Openloop SDK
Specifications
Version v0.3.1 ｜ Last updated 2026-06-12
Haudi Crypto,
Inc. President and CEO Kazunori Asada
Architecture Overview
What is the Openloop SDK?
The Openloop SDK is a multi-language library for communicating with the Openloop hardware wallet.
| Language / format | Main deliverables | Purpose |
|---|---|---|
| TypeScript / npm | @openloop/sdk-core,
@openloop/transport-* |
Web dApps, Node.js / Electron, React Native |
| Swift / SPM (planned) | — | Native iOS apps |
| Kotlin / Maven (planned) | — | Native Android |
| C# / NuGet (planned) | — | Native Windows |
About licensing: Use of the Openloop SDK requires a license agreement with Haudi Crypto, Inc. We can also customize the SDK to suit your requirements — please feel free to contact us at info@crypto.haudi.jp.
The single most important principle: private keys stay inside the device and never leave it. The SDK only sends and receives APDU (Application Protocol Data Unit) commands. All signing is performed inside the device’s secure element.
Layer Structure
What each layer does
| Layer | Role |
|---|---|
| dApp | User interface, transaction construction |
| App class | Builds chain-specific APDU commands and parses responses |
| ITransport | Physical communication with the device (USB / BLE / WebSocket, etc.) |
| Device | Private key management, signing, user approval |
Security Model
What the SDK does
- Builds and sends APDU commands
- Parses responses (addresses, signatures, and so on)
- Manages transport connection and disconnection
What the SDK does not do
- Generate, hold, or operate on private keys
- Perform signing
- Manage seed phrases
Security on the device side
- Private keys are generated and stored inside the device and never leave it
- All signing is performed inside the device
- Transaction details are shown on the device’s screen and the user approves them with a physical button
- If the user rejects, the device returns status word
0x6985and no signature is produced
Supported Chains
| Chain | App class | Elliptic curve | BIP44 coin_type |
|---|---|---|---|
| Ethereum (EVM) | EthereumApp |
secp256k1 | 60' |
| Bitcoin | BitcoinApp |
secp256k1 | 0' (mainnet), 1' (testnet) |
| Solana | SolanaApp |
Ed25519 | 501' |
| TRON | TronApp |
secp256k1 | 195' |
| XRP Ledger | XrpApp |
Ed25519 / secp256k1 | 144' |
EVM-compatible chains
EthereumApp works not only with Ethereum but with any
EVM-compatible chain. Specify the chain through the chainId
parameter of signPersonalMessage and
signTypedData.
Transport Connection Methods
The SDK offers six connection methods, covering a wide range of platforms.
| Transport | Package | Use case |
|---|---|---|
| WebHID (USB) | @openloop/transport-webhid |
Chrome/Edge on desktop |
| Web Bluetooth | @openloop/transport-webble |
Chrome/Edge + Android |
| LocalWS | @openloop/transport-local |
All browsers (via Connect) |
| Safari Extension | @openloop/transport-safari |
iOS Safari |
| USB HID (native) | @openloop/transport-usb |
Node.js / Electron |
| BLE (native) | @openloop/transport-ble |
Node.js / Electron |
| WalletConnect | Built into @openloop/sdk-core |
All browsers (remote signing) |
See the Transport Guide for details.
Package List
npm packages (TypeScript)
| Package | Description | Dependencies |
|---|---|---|
@openloop/sdk-core |
Core library (App, Types, Errors, Constants, WcTransport) | none |
@openloop/transport-webhid |
WebHID (USB) transport | sdk-core |
@openloop/transport-webble |
Web Bluetooth transport | sdk-core |
@openloop/transport-local |
LocalWS transport | sdk-core |
@openloop/transport-safari |
Safari extension transport | sdk-core (peer) |
@openloop/transport-usb |
Native USB HID transport | sdk-core (peer), node-hid |
@openloop/transport-ble |
Native BLE transport (Node.js / Electron) | sdk-core (peer), noble |
Dependency graph
sdk-core is a pure TypeScript package with no dependency
on browser APIs or native modules. Each transport package supplies the
platform-specific implementation. Swift / Kotlin / C# libraries for
native apps are planned.
APDU Protocol Overview
Communication between the SDK and the device uses APDU (Application Protocol Data Unit) commands.
Command structure
[CLA] [INS] [P1] [P2] [Lc] [Data...]| Field | Size | Description |
|---|---|---|
| CLA | 1 byte | Class byte (0xE0: Ledger-compatible, 0xF0:
Openloop-specific) |
| INS | 1 byte | Instruction code |
| P1 | 1 byte | Parameter 1 (chunking control, etc.) |
| P2 | 1 byte | Parameter 2 (curve selection, etc.) |
| Lc | 1 byte | Data length |
| Data | Lc bytes | Command data |
Response structure
[Data...] [SW1] [SW2]| Field | Size | Description |
|---|---|---|
| Data | variable | Response data |
| SW1-SW2 | 2 bytes | Status word (0x9000 = success) |
CLA bytes
| CLA | Purpose |
|---|---|
0xE0 |
Ledger-compatible commands (ETH, BTC getAddress, SOL, TRON, XRP) |
0xF0 |
Openloop-specific commands (chain_id-aware signing, PSBT, BTC xpub) |
See Error Handling for the full list of APDU status words.
Next Steps
- Quick Start — a getting-started guide for developers
- Transport Guide — the platform support matrix
- API Reference — all type definitions and interfaces