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transport.go
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transport.go
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package transport
import (
"crypto/hmac"
"crypto/rand"
"crypto/sha256"
"crypto/subtle"
"errors"
"hash"
"io"
"strconv"
"time"
"code.google.com/p/go.crypto/curve25519"
"code.google.com/p/go.crypto/nacl/secretbox"
"code.google.com/p/goprotobuf/proto"
pond "github.com/agl/pond/protos"
)
// blockSize is the size of the blocks of data that we'll send and receive when
// working in streaming mode. Each block is prefixed by two length bytes (which
// aren't counted in blockSize) and includes secretbox.Overhead bytes of MAC
// tag (which are).
const blockSize = 4096 - 2
type Conn struct {
conn io.ReadWriteCloser
isServer bool
identity, identityPublic [32]byte
Peer [32]byte
writeKey, readKey [32]byte
writeKeyValid, readKeyValid bool
writeSequence, readSequence [24]byte
// readBuffer is used to receive bytes from the network when this Conn
// is used to stream data.
readBuffer []byte
// decryptBuffer is used to store decrypted payloads when this Conn is
// used to stream data and the caller's buffer isn't large enough to
// decrypt into directly.
decryptBuffer []byte
// readPending aliases into decryptBuffer when a partial decryption had
// to be returned to a caller because of buffer size limitations.
readPending []byte
// writeBuffer is used to hold encrypted payloads when this Conn is
// used for streaming data.
writeBuffer []byte
}
func NewServer(conn io.ReadWriteCloser, identity *[32]byte) *Conn {
c := &Conn{
conn: conn,
isServer: true,
}
copy(c.identity[:], identity[:])
return c
}
func NewClient(conn io.ReadWriteCloser, myIdentity, myIdentityPublic, serverPublic *[32]byte) *Conn {
c := &Conn{
conn: conn,
}
copy(c.identity[:], myIdentity[:])
copy(c.identityPublic[:], myIdentityPublic[:])
copy(c.Peer[:], serverPublic[:])
return c
}
func incSequence(seq *[24]byte) {
n := uint32(1)
for i := 0; i < 8; i++ {
n += uint32(seq[i])
seq[i] = byte(n)
n >>= 8
}
}
type deadlineable interface {
SetDeadline(time.Time)
}
func (c *Conn) SetDeadline(t time.Time) {
if d, ok := c.conn.(deadlineable); ok {
d.SetDeadline(t)
}
}
func (c *Conn) Read(out []byte) (n int, err error) {
if len(c.readPending) > 0 {
n = copy(out, c.readPending)
c.readPending = c.readPending[n:]
return
}
if c.readBuffer == nil {
c.readBuffer = make([]byte, blockSize+2)
}
if _, err := io.ReadFull(c.conn, c.readBuffer[:2]); err != nil {
return 0, err
}
n = int(c.readBuffer[0]) | int(c.readBuffer[1])<<8
if n > len(c.readBuffer) {
return 0, errors.New("transport: peer's message too large for Read")
}
if _, err := io.ReadFull(c.conn, c.readBuffer[:n]); err != nil {
return 0, err
}
var ok bool
if len(out) >= n-secretbox.Overhead {
// We can decrypt directly into the output buffer.
out, ok = secretbox.Open(out[:0], c.readBuffer[:n], &c.readSequence, &c.readKey)
n = len(out)
} else {
// We need to decrypt into a side buffer and copy a prefix of
// the result into the caller's buffer.
c.decryptBuffer, ok = secretbox.Open(c.decryptBuffer[:0], c.readBuffer[:n], &c.readSequence, &c.readKey)
n = copy(out, c.decryptBuffer)
c.readPending = c.decryptBuffer[n:]
}
incSequence(&c.readSequence)
if !ok {
c.readPending = c.readPending[:0]
return 0, errors.New("transport: bad MAC")
}
return
}
func (c *Conn) Write(buf []byte) (n int, err error) {
if c.writeBuffer == nil {
c.writeBuffer = make([]byte, blockSize+2)
}
for len(buf) > 0 {
m := len(buf)
if m > blockSize-secretbox.Overhead {
m = blockSize - secretbox.Overhead
}
l := len(secretbox.Seal(c.writeBuffer[2:2], buf[:m], &c.writeSequence, &c.writeKey))
c.writeBuffer[0] = byte(l)
c.writeBuffer[1] = byte(l >> 8)
if _, err = c.conn.Write(c.writeBuffer[:2+l]); err != nil {
return n, err
}
n += m
buf = buf[m:]
incSequence(&c.writeSequence)
}
return
}
func (c *Conn) ReadProto(out proto.Message) error {
buf := make([]byte, pond.TransportSize+2+secretbox.Overhead)
n, err := c.read(buf)
if err != nil {
return err
}
if n != pond.TransportSize+2 {
return errors.New("transport: message wrong length")
}
n = int(buf[0]) | int(buf[1])<<8
buf = buf[2:]
if n > len(buf) {
return errors.New("transport: corrupt message")
}
return proto.Unmarshal(buf[:n], out)
}
func (c *Conn) WriteProto(msg proto.Message) error {
data, err := proto.Marshal(msg)
if err != nil {
return err
}
if len(data) > pond.TransportSize {
return errors.New("transport: message too large")
}
buf := make([]byte, pond.TransportSize+2)
buf[0] = byte(len(data))
buf[1] = byte(len(data) >> 8)
copy(buf[2:], data)
_, err = c.write(buf)
return err
}
func (c *Conn) Close() error {
if !c.isServer {
if _, err := c.write(nil); err != nil {
return err
}
}
return c.conn.Close()
}
func (c *Conn) WaitForClose() error {
if !c.isServer {
panic("non-server waited for connection close")
}
n, err := c.read(make([]byte, 128))
if err != nil {
return err
}
if n != 0 {
return errors.New("transport: non-close message received when expecting close")
}
return nil
}
func (c *Conn) read(data []byte) (n int, err error) {
var lengthBytes [2]byte
if _, err := io.ReadFull(c.conn, lengthBytes[:]); err != nil {
return 0, err
}
theirLength := int(lengthBytes[0]) + int(lengthBytes[1])<<8
if theirLength > len(data) {
return 0, errors.New("tranport: given buffer too small (" + strconv.Itoa(len(data)) + " vs " + strconv.Itoa(theirLength) + ")")
}
data = data[:theirLength]
if _, err := io.ReadFull(c.conn, data); err != nil {
return 0, err
}
decrypted, err := c.decrypt(data)
if err != nil {
return 0, err
}
copy(data, decrypted)
return len(decrypted), nil
}
func (c *Conn) write(data []byte) (n int, err error) {
encrypted := c.encrypt(data)
var lengthBytes [2]byte
lengthBytes[0] = byte(len(encrypted))
lengthBytes[1] = byte(len(encrypted) >> 8)
if _, err := c.conn.Write(lengthBytes[:]); err != nil {
return 0, err
}
if _, err := c.conn.Write(encrypted); err != nil {
return 0, err
}
return len(data), nil
}
func (c *Conn) encrypt(data []byte) []byte {
if !c.writeKeyValid {
return data
}
encrypted := secretbox.Seal(nil, data, &c.writeSequence, &c.writeKey)
incSequence(&c.writeSequence)
return encrypted
}
func (c *Conn) decrypt(data []byte) ([]byte, error) {
if !c.readKeyValid {
return data, nil
}
decrypted, ok := secretbox.Open(nil, data, &c.readSequence, &c.readKey)
incSequence(&c.readSequence)
if !ok {
return nil, errors.New("transport: bad MAC")
}
return decrypted, nil
}
var serverKeysMagic = []byte("server keys\x00")
var clientKeysMagic = []byte("client keys\x00")
func (c *Conn) setupKeys(ephemeralShared *[32]byte) {
var writeMagic, readMagic []byte
if c.isServer {
writeMagic, readMagic = serverKeysMagic, clientKeysMagic
} else {
writeMagic, readMagic = clientKeysMagic, serverKeysMagic
}
h := sha256.New()
h.Write(writeMagic)
h.Write(ephemeralShared[:])
h.Sum(c.writeKey[:0])
c.writeKeyValid = true
h.Reset()
h.Write(readMagic)
h.Write(ephemeralShared[:])
h.Sum(c.readKey[:0])
c.readKeyValid = true
}
var serverProofMagic = []byte("server proof\x00")
var clientProofMagic = []byte("client proof\x00")
var shortMessageError = errors.New("transport: received short handshake message")
func (c *Conn) Handshake() error {
var ephemeralPrivate, ephemeralPublic, ephemeralShared [32]byte
if _, err := io.ReadFull(rand.Reader, ephemeralPrivate[:]); err != nil {
return err
}
curve25519.ScalarBaseMult(&ephemeralPublic, &ephemeralPrivate)
if _, err := c.write(ephemeralPublic[:]); err != nil {
return err
}
var theirEphemeralPublic [32]byte
if n, err := c.read(theirEphemeralPublic[:]); err != nil || n != len(theirEphemeralPublic) {
if err == nil {
err = shortMessageError
}
return err
}
handshakeHash := sha256.New()
if c.isServer {
handshakeHash.Write(theirEphemeralPublic[:])
handshakeHash.Write(ephemeralPublic[:])
} else {
handshakeHash.Write(ephemeralPublic[:])
handshakeHash.Write(theirEphemeralPublic[:])
}
curve25519.ScalarMult(&ephemeralShared, &ephemeralPrivate, &theirEphemeralPublic)
c.setupKeys(&ephemeralShared)
if c.isServer {
return c.handshakeServer(handshakeHash, &theirEphemeralPublic)
}
return c.handshakeClient(handshakeHash, &ephemeralPrivate)
}
func (c *Conn) handshakeClient(handshakeHash hash.Hash, ephemeralPrivate *[32]byte) error {
var ephemeralIdentityShared [32]byte
curve25519.ScalarMult(&ephemeralIdentityShared, ephemeralPrivate, &c.Peer)
digest := handshakeHash.Sum(nil)
h := hmac.New(sha256.New, ephemeralIdentityShared[:])
h.Write(serverProofMagic)
h.Write(digest)
digest = h.Sum(digest[:0])
digestReceived := make([]byte, len(digest)+secretbox.Overhead)
n, err := c.read(digestReceived)
if err != nil {
return err
}
if n != len(digest) {
return shortMessageError
}
digestReceived = digestReceived[:n]
if subtle.ConstantTimeCompare(digest, digestReceived) != 1 {
return errors.New("transport: server identity incorrect")
}
var identityShared [32]byte
curve25519.ScalarMult(&identityShared, &c.identity, &c.Peer)
handshakeHash.Write(digest)
digest = handshakeHash.Sum(digest[:0])
h = hmac.New(sha256.New, identityShared[:])
h.Write(clientProofMagic)
h.Write(digest)
finalMessage := make([]byte, 32+sha256.Size)
copy(finalMessage, c.identityPublic[:])
h.Sum(finalMessage[32:32])
if _, err := c.write(finalMessage); err != nil {
return err
}
return nil
}
func (c *Conn) handshakeServer(handshakeHash hash.Hash, theirEphemeralPublic *[32]byte) error {
var ephemeralIdentityShared [32]byte
curve25519.ScalarMult(&ephemeralIdentityShared, &c.identity, theirEphemeralPublic)
digest := handshakeHash.Sum(nil)
h := hmac.New(sha256.New, ephemeralIdentityShared[:])
h.Write(serverProofMagic)
h.Write(digest)
digest = h.Sum(digest[:0])
if _, err := c.write(digest); err != nil {
return err
}
handshakeHash.Write(digest)
digest = handshakeHash.Sum(digest[:0])
finalMessage := make([]byte, 32+sha256.Size+secretbox.Overhead)
n, err := c.read(finalMessage)
if err != nil {
return err
}
if n != 32+sha256.Size {
return shortMessageError
}
finalMessage = finalMessage[:n]
copy(c.Peer[:], finalMessage[:32])
var identityShared [32]byte
curve25519.ScalarMult(&identityShared, &c.identity, &c.Peer)
h = hmac.New(sha256.New, identityShared[:])
h.Write(clientProofMagic)
h.Write(digest)
digest = h.Sum(digest[:0])
if subtle.ConstantTimeCompare(digest, finalMessage[32:]) != 1 {
return errors.New("transport: bad proof from client")
}
return nil
}