...

1 files changed, 1082 insertions, 0 deletions

diff --git a/accounts/scwallet/wallet.go b/accounts/scwallet/wallet.go
new file mode 100644
index 0000000..f72e685
--- /dev/null
+++ b/accounts/scwallet/wallet.go
@@ -0,0 +1,1082 @@
+// Copyright 2018 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/>.
+
+package scwallet
+
+import (
+	"bytes"
+	"context"
+	"crypto/hmac"
+	"crypto/sha256"
+	"crypto/sha512"
+	"encoding/asn1"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"math/big"
+	"regexp"
+	"sort"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/ava-labs/coreth/accounts"
+	"github.com/ava-labs/coreth/core/types"
+	ethereum "github.com/ava-labs/go-ethereum"
+	"github.com/ava-labs/go-ethereum/common"
+	"github.com/ava-labs/go-ethereum/crypto"
+	"github.com/ava-labs/go-ethereum/log"
+	pcsc "github.com/gballet/go-libpcsclite"
+	"github.com/status-im/keycard-go/derivationpath"
+)
+
+// ErrPairingPasswordNeeded is returned if opening the smart card requires pairing with a pairing
+// password. In this case, the calling application should request user input to enter
+// the pairing password and send it back.
+var ErrPairingPasswordNeeded = errors.New("smartcard: pairing password needed")
+
+// ErrPINNeeded is returned if opening the smart card requires a PIN code. In
+// this case, the calling application should request user input to enter the PIN
+// and send it back.
+var ErrPINNeeded = errors.New("smartcard: pin needed")
+
+// ErrPINUnblockNeeded is returned if opening the smart card requires a PIN code,
+// but all PIN attempts have already been exhausted. In this case the calling
+// application should request user input for the PUK and a new PIN code to set
+// fo the card.
+var ErrPINUnblockNeeded = errors.New("smartcard: pin unblock needed")
+
+// ErrAlreadyOpen is returned if the smart card is attempted to be opened, but
+// there is already a paired and unlocked session.
+var ErrAlreadyOpen = errors.New("smartcard: already open")
+
+// ErrPubkeyMismatch is returned if the public key recovered from a signature
+// does not match the one expected by the user.
+var ErrPubkeyMismatch = errors.New("smartcard: recovered public key mismatch")
+
+var (
+	appletAID = []byte{0xA0, 0x00, 0x00, 0x08, 0x04, 0x00, 0x01, 0x01, 0x01}
+	// DerivationSignatureHash is used to derive the public key from the signature of this hash
+	DerivationSignatureHash = sha256.Sum256(common.Hash{}.Bytes())
+)
+
+// List of APDU command-related constants
+const (
+	claISO7816  = 0
+	claSCWallet = 0x80
+
+	insSelect      = 0xA4
+	insGetResponse = 0xC0
+	sw1GetResponse = 0x61
+	sw1Ok          = 0x90
+
+	insVerifyPin  = 0x20
+	insUnblockPin = 0x22
+	insExportKey  = 0xC2
+	insSign       = 0xC0
+	insLoadKey    = 0xD0
+	insDeriveKey  = 0xD1
+	insStatus     = 0xF2
+)
+
+// List of ADPU command parameters
+const (
+	P1DeriveKeyFromMaster  = uint8(0x00)
+	P1DeriveKeyFromParent  = uint8(0x01)
+	P1DeriveKeyFromCurrent = uint8(0x10)
+	statusP1WalletStatus   = uint8(0x00)
+	statusP1Path           = uint8(0x01)
+	signP1PrecomputedHash  = uint8(0x01)
+	signP2OnlyBlock        = uint8(0x81)
+	exportP1Any            = uint8(0x00)
+	exportP2Pubkey         = uint8(0x01)
+)
+
+// Minimum time to wait between self derivation attempts, even it the user is
+// requesting accounts like crazy.
+const selfDeriveThrottling = time.Second
+
+// Wallet represents a smartcard wallet instance.
+type Wallet struct {
+	Hub       *Hub   // A handle to the Hub that instantiated this wallet.
+	PublicKey []byte // The wallet's public key (used for communication and identification, not signing!)
+
+	lock    sync.Mutex // Lock that gates access to struct fields and communication with the card
+	card    *pcsc.Card // A handle to the smartcard interface for the wallet.
+	session *Session   // The secure communication session with the card
+	log     log.Logger // Contextual logger to tag the base with its id
+
+	deriveNextPaths []accounts.DerivationPath // Next derivation paths for account auto-discovery (multiple bases supported)
+	deriveNextAddrs []common.Address          // Next derived account addresses for auto-discovery (multiple bases supported)
+	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
+}
+
+// NewWallet constructs and returns a new Wallet instance.
+func NewWallet(hub *Hub, card *pcsc.Card) *Wallet {
+	wallet := &Wallet{
+		Hub:  hub,
+		card: card,
+	}
+	return wallet
+}
+
+// transmit sends an APDU to the smartcard and receives and decodes the response.
+// It automatically handles requests by the card to fetch the return data separately,
+// and returns an error if the response status code is not success.
+func transmit(card *pcsc.Card, command *commandAPDU) (*responseAPDU, error) {
+	data, err := command.serialize()
+	if err != nil {
+		return nil, err
+	}
+
+	responseData, _, err := card.Transmit(data)
+	if err != nil {
+		return nil, err
+	}
+
+	response := new(responseAPDU)
+	if err = response.deserialize(responseData); err != nil {
+		return nil, err
+	}
+
+	// Are we being asked to fetch the response separately?
+	if response.Sw1 == sw1GetResponse && (command.Cla != claISO7816 || command.Ins != insGetResponse) {
+		return transmit(card, &commandAPDU{
+			Cla:  claISO7816,
+			Ins:  insGetResponse,
+			P1:   0,
+			P2:   0,
+			Data: nil,
+			Le:   response.Sw2,
+		})
+	}
+
+	if response.Sw1 != sw1Ok {
+		return nil, fmt.Errorf("Unexpected insecure response status Cla=0x%x, Ins=0x%x, Sw=0x%x%x", command.Cla, command.Ins, response.Sw1, response.Sw2)
+	}
+
+	return response, nil
+}
+
+// applicationInfo encodes information about the smartcard application - its
+// instance UID and public key.
+type applicationInfo struct {
+	InstanceUID []byte `asn1:"tag:15"`
+	PublicKey   []byte `asn1:"tag:0"`
+}
+
+// connect connects to the wallet application and establishes a secure channel with it.
+// must be called before any other interaction with the wallet.
+func (w *Wallet) connect() error {
+	w.lock.Lock()
+	defer w.lock.Unlock()
+
+	appinfo, err := w.doselect()
+	if err != nil {
+		return err
+	}
+
+	channel, err := NewSecureChannelSession(w.card, appinfo.PublicKey)
+	if err != nil {
+		return err
+	}
+
+	w.PublicKey = appinfo.PublicKey
+	w.log = log.New("url", w.URL())
+	w.session = &Session{
+		Wallet:  w,
+		Channel: channel,
+	}
+	return nil
+}
+
+// doselect is an internal (unlocked) function to send a SELECT APDU to the card.
+func (w *Wallet) doselect() (*applicationInfo, error) {
+	response, err := transmit(w.card, &commandAPDU{
+		Cla:  claISO7816,
+		Ins:  insSelect,
+		P1:   4,
+		P2:   0,
+		Data: appletAID,
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	appinfo := new(applicationInfo)
+	if _, err := asn1.UnmarshalWithParams(response.Data, appinfo, "tag:4"); err != nil {
+		return nil, err
+	}
+	return appinfo, nil
+}
+
+// ping checks the card's status and returns an error if unsuccessful.
+func (w *Wallet) ping() error {
+	w.lock.Lock()
+	defer w.lock.Unlock()
+
+	// We can't ping if not paired
+	if !w.session.paired() {
+		return nil
+	}
+	if _, err := w.session.walletStatus(); err != nil {
+		return err
+	}
+	return nil
+}
+
+// release releases any resources held by an open wallet instance.
+func (w *Wallet) release() error {
+	if w.session != nil {
+		return w.session.release()
+	}
+	return nil
+}
+
+// pair is an internal (unlocked) function for establishing a new pairing
+// with the wallet.
+func (w *Wallet) pair(puk []byte) error {
+	if w.session.paired() {
+		return fmt.Errorf("Wallet already paired")
+	}
+	pairing, err := w.session.pair(puk)
+	if err != nil {
+		return err
+	}
+	if err = w.Hub.setPairing(w, &pairing); err != nil {
+		return err
+	}
+	return w.session.authenticate(pairing)
+}
+
+// Unpair deletes an existing wallet pairing.
+func (w *Wallet) Unpair(pin []byte) error {
+	w.lock.Lock()
+	defer w.lock.Unlock()
+
+	if !w.session.paired() {
+		return fmt.Errorf("wallet %x not paired", w.PublicKey)
+	}
+	if err := w.session.verifyPin(pin); err != nil {
+		return fmt.Errorf("failed to verify pin: %s", err)
+	}
+	if err := w.session.unpair(); err != nil {
+		return fmt.Errorf("failed to unpair: %s", err)
+	}
+	if err := w.Hub.setPairing(w, nil); err != nil {
+		return err
+	}
+	return nil
+}
+
+// URL retrieves the canonical path under which this wallet is reachable. It is
+// user by upper layers to define a sorting order over all wallets from multiple
+// backends.
+func (w *Wallet) URL() accounts.URL {
+	return accounts.URL{
+		Scheme: w.Hub.scheme,
+		Path:   fmt.Sprintf("%x", w.PublicKey[1:5]), // Byte #0 isn't unique; 1:5 covers << 64K cards, bump to 1:9 for << 4M
+	}
+}
+
+// Status returns a textual status to aid the user in the current state of the
+// wallet. It also returns an error indicating any failure the wallet might have
+// encountered.
+func (w *Wallet) Status() (string, error) {
+	w.lock.Lock()
+	defer w.lock.Unlock()
+
+	// If the card is not paired, we can only wait
+	if !w.session.paired() {
+		return "Unpaired, waiting for pairing password", nil
+	}
+	// Yay, we have an encrypted session, retrieve the actual status
+	status, err := w.session.walletStatus()
+	if err != nil {
+		return fmt.Sprintf("Failed: %v", err), err
+	}
+	switch {
+	case !w.session.verified && status.PinRetryCount == 0 && status.PukRetryCount == 0:
+		return fmt.Sprintf("Bricked, waiting for full wipe"), nil
+	case !w.session.verified && status.PinRetryCount == 0:
+		return fmt.Sprintf("Blocked, waiting for PUK (%d attempts left) and new PIN", status.PukRetryCount), nil
+	case !w.session.verified:
+		return fmt.Sprintf("Locked, waiting for PIN (%d attempts left)", status.PinRetryCount), nil
+	case !status.Initialized:
+		return fmt.Sprintf("Empty, waiting for initialization"), nil
+	default:
+		return fmt.Sprintf("Online"), nil
+	}
+}
+
+// Open initializes access to a wallet instance. It is not meant to unlock or
+// decrypt account keys, rather simply to establish a connection to hardware
+// wallets and/or to access derivation seeds.
+//
+// The passphrase parameter may or may not be used by the implementation of a
+// particular wallet instance. The reason there is no passwordless open method
+// is to strive towards a uniform wallet handling, oblivious to the different
+// backend providers.
+//
+// Please note, if you open a wallet, you must close it to release any allocated
+// resources (especially important when working with hardware wallets).
+func (w *Wallet) Open(passphrase string) error {
+	w.lock.Lock()
+	defer w.lock.Unlock()
+
+	// If the session is already open, bail out
+	if w.session.verified {
+		return ErrAlreadyOpen
+	}
+	// If the smart card is not yet paired, attempt to do so either from a previous
+	// pairing key or form the supplied PUK code.
+	if !w.session.paired() {
+		// If a previous pairing exists, only ever try to use that
+		if pairing := w.Hub.pairing(w); pairing != nil {
+			if err := w.session.authenticate(*pairing); err != nil {
+				return fmt.Errorf("failed to authenticate card %x: %s", w.PublicKey[:4], err)
+			}
+			// Pairing still ok, fall through to PIN checks
+		} else {
+			// If no passphrase was supplied, request the PUK from the user
+			if passphrase == "" {
+				return ErrPairingPasswordNeeded
+			}
+			// Attempt to pair the smart card with the user supplied PUK
+			if err := w.pair([]byte(passphrase)); err != nil {
+				return err
+			}
+			// Pairing succeeded, fall through to PIN checks. This will of course fail,
+			// but we can't return ErrPINNeeded directly here becase we don't know whether
+			// a PIN check or a PIN reset is needed.
+			passphrase = ""
+		}
+	}
+	// The smart card was successfully paired, retrieve its status to check whether
+	// PIN verification or unblocking is needed.
+	status, err := w.session.walletStatus()
+	if err != nil {
+		return err
+	}
+	// Request the appropriate next authentication data, or use the one supplied
+	switch {
+	case passphrase == "" && status.PinRetryCount > 0:
+		return ErrPINNeeded
+	case passphrase == "":
+		return ErrPINUnblockNeeded
+	case status.PinRetryCount > 0:
+		if !regexp.MustCompile(`^[0-9]{6,}$`).MatchString(passphrase) {
+			w.log.Error("PIN needs to be at least 6 digits")
+			return ErrPINNeeded
+		}
+		if err := w.session.verifyPin([]byte(passphrase)); err != nil {
+			return err
+		}
+	default:
+		if !regexp.MustCompile(`^[0-9]{12,}$`).MatchString(passphrase) {
+			w.log.Error("PUK needs to be at least 12 digits")
+			return ErrPINUnblockNeeded
+		}
+		if err := w.session.unblockPin([]byte(passphrase)); err != nil {
+			return err
+		}
+	}
+	// Smart card paired and unlocked, initialize and register
+	w.deriveReq = make(chan chan struct{})
+	w.deriveQuit = make(chan chan error)
+
+	go w.selfDerive()
+
+	// Notify anyone listening for wallet events that a new device is accessible
+	go w.Hub.updateFeed.Send(accounts.WalletEvent{Wallet: w, Kind: accounts.WalletOpened})
+
+	return nil
+}
+
+// Close stops and closes the wallet, freeing any resources.
+func (w *Wallet) Close() error {
+	// Ensure the wallet was opened
+	w.lock.Lock()
+	dQuit := w.deriveQuit
+	w.lock.Unlock()
+
+	// 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.lock.Lock()
+	defer w.lock.Unlock()
+
+	w.deriveQuit = nil
+	w.deriveReq = nil
+
+	if err := w.release(); err != nil {
+		return err
+	}
+	return derr
+}
+
+// selfDerive is an account derivation loop that upon request attempts to find
+// new non-zero accounts.
+func (w *Wallet) selfDerive() {
+	w.log.Debug("Smart card wallet self-derivation started")
+	defer w.log.Debug("Smart card wallet 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.lock.Lock()
+		if w.session == nil || w.deriveChain == nil {
+			w.lock.Unlock()
+			reqc <- struct{}{}
+			continue
+		}
+		pairing := w.Hub.pairing(w)
+
+		// Device lock obtained, derive the next batch of accounts
+		var (
+			paths   []accounts.DerivationPath
+			nextAcc accounts.Account
+
+			nextPaths = append([]accounts.DerivationPath{}, w.deriveNextPaths...)
+			nextAddrs = append([]common.Address{}, w.deriveNextAddrs...)
+
+			context = context.Background()
+		)
+		for i := 0; i < len(nextAddrs); i++ {
+			for empty := false; !empty; {
+				// Retrieve the next derived Ethereum account
+				if nextAddrs[i] == (common.Address{}) {
+					if nextAcc, err = w.session.derive(nextPaths[i]); err != nil {
+						w.log.Warn("Smartcard wallet account derivation failed", "err", err)
+						break
+					}
+					nextAddrs[i] = nextAcc.Address
+				}
+				// Check the account's status against the current chain state
+				var (
+					balance *big.Int
+					nonce   uint64
+				)
+				balance, err = w.deriveChain.BalanceAt(context, nextAddrs[i], nil)
+				if err != nil {
+					w.log.Warn("Smartcard wallet balance retrieval failed", "err", err)
+					break
+				}
+				nonce, err = w.deriveChain.NonceAt(context, nextAddrs[i], nil)
+				if err != nil {
+					w.log.Warn("Smartcard wallet nonce retrieval failed", "err", err)
+					break
+				}
+				// If the next account is empty, stop self-derivation, but add for the last base path
+				if balance.Sign() == 0 && nonce == 0 {
+					empty = true
+					if i < len(nextAddrs)-1 {
+						break
+					}
+				}
+				// We've just self-derived a new account, start tracking it locally
+				path := make(accounts.DerivationPath, len(nextPaths[i]))
+				copy(path[:], nextPaths[i][:])
+				paths = append(paths, path)
+
+				// Display a log message to the user for new (or previously empty accounts)
+				if _, known := pairing.Accounts[nextAddrs[i]]; !known || !empty || nextAddrs[i] != w.deriveNextAddrs[i] {
+					w.log.Info("Smartcard wallet discovered new account", "address", nextAddrs[i], "path", path, "balance", balance, "nonce", nonce)
+				}
+				pairing.Accounts[nextAddrs[i]] = path
+
+				// Fetch the next potential account
+				if !empty {
+					nextAddrs[i] = common.Address{}
+					nextPaths[i][len(nextPaths[i])-1]++
+				}
+			}
+		}
+		// If there are new accounts, write them out
+		if len(paths) > 0 {
+			err = w.Hub.setPairing(w, pairing)
+		}
+		// Shift the self-derivation forward
+		w.deriveNextAddrs = nextAddrs
+		w.deriveNextPaths = nextPaths
+
+		// Self derivation complete, release device lock
+		w.lock.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(selfDeriveThrottling):
+				// Waited enough, willing to self-derive again
+			}
+		}
+	}
+	// In case of error, wait for termination
+	if err != nil {
+		w.log.Debug("Smartcard wallet self-derivation failed", "err", err)
+		errc = <-w.deriveQuit
+	}
+	errc <- err
+}
+
+// Accounts retrieves the list of signing accounts the wallet is currently aware
+// of. For hierarchical deterministic wallets, the list will not be exhaustive,
+// rather only contain the accounts explicitly pinned during account derivation.
+func (w *Wallet) 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
+	}
+
+	w.lock.Lock()
+	defer w.lock.Unlock()
+
+	if pairing := w.Hub.pairing(w); pairing != nil {
+		ret := make([]accounts.Account, 0, len(pairing.Accounts))
+		for address, path := range pairing.Accounts {
+			ret = append(ret, w.makeAccount(address, path))
+		}
+		sort.Sort(accounts.AccountsByURL(ret))
+		return ret
+	}
+	return nil
+}
+
+func (w *Wallet) makeAccount(address common.Address, path accounts.DerivationPath) accounts.Account {
+	return accounts.Account{
+		Address: address,
+		URL: accounts.URL{
+			Scheme: w.Hub.scheme,
+			Path:   fmt.Sprintf("%x/%s", w.PublicKey[1:3], path.String()),
+		},
+	}
+}
+
+// Contains returns whether an account is part of this particular wallet or not.
+func (w *Wallet) Contains(account accounts.Account) bool {
+	if pairing := w.Hub.pairing(w); pairing != nil {
+		_, ok := pairing.Accounts[account.Address]
+		return ok
+	}
+	return false
+}
+
+// Initialize installs a keypair generated from the provided key into the wallet.
+func (w *Wallet) Initialize(seed []byte) error {
+	go w.selfDerive()
+	// DO NOT lock at this stage, as the initialize
+	// function relies on Status()
+	return w.session.initialize(seed)
+}
+
+// Derive attempts to explicitly derive a hierarchical deterministic account at
+// the specified derivation path. If requested, the derived account will be added
+// to the wallet's tracked account list.
+func (w *Wallet) Derive(path accounts.DerivationPath, pin bool) (accounts.Account, error) {
+	w.lock.Lock()
+	defer w.lock.Unlock()
+
+	account, err := w.session.derive(path)
+	if err != nil {
+		return accounts.Account{}, err
+	}
+
+	if pin {
+		pairing := w.Hub.pairing(w)
+		pairing.Accounts[account.Address] = path
+		if err := w.Hub.setPairing(w, pairing); err != nil {
+			return accounts.Account{}, err
+		}
+	}
+
+	return account, nil
+}
+
+// SelfDerive sets a base account derivation path from which the wallet attempts
+// to discover non zero accounts and automatically add them to list of tracked
+// accounts.
+//
+// Note, self derivaton will increment the last component of the specified path
+// opposed to decending into a child path to allow discovering accounts starting
+// from non zero components.
+//
+// Some hardware wallets switched derivation paths through their evolution, so
+// this method supports providing multiple bases to discover old user accounts
+// too. Only the last base will be used to derive the next empty account.
+//
+// You can disable automatic account discovery by calling SelfDerive with a nil
+// chain state reader.
+func (w *Wallet) SelfDerive(bases []accounts.DerivationPath, chain ethereum.ChainStateReader) {
+	w.lock.Lock()
+	defer w.lock.Unlock()
+
+	w.deriveNextPaths = make([]accounts.DerivationPath, len(bases))
+	for i, base := range bases {
+		w.deriveNextPaths[i] = make(accounts.DerivationPath, len(base))
+		copy(w.deriveNextPaths[i][:], base[:])
+	}
+	w.deriveNextAddrs = make([]common.Address, len(bases))
+	w.deriveChain = chain
+}
+
+// SignData requests the wallet to sign the hash of the given data.
+//
+// It looks up the account specified either solely via its address contained within,
+// or optionally with the aid of any location metadata from the embedded URL field.
+//
+// If the wallet requires additional authentication to sign the request (e.g.
+// a password to decrypt the account, or a PIN code o verify the transaction),
+// an AuthNeededError instance will be returned, containing infos for the user
+// about which fields or actions are needed. The user may retry by providing
+// the needed details via SignDataWithPassphrase, or by other means (e.g. unlock
+// the account in a keystore).
+func (w *Wallet) SignData(account accounts.Account, mimeType string, data []byte) ([]byte, error) {
+	return w.signHash(account, crypto.Keccak256(data))
+}
+
+func (w *Wallet) signHash(account accounts.Account, hash []byte) ([]byte, error) {
+	w.lock.Lock()
+	defer w.lock.Unlock()
+
+	path, err := w.findAccountPath(account)
+	if err != nil {
+		return nil, err
+	}
+
+	return w.session.sign(path, hash)
+}
+
+// SignTx requests the wallet to sign the given transaction.
+//
+// It looks up the account specified either solely via its address contained within,
+// or optionally with the aid of any location metadata from the embedded URL field.
+//
+// If the wallet requires additional authentication to sign the request (e.g.
+// a password to decrypt the account, or a PIN code o verify the transaction),
+// an AuthNeededError instance will be returned, containing infos for the user
+// about which fields or actions are needed. The user may retry by providing
+// the needed details via SignTxWithPassphrase, or by other means (e.g. unlock
+// the account in a keystore).
+func (w *Wallet) SignTx(account accounts.Account, tx *types.Transaction, chainID *big.Int) (*types.Transaction, error) {
+	signer := types.NewEIP155Signer(chainID)
+	hash := signer.Hash(tx)
+	sig, err := w.signHash(account, hash[:])
+	if err != nil {
+		return nil, err
+	}
+	return tx.WithSignature(signer, sig)
+}
+
+// SignDataWithPassphrase requests the wallet to sign the given hash with the
+// given passphrase as extra authentication information.
+//
+// It looks up the account specified either solely via its address contained within,
+// or optionally with the aid of any location metadata from the embedded URL field.
+func (w *Wallet) SignDataWithPassphrase(account accounts.Account, passphrase, mimeType string, data []byte) ([]byte, error) {
+	return w.signHashWithPassphrase(account, passphrase, crypto.Keccak256(data))
+}
+
+func (w *Wallet) signHashWithPassphrase(account accounts.Account, passphrase string, hash []byte) ([]byte, error) {
+	if !w.session.verified {
+		if err := w.Open(passphrase); err != nil {
+			return nil, err
+		}
+	}
+
+	return w.signHash(account, hash)
+}
+
+// SignText requests the wallet to sign the hash of a given piece of data, prefixed
+// by the Ethereum prefix scheme
+// It looks up the account specified either solely via its address contained within,
+// or optionally with the aid of any location metadata from the embedded URL field.
+//
+// If the wallet requires additional authentication to sign the request (e.g.
+// a password to decrypt the account, or a PIN code o verify the transaction),
+// an AuthNeededError instance will be returned, containing infos for the user
+// about which fields or actions are needed. The user may retry by providing
+// the needed details via SignHashWithPassphrase, or by other means (e.g. unlock
+// the account in a keystore).
+func (w *Wallet) SignText(account accounts.Account, text []byte) ([]byte, error) {
+	return w.signHash(account, accounts.TextHash(text))
+}
+
+// SignTextWithPassphrase implements accounts.Wallet, attempting to sign the
+// given hash with the given account using passphrase as extra authentication
+func (w *Wallet) SignTextWithPassphrase(account accounts.Account, passphrase string, text []byte) ([]byte, error) {
+	return w.signHashWithPassphrase(account, passphrase, crypto.Keccak256(accounts.TextHash(text)))
+}
+
+// SignTxWithPassphrase requests the wallet to sign the given transaction, with the
+// given passphrase as extra authentication information.
+//
+// It looks up the account specified either solely via its address contained within,
+// or optionally with the aid of any location metadata from the embedded URL field.
+func (w *Wallet) SignTxWithPassphrase(account accounts.Account, passphrase string, tx *types.Transaction, chainID *big.Int) (*types.Transaction, error) {
+	if !w.session.verified {
+		if err := w.Open(passphrase); err != nil {
+			return nil, err
+		}
+	}
+	return w.SignTx(account, tx, chainID)
+}
+
+// findAccountPath returns the derivation path for the provided account.
+// It first checks for the address in the list of pinned accounts, and if it is
+// not found, attempts to parse the derivation path from the account's URL.
+func (w *Wallet) findAccountPath(account accounts.Account) (accounts.DerivationPath, error) {
+	pairing := w.Hub.pairing(w)
+	if path, ok := pairing.Accounts[account.Address]; ok {
+		return path, nil
+	}
+
+	// Look for the path in the URL
+	if account.URL.Scheme != w.Hub.scheme {
+		return nil, fmt.Errorf("Scheme %s does not match wallet scheme %s", account.URL.Scheme, w.Hub.scheme)
+	}
+
+	parts := strings.SplitN(account.URL.Path, "/", 2)
+	if len(parts) != 2 {
+		return nil, fmt.Errorf("Invalid URL format: %s", account.URL)
+	}
+
+	if parts[0] != fmt.Sprintf("%x", w.PublicKey[1:3]) {
+		return nil, fmt.Errorf("URL %s is not for this wallet", account.URL)
+	}
+
+	return accounts.ParseDerivationPath(parts[1])
+}
+
+// Session represents a secured communication session with the wallet.
+type Session struct {
+	Wallet   *Wallet               // A handle to the wallet that opened the session
+	Channel  *SecureChannelSession // A secure channel for encrypted messages
+	verified bool                  // Whether the pin has been verified in this session.
+}
+
+// pair establishes a new pairing over this channel, using the provided secret.
+func (s *Session) pair(secret []byte) (smartcardPairing, error) {
+	err := s.Channel.Pair(secret)
+	if err != nil {
+		return smartcardPairing{}, err
+	}
+
+	return smartcardPairing{
+		PublicKey:    s.Wallet.PublicKey,
+		PairingIndex: s.Channel.PairingIndex,
+		PairingKey:   s.Channel.PairingKey,
+		Accounts:     make(map[common.Address]accounts.DerivationPath),
+	}, nil
+}
+
+// unpair deletes an existing pairing.
+func (s *Session) unpair() error {
+	if !s.verified {
+		return fmt.Errorf("Unpair requires that the PIN be verified")
+	}
+	return s.Channel.Unpair()
+}
+
+// verifyPin unlocks a wallet with the provided pin.
+func (s *Session) verifyPin(pin []byte) error {
+	if _, err := s.Channel.transmitEncrypted(claSCWallet, insVerifyPin, 0, 0, pin); err != nil {
+		return err
+	}
+	s.verified = true
+	return nil
+}
+
+// unblockPin unblocks a wallet with the provided puk and resets the pin to the
+// new one specified.
+func (s *Session) unblockPin(pukpin []byte) error {
+	if _, err := s.Channel.transmitEncrypted(claSCWallet, insUnblockPin, 0, 0, pukpin); err != nil {
+		return err
+	}
+	s.verified = true
+	return nil
+}
+
+// release releases resources associated with the channel.
+func (s *Session) release() error {
+	return s.Wallet.card.Disconnect(pcsc.LeaveCard)
+}
+
+// paired returns true if a valid pairing exists.
+func (s *Session) paired() bool {
+	return s.Channel.PairingKey != nil
+}
+
+// authenticate uses an existing pairing to establish a secure channel.
+func (s *Session) authenticate(pairing smartcardPairing) error {
+	if !bytes.Equal(s.Wallet.PublicKey, pairing.PublicKey) {
+		return fmt.Errorf("Cannot pair using another wallet's pairing; %x != %x", s.Wallet.PublicKey, pairing.PublicKey)
+	}
+	s.Channel.PairingKey = pairing.PairingKey
+	s.Channel.PairingIndex = pairing.PairingIndex
+	return s.Channel.Open()
+}
+
+// walletStatus describes a smartcard wallet's status information.
+type walletStatus struct {
+	PinRetryCount int  // Number of remaining PIN retries
+	PukRetryCount int  // Number of remaining PUK retries
+	Initialized   bool // Whether the card has been initialized with a private key
+}
+
+// walletStatus fetches the wallet's status from the card.
+func (s *Session) walletStatus() (*walletStatus, error) {
+	response, err := s.Channel.transmitEncrypted(claSCWallet, insStatus, statusP1WalletStatus, 0, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	status := new(walletStatus)
+	if _, err := asn1.UnmarshalWithParams(response.Data, status, "tag:3"); err != nil {
+		return nil, err
+	}
+	return status, nil
+}
+
+// derivationPath fetches the wallet's current derivation path from the card.
+func (s *Session) derivationPath() (accounts.DerivationPath, error) {
+	response, err := s.Channel.transmitEncrypted(claSCWallet, insStatus, statusP1Path, 0, nil)
+	if err != nil {
+		return nil, err
+	}
+	buf := bytes.NewReader(response.Data)
+	path := make(accounts.DerivationPath, len(response.Data)/4)
+	return path, binary.Read(buf, binary.BigEndian, &path)
+}
+
+// initializeData contains data needed to initialize the smartcard wallet.
+type initializeData struct {
+	PublicKey  []byte `asn1:"tag:0"`
+	PrivateKey []byte `asn1:"tag:1"`
+	ChainCode  []byte `asn1:"tag:2"`
+}
+
+// initialize initializes the card with new key data.
+func (s *Session) initialize(seed []byte) error {
+	// Check that the wallet isn't currently initialized,
+	// otherwise the key would be overwritten.
+	status, err := s.Wallet.Status()
+	if err != nil {
+		return err
+	}
+	if status == "Online" {
+		return fmt.Errorf("card is already initialized, cowardly refusing to proceed")
+	}
+
+	s.Wallet.lock.Lock()
+	defer s.Wallet.lock.Unlock()
+
+	// HMAC the seed to produce the private key and chain code
+	mac := hmac.New(sha512.New, []byte("Bitcoin seed"))
+	mac.Write(seed)
+	seed = mac.Sum(nil)
+
+	key, err := crypto.ToECDSA(seed[:32])
+	if err != nil {
+		return err
+	}
+
+	id := initializeData{}
+	id.PublicKey = crypto.FromECDSAPub(&key.PublicKey)
+	id.PrivateKey = seed[:32]
+	id.ChainCode = seed[32:]
+	data, err := asn1.Marshal(id)
+	if err != nil {
+		return err
+	}
+
+	// Nasty hack to force the top-level struct tag to be context-specific
+	data[0] = 0xA1
+
+	_, err = s.Channel.transmitEncrypted(claSCWallet, insLoadKey, 0x02, 0, data)
+	return err
+}
+
+// derive derives a new HD key path on the card.
+func (s *Session) derive(path accounts.DerivationPath) (accounts.Account, error) {
+	startingPoint, path, err := derivationpath.Decode(path.String())
+	if err != nil {
+		return accounts.Account{}, err
+	}
+
+	var p1 uint8
+	switch startingPoint {
+	case derivationpath.StartingPointMaster:
+		p1 = P1DeriveKeyFromMaster
+	case derivationpath.StartingPointParent:
+		p1 = P1DeriveKeyFromParent
+	case derivationpath.StartingPointCurrent:
+		p1 = P1DeriveKeyFromCurrent
+	default:
+		return accounts.Account{}, fmt.Errorf("invalid startingPoint %d", startingPoint)
+	}
+
+	data := new(bytes.Buffer)
+	for _, segment := range path {
+		if err := binary.Write(data, binary.BigEndian, segment); err != nil {
+			return accounts.Account{}, err
+		}
+	}
+
+	_, err = s.Channel.transmitEncrypted(claSCWallet, insDeriveKey, p1, 0, data.Bytes())
+	if err != nil {
+		return accounts.Account{}, err
+	}
+
+	response, err := s.Channel.transmitEncrypted(claSCWallet, insSign, 0, 0, DerivationSignatureHash[:])
+	if err != nil {
+		return accounts.Account{}, err
+	}
+
+	sigdata := new(signatureData)
+	if _, err := asn1.UnmarshalWithParams(response.Data, sigdata, "tag:0"); err != nil {
+		return accounts.Account{}, err
+	}
+	rbytes, sbytes := sigdata.Signature.R.Bytes(), sigdata.Signature.S.Bytes()
+	sig := make([]byte, 65)
+	copy(sig[32-len(rbytes):32], rbytes)
+	copy(sig[64-len(sbytes):64], sbytes)
+
+	if err := confirmPublicKey(sig, sigdata.PublicKey); err != nil {
+		return accounts.Account{}, err
+	}
+	pub, err := crypto.UnmarshalPubkey(sigdata.PublicKey)
+	if err != nil {
+		return accounts.Account{}, err
+	}
+	return s.Wallet.makeAccount(crypto.PubkeyToAddress(*pub), path), nil
+}
+
+// keyExport contains information on an exported keypair.
+type keyExport struct {
+	PublicKey  []byte `asn1:"tag:0"`
+	PrivateKey []byte `asn1:"tag:1,optional"`
+}
+
+// publicKey returns the public key for the current derivation path.
+func (s *Session) publicKey() ([]byte, error) {
+	response, err := s.Channel.transmitEncrypted(claSCWallet, insExportKey, exportP1Any, exportP2Pubkey, nil)
+	if err != nil {
+		return nil, err
+	}
+	keys := new(keyExport)
+	if _, err := asn1.UnmarshalWithParams(response.Data, keys, "tag:1"); err != nil {
+		return nil, err
+	}
+	return keys.PublicKey, nil
+}
+
+// signatureData contains information on a signature - the signature itself and
+// the corresponding public key.
+type signatureData struct {
+	PublicKey []byte `asn1:"tag:0"`
+	Signature struct {
+		R *big.Int
+		S *big.Int
+	}
+}
+
+// sign asks the card to sign a message, and returns a valid signature after
+// recovering the v value.
+func (s *Session) sign(path accounts.DerivationPath, hash []byte) ([]byte, error) {
+	startTime := time.Now()
+	_, err := s.derive(path)
+	if err != nil {
+		return nil, err
+	}
+	deriveTime := time.Now()
+
+	response, err := s.Channel.transmitEncrypted(claSCWallet, insSign, signP1PrecomputedHash, signP2OnlyBlock, hash)
+	if err != nil {
+		return nil, err
+	}
+	sigdata := new(signatureData)
+	if _, err := asn1.UnmarshalWithParams(response.Data, sigdata, "tag:0"); err != nil {
+		return nil, err
+	}
+	// Serialize the signature
+	rbytes, sbytes := sigdata.Signature.R.Bytes(), sigdata.Signature.S.Bytes()
+	sig := make([]byte, 65)
+	copy(sig[32-len(rbytes):32], rbytes)
+	copy(sig[64-len(sbytes):64], sbytes)
+
+	// Recover the V value.
+	sig, err = makeRecoverableSignature(hash, sig, sigdata.PublicKey)
+	if err != nil {
+		return nil, err
+	}
+	log.Debug("Signed using smartcard", "deriveTime", deriveTime.Sub(startTime), "signingTime", time.Since(deriveTime))
+
+	return sig, nil
+}
+
+// confirmPublicKey confirms that the given signature belongs to the specified key.
+func confirmPublicKey(sig, pubkey []byte) error {
+	_, err := makeRecoverableSignature(DerivationSignatureHash[:], sig, pubkey)
+	return err
+}
+
+// makeRecoverableSignature uses a signature and an expected public key to
+// recover the v value and produce a recoverable signature.
+func makeRecoverableSignature(hash, sig, expectedPubkey []byte) ([]byte, error) {
+	var libraryError error
+	for v := 0; v < 2; v++ {
+		sig[64] = byte(v)
+		if pubkey, err := crypto.Ecrecover(hash, sig); err == nil {
+			if bytes.Equal(pubkey, expectedPubkey) {
+				return sig, nil
+			}
+		} else {
+			libraryError = err
+		}
+	}
+	if libraryError != nil {
+		return nil, libraryError
+	}
+	return nil, ErrPubkeyMismatch
+}