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package conn
import (
"bytes"
crand "crypto/rand"
"crypto/sha256"
"encoding/binary"
"errors"
"io"
"net"
"time"
"golang.org/x/crypto/chacha20poly1305"
"golang.org/x/crypto/curve25519"
"golang.org/x/crypto/nacl/box"
"github.com/tendermint/tendermint/crypto"
cmn "github.com/tendermint/tendermint/libs/common"
"golang.org/x/crypto/hkdf"
)
// 4 + 1024 == 1028 total frame size
const dataLenSize = 4
const dataMaxSize = 1024
const totalFrameSize = dataMaxSize + dataLenSize
const aeadSizeOverhead = 16 // overhead of poly 1305 authentication tag
const aeadKeySize = chacha20poly1305.KeySize
const aeadNonceSize = chacha20poly1305.NonceSize
// SecretConnection implements net.conn.
// It is an implementation of the STS protocol.
// Note we do not (yet) assume that a remote peer's pubkey
// is known ahead of time, and thus we are technically
// still vulnerable to MITM. (TODO!)
// See docs/sts-final.pdf for more info
type SecretConnection struct {
conn io.ReadWriteCloser
recvBuffer []byte
recvNonce *[aeadNonceSize]byte
sendNonce *[aeadNonceSize]byte
recvSecret *[aeadKeySize]byte
sendSecret *[aeadKeySize]byte
remPubKey crypto.PubKey
}
// MakeSecretConnection performs handshake and returns a new authenticated
// SecretConnection.
// Returns nil if there is an error in handshake.
// Caller should call conn.Close()
// See docs/sts-final.pdf for more information.
func MakeSecretConnection(conn io.ReadWriteCloser, locPrivKey crypto.PrivKey) (*SecretConnection, error) {
locPubKey := locPrivKey.PubKey()
// Generate ephemeral keys for perfect forward secrecy.
locEphPub, locEphPriv := genEphKeys()
// Write local ephemeral pubkey and receive one too.
// NOTE: every 32-byte string is accepted as a Curve25519 public key
// (see DJB's Curve25519 paper: http://cr.yp.to/ecdh/curve25519-20060209.pdf)
remEphPub, err := shareEphPubKey(conn, locEphPub)
if err != nil {
return nil, err
}
// Sort by lexical order.
loEphPub, _ := sort32(locEphPub, remEphPub)
// Check if the local ephemeral public key
// was the least, lexicographically sorted.
locIsLeast := bytes.Equal(locEphPub[:], loEphPub[:])
// Compute common diffie hellman secret using X25519.
dhSecret := computeDHSecret(remEphPub, locEphPriv)
// generate the secret used for receiving, sending, challenge via hkdf-sha2 on dhSecret
recvSecret, sendSecret, challenge := deriveSecretAndChallenge(dhSecret, locIsLeast)
// Construct SecretConnection.
sc := &SecretConnection{
conn: conn,
recvBuffer: nil,
recvNonce: new([aeadNonceSize]byte),
sendNonce: new([aeadNonceSize]byte),
recvSecret: recvSecret,
sendSecret: sendSecret,
}
// Sign the challenge bytes for authentication.
locSignature := signChallenge(challenge, locPrivKey)
// Share (in secret) each other's pubkey & challenge signature
authSigMsg, err := shareAuthSignature(sc, locPubKey, locSignature)
if err != nil {
return nil, err
}
remPubKey, remSignature := authSigMsg.Key, authSigMsg.Sig
if !remPubKey.VerifyBytes(challenge[:], remSignature) {
return nil, errors.New("Challenge verification failed")
}
// We've authorized.
sc.remPubKey = remPubKey
return sc, nil
}
// RemotePubKey returns authenticated remote pubkey
func (sc *SecretConnection) RemotePubKey() crypto.PubKey {
return sc.remPubKey
}
// Writes encrypted frames of `sealedFrameSize`
// CONTRACT: data smaller than dataMaxSize is read atomically.
func (sc *SecretConnection) Write(data []byte) (n int, err error) {
for 0 < len(data) {
var frame = make([]byte, totalFrameSize)
var chunk []byte
if dataMaxSize < len(data) {
chunk = data[:dataMaxSize]
data = data[dataMaxSize:]
} else {
chunk = data
data = nil
}
chunkLength := len(chunk)
binary.LittleEndian.PutUint32(frame, uint32(chunkLength))
copy(frame[dataLenSize:], chunk)
aead, err := chacha20poly1305.New(sc.sendSecret[:])
if err != nil {
return n, errors.New("Invalid SecretConnection Key")
}
// encrypt the frame
var sealedFrame = make([]byte, aeadSizeOverhead+totalFrameSize)
aead.Seal(sealedFrame[:0], sc.sendNonce[:], frame, nil)
incrNonce(sc.sendNonce)
// end encryption
_, err = sc.conn.Write(sealedFrame)
if err != nil {
return n, err
}
n += len(chunk)
}
return
}
// CONTRACT: data smaller than dataMaxSize is read atomically.
func (sc *SecretConnection) Read(data []byte) (n int, err error) {
if 0 < len(sc.recvBuffer) {
n = copy(data, sc.recvBuffer)
sc.recvBuffer = sc.recvBuffer[n:]
return
}
aead, err := chacha20poly1305.New(sc.recvSecret[:])
if err != nil {
return n, errors.New("Invalid SecretConnection Key")
}
sealedFrame := make([]byte, totalFrameSize+aeadSizeOverhead)
_, err = io.ReadFull(sc.conn, sealedFrame)
if err != nil {
return
}
// decrypt the frame
var frame = make([]byte, totalFrameSize)
_, err = aead.Open(frame[:0], sc.recvNonce[:], sealedFrame, nil)
if err != nil {
return n, errors.New("Failed to decrypt SecretConnection")
}
incrNonce(sc.recvNonce)
// end decryption
var chunkLength = binary.LittleEndian.Uint32(frame) // read the first four bytes
if chunkLength > dataMaxSize {
return 0, errors.New("chunkLength is greater than dataMaxSize")
}
var chunk = frame[dataLenSize : dataLenSize+chunkLength]
n = copy(data, chunk)
sc.recvBuffer = chunk[n:]
return
}
// Implements net.Conn
// nolint
func (sc *SecretConnection) Close() error { return sc.conn.Close() }
func (sc *SecretConnection) LocalAddr() net.Addr { return sc.conn.(net.Conn).LocalAddr() }
func (sc *SecretConnection) RemoteAddr() net.Addr { return sc.conn.(net.Conn).RemoteAddr() }
func (sc *SecretConnection) SetDeadline(t time.Time) error { return sc.conn.(net.Conn).SetDeadline(t) }
func (sc *SecretConnection) SetReadDeadline(t time.Time) error {
return sc.conn.(net.Conn).SetReadDeadline(t)
}
func (sc *SecretConnection) SetWriteDeadline(t time.Time) error {
return sc.conn.(net.Conn).SetWriteDeadline(t)
}
func genEphKeys() (ephPub, ephPriv *[32]byte) {
var err error
ephPub, ephPriv, err = box.GenerateKey(crand.Reader)
if err != nil {
panic("Could not generate ephemeral keypairs")
}
return
}
func shareEphPubKey(conn io.ReadWriteCloser, locEphPub *[32]byte) (remEphPub *[32]byte, err error) {
// Send our pubkey and receive theirs in tandem.
var trs, _ = cmn.Parallel(
func(_ int) (val interface{}, err error, abort bool) {
var _, err1 = cdc.MarshalBinaryWriter(conn, locEphPub)
if err1 != nil {
return nil, err1, true // abort
}
return nil, nil, false
},
func(_ int) (val interface{}, err error, abort bool) {
var _remEphPub [32]byte
var _, err2 = cdc.UnmarshalBinaryReader(conn, &_remEphPub, 1024*1024) // TODO
if err2 != nil {
return nil, err2, true // abort
}
return _remEphPub, nil, false
},
)
// If error:
if trs.FirstError() != nil {
err = trs.FirstError()
return
}
// Otherwise:
var _remEphPub = trs.FirstValue().([32]byte)
return &_remEphPub, nil
}
func deriveSecretAndChallenge(dhSecret *[32]byte, locIsLeast bool) (recvSecret, sendSecret *[aeadKeySize]byte, challenge *[32]byte) {
hash := sha256.New
hkdf := hkdf.New(hash, dhSecret[:], nil, []byte("TENDERMINT_SECRET_CONNECTION_KEY_AND_CHALLENGE_GEN"))
// get enough data for 2 aead keys, and a 32 byte challenge
res := new([2*aeadKeySize + 32]byte)
_, err := io.ReadFull(hkdf, res[:])
if err != nil {
panic(err)
}
challenge = new([32]byte)
recvSecret = new([aeadKeySize]byte)
sendSecret = new([aeadKeySize]byte)
// Use the last 32 bytes as the challenge
copy(challenge[:], res[2*aeadKeySize:2*aeadKeySize+32])
// bytes 0 through aeadKeySize - 1 are one aead key.
// bytes aeadKeySize through 2*aeadKeySize -1 are another aead key.
// which key corresponds to sending and receiving key depends on whether
// the local key is less than the remote key.
if locIsLeast {
copy(recvSecret[:], res[0:aeadKeySize])
copy(sendSecret[:], res[aeadKeySize:aeadKeySize*2])
} else {
copy(sendSecret[:], res[0:aeadKeySize])
copy(recvSecret[:], res[aeadKeySize:aeadKeySize*2])
}
return
}
func computeDHSecret(remPubKey, locPrivKey *[32]byte) (shrKey *[32]byte) {
shrKey = new([32]byte)
curve25519.ScalarMult(shrKey, locPrivKey, remPubKey)
return
}
func sort32(foo, bar *[32]byte) (lo, hi *[32]byte) {
if bytes.Compare(foo[:], bar[:]) < 0 {
lo = foo
hi = bar
} else {
lo = bar
hi = foo
}
return
}
func signChallenge(challenge *[32]byte, locPrivKey crypto.PrivKey) (signature []byte) {
signature, err := locPrivKey.Sign(challenge[:])
// TODO(ismail): let signChallenge return an error instead
if err != nil {
panic(err)
}
return
}
type authSigMessage struct {
Key crypto.PubKey
Sig []byte
}
func shareAuthSignature(sc *SecretConnection, pubKey crypto.PubKey, signature []byte) (recvMsg authSigMessage, err error) {
// Send our info and receive theirs in tandem.
var trs, _ = cmn.Parallel(
func(_ int) (val interface{}, err error, abort bool) {
var _, err1 = cdc.MarshalBinaryWriter(sc, authSigMessage{pubKey, signature})
if err1 != nil {
return nil, err1, true // abort
}
return nil, nil, false
},
func(_ int) (val interface{}, err error, abort bool) {
var _recvMsg authSigMessage
var _, err2 = cdc.UnmarshalBinaryReader(sc, &_recvMsg, 1024*1024) // TODO
if err2 != nil {
return nil, err2, true // abort
}
return _recvMsg, nil, false
},
)
// If error:
if trs.FirstError() != nil {
err = trs.FirstError()
return
}
var _recvMsg = trs.FirstValue().(authSigMessage)
return _recvMsg, nil
}
//--------------------------------------------------------------------------------
// Increment nonce little-endian by 1 with wraparound.
// Due to chacha20poly1305 expecting a 12 byte nonce we do not use the first four
// bytes. We only increment a 64 bit unsigned int in the remaining 8 bytes
// (little-endian in nonce[4:]).
func incrNonce(nonce *[aeadNonceSize]byte) {
counter := binary.LittleEndian.Uint64(nonce[4:])
counter++
binary.LittleEndian.PutUint64(nonce[4:], counter)
}