path: root/whisper/whisperv6/whisper.go

// Copyright 2016 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 whisperv6

import (
    "bytes"
    "crypto/ecdsa"
    crand "crypto/rand"
    "crypto/sha256"
    "fmt"
    "runtime"
    "sync"
    "time"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/crypto"
    "github.com/ethereum/go-ethereum/log"
    "github.com/ethereum/go-ethereum/p2p"
    "github.com/ethereum/go-ethereum/rpc"
    "github.com/syndtr/goleveldb/leveldb/errors"
    "golang.org/x/crypto/pbkdf2"
    "golang.org/x/sync/syncmap"
    set "gopkg.in/fatih/set.v0"
)

type Statistics struct {
    messagesCleared      int
    memoryCleared        int
    memoryUsed           int
    cycles               int
    totalMessagesCleared int
}

const (
    minPowIdx     = iota // Minimal PoW required by the whisper node
    maxMsgSizeIdx = iota // Maximal message length allowed by the whisper node
    overflowIdx   = iota // Indicator of message queue overflow
)

// Whisper represents a dark communication interface through the Ethereum
// network, using its very own P2P communication layer.
type Whisper struct {
    protocol p2p.Protocol // Protocol description and parameters
    filters  *Filters     // Message filters installed with Subscribe function

    privateKeys map[string]*ecdsa.PrivateKey // Private key storage
    symKeys     map[string][]byte            // Symmetric key storage
    keyMu       sync.RWMutex                 // Mutex associated with key storages

    poolMu      sync.RWMutex              // Mutex to sync the message and expiration pools
    envelopes   map[common.Hash]*Envelope // Pool of envelopes currently tracked by this node
    expirations map[uint32]*set.SetNonTS  // Message expiration pool

    peerMu sync.RWMutex       // Mutex to sync the active peer set
    peers  map[*Peer]struct{} // Set of currently active peers

    messageQueue chan *Envelope // Message queue for normal whisper messages
    p2pMsgQueue  chan *Envelope // Message queue for peer-to-peer messages (not to be forwarded any further)
    quit         chan struct{}  // Channel used for graceful exit

    settings syncmap.Map // holds configuration settings that can be dynamically changed

    statsMu sync.Mutex // guard stats
    stats   Statistics // Statistics of whisper node

    mailServer MailServer // MailServer interface
}

// New creates a Whisper client ready to communicate through the Ethereum P2P network.
func New(cfg *Config) *Whisper {
    if cfg == nil {
        cfg = &DefaultConfig
    }

    whisper := &Whisper{
        privateKeys:  make(map[string]*ecdsa.PrivateKey),
        symKeys:      make(map[string][]byte),
        envelopes:    make(map[common.Hash]*Envelope),
        expirations:  make(map[uint32]*set.SetNonTS),
        peers:        make(map[*Peer]struct{}),
        messageQueue: make(chan *Envelope, messageQueueLimit),
        p2pMsgQueue:  make(chan *Envelope, messageQueueLimit),
        quit:         make(chan struct{}),
    }

    whisper.filters = NewFilters(whisper)

    whisper.settings.Store(minPowIdx, cfg.MinimumAcceptedPOW)
    whisper.settings.Store(maxMsgSizeIdx, cfg.MaxMessageSize)
    whisper.settings.Store(overflowIdx, false)

    // p2p whisper sub protocol handler
    whisper.protocol = p2p.Protocol{
        Name:    ProtocolName,
        Version: uint(ProtocolVersion),
        Length:  NumberOfMessageCodes,
        Run:     whisper.HandlePeer,
        NodeInfo: func() interface{} {
            return map[string]interface{}{
                "version":        ProtocolVersionStr,
                "maxMessageSize": whisper.MaxMessageSize(),
                "minimumPoW":     whisper.MinPow(),
            }
        },
    }

    return whisper
}

func (w *Whisper) MinPow() float64 {
    val, _ := w.settings.Load(minPowIdx)
    return val.(float64)
}

// MaxMessageSize returns the maximum accepted message size.
func (w *Whisper) MaxMessageSize() uint32 {
    val, _ := w.settings.Load(maxMsgSizeIdx)
    return val.(uint32)
}

// Overflow returns an indication if the message queue is full.
func (w *Whisper) Overflow() bool {
    val, _ := w.settings.Load(overflowIdx)
    return val.(bool)
}

// APIs returns the RPC descriptors the Whisper implementation offers
func (w *Whisper) APIs() []rpc.API {
    return []rpc.API{
        {
            Namespace: ProtocolName,
            Version:   ProtocolVersionStr,
            Service:   NewPublicWhisperAPI(w),
            Public:    true,
        },
    }
}

// RegisterServer registers MailServer interface.
// MailServer will process all the incoming messages with p2pRequestCode.
func (w *Whisper) RegisterServer(server MailServer) {
    w.mailServer = server
}

// Protocols returns the whisper sub-protocols ran by this particular client.
func (w *Whisper) Protocols() []p2p.Protocol {
    return []p2p.Protocol{w.protocol}
}

// Version returns the whisper sub-protocols version number.
func (w *Whisper) Version() uint {
    return w.protocol.Version
}

// SetMaxMessageSize sets the maximal message size allowed by this node
func (w *Whisper) SetMaxMessageSize(size uint32) error {
    if size > MaxMessageSize {
        return fmt.Errorf("message size too large [%d>%d]", size, MaxMessageSize)
    }
    w.settings.Store(maxMsgSizeIdx, size)
    return nil
}

// SetMinimumPoW sets the minimal PoW required by this node
func (w *Whisper) SetMinimumPoW(val float64) error {
    if val <= 0.0 {
        return fmt.Errorf("invalid PoW: %f", val)
    }
    w.settings.Store(minPowIdx, val)
    return nil
}

// getPeer retrieves peer by ID
func (w *Whisper) getPeer(peerID []byte) (*Peer, error) {
    w.peerMu.Lock()
    defer w.peerMu.Unlock()
    for p := range w.peers {
        id := p.peer.ID()
        if bytes.Equal(peerID, id[:]) {
            return p, nil
        }
    }
    return nil, fmt.Errorf("Could not find peer with ID: %x", peerID)
}

// AllowP2PMessagesFromPeer marks specific peer trusted,
// which will allow it to send historic (expired) messages.
func (w *Whisper) AllowP2PMessagesFromPeer(peerID []byte) error {
    p, err := w.getPeer(peerID)
    if err != nil {
        return err
    }
    p.trusted = true
    return nil
}

// RequestHistoricMessages sends a message with p2pRequestCode to a specific peer,
// which is known to implement MailServer interface, and is supposed to process this
// request and respond with a number of peer-to-peer messages (possibly expired),
// which are not supposed to be forwarded any further.
// The whisper protocol is agnostic of the format and contents of envelope.
func (w *Whisper) RequestHistoricMessages(peerID []byte, envelope *Envelope) error {
    p, err := w.getPeer(peerID)
    if err != nil {
        return err
    }
    p.trusted = true
    return p2p.Send(p.ws, p2pRequestCode, envelope)
}

// SendP2PMessage sends a peer-to-peer message to a specific peer.
func (w *Whisper) SendP2PMessage(peerID []byte, envelope *Envelope) error {
    p, err := w.getPeer(peerID)
    if err != nil {
        return err
    }
    return w.SendP2PDirect(p, envelope)
}

// SendP2PDirect sends a peer-to-peer message to a specific peer.
func (w *Whisper) SendP2PDirect(peer *Peer, envelope *Envelope) error {
    return p2p.Send(peer.ws, p2pCode, envelope)
}

// NewKeyPair generates a new cryptographic identity for the client, and injects
// it into the known identities for message decryption. Returns ID of the new key pair.
func (w *Whisper) NewKeyPair() (string, error) {
    key, err := crypto.GenerateKey()
    if err != nil || !validatePrivateKey(key) {
        key, err = crypto.GenerateKey() // retry once
    }
    if err != nil {
        return "", err
    }
    if !validatePrivateKey(key) {
        return "", fmt.Errorf("failed to generate valid key")
    }

    id, err := GenerateRandomID()
    if err != nil {
        return "", fmt.Errorf("failed to generate ID: %s", err)
    }

    w.keyMu.Lock()
    defer w.keyMu.Unlock()

    if w.privateKeys[id] != nil {
        return "", fmt.Errorf("failed to generate unique ID")
    }
    w.privateKeys[id] = key
    return id, nil
}

// DeleteKeyPair deletes the specified key if it exists.
func (w *Whisper) DeleteKeyPair(key string) bool {
    w.keyMu.Lock()
    defer w.keyMu.Unlock()

    if w.privateKeys[key] != nil {
        delete(w.privateKeys, key)
        return true
    }
    return false
}

// AddKeyPair imports a asymmetric private key and returns it identifier.
func (w *Whisper) AddKeyPair(key *ecdsa.PrivateKey) (string, error) {
    id, err := GenerateRandomID()
    if err != nil {
        return "", fmt.Errorf("failed to generate ID: %s", err)
    }

    w.keyMu.Lock()
    w.privateKeys[id] = key
    w.keyMu.Unlock()

    return id, nil
}

// HasKeyPair checks if the the whisper node is configured with the private key
// of the specified public pair.
func (w *Whisper) HasKeyPair(id string) bool {
    w.keyMu.RLock()
    defer w.keyMu.RUnlock()
    return w.privateKeys[id] != nil
}

// GetPrivateKey retrieves the private key of the specified identity.
func (w *Whisper) GetPrivateKey(id string) (*ecdsa.PrivateKey, error) {
    w.keyMu.RLock()
    defer w.keyMu.RUnlock()
    key := w.privateKeys[id]
    if key == nil {
        return nil, fmt.Errorf("invalid id")
    }
    return key, nil
}

// GenerateSymKey generates a random symmetric key and stores it under id,
// which is then returned. Will be used in the future for session key exchange.
func (w *Whisper) GenerateSymKey() (string, error) {
    key := make([]byte, aesKeyLength)
    _, err := crand.Read(key)
    if err != nil {
        return "", err
    } else if !validateSymmetricKey(key) {
        return "", fmt.Errorf("error in GenerateSymKey: crypto/rand failed to generate random data")
    }

    id, err := GenerateRandomID()
    if err != nil {
        return "", fmt.Errorf("failed to generate ID: %s", err)
    }

    w.keyMu.Lock()
    defer w.keyMu.Unlock()

    if w.symKeys[id] != nil {
        return "", fmt.Errorf("failed to generate unique ID")
    }
    w.symKeys[id] = key
    return id, nil
}

// AddSymKeyDirect stores the key, and returns its id.
func (w *Whisper) AddSymKeyDirect(key []byte) (string, error) {
    if len(key) != aesKeyLength {
        return "", fmt.Errorf("wrong key size: %d", len(key))
    }

    id, err := GenerateRandomID()
    if err != nil {
        return "", fmt.Errorf("failed to generate ID: %s", err)
    }

    w.keyMu.Lock()
    defer w.keyMu.Unlock()

    if w.symKeys[id] != nil {
        return "", fmt.Errorf("failed to generate unique ID")
    }
    w.symKeys[id] = key
    return id, nil
}

// AddSymKeyFromPassword generates the key from password, stores it, and returns its id.
func (w *Whisper) AddSymKeyFromPassword(password string) (string, error) {
    id, err := GenerateRandomID()
    if err != nil {
        return "", fmt.Errorf("failed to generate ID: %s", err)
    }
    if w.HasSymKey(id) {
        return "", fmt.Errorf("failed to generate unique ID")
    }

    derived, err := deriveKeyMaterial([]byte(password), EnvelopeVersion)
    if err != nil {
        return "", err
    }

    w.keyMu.Lock()
    defer w.keyMu.Unlock()

    // double check is necessary, because deriveKeyMaterial() is very slow
    if w.symKeys[id] != nil {
        return "", fmt.Errorf("critical error: failed to generate unique ID")
    }
    w.symKeys[id] = derived
    return id, nil
}

// HasSymKey returns true if there is a key associated with the given id.
// Otherwise returns false.
func (w *Whisper) HasSymKey(id string) bool {
    w.keyMu.RLock()
    defer w.keyMu.RUnlock()
    return w.symKeys[id] != nil
}

// DeleteSymKey deletes the key associated with the name string if it exists.
func (w *Whisper) DeleteSymKey(id string) bool {
    w.keyMu.Lock()
    defer w.keyMu.Unlock()
    if w.symKeys[id] != nil {
        delete(w.symKeys, id)
        return true
    }
    return false
}

// GetSymKey returns the symmetric key associated with the given id.
func (w *Whisper) GetSymKey(id string) ([]byte, error) {
    w.keyMu.RLock()
    defer w.keyMu.RUnlock()
    if w.symKeys[id] != nil {
        return w.symKeys[id], nil
    }
    return nil, fmt.Errorf("non-existent key ID")
}

// Subscribe installs a new message handler used for filtering, decrypting
// and subsequent storing of incoming messages.
func (w *Whisper) Subscribe(f *Filter) (string, error) {
    return w.filters.Install(f)
}

// GetFilter returns the filter by id.
func (w *Whisper) GetFilter(id string) *Filter {
    return w.filters.Get(id)
}

// Unsubscribe removes an installed message handler.
func (w *Whisper) Unsubscribe(id string) error {
    ok := w.filters.Uninstall(id)
    if !ok {
        return fmt.Errorf("Unsubscribe: Invalid ID")
    }
    return nil
}

// Send injects a message into the whisper send queue, to be distributed in the
// network in the coming cycles.
func (w *Whisper) Send(envelope *Envelope) error {
    ok, err := w.add(envelope)
    if err != nil {
        return err
    }
    if !ok {
        return fmt.Errorf("failed to add envelope")
    }
    return err
}

// Start implements node.Service, starting the background data propagation thread
// of the Whisper protocol.
func (w *Whisper) Start(*p2p.Server) error {
    log.Info("started whisper v." + ProtocolVersionStr)
    go w.update()

    numCPU := runtime.NumCPU()
    for i := 0; i < numCPU; i++ {
        go w.processQueue()
    }

    return nil
}

// Stop implements node.Service, stopping the background data propagation thread
// of the Whisper protocol.
func (w *Whisper) Stop() error {
    close(w.quit)
    log.Info("whisper stopped")
    return nil
}

// HandlePeer is called by the underlying P2P layer when the whisper sub-protocol
// connection is negotiated.
func (wh *Whisper) HandlePeer(peer *p2p.Peer, rw p2p.MsgReadWriter) error {
    // Create the new peer and start tracking it
    whisperPeer := newPeer(wh, peer, rw)

    wh.peerMu.Lock()
    wh.peers[whisperPeer] = struct{}{}
    wh.peerMu.Unlock()

    defer func() {
        wh.peerMu.Lock()
        delete(wh.peers, whisperPeer)
        wh.peerMu.Unlock()
    }()

    // Run the peer handshake and state updates
    if err := whisperPeer.handshake(); err != nil {
        return err
    }
    whisperPeer.start()
    defer whisperPeer.stop()

    return wh.runMessageLoop(whisperPeer, rw)
}

// runMessageLoop reads and processes inbound messages directly to merge into client-global state.
func (wh *Whisper) runMessageLoop(p *Peer, rw p2p.MsgReadWriter) error {
    for {
        // fetch the next packet
        packet, err := rw.ReadMsg()
        if err != nil {
            log.Warn("message loop", "peer", p.peer.ID(), "err", err)
            return err
        }
        if packet.Size > wh.MaxMessageSize() {
            log.Warn("oversized message received", "peer", p.peer.ID())
            return errors.New("oversized message received")
        }

        switch packet.Code {
        case statusCode:
            // this should not happen, but no need to panic; just ignore this message.
            log.Warn("unxepected status message received", "peer", p.peer.ID())
        case messagesCode:
            // decode the contained envelopes
            var envelope Envelope
            if err := packet.Decode(&envelope); err != nil {
                log.Warn("failed to decode envelope, peer will be disconnected", "peer", p.peer.ID(), "err", err)
                return errors.New("invalid envelope")
            }
            cached, err := wh.add(&envelope)
            if err != nil {
                log.Warn("bad envelope received, peer will be disconnected", "peer", p.peer.ID(), "err", err)
                return errors.New("invalid envelope")
            }
            if cached {
                p.mark(&envelope)
            }
        case p2pCode:
            // peer-to-peer message, sent directly to peer bypassing PoW checks, etc.
            // this message is not supposed to be forwarded to other peers, and
            // therefore might not satisfy the PoW, expiry and other requirements.
            // these messages are only accepted from the trusted peer.
            if p.trusted {
                var envelope Envelope
                if err := packet.Decode(&envelope); err != nil {
                    log.Warn("failed to decode direct message, peer will be disconnected", "peer", p.peer.ID(), "err", err)
                    return errors.New("invalid direct message")
                }
                wh.postEvent(&envelope, true)
            }
        case p2pRequestCode:
            // Must be processed if mail server is implemented. Otherwise ignore.
            if wh.mailServer != nil {
                var request Envelope
                if err := packet.Decode(&request); err != nil {
                    log.Warn("failed to decode p2p request message, peer will be disconnected", "peer", p.peer.ID(), "err", err)
                    return errors.New("invalid p2p request")
                }
                wh.mailServer.DeliverMail(p, &request)
            }
        default:
            // New message types might be implemented in the future versions of Whisper.
            // For forward compatibility, just ignore.
        }

        packet.Discard()
    }
}

// add inserts a new envelope into the message pool to be distributed within the
// whisper network. It also inserts the envelope into the expiration pool at the
// appropriate time-stamp. In case of error, connection should be dropped.
func (wh *Whisper) add(envelope *Envelope) (bool, error) {
    now := uint32(time.Now().Unix())
    sent := envelope.Expiry - envelope.TTL

    if sent > now {
        if sent-SynchAllowance > now {
            return false, fmt.Errorf("envelope created in the future [%x]", envelope.Hash())
        } else {
            // recalculate PoW, adjusted for the time difference, plus one second for latency
            envelope.calculatePoW(sent - now + 1)
        }
    }

    if envelope.Expiry < now {
        if envelope.Expiry+SynchAllowance*2 < now {
            return false, fmt.Errorf("very old message")
        } else {
            log.Debug("expired envelope dropped", "hash", envelope.Hash().Hex())
            return false, nil // drop envelope without error
        }
    }

    if uint32(envelope.size()) > wh.MaxMessageSize() {
        return false, fmt.Errorf("huge messages are not allowed [%x]", envelope.Hash())
    }

    if len(envelope.Version) > 4 {
        return false, fmt.Errorf("oversized version [%x]", envelope.Hash())
    }

    aesNonceSize := len(envelope.AESNonce)
    if aesNonceSize != 0 && aesNonceSize != AESNonceLength {
        // the standard AES GCM nonce size is 12 bytes,
        // but constant gcmStandardNonceSize cannot be accessed (not exported)
        return false, fmt.Errorf("wrong size of AESNonce: %d bytes [env: %x]", aesNonceSize, envelope.Hash())
    }

    if envelope.PoW() < wh.MinPow() {
        log.Debug("envelope with low PoW dropped", "PoW", envelope.PoW(), "hash", envelope.Hash().Hex())
        return false, nil // drop envelope without error
    }

    hash := envelope.Hash()

    wh.poolMu.Lock()
    _, alreadyCached := wh.envelopes[hash]
    if !alreadyCached {
        wh.envelopes[hash] = envelope
        if wh.expirations[envelope.Expiry] == nil {
            wh.expirations[envelope.Expiry] = set.NewNonTS()
        }
        if !wh.expirations[envelope.Expiry].Has(hash) {
            wh.expirations[envelope.Expiry].Add(hash)
        }
    }
    wh.poolMu.Unlock()

    if alreadyCached {
        log.Trace("whisper envelope already cached", "hash", envelope.Hash().Hex())
    } else {
        log.Trace("cached whisper envelope", "hash", envelope.Hash().Hex())
        wh.statsMu.Lock()
        wh.stats.memoryUsed += envelope.size()
        wh.statsMu.Unlock()
        wh.postEvent(envelope, false) // notify the local node about the new message
        if wh.mailServer != nil {
            wh.mailServer.Archive(envelope)
        }
    }
    return true, nil
}

// postEvent queues the message for further processing.
func (w *Whisper) postEvent(envelope *Envelope, isP2P bool) {
    // if the version of incoming message is higher than
    // currently supported version, we can not decrypt it,
    // and therefore just ignore this message
    if envelope.Ver() <= EnvelopeVersion {
        if isP2P {
            w.p2pMsgQueue <- envelope
        } else {
            w.checkOverflow()
            w.messageQueue <- envelope
        }
    }
}

// checkOverflow checks if message queue overflow occurs and reports it if necessary.
func (w *Whisper) checkOverflow() {
    queueSize := len(w.messageQueue)

    if queueSize == messageQueueLimit {
        if !w.Overflow() {
            w.settings.Store(overflowIdx, true)
            log.Warn("message queue overflow")
        }
    } else if queueSize <= messageQueueLimit/2 {
        if w.Overflow() {
            w.settings.Store(overflowIdx, false)
            log.Warn("message queue overflow fixed (back to normal)")
        }
    }
}

// processQueue delivers the messages to the watchers during the lifetime of the whisper node.
func (w *Whisper) processQueue() {
    var e *Envelope
    for {
        select {
        case <-w.quit:
            return

        case e = <-w.messageQueue:
            w.filters.NotifyWatchers(e, false)

        case e = <-w.p2pMsgQueue:
            w.filters.NotifyWatchers(e, true)
        }
    }
}

// update loops until the lifetime of the whisper node, updating its internal
// state by expiring stale messages from the pool.
func (w *Whisper) update() {
    // Start a ticker to check for expirations
    expire := time.NewTicker(expirationCycle)

    // Repeat updates until termination is requested
    for {
        select {
        case <-expire.C:
            w.expire()

        case <-w.quit:
            return
        }
    }
}

// expire iterates over all the expiration timestamps, removing all stale
// messages from the pools.
func (w *Whisper) expire() {
    w.poolMu.Lock()
    defer w.poolMu.Unlock()

    w.statsMu.Lock()
    defer w.statsMu.Unlock()
    w.stats.reset()
    now := uint32(time.Now().Unix())
    for expiry, hashSet := range w.expirations {
        if expiry < now {
            // Dump all expired messages and remove timestamp
            hashSet.Each(func(v interface{}) bool {
                sz := w.envelopes[v.(common.Hash)].size()
                delete(w.envelopes, v.(common.Hash))
                w.stats.messagesCleared++
                w.stats.memoryCleared += sz
                w.stats.memoryUsed -= sz
                return true
            })
            w.expirations[expiry].Clear()
            delete(w.expirations, expiry)
        }
    }
}

// Stats returns the whisper node statistics.
func (w *Whisper) Stats() Statistics {
    w.statsMu.Lock()
    defer w.statsMu.Unlock()

    return w.stats
}

// Envelopes retrieves all the messages currently pooled by the node.
func (w *Whisper) Envelopes() []*Envelope {
    w.poolMu.RLock()
    defer w.poolMu.RUnlock()

    all := make([]*Envelope, 0, len(w.envelopes))
    for _, envelope := range w.envelopes {
        all = append(all, envelope)
    }
    return all
}

// Messages iterates through all currently floating envelopes
// and retrieves all the messages, that this filter could decrypt.
func (w *Whisper) Messages(id string) []*ReceivedMessage {
    result := make([]*ReceivedMessage, 0)
    w.poolMu.RLock()
    defer w.poolMu.RUnlock()

    if filter := w.filters.Get(id); filter != nil {
        for _, env := range w.envelopes {
            msg := filter.processEnvelope(env)
            if msg != nil {
                result = append(result, msg)
            }
        }
    }
    return result
}

// isEnvelopeCached checks if envelope with specific hash has already been received and cached.
func (w *Whisper) isEnvelopeCached(hash common.Hash) bool {
    w.poolMu.Lock()
    defer w.poolMu.Unlock()

    _, exist := w.envelopes[hash]
    return exist
}

// reset resets the node's statistics after each expiry cycle.
func (s *Statistics) reset() {
    s.cycles++
    s.totalMessagesCleared += s.messagesCleared

    s.memoryCleared = 0
    s.messagesCleared = 0
}

// ValidatePublicKey checks the format of the given public key.
func ValidatePublicKey(k *ecdsa.PublicKey) bool {
    return k != nil && k.X != nil && k.Y != nil && k.X.Sign() != 0 && k.Y.Sign() != 0
}

// validatePrivateKey checks the format of the given private key.
func validatePrivateKey(k *ecdsa.PrivateKey) bool {
    if k == nil || k.D == nil || k.D.Sign() == 0 {
        return false
    }
    return ValidatePublicKey(&k.PublicKey)
}

// validateSymmetricKey returns false if the key contains all zeros
func validateSymmetricKey(k []byte) bool {
    return len(k) > 0 && !containsOnlyZeros(k)
}

// containsOnlyZeros checks if the data contain only zeros.
func containsOnlyZeros(data []byte) bool {
    for _, b := range data {
        if b != 0 {
            return false
        }
    }
    return true
}

// bytesToUintLittleEndian converts the slice to 64-bit unsigned integer.
func bytesToUintLittleEndian(b []byte) (res uint64) {
    mul := uint64(1)
    for i := 0; i < len(b); i++ {
        res += uint64(b[i]) * mul
        mul *= 256
    }
    return res
}

// BytesToUintBigEndian converts the slice to 64-bit unsigned integer.
func BytesToUintBigEndian(b []byte) (res uint64) {
    for i := 0; i < len(b); i++ {
        res *= 256
        res += uint64(b[i])
    }
    return res
}

// deriveKeyMaterial derives symmetric key material from the key or password.
// pbkdf2 is used for security, in case people use password instead of randomly generated keys.
func deriveKeyMaterial(key []byte, version uint64) (derivedKey []byte, err error) {
    if version == 0 {
        // kdf should run no less than 0.1 seconds on average compute,
        // because it's a once in a session experience
        derivedKey := pbkdf2.Key(key, nil, 65356, aesKeyLength, sha256.New)
        return derivedKey, nil
    } else {
        return nil, unknownVersionError(version)
    }
}

// GenerateRandomID generates a random string, which is then returned to be used as a key id
func GenerateRandomID() (id string, err error) {
    buf := make([]byte, keyIdSize)
    _, err = crand.Read(buf)
    if err != nil {
        return "", err
    }
    if !validateSymmetricKey(buf) {
        return "", fmt.Errorf("error in generateRandomID: crypto/rand failed to generate random data")
    }
    id = common.Bytes2Hex(buf)
    return id, err
}