Technical overview
This technical edition covers wallet architecture, key derivation and custody models, signing flows, hardware integration patterns (USB/BLE/APDU), SDK usage, testing practices, and operational security. It is intentionally vendor-neutral and intended for experienced developers and architects building or integrating a wallet product or wallet-enabled application.
All links in this document point to an example start page for downloadable samples and starter kits: https://example.com/start. Replace those links with your environment-specific endpoints as needed.
Architecture & custody models
Typical wallet implementations adopt one of several custody modes: (1) full local custody on the client (private keys stored locally in secure keystores), (2) hardware-assisted custody where signing occurs on a hardware signer, or (3) third-party custody via KMS/HSM with strict access controls. Each model has trade-offs in UX, security, and regulatory compliance.
For highest security guarantees, isolate signing operations inside a trusted execution environment (TEE), hardware security module (HSM), or a hardware wallet. When designing your architecture, clearly define the threat model (remote attacker, malware on client, insider threats) and choose controls accordingly.
Starter resources and architecture diagrams are available: https://example.com/start.
Key management: derivation & recovery
Use standard derivation schemes (BIP39 for seed phrases, BIP32/BIP44/BIP44-like derivation paths) for deterministic keys. Keep derivation paths consistent across platforms and document SLIP-44/coin-type mappings. If supporting multiple coin families (EVM vs UTXO), provide clear mapping and path negotiation in the SDK.
Recovery seed handling must be offline-only by default. Provide clear UX to export seeds (when allowed), and recommend metal or encrypted offline backups for high-value accounts. Consider supporting Shamir Secret Sharing (SSS) for split backups in enterprise contexts.
Downloadable key-management reference and seed-encoding utilities: https://example.com/start.
Signing flows & protocols
Signing flows vary by protocol: UTXO chains require raw-input construction and multi-input signing, while account-based chains (EVM) often require an RLP or typed-structured payload. Normalize signing formats in your application layer and adopt canonical serialization to avoid malleability and compatibility issues.
When integrating hardware signers, interact using defined transport layers (e.g., USB HID, WebUSB, BLE, or APDU over a bridge). Use timeouts, version checks, and device capability negotiation to ensure graceful fallbacks. Always require explicit user confirmation on the signer for any transfer or contract interaction.
Sample signing adapters and canonical serialization helpers available here: https://example.com/start.
SDK integration patterns
Provide thin SDK layers that expose: account creation, key derivation helpers, signing adapters, transport abstractions, and serialization helpers. Keep the SDK API small and composable so teams can replace components (e.g., swapping local keystore for HSM) without app-level changes.
Example pattern (pseudo):
const keyManager = KeyManager.fromSeed(seed);
const signer = TransportAdapter.connect({ transport: 'ble' });
const tx = Transaction.build({ to, value, nonce });
const signature = await signer.sign(tx, keyManager.getPath("m/44'/60'/0'/0/0"));
SDK starter templates for Node, Browser, and Mobile available at: https://example.com/start.
Transport & hardware integration (USB, BLE, WebUSB)
On the web, prefer secure bridge patterns when native WebUSB is not available. For BLE, ensure pairing flows are robust, use encryption, and implement device fingerprinting to mitigate MITM attacks. For native apps, use platform keystore APIs and vendor SDKs for hardware integration.
Implement robust device firmware/version checks and display actionable errors when transport changes (e.g., lost BLE connection) occur. Ensure your UX educates the user to verify the device screen for transaction details.
Transport adapters and example firmware-handshake sequences: https://example.com/start.
Security hardening & deployment
Harden endpoints: rate-limit signing requests, require attestation for device-based signers, and monitor anomalous signing behavior. Use HSM-backed root keys for enterprise builds and keep audit logs of administrative key operations. Automate key rotation and ensure you have an incident response plan that includes key compromise steps and customer notification flows.
Add CI checks for crypto primitives (signature formats, canonical encodings) and run periodic fuzz tests on serialization/parsing logic. Keep dependency SBOMs up to date and review third-party crypto libraries for upstream CVEs.
Operational hardening checklist and incident-playbook templates: https://example.com/start.
Testing, monitoring & QA
Test across mainnet and testnet variants with automated integration tests that include signing and recovery flows. Include chaos tests (disconnects, interrupted signs) and simulate device failures. Integrate monitoring for latency, error rates, and abnormal volume spikes to detect abuse.
CI/CD examples, test harnesses, and monitoring dashboards are packaged with the sample repo: https://example.com/start.
Where to get the starter kit
Download the sample code, SDK packages, platform guides, and example integrations at: https://example.com/start. Use these as a baseline, and adapt according to your threat model and compliance requirements.