path: root/accounts/scwallet/hub.go

// 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/>.

// This package implements support for smartcard-based hardware wallets such as
// the one written by Status: https://github.com/status-im/hardware-wallet
//
// This implementation of smartcard wallets have a different interaction process
// to other types of hardware wallet. The process works like this:
//
// 1. (First use with a given client) Establish a pairing between hardware
//    wallet and client. This requires a secret value called a 'PUK'. You can
//    pair with an unpaired wallet with `personal.openWallet(URI, PUK)`.
// 2. (First use only) Initialize the wallet, which generates a keypair, stores
//    it on the wallet, and returns it so the user can back it up. You can
//    initialize a wallet with `personal.initializeWallet(URI)`.
// 3. Connect to the wallet using the pairing information established in step 1.
//    You can connect to a paired wallet with `personal.openWallet(URI, PIN)`.
// 4. Interact with the wallet as normal.

package scwallet

import (
    "encoding/json"
    "io/ioutil"
    "os"
    "sort"
    "sync"
    "time"

    "github.com/ebfe/scard"
    "github.com/ethereum/go-ethereum/accounts"
    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/event"
    "github.com/ethereum/go-ethereum/log"
)

// Scheme is the URI prefix for smartcard wallets.
const Scheme = "pcsc"

// refreshCycle is the maximum time between wallet refreshes (if USB hotplug
// notifications don't work).
const refreshCycle = time.Second

// refreshThrottling is the minimum time between wallet refreshes to avoid thrashing.
const refreshThrottling = 500 * time.Millisecond

// smartcardPairing contains information about a smart card we have paired with
// or might pair with the hub.
type smartcardPairing struct {
    PublicKey    []byte                                     `json:"publicKey"`
    PairingIndex uint8                                      `json:"pairingIndex"`
    PairingKey   []byte                                     `json:"pairingKey"`
    Accounts     map[common.Address]accounts.DerivationPath `json:"accounts"`
}

// Hub is a accounts.Backend that can find and handle generic PC/SC hardware wallets.
type Hub struct {
    scheme string // Protocol scheme prefixing account and wallet URLs.

    context  *scard.Context
    datadir  string
    pairings map[string]smartcardPairing

    refreshed   time.Time               // Time instance when the list of wallets was last refreshed
    wallets     map[string]*Wallet      // Mapping from reader names to wallet instances
    updateFeed  event.Feed              // Event feed to notify wallet additions/removals
    updateScope event.SubscriptionScope // Subscription scope tracking current live listeners
    updating    bool                    // Whether the event notification loop is running

    quit chan chan error

    stateLock sync.RWMutex // Protects the internals of the hub from racey access
}

func (hub *Hub) readPairings() error {
    hub.pairings = make(map[string]smartcardPairing)
    pairingFile, err := os.Open(hub.datadir + "/smartcards.json")
    if err != nil {
        if os.IsNotExist(err) {
            return nil
        }
        return err
    }

    pairingData, err := ioutil.ReadAll(pairingFile)
    if err != nil {
        return err
    }
    var pairings []smartcardPairing
    if err := json.Unmarshal(pairingData, &pairings); err != nil {
        return err
    }

    for _, pairing := range pairings {
        hub.pairings[string(pairing.PublicKey)] = pairing
    }
    return nil
}

func (hub *Hub) writePairings() error {
    pairingFile, err := os.OpenFile(hub.datadir+"/smartcards.json", os.O_RDWR|os.O_CREATE, 0755)
    if err != nil {
        return err
    }

    pairings := make([]smartcardPairing, 0, len(hub.pairings))
    for _, pairing := range hub.pairings {
        pairings = append(pairings, pairing)
    }

    pairingData, err := json.Marshal(pairings)
    if err != nil {
        return err
    }

    if _, err := pairingFile.Write(pairingData); err != nil {
        return err
    }

    return pairingFile.Close()
}

func (hub *Hub) pairing(wallet *Wallet) *smartcardPairing {
    pairing, ok := hub.pairings[string(wallet.PublicKey)]
    if ok {
        return &pairing
    }
    return nil
}

func (hub *Hub) setPairing(wallet *Wallet, pairing *smartcardPairing) error {
    if pairing == nil {
        delete(hub.pairings, string(wallet.PublicKey))
    } else {
        hub.pairings[string(wallet.PublicKey)] = *pairing
    }
    return hub.writePairings()
}

// NewHub creates a new hardware wallet manager for smartcards.
func NewHub(scheme string, datadir string) (*Hub, error) {
    context, err := scard.EstablishContext()
    if err != nil {
        return nil, err
    }
    hub := &Hub{
        scheme:  scheme,
        context: context,
        datadir: datadir,
        wallets: make(map[string]*Wallet),
        quit:    make(chan chan error),
    }
    if err := hub.readPairings(); err != nil {
        return nil, err
    }
    hub.refreshWallets()
    return hub, nil
}

// Wallets implements accounts.Backend, returning all the currently tracked smart
// cards that appear to be hardware wallets.
func (hub *Hub) Wallets() []accounts.Wallet {
    // Make sure the list of wallets is up to date
    hub.refreshWallets()

    hub.stateLock.RLock()
    defer hub.stateLock.RUnlock()

    cpy := make([]accounts.Wallet, 0, len(hub.wallets))
    for _, wallet := range hub.wallets {
        cpy = append(cpy, wallet)
    }
    sort.Sort(accounts.WalletsByURL(cpy))
    return cpy
}

// refreshWallets scans the devices attached to the machine and updates the
// list of wallets based on the found devices.
func (hub *Hub) refreshWallets() {
    // Don't scan the USB like crazy it the user fetches wallets in a loop
    hub.stateLock.RLock()
    elapsed := time.Since(hub.refreshed)
    hub.stateLock.RUnlock()

    if elapsed < refreshThrottling {
        return
    }
    // Retrieve all the smart card reader to check for cards
    readers, err := hub.context.ListReaders()
    if err != nil {
        // This is a perverted hack, the scard library returns an error if no card
        // readers are present instead of simply returning an empty list. We don't
        // want to fill the user's log with errors, so filter those out.
        if err.Error() != "scard: Cannot find a smart card reader." {
            log.Error("Failed to enumerate smart card readers", "err", err)
        }
    }
    // Transform the current list of wallets into the new one
    hub.stateLock.Lock()

    events := []accounts.WalletEvent{}
    seen := make(map[string]struct{})

    for _, reader := range readers {
        // Mark the reader as present
        seen[reader] = struct{}{}

        // If we alreay know about this card, skip to the next reader, otherwise clean up
        if wallet, ok := hub.wallets[reader]; ok {
            if err := wallet.ping(); err == nil {
                continue
            }
            wallet.Close()
            events = append(events, accounts.WalletEvent{Wallet: wallet, Kind: accounts.WalletDropped})
            delete(hub.wallets, reader)
        }
        // New card detected, try to connect to it
        card, err := hub.context.Connect(reader, scard.ShareShared, scard.ProtocolAny)
        if err != nil {
            log.Debug("Failed to open smart card", "reader", reader, "err", err)
            continue
        }
        wallet := NewWallet(hub, card)
        if err = wallet.connect(); err != nil {
            log.Debug("Failed to connect to smart card", "reader", reader, "err", err)
            card.Disconnect(scard.LeaveCard)
            continue
        }
        // Card connected, start tracking in amongs the wallets
        hub.wallets[reader] = wallet
        events = append(events, accounts.WalletEvent{Wallet: wallet, Kind: accounts.WalletArrived})
    }
    // Remove any wallets no longer present
    for reader, wallet := range hub.wallets {
        if _, ok := seen[reader]; !ok {
            wallet.Close()
            events = append(events, accounts.WalletEvent{Wallet: wallet, Kind: accounts.WalletDropped})
            delete(hub.wallets, reader)
        }
    }
    hub.refreshed = time.Now()
    hub.stateLock.Unlock()

    for _, event := range events {
        hub.updateFeed.Send(event)
    }
}

// Subscribe implements accounts.Backend, creating an async subscription to
// receive notifications on the addition or removal of smart card wallets.
func (hub *Hub) Subscribe(sink chan<- accounts.WalletEvent) event.Subscription {
    // We need the mutex to reliably start/stop the update loop
    hub.stateLock.Lock()
    defer hub.stateLock.Unlock()

    // Subscribe the caller and track the subscriber count
    sub := hub.updateScope.Track(hub.updateFeed.Subscribe(sink))

    // Subscribers require an active notification loop, start it
    if !hub.updating {
        hub.updating = true
        go hub.updater()
    }
    return sub
}

// updater is responsible for maintaining an up-to-date list of wallets managed
// by the smart card hub, and for firing wallet addition/removal events.
func (hub *Hub) updater() {
    for {
        // TODO: Wait for a USB hotplug event (not supported yet) or a refresh timeout
        // <-hub.changes
        time.Sleep(refreshCycle)

        // Run the wallet refresher
        hub.refreshWallets()

        // If all our subscribers left, stop the updater
        hub.stateLock.Lock()
        if hub.updateScope.Count() == 0 {
            hub.updating = false
            hub.stateLock.Unlock()
            return
        }
        hub.stateLock.Unlock()
    }
}