package conn import ( "bytes" "crypto/cipher" crand "crypto/rand" "crypto/sha256" "crypto/subtle" "encoding/binary" "io" "math" "net" "sync" "time" pool "github.com/libp2p/go-buffer-pool" "github.com/pkg/errors" "golang.org/x/crypto/chacha20poly1305" "golang.org/x/crypto/curve25519" "golang.org/x/crypto/hkdf" "golang.org/x/crypto/nacl/box" "github.com/tendermint/tendermint/crypto" "github.com/tendermint/tendermint/crypto/ed25519" cmn "github.com/tendermint/tendermint/libs/common" ) // 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 var ( ErrSmallOrderRemotePubKey = errors.New("detected low order point from remote peer") ErrSharedSecretIsZero = errors.New("shared secret is all zeroes") ) // SecretConnection implements net.Conn. // It is an implementation of the STS protocol. // See https://github.com/tendermint/tendermint/blob/0.1/docs/sts-final.pdf for // details on the protocol. // // Consumers of the SecretConnection are responsible for authenticating // the remote peer's pubkey against known information, like a nodeID. // Otherwise they are vulnerable to MITM. // (TODO(ismail): see also https://github.com/tendermint/tendermint/issues/3010) type SecretConnection struct { // immutable recvAead cipher.AEAD sendAead cipher.AEAD remPubKey crypto.PubKey conn io.ReadWriteCloser // net.Conn must be thread safe: // https://golang.org/pkg/net/#Conn. // Since we have internal mutable state, // we need mtxs. But recv and send states // are independent, so we can use two mtxs. // All .Read are covered by recvMtx, // all .Write are covered by sendMtx. recvMtx sync.Mutex recvBuffer []byte recvNonce *[aeadNonceSize]byte sendMtx sync.Mutex sendNonce *[aeadNonceSize]byte } // 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) { var ( hash = sha256.New hdkfState = new([32]byte) 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, hiEphPub := sort32(locEphPub, remEphPub) hkdfInit := hkdf.New(hash, []byte("INIT_HANDSHAKE"), nil, []byte("TENDERMINT_SECRET_CONNECTION_TRANSCRIPT_HASH")) if _, err := io.ReadFull(hkdfInit, hdkfState[:]); err != nil { return nil, err } hkdfLoEphPub := hkdf.New(hash, loEphPub[:], hdkfState[:], []byte("TENDERMINT_SECRET_CONNECTION_TRANSCRIPT_HASH")) if _, err := io.ReadFull(hkdfLoEphPub, hdkfState[:]); err != nil { return nil, err } hkdfHiEphPub := hkdf.New(hash, hiEphPub[:], hdkfState[:], []byte("TENDERMINT_SECRET_CONNECTION_TRANSCRIPT_HASH")) // 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, err := computeDHSecret(remEphPub, locEphPriv) if err != nil { return nil, err } if _, err := io.ReadFull(hkdfHiEphPub, hdkfState[:]); err != nil { return nil, err } hkdfSecret := hkdf.New(hash, dhSecret[:], hdkfState[:], []byte("TENDERMINT_SECRET_CONNECTION_TRANSCRIPT_HASH")) if _, err := io.ReadFull(hkdfSecret, hdkfState[:]); err != nil { return nil, err } // Generate the secret used for receiving, sending, challenge via HKDF-SHA2 // on the transcript state (which itself also uses HKDF-SHA2 to derive a key // from the dhSecret). recvSecret, sendSecret, challenge := deriveSecretAndChallenge(hdkfState, locIsLeast) sendAead, err := chacha20poly1305.New(sendSecret[:]) if err != nil { return nil, errors.New("invalid send SecretConnection Key") } recvAead, err := chacha20poly1305.New(recvSecret[:]) if err != nil { return nil, errors.New("invalid receive SecretConnection Key") } sc := &SecretConnection{ conn: conn, recvBuffer: nil, recvNonce: new([aeadNonceSize]byte), sendNonce: new([aeadNonceSize]byte), recvAead: recvAead, sendAead: sendAead, } // 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 _, ok := remPubKey.(ed25519.PubKeyEd25519); !ok { return nil, errors.Errorf("expected ed25519 pubkey, got %T", remPubKey) } 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 `totalFrameSize + aeadSizeOverhead`. // CONTRACT: data smaller than dataMaxSize is written atomically. func (sc *SecretConnection) Write(data []byte) (n int, err error) { sc.sendMtx.Lock() defer sc.sendMtx.Unlock() for 0 < len(data) { if err := func() error { var sealedFrame = pool.Get(aeadSizeOverhead + totalFrameSize) var frame = pool.Get(totalFrameSize) defer func() { pool.Put(sealedFrame) pool.Put(frame) }() 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) // encrypt the frame sc.sendAead.Seal(sealedFrame[:0], sc.sendNonce[:], frame, nil) incrNonce(sc.sendNonce) // end encryption _, err = sc.conn.Write(sealedFrame) if err != nil { return err } n += len(chunk) return nil }(); err != nil { return n, err } } return n, err } // CONTRACT: data smaller than dataMaxSize is read atomically. func (sc *SecretConnection) Read(data []byte) (n int, err error) { sc.recvMtx.Lock() defer sc.recvMtx.Unlock() // read off and update the recvBuffer, if non-empty if 0 < len(sc.recvBuffer) { n = copy(data, sc.recvBuffer) sc.recvBuffer = sc.recvBuffer[n:] return } // read off the conn var sealedFrame = pool.Get(aeadSizeOverhead + totalFrameSize) defer pool.Put(sealedFrame) _, err = io.ReadFull(sc.conn, sealedFrame) if err != nil { return } // decrypt the frame. // reads and updates the sc.recvNonce var frame = pool.Get(totalFrameSize) defer pool.Put(frame) _, err = sc.recvAead.Open(frame[:0], sc.recvNonce[:], sealedFrame, nil) if err != nil { return n, errors.New("failed to decrypt SecretConnection") } incrNonce(sc.recvNonce) // end decryption // copy checkLength worth into data, // set recvBuffer to the rest. 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) if n < len(chunk) { sc.recvBuffer = make([]byte, len(chunk)-n) copy(sc.recvBuffer, chunk[n:]) } return n, err } // 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 // TODO: Probably not a problem but ask Tony: different from the rust implementation (uses x25519-dalek), // we do not "clamp" the private key scalar: // see: https://github.com/dalek-cryptography/x25519-dalek/blob/34676d336049df2bba763cc076a75e47ae1f170f/src/x25519.rs#L56-L74 ephPub, ephPriv, err = box.GenerateKey(crand.Reader) if err != nil { panic("Could not generate ephemeral key-pair") } return } func shareEphPubKey(conn io.ReadWriter, locEphPub *[32]byte) (remEphPub *[32]byte, err error) { // Send our pubkey and receive theirs in tandem. var trs, _ = cmn.Parallel( func(_ int) (val interface{}, abort bool, err error) { var _, err1 = cdc.MarshalBinaryLengthPrefixedWriter(conn, locEphPub) if err1 != nil { return nil, true, err1 // abort } return nil, false, nil }, func(_ int) (val interface{}, abort bool, err error) { var _remEphPub [32]byte var _, err2 = cdc.UnmarshalBinaryLengthPrefixedReader(conn, &_remEphPub, 1024*1024) // TODO if err2 != nil { return nil, true, err2 // abort } return _remEphPub, false, nil }, ) // 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 } // computeDHSecret computes a Diffie-Hellman shared secret key // from our own local private key and the other's public key. // // It returns an error if the computed shared secret is all zeroes. func computeDHSecret(remPubKey, locPrivKey *[32]byte) (shrKey *[32]byte, err error) { shrKey = new([32]byte) curve25519.ScalarMult(shrKey, locPrivKey, remPubKey) // reject if the returned shared secret is all zeroes // related to: https://github.com/tendermint/tendermint/issues/3010 zero := new([32]byte) if subtle.ConstantTimeCompare(shrKey[:], zero[:]) == 1 { return nil, ErrSharedSecretIsZero } 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 io.ReadWriter, 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{}, abort bool, err error) { var _, err1 = cdc.MarshalBinaryLengthPrefixedWriter(sc, authSigMessage{pubKey, signature}) if err1 != nil { return nil, true, err1 // abort } return nil, false, nil }, func(_ int) (val interface{}, abort bool, err error) { var _recvMsg authSigMessage var _, err2 = cdc.UnmarshalBinaryLengthPrefixedReader(sc, &_recvMsg, 1024*1024) // TODO if err2 != nil { return nil, true, err2 // abort } return _recvMsg, false, nil }, ) // 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:]) if counter == math.MaxUint64 { // Terminates the session and makes sure the nonce would not re-used. // See https://github.com/tendermint/tendermint/issues/3531 panic("can't increase nonce without overflow") } counter++ binary.LittleEndian.PutUint64(nonce[4:], counter) }