path: root/accounts/usbwallet/ledger_wallet.go

// Copyright 2017 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

// This file contains the implementation for interacting with the Ledger hardware
// wallets. The wire protocol spec can be found in the Ledger Blue GitHub repo:
// https://raw.githubusercontent.com/LedgerHQ/blue-app-eth/master/doc/ethapp.asc

package usbwallet

import (
    "context"
    "encoding/binary"
    "encoding/hex"
    "errors"
    "fmt"
    "io"
    "math/big"
    "sync"
    "time"

    ethereum "github.com/ethereum/go-ethereum"
    "github.com/ethereum/go-ethereum/accounts"
    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/common/hexutil"
    "github.com/ethereum/go-ethereum/core/types"
    "github.com/ethereum/go-ethereum/log"
    "github.com/ethereum/go-ethereum/rlp"
    "github.com/karalabe/hid"
)

// Maximum time between wallet health checks to detect USB unplugs.
const ledgerHeartbeatCycle = time.Second

// Minimum time to wait between self derivation attempts, even it the user is
// requesting accounts like crazy.
const ledgerSelfDeriveThrottling = time.Second

// ledgerOpcode is an enumeration encoding the supported Ledger opcodes.
type ledgerOpcode byte

// ledgerParam1 is an enumeration encoding the supported Ledger parameters for
// specific opcodes. The same parameter values may be reused between opcodes.
type ledgerParam1 byte

// ledgerParam2 is an enumeration encoding the supported Ledger parameters for
// specific opcodes. The same parameter values may be reused between opcodes.
type ledgerParam2 byte

const (
    ledgerOpRetrieveAddress  ledgerOpcode = 0x02 // Returns the public key and Ethereum address for a given BIP 32 path
    ledgerOpSignTransaction  ledgerOpcode = 0x04 // Signs an Ethereum transaction after having the user validate the parameters
    ledgerOpGetConfiguration ledgerOpcode = 0x06 // Returns specific wallet application configuration

    ledgerP1DirectlyFetchAddress    ledgerParam1 = 0x00 // Return address directly from the wallet
    ledgerP1ConfirmFetchAddress     ledgerParam1 = 0x01 // Require a user confirmation before returning the address
    ledgerP1InitTransactionData     ledgerParam1 = 0x00 // First transaction data block for signing
    ledgerP1ContTransactionData     ledgerParam1 = 0x80 // Subsequent transaction data block for signing
    ledgerP2DiscardAddressChainCode ledgerParam2 = 0x00 // Do not return the chain code along with the address
    ledgerP2ReturnAddressChainCode  ledgerParam2 = 0x01 // Require a user confirmation before returning the address
)

// errReplyInvalidHeader is the error message returned by a Ledger data exchange
// if the device replies with a mismatching header. This usually means the device
// is in browser mode.
var errReplyInvalidHeader = errors.New("invalid reply header")

// errInvalidVersionReply is the error message returned by a Ledger version retrieval
// when a response does arrive, but it does not contain the expected data.
var errInvalidVersionReply = errors.New("invalid version reply")

// ledgerWallet represents a live USB Ledger hardware wallet.
type ledgerWallet struct {
    hub *LedgerHub    // USB hub the device originates from (TODO(karalabe): remove if hotplug lands on Windows)
    url *accounts.URL // Textual URL uniquely identifying this wallet

    info    hid.DeviceInfo // Known USB device infos about the wallet
    device  *hid.Device    // USB device advertising itself as a Ledger wallet
    failure error          // Any failure that would make the device unusable

    version  [3]byte                                    // Current version of the Ledger Ethereum app (zero if app is offline)
    browser  bool                                       // Flag whether the Ledger is in browser mode (reply channel mismatch)
    accounts []accounts.Account                         // List of derive accounts pinned on the Ledger
    paths    map[common.Address]accounts.DerivationPath // Known derivation paths for signing operations

    deriveNextPath accounts.DerivationPath   // Next derivation path for account auto-discovery
    deriveNextAddr common.Address            // Next derived account address for auto-discovery
    deriveChain    ethereum.ChainStateReader // Blockchain state reader to discover used account with
    deriveReq      chan chan struct{}        // Channel to request a self-derivation on
    deriveQuit     chan chan error           // Channel to terminate the self-deriver with

    healthQuit chan chan error

    // Locking a hardware wallet is a bit special. Since hardware devices are lower
    // performing, any communication with them might take a non negligible amount of
    // time. Worse still, waiting for user confirmation can take arbitrarily long,
    // but exclusive communication must be upheld during. Locking the entire wallet
    // in the mean time however would stall any parts of the system that don't want
    // to communicate, just read some state (e.g. list the accounts).
    //
    // As such, a hardware wallet needs two locks to function correctly. A state
    // lock can be used to protect the wallet's software-side internal state, which
    // must not be held exlusively during hardware communication. A communication
    // lock can be used to achieve exclusive access to the device itself, this one
    // however should allow "skipping" waiting for operations that might want to
    // use the device, but can live without too (e.g. account self-derivation).
    //
    // Since we have two locks, it's important to know how to properly use them:
    //   - Communication requires the `device` to not change, so obtaining the
    //     commsLock should be done after having a stateLock.
    //   - Communication must not disable read access to the wallet state, so it
    //     must only ever hold a *read* lock to stateLock.
    commsLock chan struct{} // Mutex (buf=1) for the USB comms without keeping the state locked
    stateLock sync.RWMutex  // Protects read and write access to the wallet struct fields

    log log.Logger // Contextual logger to tag the ledger with its id
}

// URL implements accounts.Wallet, returning the URL of the Ledger device.
func (w *ledgerWallet) URL() accounts.URL {
    return *w.url // Immutable, no need for a lock
}

// Status implements accounts.Wallet, always whether the Ledger is opened, closed
// or whether the Ethereum app was not started on it.
func (w *ledgerWallet) Status() string {
    w.stateLock.RLock() // No device communication, state lock is enough
    defer w.stateLock.RUnlock()

    if w.failure != nil {
        return fmt.Sprintf("Failed: %v", w.failure)
    }
    if w.device == nil {
        return "Closed"
    }
    if w.browser {
        return "Ethereum app in browser mode"
    }
    if w.offline() {
        return "Ethereum app offline"
    }
    return fmt.Sprintf("Ethereum app v%d.%d.%d online", w.version[0], w.version[1], w.version[2])
}

// offline returns whether the wallet and the Ethereum app is offline or not.
//
// The method assumes that the state lock is held!
func (w *ledgerWallet) offline() bool {
    return w.version == [3]byte{0, 0, 0}
}

// failed returns if the USB device wrapped by the wallet failed for some reason.
// This is used by the device scanner to report failed wallets as departed.
//
// The method assumes that the state lock is *not* held!
func (w *ledgerWallet) failed() bool {
    w.stateLock.RLock() // No device communication, state lock is enough
    defer w.stateLock.RUnlock()

    return w.failure != nil
}

// Open implements accounts.Wallet, attempting to open a USB connection to the
// Ledger hardware wallet. The Ledger does not require a user passphrase, so that
// parameter is silently discarded.
func (w *ledgerWallet) Open(passphrase string) error {
    w.stateLock.Lock() // State lock is enough since there's no connection yet at this point
    defer w.stateLock.Unlock()

    // If the wallet was already opened, don't try to open again
    if w.device != nil {
        return accounts.ErrWalletAlreadyOpen
    }
    // Otherwise iterate over all USB devices and find this again (no way to directly do this)
    device, err := w.info.Open()
    if err != nil {
        return err
    }
    // Wallet seems to be successfully opened, guess if the Ethereum app is running
    w.device = device
    w.commsLock = make(chan struct{}, 1)
    w.commsLock <- struct{}{} // Enable lock

    w.paths = make(map[common.Address]accounts.DerivationPath)

    w.deriveReq = make(chan chan struct{})
    w.deriveQuit = make(chan chan error)
    w.healthQuit = make(chan chan error)

    defer func() {
        go w.heartbeat()
        go w.selfDerive()
    }()

    if _, err = w.ledgerDerive(accounts.DefaultBaseDerivationPath); err != nil {
        // Ethereum app is not running or in browser mode, nothing more to do, return
        if err == errReplyInvalidHeader {
            w.browser = true
        }
        return nil
    }
    // Try to resolve the Ethereum app's version, will fail prior to v1.0.2
    if w.version, err = w.ledgerVersion(); err != nil {
        w.version = [3]byte{1, 0, 0} // Assume worst case, can't verify if v1.0.0 or v1.0.1
    }
    return nil
}

// heartbeat is a health check loop for the Ledger wallets to periodically verify
// whether they are still present or if they malfunctioned. It is needed because:
//  - libusb on Windows doesn't support hotplug, so we can't detect USB unplugs
//  - communication timeout on the Ledger requires a device power cycle to fix
func (w *ledgerWallet) heartbeat() {
    w.log.Debug("Ledger health-check started")
    defer w.log.Debug("Ledger health-check stopped")

    // Execute heartbeat checks until termination or error
    var (
        errc chan error
        err  error
    )
    for errc == nil && err == nil {
        // Wait until termination is requested or the heartbeat cycle arrives
        select {
        case errc = <-w.healthQuit:
            // Termination requested
            continue
        case <-time.After(ledgerHeartbeatCycle):
            // Heartbeat time
        }
        // Execute a tiny data exchange to see responsiveness
        w.stateLock.RLock()
        if w.device == nil {
            // Terminated while waiting for the lock
            w.stateLock.RUnlock()
            continue
        }
        <-w.commsLock // Don't lock state while resolving version
        _, err = w.ledgerVersion()
        w.commsLock <- struct{}{}
        w.stateLock.RUnlock()

        if err != nil && err != errInvalidVersionReply {
            w.stateLock.Lock() // Lock state to tear the wallet down
            w.failure = err
            w.close()
            w.stateLock.Unlock()
        }
        // Ignore non hardware related errors
        err = nil
    }
    // In case of error, wait for termination
    if err != nil {
        w.log.Debug("Ledger health-check failed", "err", err)
        errc = <-w.healthQuit
    }
    errc <- err
}

// Close implements accounts.Wallet, closing the USB connection to the Ledger.
func (w *ledgerWallet) Close() error {
    // Ensure the wallet was opened
    w.stateLock.RLock()
    hQuit, dQuit := w.healthQuit, w.deriveQuit
    w.stateLock.RUnlock()

    // Terminate the health checks
    var herr error
    if hQuit != nil {
        errc := make(chan error)
        hQuit <- errc
        herr = <-errc // Save for later, we *must* close the USB
    }
    // Terminate the self-derivations
    var derr error
    if dQuit != nil {
        errc := make(chan error)
        dQuit <- errc
        derr = <-errc // Save for later, we *must* close the USB
    }
    // Terminate the device connection
    w.stateLock.Lock()
    defer w.stateLock.Unlock()

    w.healthQuit = nil
    w.deriveQuit = nil
    w.deriveReq = nil

    if err := w.close(); err != nil {
        return err
    }
    if herr != nil {
        return herr
    }
    return derr
}

// close is the internal wallet closer that terminates the USB connection and
// resets all the fields to their defaults.
//
// Note, close assumes the state lock is held!
func (w *ledgerWallet) close() error {
    // Allow duplicate closes, especially for health-check failures
    if w.device == nil {
        return nil
    }
    // Close the device, clear everything, then return
    w.device.Close()
    w.device = nil

    w.browser, w.version = false, [3]byte{}
    w.accounts, w.paths = nil, nil

    return nil
}

// Accounts implements accounts.Wallet, returning the list of accounts pinned to
// the Ledger hardware wallet. If self-derivation was enabled, the account list
// is periodically expanded based on current chain state.
func (w *ledgerWallet) Accounts() []accounts.Account {
    // Attempt self-derivation if it's running
    reqc := make(chan struct{}, 1)
    select {
    case w.deriveReq <- reqc:
        // Self-derivation request accepted, wait for it
        <-reqc
    default:
        // Self-derivation offline, throttled or busy, skip
    }
    // Return whatever account list we ended up with
    w.stateLock.RLock()
    defer w.stateLock.RUnlock()

    cpy := make([]accounts.Account, len(w.accounts))
    copy(cpy, w.accounts)
    return cpy
}

// selfDerive is an account derivation loop that upon request attempts to find
// new non-zero accounts.
func (w *ledgerWallet) selfDerive() {
    w.log.Debug("Ledger self-derivation started")
    defer w.log.Debug("Ledger self-derivation stopped")

    // Execute self-derivations until termination or error
    var (
        reqc chan struct{}
        errc chan error
        err  error
    )
    for errc == nil && err == nil {
        // Wait until either derivation or termination is requested
        select {
        case errc = <-w.deriveQuit:
            // Termination requested
            continue
        case reqc = <-w.deriveReq:
            // Account discovery requested
        }
        // Derivation needs a chain and device access, skip if either unavailable
        w.stateLock.RLock()
        if w.device == nil || w.deriveChain == nil || w.offline() {
            w.stateLock.RUnlock()
            reqc <- struct{}{}
            continue
        }
        select {
        case <-w.commsLock:
        default:
            w.stateLock.RUnlock()
            reqc <- struct{}{}
            continue
        }
        // Device lock obtained, derive the next batch of accounts
        var (
            accs  []accounts.Account
            paths []accounts.DerivationPath

            nextAddr = w.deriveNextAddr
            nextPath = w.deriveNextPath

            context = context.Background()
        )
        for empty := false; !empty; {
            // Retrieve the next derived Ethereum account
            if nextAddr == (common.Address{}) {
                if nextAddr, err = w.ledgerDerive(nextPath); err != nil {
                    w.log.Warn("Ledger account derivation failed", "err", err)
                    break
                }
            }
            // Check the account's status against the current chain state
            var (
                balance *big.Int
                nonce   uint64
            )
            balance, err = w.deriveChain.BalanceAt(context, nextAddr, nil)
            if err != nil {
                w.log.Warn("Ledger balance retrieval failed", "err", err)
                break
            }
            nonce, err = w.deriveChain.NonceAt(context, nextAddr, nil)
            if err != nil {
                w.log.Warn("Ledger nonce retrieval failed", "err", err)
                break
            }
            // If the next account is empty, stop self-derivation, but add it nonetheless
            if balance.Sign() == 0 && nonce == 0 {
                empty = true
            }
            // We've just self-derived a new account, start tracking it locally
            path := make(accounts.DerivationPath, len(nextPath))
            copy(path[:], nextPath[:])
            paths = append(paths, path)

            account := accounts.Account{
                Address: nextAddr,
                URL:     accounts.URL{Scheme: w.url.Scheme, Path: fmt.Sprintf("%s/%s", w.url.Path, path)},
            }
            accs = append(accs, account)

            // Display a log message to the user for new (or previously empty accounts)
            if _, known := w.paths[nextAddr]; !known || (!empty && nextAddr == w.deriveNextAddr) {
                w.log.Info("Ledger discovered new account", "address", nextAddr, "path", path, "balance", balance, "nonce", nonce)
            }
            // Fetch the next potential account
            if !empty {
                nextAddr = common.Address{}
                nextPath[len(nextPath)-1]++
            }
        }
        // Self derivation complete, release device lock
        w.commsLock <- struct{}{}
        w.stateLock.RUnlock()

        // Insert any accounts successfully derived
        w.stateLock.Lock()
        for i := 0; i < len(accs); i++ {
            if _, ok := w.paths[accs[i].Address]; !ok {
                w.accounts = append(w.accounts, accs[i])
                w.paths[accs[i].Address] = paths[i]
            }
        }
        // Shift the self-derivation forward
        // TODO(karalabe): don't overwrite changes from wallet.SelfDerive
        w.deriveNextAddr = nextAddr
        w.deriveNextPath = nextPath
        w.stateLock.Unlock()

        // Notify the user of termination and loop after a bit of time (to avoid trashing)
        reqc <- struct{}{}
        if err == nil {
            select {
            case errc = <-w.deriveQuit:
                // Termination requested, abort
            case <-time.After(ledgerSelfDeriveThrottling):
                // Waited enough, willing to self-derive again
            }
        }
    }
    // In case of error, wait for termination
    if err != nil {
        w.log.Debug("Ledger self-derivation failed", "err", err)
        errc = <-w.deriveQuit
    }
    errc <- err
}

// Contains implements accounts.Wallet, returning whether a particular account is
// or is not pinned into this Ledger instance. Although we could attempt to resolve
// unpinned accounts, that would be an non-negligible hardware operation.
func (w *ledgerWallet) Contains(account accounts.Account) bool {
    w.stateLock.RLock()
    defer w.stateLock.RUnlock()

    _, exists := w.paths[account.Address]
    return exists
}

// Derive implements accounts.Wallet, deriving a new account at the specific
// derivation path. If pin is set to true, the account will be added to the list
// of tracked accounts.
func (w *ledgerWallet) Derive(path accounts.DerivationPath, pin bool) (accounts.Account, error) {
    // Try to derive the actual account and update its URL if successful
    w.stateLock.RLock() // Avoid device disappearing during derivation

    if w.device == nil || w.offline() {
        w.stateLock.RUnlock()
        return accounts.Account{}, accounts.ErrWalletClosed
    }
    <-w.commsLock // Avoid concurrent hardware access
    address, err := w.ledgerDerive(path)
    w.commsLock <- struct{}{}

    w.stateLock.RUnlock()

    // If an error occurred or no pinning was requested, return
    if err != nil {
        return accounts.Account{}, err
    }
    account := accounts.Account{
        Address: address,
        URL:     accounts.URL{Scheme: w.url.Scheme, Path: fmt.Sprintf("%s/%s", w.url.Path, path)},
    }
    if !pin {
        return account, nil
    }
    // Pinning needs to modify the state
    w.stateLock.Lock()
    defer w.stateLock.Unlock()

    if _, ok := w.paths[address]; !ok {
        w.accounts = append(w.accounts, account)
        w.paths[address] = path
    }
    return account, nil
}

// SelfDerive implements accounts.Wallet, trying to discover accounts that the
// user used previously (based on the chain state), but ones that he/she did not
// explicitly pin to the wallet manually. To avoid chain head monitoring, self
// derivation only runs during account listing (and even then throttled).
func (w *ledgerWallet) SelfDerive(base accounts.DerivationPath, chain ethereum.ChainStateReader) {
    w.stateLock.Lock()
    defer w.stateLock.Unlock()

    w.deriveNextPath = make(accounts.DerivationPath, len(base))
    copy(w.deriveNextPath[:], base[:])

    w.deriveNextAddr = common.Address{}
    w.deriveChain = chain
}

// SignHash implements accounts.Wallet, however signing arbitrary data is not
// supported for Ledger wallets, so this method will always return an error.
func (w *ledgerWallet) SignHash(acc accounts.Account, hash []byte) ([]byte, error) {
    return nil, accounts.ErrNotSupported
}

// SignTx implements accounts.Wallet. It sends the transaction over to the Ledger
// wallet to request a confirmation from the user. It returns either the signed
// transaction or a failure if the user denied the transaction.
//
// Note, if the version of the Ethereum application running on the Ledger wallet is
// too old to sign EIP-155 transactions, but such is requested nonetheless, an error
// will be returned opposed to silently signing in Homestead mode.
func (w *ledgerWallet) SignTx(account accounts.Account, tx *types.Transaction, chainID *big.Int) (*types.Transaction, error) {
    w.stateLock.RLock() // Comms have own mutex, this is for the state fields
    defer w.stateLock.RUnlock()

    // If the wallet is closed, or the Ethereum app doesn't run, abort
    if w.device == nil || w.offline() {
        return nil, accounts.ErrWalletClosed
    }
    // Make sure the requested account is contained within
    path, ok := w.paths[account.Address]
    if !ok {
        return nil, accounts.ErrUnknownAccount
    }
    // Ensure the wallet is capable of signing the given transaction
    if chainID != nil && w.version[0] <= 1 && w.version[1] <= 0 && w.version[2] <= 2 {
        return nil, fmt.Errorf("Ledger v%d.%d.%d doesn't support signing this transaction, please update to v1.0.3 at least", w.version[0], w.version[1], w.version[2])
    }
    // All infos gathered and metadata checks out, request signing
    <-w.commsLock
    defer func() { w.commsLock <- struct{}{} }()

    // Ensure the device isn't screwed with while user confirmation is pending
    // TODO(karalabe): remove if hotplug lands on Windows
    w.hub.commsLock.RLock()
    defer w.hub.commsLock.RUnlock()

    return w.ledgerSign(path, account.Address, tx, chainID)
}

// SignHashWithPassphrase implements accounts.Wallet, however signing arbitrary
// data is not supported for Ledger wallets, so this method will always return
// an error.
func (w *ledgerWallet) SignHashWithPassphrase(account accounts.Account, passphrase string, hash []byte) ([]byte, error) {
    return nil, accounts.ErrNotSupported
}

// SignTxWithPassphrase implements accounts.Wallet, attempting to sign the given
// transaction with the given account using passphrase as extra authentication.
// Since the Ledger does not support extra passphrases, it is silently ignored.
func (w *ledgerWallet) SignTxWithPassphrase(account accounts.Account, passphrase string, tx *types.Transaction, chainID *big.Int) (*types.Transaction, error) {
    return w.SignTx(account, tx, chainID)
}

// ledgerVersion retrieves the current version of the Ethereum wallet app running
// on the Ledger wallet.
//
// The version retrieval protocol is defined as follows:
//
//   CLA | INS | P1 | P2 | Lc | Le
//   ----+-----+----+----+----+---
//    E0 | 06  | 00 | 00 | 00 | 04
//
// With no input data, and the output data being:
//
//   Description                                        | Length
//   ---------------------------------------------------+--------
//   Flags 01: arbitrary data signature enabled by user | 1 byte
//   Application major version                          | 1 byte
//   Application minor version                          | 1 byte
//   Application patch version                          | 1 byte
func (w *ledgerWallet) ledgerVersion() ([3]byte, error) {
    // Send the request and wait for the response
    reply, err := w.ledgerExchange(ledgerOpGetConfiguration, 0, 0, nil)
    if err != nil {
        return [3]byte{}, err
    }
    if len(reply) != 4 {
        return [3]byte{}, errInvalidVersionReply
    }
    // Cache the version for future reference
    var version [3]byte
    copy(version[:], reply[1:])
    return version, nil
}

// ledgerDerive retrieves the currently active Ethereum address from a Ledger
// wallet at the specified derivation path.
//
// The address derivation protocol is defined as follows:
//
//   CLA | INS | P1 | P2 | Lc  | Le
//   ----+-----+----+----+-----+---
//    E0 | 02  | 00 return address
//               01 display address and confirm before returning
//                  | 00: do not return the chain code
//                  | 01: return the chain code
//                       | var | 00
//
// Where the input data is:
//
//   Description                                      | Length
//   -------------------------------------------------+--------
//   Number of BIP 32 derivations to perform (max 10) | 1 byte
//   First derivation index (big endian)              | 4 bytes
//   ...                                              | 4 bytes
//   Last derivation index (big endian)               | 4 bytes
//
// And the output data is:
//
//   Description             | Length
//   ------------------------+-------------------
//   Public Key length       | 1 byte
//   Uncompressed Public Key | arbitrary
//   Ethereum address length | 1 byte
//   Ethereum address        | 40 bytes hex ascii
//   Chain code if requested | 32 bytes
func (w *ledgerWallet) ledgerDerive(derivationPath []uint32) (common.Address, error) {
    // Flatten the derivation path into the Ledger request
    path := make([]byte, 1+4*len(derivationPath))
    path[0] = byte(len(derivationPath))
    for i, component := range derivationPath {
        binary.BigEndian.PutUint32(path[1+4*i:], component)
    }
    // Send the request and wait for the response
    reply, err := w.ledgerExchange(ledgerOpRetrieveAddress, ledgerP1DirectlyFetchAddress, ledgerP2DiscardAddressChainCode, path)
    if err != nil {
        return common.Address{}, err
    }
    // Discard the public key, we don't need that for now
    if len(reply) < 1 || len(reply) < 1+int(reply[0]) {
        return common.Address{}, errors.New("reply lacks public key entry")
    }
    reply = reply[1+int(reply[0]):]

    // Extract the Ethereum hex address string
    if len(reply) < 1 || len(reply) < 1+int(reply[0]) {
        return common.Address{}, errors.New("reply lacks address entry")
    }
    hexstr := reply[1 : 1+int(reply[0])]

    // Decode the hex sting into an Ethereum address and return
    var address common.Address
    hex.Decode(address[:], hexstr)
    return address, nil
}

// ledgerSign sends the transaction to the Ledger wallet, and waits for the user
// to confirm or deny the transaction.
//
// The transaction signing protocol is defined as follows:
//
//   CLA | INS | P1 | P2 | Lc  | Le
//   ----+-----+----+----+-----+---
//    E0 | 04  | 00: first transaction data block
//               80: subsequent transaction data block
//                  | 00 | variable | variable
//
// Where the input for the first transaction block (first 255 bytes) is:
//
//   Description                                      | Length
//   -------------------------------------------------+----------
//   Number of BIP 32 derivations to perform (max 10) | 1 byte
//   First derivation index (big endian)              | 4 bytes
//   ...                                              | 4 bytes
//   Last derivation index (big endian)               | 4 bytes
//   RLP transaction chunk                            | arbitrary
//
// And the input for subsequent transaction blocks (first 255 bytes) are:
//
//   Description           | Length
//   ----------------------+----------
//   RLP transaction chunk | arbitrary
//
// And the output data is:
//
//   Description | Length
//   ------------+---------
//   signature V | 1 byte
//   signature R | 32 bytes
//   signature S | 32 bytes
func (w *ledgerWallet) ledgerSign(derivationPath []uint32, address common.Address, tx *types.Transaction, chainID *big.Int) (*types.Transaction, error) {
    // Flatten the derivation path into the Ledger request
    path := make([]byte, 1+4*len(derivationPath))
    path[0] = byte(len(derivationPath))
    for i, component := range derivationPath {
        binary.BigEndian.PutUint32(path[1+4*i:], component)
    }
    // Create the transaction RLP based on whether legacy or EIP155 signing was requeste
    var (
        txrlp []byte
        err   error
    )
    if chainID == nil {
        if txrlp, err = rlp.EncodeToBytes([]interface{}{tx.Nonce(), tx.GasPrice(), tx.Gas(), tx.To(), tx.Value(), tx.Data()}); err != nil {
            return nil, err
        }
    } else {
        if txrlp, err = rlp.EncodeToBytes([]interface{}{tx.Nonce(), tx.GasPrice(), tx.Gas(), tx.To(), tx.Value(), tx.Data(), chainID, big.NewInt(0), big.NewInt(0)}); err != nil {
            return nil, err
        }
    }
    payload := append(path, txrlp...)

    // Send the request and wait for the response
    var (
        op    = ledgerP1InitTransactionData
        reply []byte
    )
    for len(payload) > 0 {
        // Calculate the size of the next data chunk
        chunk := 255
        if chunk > len(payload) {
            chunk = len(payload)
        }
        // Send the chunk over, ensuring it's processed correctly
        reply, err = w.ledgerExchange(ledgerOpSignTransaction, op, 0, payload[:chunk])
        if err != nil {
            return nil, err
        }
        // Shift the payload and ensure subsequent chunks are marked as such
        payload = payload[chunk:]
        op = ledgerP1ContTransactionData
    }
    // Extract the Ethereum signature and do a sanity validation
    if len(reply) != 65 {
        return nil, errors.New("reply lacks signature")
    }
    signature := append(reply[1:], reply[0])

    // Create the correct signer and signature transform based on the chain ID
    var signer types.Signer
    if chainID == nil {
        signer = new(types.HomesteadSigner)
    } else {
        signer = types.NewEIP155Signer(chainID)
        signature[64] = signature[64] - byte(chainID.Uint64()*2+35)
    }
    // Inject the final signature into the transaction and sanity check the sender
    signed, err := tx.WithSignature(signer, signature)
    if err != nil {
        return nil, err
    }
    sender, err := types.Sender(signer, signed)
    if err != nil {
        return nil, err
    }
    if sender != address {
        return nil, fmt.Errorf("signer mismatch: expected %s, got %s", address.Hex(), sender.Hex())
    }
    return signed, nil
}

// ledgerExchange performs a data exchange with the Ledger wallet, sending it a
// message and retrieving the response.
//
// The common transport header is defined as follows:
//
//  Description                           | Length
//  --------------------------------------+----------
//  Communication channel ID (big endian) | 2 bytes
//  Command tag                           | 1 byte
//  Packet sequence index (big endian)    | 2 bytes
//  Payload                               | arbitrary
//
// The Communication channel ID allows commands multiplexing over the same
// physical link. It is not used for the time being, and should be set to 0101
// to avoid compatibility issues with implementations ignoring a leading 00 byte.
//
// The Command tag describes the message content. Use TAG_APDU (0x05) for standard
// APDU payloads, or TAG_PING (0x02) for a simple link test.
//
// The Packet sequence index describes the current sequence for fragmented payloads.
// The first fragment index is 0x00.
//
// APDU Command payloads are encoded as follows:
//
//  Description              | Length
//  -----------------------------------
//  APDU length (big endian) | 2 bytes
//  APDU CLA                 | 1 byte
//  APDU INS                 | 1 byte
//  APDU P1                  | 1 byte
//  APDU P2                  | 1 byte
//  APDU length              | 1 byte
//  Optional APDU data       | arbitrary
func (w *ledgerWallet) ledgerExchange(opcode ledgerOpcode, p1 ledgerParam1, p2 ledgerParam2, data []byte) ([]byte, error) {
    // Construct the message payload, possibly split into multiple chunks
    apdu := make([]byte, 2, 7+len(data))

    binary.BigEndian.PutUint16(apdu, uint16(5+len(data)))
    apdu = append(apdu, []byte{0xe0, byte(opcode), byte(p1), byte(p2), byte(len(data))}...)
    apdu = append(apdu, data...)

    // Stream all the chunks to the device
    header := []byte{0x01, 0x01, 0x05, 0x00, 0x00} // Channel ID and command tag appended
    chunk := make([]byte, 64)
    space := len(chunk) - len(header)

    for i := 0; len(apdu) > 0; i++ {
        // Construct the new message to stream
        chunk = append(chunk[:0], header...)
        binary.BigEndian.PutUint16(chunk[3:], uint16(i))

        if len(apdu) > space {
            chunk = append(chunk, apdu[:space]...)
            apdu = apdu[space:]
        } else {
            chunk = append(chunk, apdu...)
            apdu = nil
        }
        // Send over to the device
        w.log.Trace("Data chunk sent to the Ledger", "chunk", hexutil.Bytes(chunk))
        if _, err := w.device.Write(chunk); err != nil {
            return nil, err
        }
    }
    // Stream the reply back from the wallet in 64 byte chunks
    var reply []byte
    chunk = chunk[:64] // Yeah, we surely have enough space
    for {
        // Read the next chunk from the Ledger wallet
        if _, err := io.ReadFull(w.device, chunk); err != nil {
            return nil, err
        }
        w.log.Trace("Data chunk received from the Ledger", "chunk", hexutil.Bytes(chunk))

        // Make sure the transport header matches
        if chunk[0] != 0x01 || chunk[1] != 0x01 || chunk[2] != 0x05 {
            return nil, errReplyInvalidHeader
        }
        // If it's the first chunk, retrieve the total message length
        var payload []byte

        if chunk[3] == 0x00 && chunk[4] == 0x00 {
            reply = make([]byte, 0, int(binary.BigEndian.Uint16(chunk[5:7])))
            payload = chunk[7:]
        } else {
            payload = chunk[5:]
        }
        // Append to the reply and stop when filled up
        if left := cap(reply) - len(reply); left > len(payload) {
            reply = append(reply, payload...)
        } else {
            reply = append(reply, payload[:left]...)
            break
        }
    }
    return reply[:len(reply)-2], nil
}