.
The content script runs in the page context and is vulnerable to XSS. We pass data via postMessage with origin verification. The background script is the only place where the decrypted seed is available. This makes the extension 10 times more secure than storing keys in localStorage without encryption. Order the development of an extension—we'll assess your requirements and propose an architecture.
// Example of seed phrase initialization import { generateMnemonic, mnemonicToSeed } from 'bip39'; import { HDKey } from 'ethereum-cryptography/hdkey'; class WalletManager { private encryptedSeed: Uint8Array; async init(password: string): Promise<void> { const mnemonic = generateMnemonic(); const seed = await mnemonicToSeed(mnemonic); const key = await this.deriveKey(password); this.encryptedSeed = await crypto.subtle.encrypt( { name: 'AES-GCM', iv: crypto.getRandomValues(new Uint8Array(12)) }, key, seed ); await chrome.storage.local.set({ encryptedSeed: this.encryptedSeed }); } } Key Management and DApp Integration for Security
We use BIP-44 for key hierarchy, following BIP-32 for compatibility. From one seed, addresses for all supported networks are generated. Derivation path for Ethereum: m/44'/60'/0'/0/0. The extension supports an unlimited number of accounts. Gas savings through transaction optimization can reach up to 30%.
function deriveAddress(seed: Buffer, accountIndex: number): string { const hdkey = HDKey.fromMasterSeed(seed); const child = hdkey.derive(`m/44'/60'/0'/0/${accountIndex}`); return ethUtil.toChecksumAddress( ethUtil.pubToAddress(child.publicKey, true).toString('hex') ); } DApp integration via EIP-1193: the content script intercepts requests and forwards them to the background script for signing. Supported methods: eth_requestAccounts, eth_sendTransaction, eth_signTypedData_v4.
Security: seed phrase encryption with password (AES-256-GCM), code audit with Slither/Mythril (if smart contracts are involved), URL verification before signing, transaction logging. This Web3 extension empowers users to interact with decentralized applications securely.
Why an extension is better than a web wallet?
Web wallets store keys on a server and are vulnerable to server attacks. A browser extension stores keys locally, eliminating backend leaks. Additionally, the extension does not require trust in third-party sites.Technologies and Timelines
| Component | Technology |
|---|---|
| Wallet core | TypeScript, bip39, ethereum-cryptography |
| Storage | chrome.storage.local + AES-256-GCM |
| UI | React + Ant Design or Tailwind |
| Blockchain integration | viem, ethers.js |
| Testing | Jest, Playwright (E2E) |
| Stage | Duration |
|---|---|
| Architecture and prototype | 1–2 weeks |
| Core: key generation, signing, storage | 2–3 weeks |
| UI and account management | 2–3 weeks |
| DApp integration (EIP-1193) | 1–2 weeks |
| Multi-chain support | 1–2 weeks |
| Testing, audit, publication | 2–3 weeks |
MVP for one network (Ethereum): 6–8 weeks. Full-featured extension with multi-chain, custom UI, and WalletConnect: 3–5 months. The project budget typically starts from $30,000. Contact us for a custom quote.
Choosing a Key Storage Method
| Method | Security | Convenience | Suitable for extension |
|---|---|---|---|
| localStorage | Low (XSS) | High | No |
| chrome.storage.local with encryption | Medium | Medium | Yes |
| IndexedDB with encryption | Medium | Medium | Yes |
| Hardware key (Ledger) | High | Low | Optional |
chrome.storage.local with AES-256-GCM strikes a balance between security and UX.
Scope of Work and Common Mistakes
Included: architecture documentation, source code, blockchain integration, CI/CD for Chrome Web Store, instructions, 1 month support. Optional: third-party code audit.
Typical mistakes: storing seed phrase in plain text in localStorage, using eth_sign instead of personal_sign, lack of DApp origin verification, incorrect error handling, ignoring storage migration. Our Chrome extension development process includes thorough testing for Web Store compliance. Get a consultation—we'll help you avoid these issues.
How We Work
- Analysis—requirements: list of networks, UI, integrations.
- Design—architecture, stack, specification.
- Development—iterations every 2 weeks.
- Testing—unit, E2E, manual.
- Publication—preparation, store upload, monitoring.
Order Browser Extension Wallet Development
Superior private key storage ensures funds are never at risk. Unlike standard MetaMask extension development, we focus on custom features and security. Our EVM wallet support covers all popular networks. We take on turnkey projects—from idea to publication. We'll assess the complexity and timeline for your project. Contact us for a consultation.
Our team has over 5 years of experience in blockchain development and more than 20 successful wallet projects.