lnd.xprv/brontide/conn.go

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package brontide
import (
"bytes"
"io"
"math"
"net"
"time"
"github.com/btcsuite/btcd/btcec"
"github.com/lightningnetwork/lnd/keychain"
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"github.com/lightningnetwork/lnd/lnwire"
"github.com/lightningnetwork/lnd/tor"
)
// Conn is an implementation of net.Conn which enforces an authenticated key
// exchange and message encryption protocol dubbed "Brontide" after initial TCP
// connection establishment. In the case of a successful handshake, all
// messages sent via the .Write() method are encrypted with an AEAD cipher
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// along with an encrypted length-prefix. See the Machine struct for
// additional details w.r.t to the handshake and encryption scheme.
type Conn struct {
conn net.Conn
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noise *Machine
readBuf bytes.Buffer
}
// A compile-time assertion to ensure that Conn meets the net.Conn interface.
var _ net.Conn = (*Conn)(nil)
// Dial attempts to establish an encrypted+authenticated connection with the
// remote peer located at address which has remotePub as its long-term static
// public key. In the case of a handshake failure, the connection is closed and
// a non-nil error is returned.
func Dial(local keychain.SingleKeyECDH, netAddr *lnwire.NetAddress,
timeout time.Duration, dialer tor.DialFunc) (*Conn, error) {
ipAddr := netAddr.Address.String()
var conn net.Conn
var err error
conn, err = dialer("tcp", ipAddr, timeout)
if err != nil {
return nil, err
}
b := &Conn{
conn: conn,
noise: NewBrontideMachine(true, local, netAddr.IdentityKey),
}
// Initiate the handshake by sending the first act to the receiver.
actOne, err := b.noise.GenActOne()
if err != nil {
b.conn.Close()
return nil, err
}
if _, err := conn.Write(actOne[:]); err != nil {
b.conn.Close()
return nil, err
}
// We'll ensure that we get ActTwo from the remote peer in a timely
// manner. If they don't respond within 1s, then we'll kill the
// connection.
err = conn.SetReadDeadline(time.Now().Add(handshakeReadTimeout))
if err != nil {
b.conn.Close()
return nil, err
}
// If the first act was successful (we know that address is actually
// remotePub), then read the second act after which we'll be able to
// send our static public key to the remote peer with strong forward
// secrecy.
var actTwo [ActTwoSize]byte
if _, err := io.ReadFull(conn, actTwo[:]); err != nil {
b.conn.Close()
return nil, err
}
if err := b.noise.RecvActTwo(actTwo); err != nil {
b.conn.Close()
return nil, err
}
// Finally, complete the handshake by sending over our encrypted static
// key and execute the final ECDH operation.
actThree, err := b.noise.GenActThree()
if err != nil {
b.conn.Close()
return nil, err
}
if _, err := conn.Write(actThree[:]); err != nil {
b.conn.Close()
return nil, err
}
// We'll reset the deadline as it's no longer critical beyond the
// initial handshake.
err = conn.SetReadDeadline(time.Time{})
if err != nil {
b.conn.Close()
return nil, err
}
return b, nil
}
// ReadNextMessage uses the connection in a message-oriented manner, instructing
// it to read the next _full_ message with the brontide stream. This function
// will block until the read of the header and body succeeds.
//
// NOTE: This method SHOULD NOT be used in the case that the connection may be
// adversarial and induce long delays. If the caller needs to set read deadlines
// appropriately, it is preferred that they use the split ReadNextHeader and
// ReadNextBody methods so that the deadlines can be set appropriately on each.
func (c *Conn) ReadNextMessage() ([]byte, error) {
return c.noise.ReadMessage(c.conn)
}
// ReadNextHeader uses the connection to read the next header from the brontide
// stream. This function will block until the read of the header succeeds and
// return the packet length (including MAC overhead) that is expected from the
// subsequent call to ReadNextBody.
func (c *Conn) ReadNextHeader() (uint32, error) {
return c.noise.ReadHeader(c.conn)
}
// ReadNextBody uses the connection to read the next message body from the
// brontide stream. This function will block until the read of the body succeeds
// and return the decrypted payload. The provided buffer MUST be the packet
// length returned by the preceding call to ReadNextHeader.
func (c *Conn) ReadNextBody(buf []byte) ([]byte, error) {
return c.noise.ReadBody(c.conn, buf)
}
// Read reads data from the connection. Read can be made to time out and
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// return an Error with Timeout() == true after a fixed time limit; see
// SetDeadline and SetReadDeadline.
//
// Part of the net.Conn interface.
func (c *Conn) Read(b []byte) (n int, err error) {
// In order to reconcile the differences between the record abstraction
// of our AEAD connection, and the stream abstraction of TCP, we
// maintain an intermediate read buffer. If this buffer becomes
// depleted, then we read the next record, and feed it into the
// buffer. Otherwise, we read directly from the buffer.
if c.readBuf.Len() == 0 {
plaintext, err := c.noise.ReadMessage(c.conn)
if err != nil {
return 0, err
}
if _, err := c.readBuf.Write(plaintext); err != nil {
return 0, err
}
}
return c.readBuf.Read(b)
}
// Write writes data to the connection. Write can be made to time out and
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// return an Error with Timeout() == true after a fixed time limit; see
// SetDeadline and SetWriteDeadline.
//
// Part of the net.Conn interface.
func (c *Conn) Write(b []byte) (n int, err error) {
// If the message doesn't require any chunking, then we can go ahead
// with a single write.
if len(b) <= math.MaxUint16 {
err = c.noise.WriteMessage(b)
if err != nil {
return 0, err
}
return c.noise.Flush(c.conn)
}
// If we need to split the message into fragments, then we'll write
// chunks which maximize usage of the available payload.
chunkSize := math.MaxUint16
bytesToWrite := len(b)
bytesWritten := 0
for bytesWritten < bytesToWrite {
// If we're on the last chunk, then truncate the chunk size as
// necessary to avoid an out-of-bounds array memory access.
if bytesWritten+chunkSize > len(b) {
chunkSize = len(b) - bytesWritten
}
// Slice off the next chunk to be written based on our running
// counter and next chunk size.
chunk := b[bytesWritten : bytesWritten+chunkSize]
if err := c.noise.WriteMessage(chunk); err != nil {
return bytesWritten, err
}
n, err := c.noise.Flush(c.conn)
bytesWritten += n
if err != nil {
return bytesWritten, err
}
}
return bytesWritten, nil
}
// WriteMessage encrypts and buffers the next message p for the connection. The
// ciphertext of the message is prepended with an encrypt+auth'd length which
// must be used as the AD to the AEAD construction when being decrypted by the
// other side.
//
// NOTE: This DOES NOT write the message to the wire, it should be followed by a
// call to Flush to ensure the message is written.
func (c *Conn) WriteMessage(b []byte) error {
return c.noise.WriteMessage(b)
}
// Flush attempts to write a message buffered using WriteMessage to the
// underlying connection. If no buffered message exists, this will result in a
// NOP. Otherwise, it will continue to write the remaining bytes, picking up
// where the byte stream left off in the event of a partial write. The number of
// bytes returned reflects the number of plaintext bytes in the payload, and
// does not account for the overhead of the header or MACs.
//
// NOTE: It is safe to call this method again iff a timeout error is returned.
func (c *Conn) Flush() (int, error) {
return c.noise.Flush(c.conn)
}
// Close closes the connection. Any blocked Read or Write operations will be
// unblocked and return errors.
//
// Part of the net.Conn interface.
func (c *Conn) Close() error {
// TODO(roasbeef): reset brontide state?
return c.conn.Close()
}
// LocalAddr returns the local network address.
//
// Part of the net.Conn interface.
func (c *Conn) LocalAddr() net.Addr {
return c.conn.LocalAddr()
}
// RemoteAddr returns the remote network address.
//
// Part of the net.Conn interface.
func (c *Conn) RemoteAddr() net.Addr {
return c.conn.RemoteAddr()
}
// SetDeadline sets the read and write deadlines associated with the
// connection. It is equivalent to calling both SetReadDeadline and
// SetWriteDeadline.
//
// Part of the net.Conn interface.
func (c *Conn) SetDeadline(t time.Time) error {
return c.conn.SetDeadline(t)
}
// SetReadDeadline sets the deadline for future Read calls. A zero value for t
// means Read will not time out.
//
// Part of the net.Conn interface.
func (c *Conn) SetReadDeadline(t time.Time) error {
return c.conn.SetReadDeadline(t)
}
// SetWriteDeadline sets the deadline for future Write calls. Even if write
// times out, it may return n > 0, indicating that some of the data was
// successfully written. A zero value for t means Write will not time out.
//
// Part of the net.Conn interface.
func (c *Conn) SetWriteDeadline(t time.Time) error {
return c.conn.SetWriteDeadline(t)
}
// RemotePub returns the remote peer's static public key.
func (c *Conn) RemotePub() *btcec.PublicKey {
return c.noise.remoteStatic
}
// LocalPub returns the local peer's static public key.
func (c *Conn) LocalPub() *btcec.PublicKey {
return c.noise.localStatic.PubKey()
}