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

// +build !ios

package usbwallet

import (
    "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/core/types"
    "github.com/ethereum/go-ethereum/logger"
    "github.com/ethereum/go-ethereum/logger/glog"
    "github.com/ethereum/go-ethereum/rlp"
    "github.com/karalabe/gousb/usb"
    "golang.org/x/net/context"
)

// 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
)

// ledgerWallet represents a live USB Ledger hardware wallet.
type ledgerWallet struct {
    context    *usb.Context  // USB context to interface libusb through
    hardwareID deviceID      // USB identifiers to identify this device type
    locationID uint16        // USB bus and address to identify this device instance
    url        *accounts.URL // Textual URL uniquely identifying this wallet

    device  *usb.Device  // USB device advertising itself as a Ledger wallet
    input   usb.Endpoint // Input endpoint to send data to this device
    output  usb.Endpoint // Output endpoint to receive data from this device
    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)
    accounts []accounts.Account                         // List of derive accounts pinned on the Ledger
    paths    map[common.Address]accounts.DerivationPath // Known derivation paths for signing operations

    selfDeriveNextPath accounts.DerivationPath   // Next derivation path for account auto-discovery
    selfDeriveNextAddr common.Address            // Next derived account address for auto-discovery
    selfDerivePrevZero common.Address            // Last zero-address where auto-discovery stopped
    selfDeriveChain    ethereum.ChainStateReader // Blockchain state reader to discover used account with
    selfDeriveTime     time.Time                 // Timestamp of the last self-derivation to avoid thrashing

    quit chan chan error
    lock sync.RWMutex
}

// URL implements accounts.Wallet, returning the URL of the Ledger device.
func (w *ledgerWallet) URL() accounts.URL {
    return *w.url
}

// 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.lock.RLock()
    defer w.lock.RUnlock()

    if w.failure != nil {
        return fmt.Sprintf("Failed: %v", w.failure)
    }
    if w.device == nil {
        return "Closed"
    }
    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.
func (w *ledgerWallet) offline() bool {
    return w.version == [3]byte{0, 0, 0}
}

// 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
// is silently discarded.
func (w *ledgerWallet) Open(passphrase string) error {
    w.lock.Lock()
    defer w.lock.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)
    // Iterate over all attached devices and fetch those seemingly Ledger
    devices, err := w.context.ListDevices(func(desc *usb.Descriptor) bool {
        // Only open this single specific device
        return desc.Vendor == w.hardwareID.Vendor && desc.Product == w.hardwareID.Product &&
            uint16(desc.Bus)<<8+uint16(desc.Address) == w.locationID
    })
    if err != nil {
        return err
    }
    // Device opened, attach to the input and output endpoints
    device := devices[0]

    var invalid string
    switch {
    case len(device.Descriptor.Configs) == 0:
        invalid = "no endpoint config available"
    case len(device.Descriptor.Configs[0].Interfaces) == 0:
        invalid = "no endpoint interface available"
    case len(device.Descriptor.Configs[0].Interfaces[0].Setups) == 0:
        invalid = "no endpoint setup available"
    case len(device.Descriptor.Configs[0].Interfaces[0].Setups[0].Endpoints) < 2:
        invalid = "not enough IO endpoints available"
    }
    if invalid != "" {
        device.Close()
        return fmt.Errorf("ledger wallet [%s] invalid: %s", w.url, invalid)
    }
    // Open the input and output endpoints to the device
    input, err := device.OpenEndpoint(
        device.Descriptor.Configs[0].Config,
        device.Descriptor.Configs[0].Interfaces[0].Number,
        device.Descriptor.Configs[0].Interfaces[0].Setups[0].Number,
        device.Descriptor.Configs[0].Interfaces[0].Setups[0].Endpoints[1].Address,
    )
    if err != nil {
        device.Close()
        return fmt.Errorf("ledger wallet [%s] input open failed: %v", w.url, err)
    }
    output, err := device.OpenEndpoint(
        device.Descriptor.Configs[0].Config,
        device.Descriptor.Configs[0].Interfaces[0].Number,
        device.Descriptor.Configs[0].Interfaces[0].Setups[0].Number,
        device.Descriptor.Configs[0].Interfaces[0].Setups[0].Endpoints[0].Address,
    )
    if err != nil {
        device.Close()
        return fmt.Errorf("ledger wallet [%s] output open failed: %v", w.url, err)
    }
    // Wallet seems to be successfully opened, guess if the Ethereum app is running
    w.device, w.input, w.output = device, input, output

    w.paths = make(map[common.Address]accounts.DerivationPath)
    w.quit = make(chan chan error)
    defer func() {
        go w.heartbeat()
    }()

    if _, err := w.deriveAddress(accounts.DefaultBaseDerivationPath); err != nil {
        // Ethereum app is not running, nothing more to do, return
        return nil
    }
    // Try to resolve the Ethereum app's version, will fail prior to v1.0.2
    if w.resolveVersion() != 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() {
    // Execute heartbeat checks until termination or error
    var (
        errc chan error
        fail error
    )
    for errc == nil && fail == nil {
        // Wait until termination is requested or the heartbeat cycle arrives
        select {
        case errc = <-w.quit:
            // Termination requested
            continue
        case <-time.After(ledgerHeartbeatCycle):
            // Heartbeat time
        }
        // Execute a tiny data exchange to see responsiveness
        w.lock.Lock()
        if err := w.resolveVersion(); err == usb.ERROR_IO || err == usb.ERROR_NO_DEVICE {
            w.failure = err
            fail = err
        }
        w.lock.Unlock()
    }
    // In case of error, wait for termination
    if fail != nil {
        errc = <-w.quit
    }
    errc <- fail
}

// Close implements accounts.Wallet, closing the USB connection to the Ledger.
func (w *ledgerWallet) Close() error {
    // Terminate the health checks
    errc := make(chan error)
    w.quit <- errc
    herr := <-errc // Save for later, we *must* close the USB

    // Terminate the device connection
    w.lock.Lock()
    defer w.lock.Unlock()

    if err := w.device.Close(); err != nil {
        return err
    }
    w.device, w.input, w.output, w.paths, w.quit = nil, nil, nil, nil, nil
    w.version = [3]byte{}

    return herr // If all went well, return any health-check errors
}

// 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 {
    w.lock.Lock()
    defer w.lock.Unlock()

    // If the wallet is offline, there are no accounts to return
    if w.offline() {
        return nil
    }
    // If no self derivation is done (or throttled), return the current accounts
    if w.selfDeriveChain == nil || time.Since(w.selfDeriveTime) < ledgerSelfDeriveThrottling {
        cpy := make([]accounts.Account, len(w.accounts))
        copy(cpy, w.accounts)
        return cpy
    }
    // Self derivation requested, try to expand our account list
    ctx := context.Background()
    for empty := false; !empty; {
        // Retrieve the next derived Ethereum account
        var err error
        if w.selfDeriveNextAddr == (common.Address{}) {
            w.selfDeriveNextAddr, err = w.deriveAddress(w.selfDeriveNextPath)
            if err != nil {
                // Derivation failed, disable auto discovery
                glog.V(logger.Warn).Infof("self-derivation failed: %v", err)
                w.selfDeriveChain = nil
                break
            }
        }
        // Check the account's status against the current chain state
        balance, err := w.selfDeriveChain.BalanceAt(ctx, w.selfDeriveNextAddr, nil)
        if err != nil {
            glog.V(logger.Warn).Infof("self-derivation balance retrieval failed: %v", err)
            w.selfDeriveChain = nil
            break
        }
        nonce, err := w.selfDeriveChain.NonceAt(ctx, w.selfDeriveNextAddr, nil)
        if err != nil {
            glog.V(logger.Warn).Infof("self-derivation nonce retrieval failed: %v", err)
            w.selfDeriveChain = nil
            break
        }
        // If the next account is empty, stop self-derivation, but add it nonetheless
        if balance.BitLen() == 0 && nonce == 0 {
            w.selfDerivePrevZero = w.selfDeriveNextAddr
            empty = true
        }
        // We've just self-derived a new non-zero account, start tracking it
        path := make(accounts.DerivationPath, len(w.selfDeriveNextPath))
        copy(path[:], w.selfDeriveNextPath[:])

        account := accounts.Account{
            Address: w.selfDeriveNextAddr,
            URL:     accounts.URL{Scheme: w.url.Scheme, Path: fmt.Sprintf("%s/%s", w.url.Path, path)},
        }
        _, known := w.paths[w.selfDeriveNextAddr]
        if !known || (!empty && w.selfDeriveNextAddr == w.selfDerivePrevZero) {
            // Either fully new account, or previous zero. Report discovery either way
            glog.V(logger.Info).Infof("%s discovered %s (balance %d, nonce %d) at %s", w.url.String(), w.selfDeriveNextAddr.Hex(), balance, nonce, path)
        }
        if !known {
            w.accounts = append(w.accounts, account)
            w.paths[w.selfDeriveNextAddr] = path
        }
        // Fetch the next potential account
        if !empty {
            w.selfDeriveNextAddr = common.Address{}
            w.selfDeriveNextPath[len(w.selfDeriveNextPath)-1]++
        }
    }
    w.selfDeriveTime = time.Now()

    // Return whatever account list we ended up with
    cpy := make([]accounts.Account, len(w.accounts))
    copy(cpy, w.accounts)
    return cpy
}

// 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.lock.RLock()
    defer w.lock.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) {
    w.lock.Lock()
    defer w.lock.Unlock()

    // If the wallet is closed, or the Ethereum app doesn't run, abort
    if w.device == nil || w.offline() {
        return accounts.Account{}, accounts.ErrWalletClosed
    }
    // Try to derive the actual account and update it's URL if succeeful
    address, err := w.deriveAddress(path)
    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 pinning was requested, track the account
    if pin {
        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.lock.Lock()
    defer w.lock.Unlock()

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

    w.selfDeriveNextAddr = common.Address{}
    w.selfDeriveChain = 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.lock.Lock()
    defer w.lock.Unlock()

    // 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])
    }
    return w.sign(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)
}

// resolveVersion retrieves the current version of the Ethereum wallet app running
// on the Ledger wallet and caches it for future reference.
//
// 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 (wallet *ledgerWallet) resolveVersion() error {
    // Send the request and wait for the response
    reply, err := wallet.exchange(ledgerOpGetConfiguration, 0, 0, nil)
    if err != nil {
        return err
    }
    if len(reply) != 4 {
        return errors.New("reply not of correct size")
    }
    // Cache the version for future reference
    copy(wallet.version[:], reply[1:])
    return nil
}

// deriveAddress 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) deriveAddress(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.exchange(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
}

// sign 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) sign(derivationPath []uint32, address common.Address, tx *types.Transaction, chainID *big.Int) (*types.Transaction, error) {
    // We need to modify the timeouts to account for user feedback
    defer func(old time.Duration) { w.device.ReadTimeout = old }(w.device.ReadTimeout)
    w.device.ReadTimeout = time.Minute

    // 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.exchange(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]-34)/2 - byte(chainID.Uint64())
    }
    // 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
}

// exchange 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) exchange(opcode ledgerOpcode, p1 ledgerParam1, p2 ledgerParam2, data []byte) ([]byte, error) {
    // Construct the message payload, possibly split into multiple chunks
    var chunks [][]byte
    for left := data; len(left) > 0 || len(chunks) == 0; {
        // Create the chunk header
        var chunk []byte

        if len(chunks) == 0 {
            // The first chunk encodes the length and all the opcodes
            chunk = []byte{0x00, 0x00, 0xe0, byte(opcode), byte(p1), byte(p2), byte(len(data))}
            binary.BigEndian.PutUint16(chunk, uint16(5+len(data)))
        }
        // Append the data blob to the end of the chunk
        space := 64 - len(chunk) - 5 // 5 == header size
        if len(left) > space {
            chunks, left = append(chunks, append(chunk, left[:space]...)), left[space:]
            continue
        }
        chunks, left = append(chunks, append(chunk, left...)), nil
    }
    // Stream all the chunks to the device
    for i, chunk := range chunks {
        // Construct the new message to stream
        header := []byte{0x01, 0x01, 0x05, 0x00, 0x00} // Channel ID and command tag appended
        binary.BigEndian.PutUint16(header[3:], uint16(i))

        msg := append(header, chunk...)

        // Send over to the device
        if glog.V(logger.Core) {
            glog.Infof("-> %03d.%03d: %x", w.device.Bus, w.device.Address, msg)
        }
        if _, err := w.input.Write(msg); err != nil {
            return nil, err
        }
    }
    // Stream the reply back from the wallet in 64 byte chunks
    var reply []byte
    for {
        // Read the next chunk from the Ledger wallet
        chunk := make([]byte, 64)
        if _, err := io.ReadFull(w.output, chunk); err != nil {
            return nil, err
        }
        if glog.V(logger.Core) {
            glog.Infof("<- %03d.%03d: %x", w.device.Bus, w.device.Address, chunk)
        }
        // Make sure the transport header matches
        if chunk[0] != 0x01 || chunk[1] != 0x01 || chunk[2] != 0x05 {
            return nil, fmt.Errorf("invalid reply header: %x", chunk[:3])
        }
        // If it's the first chunk, retrieve the total message length
        if chunk[3] == 0x00 && chunk[4] == 0x00 {
            reply = make([]byte, 0, int(binary.BigEndian.Uint16(chunk[5:7])))
            chunk = chunk[7:]
        } else {
            chunk = chunk[5:]
        }
        // Append to the reply and stop when filled up
        if left := cap(reply) - len(reply); left > len(chunk) {
            reply = append(reply, chunk...)
        } else {
            reply = append(reply, chunk[:left]...)
            break
        }
    }
    return reply[:len(reply)-2], nil
}