lx: re-graft AmneziaWG 2.0 obfuscation onto sagernet/wireguard-go v0.0.5

Rebase of the AWG obf graft (was e5feca7 on v0.0.3) onto v0.0.5
(2c27bbf4f9, 'Add L3 forwarding support'). 15 of 16 graft files
applied clean via 3-way; only send.go conflicted, on a single line
(upstream queuedOutboundPackets backpressure decrement vs a graft
blank line — took upstream).

Key invariant preserved: MessageEncapsulatingTransportSize=0 (graft
zeroes the sagernet encapsulating headroom; AWG obfuscation composes
the prefix itself via SendBuffers, not Bind.Send prepend). Upstream's
InputPacket/InputPackets and the new size-based outbound buffer pool
(GetOutboundBuffer/PutOutboundBuffer) are taken verbatim; the graft's
RoutineEncryption (header at buffer start) and transport-padding shift
in RoutineSequentialSender re-woven around them.

Builds clean on linux/android/windows/darwin (device/conn/tun).

device/cookie.go

@@ -118,6 +118,7 @@ func (st *CookieChecker) CreateReply(
 	msg []byte,
 	recv uint32,
 	src []byte,
+	msgType uint32,
 ) (*MessageCookieReply, error) {
 	st.RLock()
 
@@ -153,7 +154,7 @@ func (st *CookieChecker) CreateReply(
 	smac1 := smac2 - blake2s.Size128
 
 	reply := new(MessageCookieReply)
-	reply.Type = MessageCookieReplyType
+	reply.Type = msgType
 	reply.Receiver = recv
 
 	_, err := rand.Read(reply.Nonce[:])

device/device.go

@@ -99,6 +99,29 @@ type Device struct {
 	closed       chan struct{}
 	log          *Logger
 	pauseManager pause.Manager
+
+	// lx: AmneziaWG obfuscation state (grafted from amneziawg-go).
+	junk struct {
+		min   int
+		max   int
+		count int
+	}
+
+	headers struct {
+		init      *magicHeader
+		cookie    *magicHeader
+		response  *magicHeader
+		transport *magicHeader
+	}
+
+	paddings struct {
+		init      int
+		response  int
+		cookie    int
+		transport int
+	}
+
+	ipackets [5]*obfChain
 }
 
 // deviceState represents the state of a Device.
@@ -172,7 +195,8 @@ func (device *Device) changeState(want deviceState) (err error) {
 			err = errDown
 		}
 	}
-	device.log.Verbosef("Interface state was %s, requested %s, now %s", old, want, device.deviceState())
+	device.log.Verbosef(
+		"Interface state was %s, requested %s, now %s", old, want, device.deviceState())
 	return
 }
 
@@ -317,6 +341,11 @@ func NewDevice(ctx context.Context, tunDevice tun.Device, bind conn.Bind, logger
 	device.rate.limiter.Init()
 	device.indexTable.Init()
 
+	device.headers.init = &magicHeader{start: MessageInitiationType, end: MessageInitiationType}
+	device.headers.response = &magicHeader{start: MessageResponseType, end: MessageResponseType}
+	device.headers.cookie = &magicHeader{start: MessageCookieReplyType, end: MessageCookieReplyType}
+	device.headers.transport = &magicHeader{start: MessageTransportType, end: MessageTransportType}
+
 	device.PopulatePools()
 
 	// create queues

device/magic-header.go

@@ -0,0 +1,63 @@
+package device
+
+import (
+	"crypto/rand"
+	"errors"
+	"fmt"
+	"math/big"
+	"strconv"
+	"strings"
+)
+
+type magicHeader struct {
+	start uint32
+	end   uint32
+}
+
+func newMagicHeader(spec string) (*magicHeader, error) {
+	parts := strings.Split(spec, "-")
+	if len(parts) < 1 || len(parts) > 2 {
+		return nil, errors.New("bad format")
+	}
+
+	start, err := strconv.ParseUint(parts[0], 10, 32)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse %s: %w", parts[0], err)
+	}
+
+	var end uint64
+	if len(parts) > 1 {
+		end, err = strconv.ParseUint(parts[1], 10, 32)
+		if err != nil {
+			return nil, fmt.Errorf("failed to parse %s: %w", parts[1], err)
+		}
+	} else {
+		end = start
+	}
+
+	if end < start {
+		return nil, errors.New("wrong range specified")
+	}
+
+	return &magicHeader{
+		start: uint32(start),
+		end:   uint32(end),
+	}, nil
+}
+
+func (h *magicHeader) GenSpec() string {
+	if h.start == h.end {
+		return fmt.Sprintf("%d", h.start)
+	}
+	return fmt.Sprintf("%d-%d", h.start, h.end)
+}
+
+func (h *magicHeader) Validate(val uint32) bool {
+	return h.start <= val && val <= h.end
+}
+
+func (h *magicHeader) Generate() uint32 {
+	high := int64(h.end - h.start + 1)
+	r, _ := rand.Int(rand.Reader, big.NewInt(high))
+	return h.start + uint32(r.Int64())
+}

device/noise-protocol.go

@@ -54,10 +54,11 @@ const (
 )
 
 const (
-	MessageInitiationType  = 1
+	MessageUnknownType     uint32 = 0
-	MessageResponseType    = 2
+	MessageInitiationType  uint32 = 1
-	MessageCookieReplyType = 3
+	MessageResponseType    uint32 = 2
-	MessageTransportType   = 4
+	MessageCookieReplyType uint32 = 3
+	MessageTransportType   uint32 = 4
 )
 
 const (
@@ -65,7 +66,7 @@ const (
 	MessageResponseSize               = 92                                            // size of response message
 	MessageCookieReplySize            = 64                                            // size of cookie reply message
 	MessageTransportHeaderSize        = 16                                            // size of data preceding content in transport message
-	MessageEncapsulatingTransportSize = 8                                             // size of optional, free (for use by conn.Bind.Send()) space preceding the transport header
+	MessageEncapsulatingTransportSize = 0                                             // lx: zeroed so AmneziaWG obfuscation composes without sagernet headroom (AWG path doesn't use the Bind.Send prepend)
 	MessageTransportSize              = MessageTransportHeaderSize + poly1305.TagSize // size of empty transport
 	MessageKeepaliveSize              = MessageTransportSize                          // size of keepalive
 	MessageHandshakeSize              = MessageInitiationSize                         // size of largest handshake related message
@@ -218,7 +219,7 @@ type Handshake struct {
 	localEphemeral            NoisePrivateKey          // ephemeral secret key
 	localIndex                uint32                   // used to clear hash-table
 	remoteIndex               uint32                   // index for sending
-	remoteStatic              NoisePublicKey           // long term key
+	remoteStatic              NoisePublicKey           // long term key, never changes, can be accessed without mutex
 	remoteEphemeral           NoisePublicKey           // ephemeral public key
 	precomputedStaticStatic   [NoisePublicKeySize]byte // precomputed shared secret
 	lastTimestamp             tai64n.Timestamp
@@ -287,8 +288,10 @@ func (device *Device) CreateMessageInitiation(peer *Peer) (*MessageInitiation, e
 
 	handshake.mixHash(handshake.remoteStatic[:])
 
+	msgType := device.headers.init.Generate()
+
 	msg := MessageInitiation{
-		Type:      MessageInitiationType,
+		Type:      msgType,
 		Ephemeral: handshake.localEphemeral.publicKey(),
 	}
 
@@ -471,7 +474,7 @@ func (device *Device) CreateMessageResponse(peer *Peer) (*MessageResponse, error
 	}
 
 	var msg MessageResponse
-	msg.Type = MessageResponseType
+	msg.Type = device.headers.response.Generate()
 	msg.Sender = handshake.localIndex
 	msg.Receiver = handshake.remoteIndex
 

device/obf.go

@@ -0,0 +1,140 @@
+package device
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+)
+
+type obfBuilder func(val string) (obf, error)
+
+var obfBuilders = map[string]obfBuilder{
+	"b":  newBytesObf,
+	"t":  newTimestampObf,
+	"r":  newRandObf,
+	"rc": newRandCharObf,
+	"rd": newRandDigitsObf,
+	"d":  newDataObf,
+	"ds": newDataStringObf,
+	"dz": newDataSizeObf,
+}
+
+type obf interface {
+	Obfuscate(dst, src []byte)
+	Deobfuscate(dst, src []byte) bool
+	ObfuscatedLen(srcLen int) int
+	DeobfuscatedLen(srcLen int) int
+}
+
+type obfChain struct {
+	Spec string
+	obfs []obf
+}
+
+func newObfChain(spec string) (*obfChain, error) {
+	var (
+		obfs []obf
+		errs []error
+	)
+
+	remaining := spec[:]
+	for {
+		start := strings.IndexByte(remaining, '<')
+		if start == -1 {
+			break
+		}
+
+		end := strings.IndexByte(remaining[start:], '>')
+		if end == -1 {
+			return nil, errors.New("missing enclosing >")
+		}
+		end += start
+
+		tag := remaining[start+1 : end]
+		parts := strings.Fields(tag)
+		if len(parts) == 0 {
+			errs = append(errs, errors.New("empty tag"))
+			remaining = remaining[end+1:]
+			continue
+		}
+
+		key := parts[0]
+		builder, ok := obfBuilders[key]
+		if !ok {
+			errs = append(errs, fmt.Errorf("unknown tag <%s>", key))
+			remaining = remaining[end+1:]
+			continue
+		}
+
+		val := ""
+		if len(parts) > 1 {
+			val = parts[1]
+		}
+
+		o, err := builder(val)
+		if err != nil {
+			errs = append(errs, fmt.Errorf("failed to build <%s>: %w", key, err))
+			remaining = remaining[end+1:]
+			continue
+		}
+
+		obfs = append(obfs, o)
+		remaining = remaining[end+1:]
+	}
+
+	if len(errs) > 0 {
+		return nil, errors.Join(errs...)
+	}
+
+	return &obfChain{
+		Spec: spec,
+		obfs: obfs,
+	}, nil
+}
+
+func (c *obfChain) Obfuscate(dst, src []byte) {
+	written := 0
+	for _, o := range c.obfs {
+		obfLen := o.ObfuscatedLen(len(src))
+		o.Obfuscate(dst[written:written+obfLen], src)
+		written += obfLen
+	}
+}
+
+func (c *obfChain) Deobfuscate(dst, src []byte) bool {
+	dynamicLen := len(src) - c.ObfuscatedLen(0)
+
+	written, read := 0, 0
+
+	for _, o := range c.obfs {
+		deobfLen := o.DeobfuscatedLen(dynamicLen)
+		obfLen := o.ObfuscatedLen(deobfLen)
+
+		if !o.Deobfuscate(dst[written:written+deobfLen], src[read:read+obfLen]) {
+			return false
+		}
+
+		written += deobfLen
+		read += obfLen
+	}
+
+	return true
+}
+
+func (c *obfChain) ObfuscatedLen(n int) int {
+	total := 0
+	for _, o := range c.obfs {
+		total += o.ObfuscatedLen(n)
+	}
+	return total
+}
+
+func (c *obfChain) DeobfuscatedLen(n int) int {
+	dynamicLen := n - c.ObfuscatedLen(0)
+
+	total := 0
+	for _, o := range c.obfs {
+		total += o.DeobfuscatedLen(dynamicLen)
+	}
+	return total
+}

device/obf_bytes.go

@@ -0,0 +1,47 @@
+package device
+
+import (
+	"bytes"
+	"encoding/hex"
+	"errors"
+	"strings"
+)
+
+func newBytesObf(val string) (obf, error) {
+	val = strings.TrimPrefix(val, "0x")
+
+	if len(val) == 0 {
+		return nil, errors.New("empty argument")
+	}
+
+	if len(val)%2 != 0 {
+		return nil, errors.New("odd amount of symbols")
+	}
+
+	bytes, err := hex.DecodeString(val)
+	if err != nil {
+		return nil, err
+	}
+
+	return &bytesObf{data: bytes}, nil
+}
+
+type bytesObf struct {
+	data []byte
+}
+
+func (o *bytesObf) Obfuscate(dst, src []byte) {
+	copy(dst, o.data)
+}
+
+func (o *bytesObf) Deobfuscate(dst, src []byte) bool {
+	return bytes.Equal(o.data, src[:o.ObfuscatedLen(0)])
+}
+
+func (o *bytesObf) ObfuscatedLen(srcLen int) int {
+	return len(o.data)
+}
+
+func (o *bytesObf) DeobfuscatedLen(srcLen int) int {
+	return 0
+}

device/obf_data.go

@@ -0,0 +1,25 @@
+package device
+
+func newDataObf(val string) (obf, error) {
+	return &dataObf{}, nil
+}
+
+type dataObf struct {
+}
+
+func (obf *dataObf) Obfuscate(dst, src []byte) {
+	copy(dst, src)
+}
+
+func (obf *dataObf) Deobfuscate(dst, src []byte) bool {
+	copy(dst, src)
+	return true
+}
+
+func (o *dataObf) ObfuscatedLen(n int) int {
+	return n
+}
+
+func (o *dataObf) DeobfuscatedLen(n int) int {
+	return n
+}

device/obf_datasize.go

@@ -0,0 +1,38 @@
+package device
+
+import "strconv"
+
+func newDataSizeObf(val string) (obf, error) {
+	length, err := strconv.Atoi(val)
+	if err != nil {
+		return nil, err
+	}
+
+	return &dataSizeObf{
+		length: length,
+	}, nil
+}
+
+type dataSizeObf struct {
+	length int
+}
+
+func (o *dataSizeObf) Obfuscate(dst, src []byte) {
+	srcLen := len(src)
+	for i := o.length - 1; i >= 0; i-- {
+		dst[i] = byte(srcLen & 0xFF)
+		srcLen >>= 8
+	}
+}
+
+func (o *dataSizeObf) Deobfuscate(dst, src []byte) bool {
+	return true
+}
+
+func (o *dataSizeObf) ObfuscatedLen(srcLen int) int {
+	return o.length
+}
+
+func (o *dataSizeObf) DeobfuscatedLen(srcLen int) int {
+	return 0
+}

device/obf_datastring.go

@@ -0,0 +1,29 @@
+package device
+
+import (
+	"encoding/base64"
+)
+
+func newDataStringObf(val string) (obf, error) {
+	return &dataStringObf{}, nil
+}
+
+type dataStringObf struct {
+}
+
+func (o *dataStringObf) Obfuscate(dst, src []byte) {
+	base64.RawStdEncoding.Encode(dst, src)
+}
+
+func (o *dataStringObf) Deobfuscate(dst, src []byte) bool {
+	base64.RawStdEncoding.Decode(dst, src)
+	return true
+}
+
+func (o *dataStringObf) ObfuscatedLen(n int) int {
+	return base64.RawStdEncoding.EncodedLen(n)
+}
+
+func (o *dataStringObf) DeobfuscatedLen(n int) int {
+	return base64.RawStdEncoding.DecodedLen(n)
+}

device/obf_rand.go

@@ -0,0 +1,39 @@
+package device
+
+import (
+	"crypto/rand"
+	"strconv"
+)
+
+func newRandObf(val string) (obf, error) {
+	length, err := strconv.Atoi(val)
+	if err != nil {
+		return nil, err
+	}
+
+	return &randObf{
+		length: length,
+	}, nil
+}
+
+type randObf struct {
+	length int
+}
+
+func (o *randObf) Obfuscate(dst, src []byte) {
+	rand.Read(dst[:o.length])
+}
+
+func (o *randObf) Deobfuscate(dst, src []byte) bool {
+	// there is no way to validate randomness :)
+	// assume that it is always true
+	return true
+}
+
+func (o *randObf) ObfuscatedLen(n int) int {
+	return o.length
+}
+
+func (o *randObf) DeobfuscatedLen(n int) int {
+	return 0
+}

device/obf_randchars.go

@@ -0,0 +1,48 @@
+package device
+
+import (
+	"crypto/rand"
+	"strconv"
+	"unicode"
+)
+
+const chars52 = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
+
+func newRandCharObf(val string) (obf, error) {
+	length, err := strconv.Atoi(val)
+	if err != nil {
+		return nil, err
+	}
+
+	return &randCharObf{
+		length: length,
+	}, nil
+}
+
+type randCharObf struct {
+	length int
+}
+
+func (o *randCharObf) Obfuscate(dst, src []byte) {
+	rand.Read(dst[:o.length])
+	for i := range dst[:o.length] {
+		dst[i] = chars52[dst[i]%52]
+	}
+}
+
+func (o *randCharObf) Deobfuscate(dst, src []byte) bool {
+	for _, b := range src[:o.length] {
+		if !unicode.IsLetter(rune(b)) {
+			return false
+		}
+	}
+	return true
+}
+
+func (o *randCharObf) ObfuscatedLen(n int) int {
+	return o.length
+}
+
+func (o *randCharObf) DeobfuscatedLen(n int) int {
+	return 0
+}

device/obf_randdigits.go

@@ -0,0 +1,48 @@
+package device
+
+import (
+	"crypto/rand"
+	"strconv"
+	"unicode"
+)
+
+const digits10 = "0123456789"
+
+func newRandDigitsObf(val string) (obf, error) {
+	length, err := strconv.Atoi(val)
+	if err != nil {
+		return nil, err
+	}
+
+	return &randDigitObf{
+		length: length,
+	}, nil
+}
+
+type randDigitObf struct {
+	length int
+}
+
+func (o *randDigitObf) Obfuscate(dst, src []byte) {
+	rand.Read(dst[:o.length])
+	for i := range dst[:o.length] {
+		dst[i] = digits10[dst[i]%10]
+	}
+}
+
+func (o *randDigitObf) Deobfuscate(dst, src []byte) bool {
+	for _, b := range src[:o.length] {
+		if !unicode.IsDigit(rune(b)) {
+			return false
+		}
+	}
+	return true
+}
+
+func (o *randDigitObf) ObfuscatedLen(n int) int {
+	return o.length
+}
+
+func (o *randDigitObf) DeobfuscatedLen(n int) int {
+	return 0
+}

device/obf_timestamp.go

@@ -0,0 +1,31 @@
+package device
+
+import (
+	"encoding/binary"
+	"time"
+)
+
+func newTimestampObf(_ string) (obf, error) {
+	return &timestampObf{}, nil
+}
+
+type timestampObf struct{}
+
+func (o *timestampObf) Obfuscate(dst, src []byte) {
+	t := uint32(time.Now().Unix())
+	binary.BigEndian.PutUint32(dst, t)
+}
+
+func (o *timestampObf) Deobfuscate(dst, src []byte) bool {
+	// replay attack check?
+	// requires time to be always synchronized
+	return true
+}
+
+func (o *timestampObf) ObfuscatedLen(n int) int {
+	return 4
+}
+
+func (o *timestampObf) DeobfuscatedLen(n int) int {
+	return 0
+}

device/receive.go

@@ -76,7 +76,10 @@ func (peer *Peer) keepKeyFreshReceiving() {
  * Every time the bind is updated a new routine is started for
  * IPv4 and IPv6 (separately)
  */
-func (device *Device) RoutineReceiveIncoming(maxBatchSize int, recv conn.ReceiveFunc) {
+func (device *Device) RoutineReceiveIncoming(
+	maxBatchSize int,
+	recv conn.ReceiveFunc,
+) {
 	recvName := recv.PrettyName()
 	defer func() {
 		device.log.Verbosef("Routine: receive incoming %s - stopped", recvName)
@@ -139,9 +142,14 @@ func (device *Device) RoutineReceiveIncoming(maxBatchSize int, recv conn.Receive
 			}
 
 			// check size of packet
-
 			packet := bufsArrs[i][:size]
-			msgType := binary.LittleEndian.Uint32(packet[:4])
+
+			// get message padding and type based on information from S1-S4 and H1-H4
+			msgType, padding := device.DeterminePacketTypeAndPadding(packet, MessageUnknownType)
+			if padding > 0 {
+				copy(packet, packet[padding:])
+				packet = packet[:len(packet)-padding]
+			}
 
 			switch msgType {
 
@@ -283,7 +291,6 @@ func (device *Device) RoutineHandshake(id int) {
 	device.log.Verbosef("Routine: handshake worker %d - started", id)
 
 	for elem := range device.queue.handshake.c {
-
 		// handle cookie fields and ratelimiting
 
 		switch elem.msgType {
@@ -310,9 +317,14 @@ func (device *Device) RoutineHandshake(id int) {
 			// consume reply
 
 			if peer := entry.peer; peer.isRunning.Load() {
-				device.log.Verbosef("Receiving cookie response from %s", elem.endpoint.DstToString())
+				device.log.Verbosef(
+					"Receiving cookie response from %s",
+					elem.endpoint.DstToString(),
+				)
 				if !peer.cookieGenerator.ConsumeReply(&reply) {
-					device.log.Verbosef("Could not decrypt invalid cookie response")
+					device.log.Verbosef(
+						"Could not decrypt invalid cookie response",
+					)
 				}
 			}
 
@@ -354,9 +366,7 @@ func (device *Device) RoutineHandshake(id int) {
 
 		switch elem.msgType {
 		case MessageInitiationType:
-
 			// unmarshal
-
 			var msg MessageInitiation
 			err := msg.unmarshal(elem.packet)
 			if err != nil {
@@ -364,7 +374,8 @@ func (device *Device) RoutineHandshake(id int) {
 				goto skip
 			}
 
-			// consume initiation
+			// have to reassign msgType for ranged msgType to work
+			msg.Type = elem.msgType
 
 			peer := device.ConsumeMessageInitiation(&msg, elem.endpoint)
 			if peer == nil {
@@ -396,6 +407,9 @@ func (device *Device) RoutineHandshake(id int) {
 				goto skip
 			}
 
+			// have to reassign msgType for ranged msgType to work
+			msg.Type = elem.msgType
+
 			// consume response
 
 			peer := device.ConsumeMessageResponse(&msg)
@@ -573,3 +587,57 @@ func (peer *Peer) processInboundContainer(elemsContainer *QueueInboundElementsCo
 		device.PutInboundElement(elem)
 	}
 }
+
+func (device *Device) DeterminePacketTypeAndPadding(packet []byte, expectedType uint32) (uint32, int) {
+	size := len(packet)
+
+	if expectedType == MessageUnknownType || expectedType == MessageInitiationType {
+		padding := device.paddings.init
+		header := device.headers.init
+
+		if size == padding+MessageInitiationSize {
+			data := packet[padding:]
+			if header.Validate(binary.LittleEndian.Uint32(data)) {
+				return MessageInitiationType, padding
+			}
+		}
+	}
+
+	if expectedType == MessageUnknownType || expectedType == MessageResponseType {
+		padding := device.paddings.response
+		header := device.headers.response
+
+		if size == padding+MessageResponseSize {
+			data := packet[padding:]
+			if header.Validate(binary.LittleEndian.Uint32(data)) {
+				return MessageResponseType, padding
+			}
+		}
+	}
+
+	if expectedType == MessageUnknownType || expectedType == MessageCookieReplyType {
+		padding := device.paddings.cookie
+		header := device.headers.cookie
+
+		if size == padding+MessageCookieReplySize {
+			data := packet[padding:]
+			if header.Validate(binary.LittleEndian.Uint32(data)) {
+				return MessageCookieReplyType, padding
+			}
+		}
+	}
+
+	if expectedType == MessageUnknownType || expectedType == MessageTransportType {
+		padding := device.paddings.transport
+		header := device.headers.transport
+
+		if size >= padding+MessageTransportHeaderSize {
+			data := packet[padding:]
+			if header.Validate(binary.LittleEndian.Uint32(data)) {
+				return MessageTransportType, padding
+			}
+		}
+	}
+
+	return MessageUnknownType, 0
+}

device/send.go

@@ -6,9 +6,12 @@
 package device
 
 import (
+	"bytes"
+	"crypto/rand"
 	"encoding/binary"
 	"errors"
 	"fmt"
+	"math/big"
 	"net"
 	"net/netip"
 	"os"
@@ -199,15 +202,48 @@ func (peer *Peer) SendHandshakeInitiation(isRetry bool) error {
 		return err
 	}
 
-	buf := make([]byte, MessageEncapsulatingTransportSize+MessageInitiationSize)
+	var sendBuffer [][]byte
-	packet := buf[MessageEncapsulatingTransportSize:]
+
-	_ = msg.marshal(packet)
+	for _, ipacket := range peer.device.ipackets {
+		if ipacket != nil {
+			buf := make([]byte, ipacket.ObfuscatedLen(0))
+			ipacket.Obfuscate(buf, nil)
+			sendBuffer = append(sendBuffer, buf)
+		}
+	}
+
+	jc := peer.device.junk.count
+	jmin := peer.device.junk.min
+	jmax := peer.device.junk.max
+
+	for i := 0; i < jc; i++ {
+		nBig, _ := rand.Int(rand.Reader, big.NewInt(int64(jmax-jmin+1)))
+		n := int(nBig.Int64()) + jmin
+
+		buf := make([]byte, n)
+		rand.Read(buf)
+		sendBuffer = append(sendBuffer, buf)
+	}
+
+	var buf [MessageInitiationSize]byte
+	writer := bytes.NewBuffer(buf[:0])
+	binary.Write(writer, binary.LittleEndian, msg)
+	packet := writer.Bytes()
 	peer.cookieGenerator.AddMacs(packet)
 
 	peer.timersAnyAuthenticatedPacketTraversal()
 	peer.timersAnyAuthenticatedPacketSent()
 
-	err = peer.SendBuffers([][]byte{buf})
+	if padding := peer.device.paddings.init; padding > 0 {
+		buf := make([]byte, padding+len(packet))
+		rand.Read(buf[:padding])
+		copy(buf[padding:], packet)
+		packet = buf
+	}
+
+	sendBuffer = append(sendBuffer, packet)
+
+	err = peer.SendBuffers(sendBuffer)
 	if err != nil {
 		peer.device.log.Errorf("%v - Failed to send handshake initiation: %v", peer, err)
 	}
@@ -229,9 +265,11 @@ func (peer *Peer) SendHandshakeResponse() error {
 		return err
 	}
 
-	buf := make([]byte, MessageEncapsulatingTransportSize+MessageResponseSize)
+	var buf [MessageResponseSize]byte
-	packet := buf[MessageEncapsulatingTransportSize:]
+	writer := bytes.NewBuffer(buf[:0])
-	_ = response.marshal(packet)
+
+	binary.Write(writer, binary.LittleEndian, response)
+	packet := writer.Bytes()
 	peer.cookieGenerator.AddMacs(packet)
 
 	err = peer.BeginSymmetricSession()
@@ -244,8 +282,15 @@ func (peer *Peer) SendHandshakeResponse() error {
 	peer.timersAnyAuthenticatedPacketTraversal()
 	peer.timersAnyAuthenticatedPacketSent()
 
+	if padding := peer.device.paddings.response; padding > 0 {
+		buf := make([]byte, padding+len(packet))
+		rand.Read(buf[:padding])
+		copy(buf[padding:], packet)
+		packet = buf
+	}
+
 	// TODO: allocation could be avoided
-	err = peer.SendBuffers([][]byte{buf})
+	err = peer.SendBuffers([][]byte{packet})
 	if err != nil {
 		peer.device.log.Errorf("%v - Failed to send handshake response: %v", peer, err)
 	}
@@ -256,18 +301,33 @@ func (device *Device) SendHandshakeCookie(initiatingElem *QueueHandshakeElement)
 	device.log.Verbosef("Sending cookie response for denied handshake message for %v", initiatingElem.endpoint.DstToString())
 
 	sender := binary.LittleEndian.Uint32(initiatingElem.packet[4:8])
-	reply, err := device.cookieChecker.CreateReply(initiatingElem.packet, sender, initiatingElem.endpoint.DstToBytes())
+	msgType := device.headers.cookie.Generate()
+
+	reply, err := device.cookieChecker.CreateReply(
+		initiatingElem.packet,
+		sender,
+		initiatingElem.endpoint.DstToBytes(),
+		msgType,
+	)
 	if err != nil {
 		device.log.Errorf("Failed to create cookie reply: %v", err)
 		return err
 	}
 
-	buf := make([]byte, MessageEncapsulatingTransportSize+MessageCookieReplySize)
+	var buf [MessageCookieReplySize]byte
-	packet := buf[MessageEncapsulatingTransportSize:]
+	writer := bytes.NewBuffer(buf[:0])
-	_ = reply.marshal(packet)
+	binary.Write(writer, binary.LittleEndian, reply)
-	// TODO: allocation could be avoided
+	packet := writer.Bytes()
-	device.net.bind.Send([][]byte{buf}, initiatingElem.endpoint, MessageEncapsulatingTransportSize)
 
+	if padding := device.paddings.cookie; padding > 0 {
+		buf := make([]byte, padding+len(packet))
+		rand.Read(buf[:padding])
+		copy(buf[padding:], packet)
+		packet = buf
+	}
+
+	// TODO: allocation could be avoided
+	device.net.bind.Send([][]byte{packet}, initiatingElem.endpoint, 0)
 	return nil
 }
 
@@ -687,7 +747,9 @@ func (device *Device) RoutineEncryption(id int) {
 			fieldReceiver := header[4:8]
 			fieldNonce := header[8:16]
 
-			binary.LittleEndian.PutUint32(fieldType, MessageTransportType)
+			msgType := device.headers.transport.Generate()
+
+			binary.LittleEndian.PutUint32(fieldType, msgType)
 			binary.LittleEndian.PutUint32(fieldReceiver, elem.keypair.remoteIndex)
 			binary.LittleEndian.PutUint64(fieldNonce, elem.nonce)
 
@@ -704,9 +766,6 @@ func (device *Device) RoutineEncryption(id int) {
 				elem.packet,
 				nil,
 			)
-
-			// re-slice packet to include encapsulating transport space
-			elem.packet = elem.buffer[:MessageEncapsulatingTransportSize+len(elem.packet)]
 		}
 		elemsContainer.filling.Done()
 	}
@@ -775,6 +834,19 @@ func (peer *Peer) processOutboundContainer(elemsContainer *QueueOutboundElements
 		if len(elem.packet[MessageEncapsulatingTransportSize:]) != MessageKeepaliveSize {
 			dataSent = true
 		}
+		// lx:begin awg (SPEC 025 — AmneziaWG transport padding, S4)
+		// Prepend `transport` random bytes ahead of the transport header. The AWG
+		// path zeroes MessageEncapsulatingTransportSize (see noise-protocol.go), so
+		// elem.packet starts at buffer offset 0 and this shift is what creates the
+		// prefix; the buffer is allocated with PaddingMultiple headroom.
+		if padding := device.paddings.transport; padding > 0 {
+			for i := len(elem.packet) - 1; i >= 0; i-- {
+				elem.buffer[i+padding] = elem.buffer[i]
+			}
+			rand.Read(elem.buffer[:padding])
+			elem.packet = elem.buffer[:padding+len(elem.packet)]
+		}
+		// lx:end awg
 		scratch = append(scratch, elem.packet)
 	}
 

device/uapi.go

@@ -97,6 +97,56 @@ func (device *Device) IpcGetOperation(w io.Writer) error {
 			sendf("fwmark=%d", device.net.fwmark)
 		}
 
+		if device.junk.count != 0 {
+			sendf("jc=%d", device.junk.count)
+		}
+
+		if device.junk.min != 0 {
+			sendf("jmin=%d", device.junk.min)
+		}
+
+		if device.junk.max != 0 {
+			sendf("jmax=%d", device.junk.max)
+		}
+
+		if device.paddings.init != 0 {
+			sendf("s1=%d", device.paddings.init)
+		}
+
+		if device.paddings.response != 0 {
+			sendf("s2=%d", device.paddings.response)
+		}
+
+		if device.paddings.cookie != 0 {
+			sendf("s3=%d", device.paddings.cookie)
+		}
+
+		if device.paddings.transport != 0 {
+			sendf("s4=%d", device.paddings.transport)
+		}
+
+		if device.headers.init != nil {
+			sendf("h1=%s", device.headers.init.GenSpec())
+		}
+
+		if device.headers.response != nil {
+			sendf("h2=%s", device.headers.response.GenSpec())
+		}
+
+		if device.headers.cookie != nil {
+			sendf("h3=%s", device.headers.cookie.GenSpec())
+		}
+
+		if device.headers.transport != nil {
+			sendf("h4=%s", device.headers.transport.GenSpec())
+		}
+
+		for i, ipacket := range device.ipackets {
+			if ipacket != nil {
+				sendf("i%d=%s", i+1, ipacket.Spec)
+			}
+		}
+
 		for _, peer := range device.peers.keyMap {
 			// Serialize peer state.
 			peer.handshake.mutex.RLock()
@@ -147,6 +197,7 @@ func (device *Device) IpcSetOperation(r io.Reader) (err error) {
 		}
 	}()
 
+	ipcDev := new(ipcSetDevice)
 	peer := new(ipcSetPeer)
 	deviceConfig := true
 
@@ -155,12 +206,20 @@ func (device *Device) IpcSetOperation(r io.Reader) (err error) {
 		line := scanner.Text()
 		if line == "" {
 			// Blank line means terminate operation.
+			err := ipcDev.mergeWithDevice(device)
+			if err != nil {
+				return ipcErrorf(ipc.IpcErrorInvalid, "failed to merge with device: %w", err)
+			}
 			peer.handlePostConfig()
 			return nil
 		}
 		key, value, ok := strings.Cut(line, "=")
 		if !ok {
-			return ipcErrorf(ipc.IpcErrorProtocol, "failed to parse line %q", line)
+			return ipcErrorf(
+				ipc.IpcErrorProtocol,
+				"failed to parse line %q",
+				line,
+			)
 		}
 
 		if key == "public_key" {
@@ -186,6 +245,10 @@ func (device *Device) IpcSetOperation(r io.Reader) (err error) {
 			return err
 		}
 	}
+	err = ipcDev.mergeWithDevice(device)
+	if err != nil {
+		return ipcErrorf(ipc.IpcErrorInvalid, "failed to merge with device: %w", err)
+	}
 	peer.handlePostConfig()
 
 	if err := scanner.Err(); err != nil {
@@ -235,11 +298,155 @@ func (device *Device) handleDeviceLine(key, value string) error {
 
 	case "replace_peers":
 		if value != "true" {
-			return ipcErrorf(ipc.IpcErrorInvalid, "failed to set replace_peers, invalid value: %v", value)
+			return ipcErrorf(
+				ipc.IpcErrorInvalid,
+				"failed to set replace_peers, invalid value: %v",
+				value,
+			)
 		}
 		device.log.Verbosef("UAPI: Removing all peers")
 		device.RemoveAllPeers()
 
+	case "jc":
+		jc, err := strconv.Atoi(value)
+		if err != nil {
+			return ipcErrorf(ipc.IpcErrorInvalid, "failed to parse jc: %w", err)
+		}
+		if jc <= 0 {
+			return ipcErrorf(ipc.IpcErrorInvalid, "jc must be a positive value")
+		}
+		device.log.Verbosef("UAPI: Updating junk count")
+		device.junk.count = jc
+
+	case "jmin":
+		jmin, err := strconv.Atoi(value)
+		if err != nil {
+			return ipcErrorf(ipc.IpcErrorInvalid, "failed to parse jmin: %w", err)
+		}
+		if jmin <= 0 {
+			return ipcErrorf(ipc.IpcErrorInvalid, "jmin must be a positive value")
+		}
+		device.log.Verbosef("UAPI: Updating junk min")
+		device.junk.min = jmin
+
+	case "jmax":
+		jmax, err := strconv.Atoi(value)
+		if err != nil {
+			return ipcErrorf(ipc.IpcErrorInvalid, "failed to parse jmax: %w", err)
+		}
+		if jmax <= 0 {
+			return ipcErrorf(ipc.IpcErrorInvalid, "jmax must be a positive value")
+		}
+		device.log.Verbosef("UAPI: Updating junk max")
+		device.junk.max = jmax
+
+	case "s1":
+		padding, err := strconv.Atoi(value)
+		if err != nil {
+			return ipcErrorf(ipc.IpcErrorInvalid, "failed to parse s1: %w", err)
+		}
+		if padding < 0 {
+			return ipcErrorf(ipc.IpcErrorInvalid, "s1 must be non-negative")
+		}
+		device.log.Verbosef("UAPI: Updating s1 padding")
+		device.paddings.init = padding
+
+	case "s2":
+		padding, err := strconv.Atoi(value)
+		if err != nil {
+			return ipcErrorf(ipc.IpcErrorInvalid, "failed to parse s2: %w", err)
+		}
+		if padding < 0 {
+			return ipcErrorf(ipc.IpcErrorInvalid, "s2 must be non-negative")
+		}
+		device.log.Verbosef("UAPI: Updating s2 padding")
+		device.paddings.response = padding
+
+	case "s3":
+		padding, err := strconv.Atoi(value)
+		if err != nil {
+			return ipcErrorf(ipc.IpcErrorInvalid, "failed to parse s3: %w", err)
+		}
+		if padding < 0 {
+			return ipcErrorf(ipc.IpcErrorInvalid, "s3 must be non-negative")
+		}
+		device.log.Verbosef("UAPI: Updating s3 padding")
+		device.paddings.cookie = padding
+
+	case "s4":
+		padding, err := strconv.Atoi(value)
+		if err != nil {
+			return ipcErrorf(ipc.IpcErrorInvalid, "failed to parse s4: %w", err)
+		}
+		if padding < 0 {
+			return ipcErrorf(ipc.IpcErrorInvalid, "s4 must be non-negative")
+		}
+		device.log.Verbosef("UAPI: Updating s4 padding")
+		device.paddings.transport = padding
+
+	case "h1":
+		header, err := newMagicHeader(value)
+		if err != nil {
+			return ipcErrorf(ipc.IpcErrorInvalid, "failed to parse H1: %w", err)
+		}
+		device.headers.init = header
+
+	case "h2":
+		header, err := newMagicHeader(value)
+		if err != nil {
+			return ipcErrorf(ipc.IpcErrorInvalid, "failed to parse H2: %w", err)
+		}
+		device.headers.response = header
+
+	case "h3":
+		header, err := newMagicHeader(value)
+		if err != nil {
+			return ipcErrorf(ipc.IpcErrorInvalid, "failed to parse H3: %w", err)
+		}
+		device.headers.cookie = header
+
+	case "h4":
+		header, err := newMagicHeader(value)
+		if err != nil {
+			return ipcErrorf(ipc.IpcErrorInvalid, "failed to parse H4: %w", err)
+		}
+		device.headers.transport = header
+
+	case "i1":
+		chain, err := newObfChain(value)
+		if err != nil {
+			return ipcErrorf(ipc.IpcErrorInvalid, "failed to parse I1: %w", err)
+		}
+		device.ipackets[0] = chain
+
+	case "i2":
+		chain, err := newObfChain(value)
+		if err != nil {
+			return ipcErrorf(ipc.IpcErrorInvalid, "failed to parse I2: %w", err)
+		}
+		device.ipackets[1] = chain
+
+	case "i3":
+		chain, err := newObfChain(value)
+		if err != nil {
+			return ipcErrorf(ipc.IpcErrorInvalid, "failed to parse I3: %w", err)
+		}
+		device.ipackets[2] = chain
+
+	case "i4":
+		chain, err := newObfChain(value)
+		if err != nil {
+			return ipcErrorf(ipc.IpcErrorInvalid, "failed to parse I4: %w", err)
+		}
+		device.ipackets[3] = chain
+
+	case "i5":
+		chain, err := newObfChain(value)
+		if err != nil {
+			return ipcErrorf(ipc.IpcErrorInvalid, "failed to parse I5: %w", err)
+		}
+		device.ipackets[4] = chain
+
 	default:
 		return ipcErrorf(ipc.IpcErrorInvalid, "invalid UAPI device key: %v", key)
 	}
@@ -271,7 +478,10 @@ func (peer *ipcSetPeer) handlePostConfig() {
 	}
 }
 
-func (device *Device) handlePublicKeyLine(peer *ipcSetPeer, value string) error {
+func (device *Device) handlePublicKeyLine(
+	peer *ipcSetPeer,
+	value string,
+) error {
 	// Load/create the peer we are configuring.
 	var publicKey NoisePublicKey
 	err := publicKey.FromHex(value)
@@ -301,12 +511,19 @@ func (device *Device) handlePublicKeyLine(peer *ipcSetPeer, value string) error
 	return nil
 }
 
-func (device *Device) handlePeerLine(peer *ipcSetPeer, key, value string) error {
+func (device *Device) handlePeerLine(
+	peer *ipcSetPeer,
+	key, value string,
+) error {
 	switch key {
 	case "update_only":
 		// allow disabling of creation
 		if value != "true" {
-			return ipcErrorf(ipc.IpcErrorInvalid, "failed to set update only, invalid value: %v", value)
+			return ipcErrorf(
+				ipc.IpcErrorInvalid,
+				"failed to set update only, invalid value: %v",
+				value,
+			)
 		}
 		if peer.created && !peer.dummy {
 			device.RemovePeer(peer.handshake.remoteStatic)
@@ -352,7 +569,11 @@ func (device *Device) handlePeerLine(peer *ipcSetPeer, key, value string) error
 
 		secs, err := strconv.ParseUint(value, 10, 16)
 		if err != nil {
-			return ipcErrorf(ipc.IpcErrorInvalid, "failed to set persistent keepalive interval: %w", err)
+			return ipcErrorf(
+				ipc.IpcErrorInvalid,
+				"failed to set persistent keepalive interval: %w",
+				err,
+			)
 		}
 
 		old := peer.persistentKeepaliveInterval.Swap(uint32(secs))
@@ -363,7 +584,11 @@ func (device *Device) handlePeerLine(peer *ipcSetPeer, key, value string) error
 	case "replace_allowed_ips":
 		device.log.Verbosef("%v - UAPI: Removing all allowedips", peer.Peer)
 		if value != "true" {
-			return ipcErrorf(ipc.IpcErrorInvalid, "failed to replace allowedips, invalid value: %v", value)
+			return ipcErrorf(
+				ipc.IpcErrorInvalid,
+				"failed to replace allowedips, invalid value: %v",
+				value,
+			)
 		}
 		if peer.dummy {
 			return nil
@@ -442,7 +667,11 @@ func (device *Device) IpcHandle(socket net.Conn) {
 				return
 			}
 			if nextByte != '\n' {
-				err = ipcErrorf(ipc.IpcErrorInvalid, "trailing character in UAPI get: %q", nextByte)
+				err = ipcErrorf(
+					ipc.IpcErrorInvalid,
+					"trailing character in UAPI get: %q",
+					nextByte,
+				)
 				break
 			}
 			err = device.IpcGetOperation(buffered.Writer)
@@ -466,3 +695,49 @@ func (device *Device) IpcHandle(socket net.Conn) {
 		buffered.Flush()
 	}
 }
+
+type ipcSetDevice struct {
+	headers struct {
+		init      *magicHeader
+		response  *magicHeader
+		cookie    *magicHeader
+		transport *magicHeader
+	}
+}
+
+func (d *ipcSetDevice) mergeWithDevice(device *Device) error {
+	if d.headers.init == nil {
+		d.headers.init = device.headers.init
+	}
+
+	if d.headers.response == nil {
+		d.headers.response = device.headers.response
+	}
+
+	if d.headers.cookie == nil {
+		d.headers.cookie = device.headers.cookie
+	}
+
+	if d.headers.transport == nil {
+		d.headers.transport = device.headers.transport
+	}
+
+	headers := []*magicHeader{d.headers.init, d.headers.response, d.headers.cookie, d.headers.transport}
+	for i := 0; i < len(headers); i++ {
+		for j := i + 1; j < len(headers); j++ {
+			left := headers[i]
+			right := headers[j]
+
+			if left.start <= right.end && right.start <= left.end {
+				return errors.New("headers must not overlap")
+			}
+		}
+	}
+
+	device.headers.init = d.headers.init
+	device.headers.response = d.headers.response
+	device.headers.cookie = d.headers.cookie
+	device.headers.transport = d.headers.transport
+
+	return nil
+}