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.

Technologies and Timelines

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

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

1. Analysis—requirements: list of networks, UI, integrations.
2. Design—architecture, stack, specification.
3. Development—iterations every 2 weeks.
4. Testing—unit, E2E, manual.
5. 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.

The TrueTech team has over 5 years of experience in blockchain development and more than 20 successful wallet projects.

We develop crypto wallets turnkey — from custodial solutions for fintech to smart contract accounts on EIP-4337. 5+ years in blockchain development, 40+ projects implemented. Let's examine which architecture to choose for your task and why MPC or Account Abstraction solve the private key problem that MetaMask and classic HD wallets could not close.

Why are classic wallets dangerous for business?

A seed phrase in a browser extension is the only way to restore access. For retail users, this is a barrier to entry (lost phrase = lost money). For corporate treasuries, it is incompatible with compliance (KYC/AML, role model, multisignature). Any single key leak compromises all funds. These risks are built into the architecture, not poor UX.

We eliminate them at the protocol level: MPC wallets (key never fully assembled), smart contract wallets (authorization logic in code), hardware HSM for institutional storage. Details below.

What is the real difference between custodial and non-custodial?

Custodial — the provider stores the private key. User authenticates via email/password/OAuth. Recovery is trivial, KYC/AML built-in. For centralized financial applications, often the only regulatory acceptable option. Risk: single point of failure (e.g., Bitfinex hack — $72M, FTX — $600M+ client funds).

Non-custodial — keys are with the user. Provider has no access to funds. Storage responsibility falls on the user. For 99% of people, this model is unworkable without additional protection — hence MPC.

MPC wallets: the key that doesn't exist

Multi-Party Computation (MPC) is a cryptographic protocol that allows multiple parties to jointly sign a transaction without revealing their partial secrets. The private key never exists in its assembled form.

Standard scheme: 2-of-3 MPC between user (share on device), provider server, and backup cloud storage. Transaction is signed by any two of three parties. Lost phone — recovery via server + cloud. Server compromised — attacker holds only one share, signing impossible.

TSS (Threshold Signature Scheme) is a concrete implementation of MPC for ECDSA/EdDSA. Algorithms: GG18, GG20, CGGMP21 (the latter is faster and has better security proofs). Libraries: tss-lib (Go, from Binance), multi-party-sig (Go, from Coinbase), ZenGo-X/multi-party-ecdsa (Rust).

MPC requires no on-chain changes — to the blockchain, the signature looks like a normal single-key signature. This saves gas and keeps the key management scheme confidential (not published in chain) — unlike multisig.

Account Abstraction (EIP-4337): smart contract as wallet

EIP-4337 completely changes the model: instead of EOA (Externally Owned Account), a smart contract Account is used. Authorization logic is in contract code, not in protocol cryptography. This opens up arbitrary signing logic, social recovery, session keys, sponsored transactions, and batch operations.

How the EIP-4337 stack works:

User → UserOperation → Bundler → EntryPoint contract → Account contract
                                          ↑
                                    Paymaster (optional, pays gas)

UserOperation — a new type of object (not an L1 transaction). Bundler collects UserOps from an alternative mempool, packs them into one transaction, and sends to EntryPoint. EntryPoint calls validateUserOp on the Account contract — Account decides if the signature is valid.

Practical capabilities:

Social recovery. The contract stores a list of guardians (other addresses or a service). Lost key — guardians vote for replacement. Argent has used this scheme since 2020.

Session keys. A temporary key with limited rights: interaction only with a specific contract, until a certain date, up to a certain amount. For GameFi and dApps — user does not sign every micro-transaction.

Paymaster. A third-party contract pays gas for the user. Onboarding pattern: user does not hold ETH, gas is sponsored by dApp or taken from ERC-20 tokens.

Implementations: Safe{Core} Protocol, Biconomy SDK (Stackup), ZeroDev (Kernel), Alchemy (Rundler bundler). EntryPoint v0.6/v0.7 is deployed and active on Ethereum mainnet, Polygon, Arbitrum, Optimism. We guarantee compatibility with the latest contract versions.

What is a Hardware Security Module for corporate wallets?

For treasuries and institutional storage: HSM (Hardware Security Module). The key is generated and never leaves the secure chip. Signing happens inside the HSM. Hardware attestation is supported. Solutions used: AWS CloudHSM, Azure Dedicated HSM, Thales Luna, YubiHSM 2 (for small volumes). Integration via PKCS#11 or cloud-specific API.

A combination of HSM + MPC is optimal for institutional use: key shares are stored in HSMs on different servers/jurisdictions, signing via TSS. This ensures compliance with regulatory requirements (e.g., for crypto custodians).

Integration with dApps: WalletConnect and standards

Any wallet must be able to interact with dApps. Standard: WalletConnect v2 (Sign API): QR code or deep link, peer-to-peer encrypted channel via relay server. For browser extensions: EIP-1193 (Ethereum Provider API).

On the frontend, we use wagmi + viem — one interface for MetaMask, WalletConnect, Coinbase Wallet, injected providers. For Account Abstraction: EIP-5792 (wallet capabilities) and EIP-7677 (paymaster service).

Development process

1. Threat model — who is the user (B2C, B2B, institutional), what operations, what is the acceptable risk model. Architecture depends on this.
2. Selection and design of key storage scheme — MPC, HSM, multisig, or a combination.
3. Development of Account contract (if EIP-4337) or integration of MPC library.
4. Backend — MPC coordination, session management, paymaster service (if needed).
5. Mobile/browser application — UI with WalletConnect integration, biometrics, QR.
6. Integration with dApps — EIP-1193, WalletConnect v2.
7. Audit of contracts and cryptographic implementations — mandatory step. MPC libraries have known vulnerabilities (GG18 susceptible to attack with malicious participant without abort protocol). We use libraries with up-to-date security reviews (CGGMP21). Experience passing audits with Certik, Hacken, Trail of Bits — we have certificates.

What is included in the work (deliverables)

• Source code of smart contracts (Solidity/Rust) with documentation
• Backend MPC coordination service (Go or Rust) with API
• Mobile application (iOS/Android) or browser extension
• Integration with WalletConnect, Ledger/Trezor (if required)
• Preparation for security audit (vulnerability report)
• Administrator and user documentation
• Access to repository, CI/CD, monitoring (Tenderly, Etherscan API)
• Training of your team (2-3 sessions)
• Post-launch support — 1 month

Timeline and cost

Cost is calculated individually for your project. We will estimate within one day — contact us by email or Telegram. We provide a guarantee on code and timeline.

Typical mistakes in crypto wallet development (and how to avoid them)

• Using outdated MPC libraries — GG18 without abort protocol. Choose CGGMP21 or tss-lib with up-to-date audit reports.
• Tight coupling to a single blockchain — not abstracting for L2/sidechains. Use viem/wagmi for cross-chain.
• Ignoring MEV attacks — when using multisig without timelocks. Add tx simulation (Tenderly) and sandwiching protection.
• Lack of fallback recovery mechanism — for Account Abstraction, not setting up social recovery. Include from the first release.

We eliminate these pitfalls at the design stage — for each project, we create a threat model and security checklist.

Need a reliable wallet with no compromises? Get a consultation from our architect — we will analyze your task and propose an architecture with a precise estimate. Leave a request — we will respond within a day.