Bitcoin Signer Kit

This module provides the implementation of the Ledger Bitcoin signer of the Device Management Kit. It enables interaction with the Bitcoin application on a Ledger device including:

Retrieving the Bitcoin public key using a given address index;
Signing a message displayed on a Ledger device;
Signing a Bitcoin partially signed transaction (PSBT);
Signing a Bitcoin transaction;

🔹 How it works

The Ledger Bitcoin Signer utilizes the advanced capabilities of the Ledger device to provide secure operations for end users. It takes advantage of the interface provided by the Device Management Kit to establish communication with the Ledger device and execute various operations. The communication with the Ledger device is performed using APDUs (Application Protocol Data Units), which are encapsulated within the Command object. These commands are then organized into tasks, allowing for the execution of complex operations with one or more APDUs. The tasks are further encapsulated within DeviceAction objects to handle different real-world scenarios. Finally, the Signer exposes dedicated and independent use cases that can be directly utilized by end users.

🔹 Installation

Note: This module is not standalone; it depends on the @ledgerhq/device-management-kit package, so you need to install it first.

To install the device-signer-kit-bitcoin package, run the following command:

npm install @ledgerhq/device-signer-kit-bitcoin

🔹 Initialisation

To initialise a Bitcoin signer instance, you need a Ledger Device Management Kit instance and the ID of the session of the connected device. Use the SignerBtcBuilder along with the Context Module by default developed by Ledger:

// Initialise a Bitcoin signer instance
const signerBitcoin = new SignerBtcBuilder({ sdk, sessionId }).build();

🔹 Use Cases

The SignerBtcBuilder.build() method will return a SignerBitcoin instance that exposes 5 dedicated methods, each of which calls an independent use case. Each use case will return an object that contains an observable and a method called cancel.

Use Case 1: Get extended public key

This method allows users to retrieve the Bitcoin extended public key based on a given derivationPath.

const { observable, cancel } = signerBitcoin.getExtendedPublicKey(
  derivationPath,
  options,
);

Parameters

derivationPath
- Required
- Type: string (e.g. "84'/0'/0'" for a Native SegWit wallet)
- The derivation path used for the Bitcoin address. See here for more information.
options
- Optional
- Type: AddressOptions
```
type AddressOptions = {
  checkOnDevice?: boolean;
};
```
- checkOnDevice: An optional boolean indicating whether user confirmation on the device is required (true) or not (false).

Returns

observable Emits DeviceActionState updates, including the following details:

type GetAddressCommandResponse = {
  extendedPublicKey: string;
};

cancel A function to cancel the action on the Ledger device.

Use Case 2: Sign message

This method allows users to sign a text string that is displayed on Ledger devices.

const { observable, cancel } = signerBitcoin.signMessage(
  derivationPath,
  message,
);

Parameters

derivationPath
- Required
- Type: string (e.g. "84'/0'/0'" for a Native SegWit wallet)
- The derivation path used for the Bitcoin address. See here for more information.
message
- Required
- Type: string
- The message to be signed, which will be displayed on the Ledger device.

Returns

observable Emits DeviceActionState updates, including the following details:

type Signature = {
  r: `0x${string}`; // R component of the signature
  s: `0x${string}`; // S component of the signature
  v: number; // Recovery parameter
};

cancel A function to cancel the action on the Ledger device.

Use Case 3: Sign PSBT

This method allows users to sign a partially signed transaction.

const { observable, cancel } = signerBitcoin.signPsbt(
  new DefaultWallet(path, descriptorTemplate),
  psbt,
);

Parameters

wallet

Required
Type: Wallet

type Wallet = DefaultWallet | RegisteredWallet;
 
class DefaultWallet {
  constructor(
    // Derivation path without master key representation.
    // Format example: /44'/0'/0'
    public derivationPath: string,
    public template: DefaultDescriptorTemplate,
  ) {}
}
 
class RegisteredWallet {
  constructor(
    public name: string,
    public descriptorTemplate: string,
    public keys: string[],
    public hmac: Uint8Array,
  ) {}
}

psbt
- Required
- Type: string | Psbt
- A base64/hex psbt string or bitcoin-js Psbt

Returns

observable Emits DeviceActionState updates, including the following details:

type PartialSignature = {
  inputIndex: number;
  pubkey: Uint8Array;
  signature: Uint8Array;
  tapleafHash?: Uint8Array;
};
 
type MusigPubNonce = {
  inputIndex: number;
  participantPubkey: Uint8Array;
  aggregatedPubkey: Uint8Array;
  tapleafHash: Uint8Array;
  pubnonce: Uint8Array;
};
 
type MusigPartialSignature = {
  inputIndex: number;
  participantPubkey: Uint8Array;
  aggregatedPubkey: Uint8Array;
  tapleafHash: Uint8Array;
  partialSignature: Uint8Array;
};
 
type PsbtSignature = PartialSignature | MusigPartialSignature | MusigPubNonce;

cancel A function to cancel the action on the Ledger device.

Use Case 4: Sign transaction

This method allows users to sign a Bitcoin transaction.

const { observable, cancel } = signerBitcoin.signTransaction(
  new DefaultWallet(path, descriptorTemplate),
  psbt,
);

Parameters

wallet

Required
Type: Wallet

type Wallet = DefaultWallet | RegisteredWallet;
 
class DefaultWallet {
  constructor(
    // Derivation path without master key representation.
    // Format example: /44'/0'/0'
    public derivationPath: string,
    public template: DefaultDescriptorTemplate,
  ) {}
}
 
class RegisteredWallet {
  constructor(
    public name: string,
    public descriptorTemplate: string,
    public keys: string[],
    public hmac: Uint8Array,
  ) {}
}

psbt
- Required
- Type: string | Psbt
- A base64/hex psbt string or bitcoin-js Psbt

Returns

observable Emits DeviceActionState updates, including the following details:

type TransactionHash = `0x${string}`;

cancel A function to cancel the action on the Ledger device.

Use Case 5: Get wallet address

This method allows users to get the wallet address linked to a Ledger device.

const { observable, cancel } = signerBitcoin.getWalletAddress(
  derivationPath,
  addressIndex,
  options,
);

Parameters

derivationPath
- Required
- Type: string (e.g. "84'/0'/0'" for a Native SegWit wallet)
- The derivation path used for the Bitcoin address. See here for more information.
addressIndex
- Required
- Type: number
- The desired address index on the Ledger device.

options

Optional
Type: WalletAddressOptions

type WalletAddressOptions = {
  checkOnDevice?: boolean;
  change?: boolean;
};

Returns

observable Emits DeviceActionState updates, including the following details:

type WalletAddress = {
  address: string;
};

cancel A function to cancel the action on the Ledger device.

🔹 Observable Behavior

Each method returns an Observable emitting updates structured as DeviceActionState. These updates reflect the operation’s progress and status:

NotStarted: The operation hasn’t started.
Pending: The operation is in progress and may require user interaction.
Stopped: The operation was canceled or stopped.
Completed: The operation completed successfully, with results available.
Error: An error occurred.

Example Observable Subscription:

observable.subscribe({
  next: (state: DeviceActionState) => {
    switch (state.status) {
      case DeviceActionStatus.NotStarted: {
        console.log("The action is not started yet.");
        break;
      }
      case DeviceActionStatus.Pending: {
        const {
          intermediateValue: { requiredUserInteraction },
        } = state;
        // Access the intermediate value here, explained below
        console.log(
          "The action is pending and the intermediate value is: ",
          intermediateValue,
        );
        break;
      }
      case DeviceActionStatus.Stopped: {
        console.log("The action has been stopped.");
        break;
      }
      case DeviceActionStatus.Completed: {
        const { output } = state;
        // Access the output of the completed action here
        console.log("The action has been completed: ", output);
        break;
      }
      case DeviceActionStatus.Error: {
        const { error } = state;
        // Access the error here if occurred
        console.log("An error occurred during the action: ", error);
        break;
      }
    }
  },
});

Intermediate Values in Pending Status:

When the status is DeviceActionStatus.Pending, the state will include an intermediateValue object that provides useful information for interaction:

const { requiredUserInteraction } = intermediateValue;
 
switch (requiredUserInteraction) {
  case UserInteractionRequired.VerifyAddress: {
    // User needs to verify the address displayed on the device
    console.log("User needs to verify the address displayed on the device.");
    break;
  }
  case UserInteractionRequired.SignTransaction: {
    // User needs to sign the transaction displayed on the device
    console.log("User needs to sign the transaction displayed on the device.");
    break;
  }
  case UserInteractionRequired.SignTypedData: {
    // User needs to sign the typed data displayed on the device
    console.log("User needs to sign the typed data displayed on the device.");
    break;
  }
  case UserInteractionRequired.SignPersonalMessage: {
    // User needs to sign the message displayed on the device
    console.log("User needs to sign the message displayed on the device.");
    break;
  }
  case UserInteractionRequired.None: {
    // No user action required
    console.log("No user action needed.");
    break;
  }
  case UserInteractionRequired.UnlockDevice: {
    // User needs to unlock the device
    console.log("The user needs to unlock the device.");
    break;
  }
  case UserInteractionRequired.ConfirmOpenApp: {
    // User needs to confirm on the device to open the app
    console.log("The user needs to confirm on the device to open the app.");
    break;
  }
  default:
    // Type guard to ensure all cases are handled
    const uncaughtUserInteraction: never = requiredUserInteraction;
    console.error("Unhandled user interaction case:", uncaughtUserInteraction);
}

🔹 Example

We encourage you to explore the Bitcoin Signer by trying it out in our online sample application. Experience how it works and see its capabilities in action. Of course, you will need a Ledger device connected.

Signer Solana TS Doc