zwing v0.1.0: Z-Wing PQ secure channel for Lux

Z-Wing is the canonical Lux post-quantum secure channel. One construction, one wire format, no negotiation. Layered design exposes a net.Conn so luxfi/api/zap (and any other stream protocol) runs unchanged on top. KEM: X-Wing (X25519 + ML-KEM-768, IETF draft-connolly-cfrg-xwing-kem SHA3-256 combiner: "\./" || "X-Wing" || ssM || ssX || ctX || pkX) Identity: Ed25519 + ML-DSA-65 hybrid signatures AEAD: ChaCha20-Poly1305 with sequence-numbered nonces (per direction) Transport: TCP (RNS routing is a follow-up package) Public API: GenerateIdentity / Dial / Listen / Client / Server. Six tests cover the spec end-to-end: handshake round-trip, TCP dial+listen, ExpectedRemote pinning, key-zero-after-handshake forward secrecy, sequenced nonces, and ZAP-over-Z-Wing application round-trip.
2026-09-24 00:24:38 +00:00 · 2026-05-06 12:18:21 -07:00
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+BSD 3-Clause License
+
+Copyright (c) 2024, Lux Partners Limited
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+1. Redistributions of source code must retain the above copyright notice, this
+   list of conditions and the following disclaimer.
+
+2. Redistributions in binary form must reproduce the above copyright notice,
+   this list of conditions and the following disclaimer in the documentation
+   and/or other materials provided with the distribution.
+
+3. Neither the name of the copyright holder nor the names of its
+   contributors may be used to endorse or promote products derived from
+   this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
@@ -0,0 +1,202 @@
+# Z-Wing — Lux Post-Quantum Secure Channel
+
+## Overview
+
+Z-Wing is the canonical Lux PQ secure channel. One construction, one wire
+format, no negotiation. If two endpoints don't both speak Z-Wing v1, they
+don't talk.
+
+Layering:
+
+```
+Application:  ZAP RPC (luxfi/api/zap)            <- unchanged
+Channel:      Z-Wing                              <- this package
+  KEM:        X-Wing  (X25519 + ML-KEM-768, IETF draft-connolly-cfrg-xwing-kem)
+  Identity:   Ed25519 + ML-DSA-65 hybrid signatures
+  AEAD:       ChaCha20-Poly1305 with sequence-numbered nonces
+Routing:      Plain TCP (this version) or RNS (follow-up)
+```
+
+The `Conn` returned by `Dial` / `Listener.Accept()` implements `net.Conn`,
+so any Lux service that already speaks ZAP gets PQ on the wire by simply
+swapping its dialer:
+
+```go
+raw, _ := zwing.Dial(ctx, "host:9999", &zwing.Config{LocalIdentity: id})
+zapConn := zap.NewConn(raw, nil)   // ZAP unchanged
+```
+
+## Default port
+
+Z-Wing inherits the canonical Lux ZAP port: **TCP 9999**. Override only
+when running multiple Z-Wing servers on the same host.
+
+## Wire format
+
+### Frame
+
+Every transport frame on a Z-Wing channel:
+
+```
+[4 bytes BE: payload length][payload bytes]
+```
+
+`MaxFrameSize` = 1 MiB. The `payload` is either a handshake message
+(during the handshake) or an AEAD-sealed application record (after).
+
+### Handshake (1-RTT)
+
+```
+Initiator -> Responder : HandshakeInit
+    [2 BE idLen][IdentityPublic bytes][2 BE sigLen][hybrid signature]
+
+Responder -> Initiator : HandshakeResponse
+    [XWingCiphertextSize bytes: ML-KEM ct || X25519 ephemeral pk]
+    [2 BE encLen][AEAD-sealed responder identity + signature]
+```
+
+* The initiator signs `(label || IdentityPublic)` so a passive observer
+  cannot lift the public identity onto another protocol.
+* The responder signs the **transcript hash** that covers the initiator's
+  public identity AND the X-Wing ciphertext, binding the signature to
+  the session.
+* The responder identity is encrypted under an HKDF-derived key from the
+  X-Wing shared secret, so passive observers do not learn the responder's
+  long-term identity.
+
+### IdentityPublic
+
+```
+[Ed25519 pk: 32][ML-DSA-65 pk: 1952][X-Wing pk: 1216]
+              total: 3200 bytes
+```
+
+`X-Wing pk = ML-KEM-768 pk (1184) || X25519 pk (32)`.
+
+## X-Wing combiner (IETF spec, exact)
+
+```
+shared_secret = SHA3-256( "\./" || "X-Wing" || ss_M || ss_X || ct_X || pk_X )
+```
+
+| Input | Bytes | Source |
+|---|---|---|
+| `"\./"`   | 3   | label prefix (backslash, dot, slash) |
+| `"X-Wing"` | 6   | ASCII protocol name |
+| `ss_M`    | 32  | ML-KEM-768 shared secret |
+| `ss_X`    | 32  | X25519 shared secret |
+| `ct_X`    | 32  | X25519 ephemeral public key from encapsulator |
+| `pk_X`    | 32  | X25519 static public key of recipient |
+
+Hash construction: SHA3-256, no HKDF. Inputs are fixed-length so no
+length separators are required.
+
+In the Z-Wing handshake the **responder is the encapsulator** (it sends
+ct_X) and the **initiator is the recipient** (its X-Wing static is the
+target of the encapsulation).
+
+## Channel keys
+
+After the handshake:
+
+```
+keyI2R = HKDF-SHA256(shared, "lux.zwing.v1/i2r", 32)
+keyR2I = HKDF-SHA256(shared, "lux.zwing.v1/r2i", 32)
+```
+
+Each direction has its own ChaCha20-Poly1305 key. Nonce = 12 bytes,
+high 4 bytes zero, low 8 bytes are the big-endian sequence counter.
+A 64-bit counter would last 5.8e11 years at one record per nanosecond;
+exhausting it returns `ErrSequenceExhausted`.
+
+Forward secrecy comes from the X25519 ephemeral inside X-Wing. The
+ephemeral private key and intermediate `ss_M` / `ss_X` values are zeroed
+once the shared secret is derived. Channel keys are zeroed after the
+AEADs have been constructed.
+
+## Identity signatures
+
+The `Identity` type holds three keypairs: Ed25519, ML-DSA-65, and X-Wing.
+Signature wire format:
+
+```
+[Ed25519 sig: 64][ML-DSA-65 sig: 3309]   total: 3373 bytes
+```
+
+Both must verify or `ErrSignatureInvalid` is returned. ML-DSA is signed
+with the `lux.zwing.v1` context per FIPS 204 §5.2 so signatures are not
+portable across protocols that share identity keys.
+
+## Public API
+
+```go
+// Identity
+id, _ := zwing.GenerateIdentity()
+pub  := id.Public()                   // serialise + hand to a peer
+
+// Server
+ln, _ := zwing.Listen(":9999", &zwing.Config{LocalIdentity: id})
+for {
+    conn, err := ln.Accept()          // post-handshake net.Conn
+    if err != nil { break }
+    go handle(conn)
+}
+
+// Client
+conn, _ := zwing.Dial(ctx, "host:9999", &zwing.Config{
+    LocalIdentity:  clientID,
+    ExpectedRemote: pinnedServerPub,  // optional; nil = any valid peer
+})
+```
+
+`Client(net.Conn, *Config)` and `Server(net.Conn, *Config)` wrap an
+existing connection (Unix socket, TLS conn, in-memory pipe, RNS link)
+without TCP `Dial`/`Listen`.
+
+## What's NOT in this version
+
+* RNS routing. Z-Wing-over-RNS is a follow-up package (LP-9702 deployment
+  path); v0.1.0 ships Z-Wing-over-TCP only.
+* AES-256-GCM AEAD. Single ciphersuite; ChaCha20-Poly1305 only.
+* Cipher / KEM negotiation. There is one Z-Wing v1.
+
+## Testing
+
+```
+GOWORK=off go test ./... -count=1
+```
+
+Six tests cover the spec:
+
+| Test | What it proves |
+|---|---|
+| `TestHandshakeRoundTrip`   | end-to-end handshake; both peers see correct remote identity; bidirectional traffic works |
+| `TestDialListen`           | TCP `Dial` + `Listener.Accept`, payload round-trip |
+| `TestIdentityMismatch`     | `Config.ExpectedRemote = wrong` returns `ErrIdentityMismatch` |
+| `TestForwardSecrecy`       | channel keys are zeroed after the AEAD is constructed |
+| `TestSequencedNonces`      | three sequential records each decrypt cleanly under increasing nonces |
+| `TestZAPOverZWing`         | `zap.NewConn` over a Z-Wing client; one ZAP RPC round-trip succeeds |
+
+## Files
+
+| File | Purpose |
+|---|---|
+| `doc.go`        | package documentation |
+| `errors.go`     | typed errors |
+| `kem.go`        | X-Wing KEM (X25519 + ML-KEM-768 + SHA3-256 combiner) |
+| `identity.go`   | hybrid Ed25519 + ML-DSA-65 identity with X-Wing static key |
+| `wire.go`       | length-prefixed framing |
+| `handshake.go`  | initiator/responder state machines |
+| `channel.go`    | post-handshake `net.Conn` with ChaCha20-Poly1305 |
+| `config.go`     | `Config` and `DefaultPort` |
+| `dial.go`       | `Dial` / `Client` |
+| `listen.go`     | `Listen` / `Listener` |
+| `zwing_test.go` | core protocol tests |
+| `zap_test.go`   | ZAP-over-Z-Wing integration |
+
+## See also
+
+* `~/work/lux/api/zap/LLM.md` — the application protocol that runs on top
+* `~/work/zap/zap/src/crypto.rs` — Rust hybrid handshake reference
+* `~/work/lux/crypto` — ML-KEM, ML-DSA, Ed25519 primitives used here
+* `draft-connolly-cfrg-xwing-kem` — IETF X-Wing combiner spec
@@ -0,0 +1,200 @@
+// Copyright (C) 2020-2026, Lux Industries Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package zwing
+
+import (
+	"crypto/cipher"
+	"encoding/binary"
+	"errors"
+	"net"
+	"sync"
+	"time"
+
+	"golang.org/x/crypto/chacha20poly1305"
+)
+
+// Conn is a Z-Wing secure channel implementing net.Conn. After the
+// handshake, every Read/Write goes through ChaCha20-Poly1305 with
+// per-direction sequence-numbered nonces.
+type Conn struct {
+	raw    net.Conn
+	remote *IdentityPublic
+
+	readMu   sync.Mutex
+	readAEAD cipher.AEAD
+	readSeq  uint64
+	readBuf  []byte // overflow from a previous Read
+
+	writeMu   sync.Mutex
+	writeAEAD cipher.AEAD
+	writeSeq  uint64
+}
+
+// newConn wraps a freshly handshaken net.Conn. role determines which
+// direction's key is used for reading vs writing.
+func newConn(raw net.Conn, res *handshakeResult, initiator bool) (*Conn, error) {
+	c := &Conn{raw: raw, remote: res.remote}
+	var rxKey, txKey []byte
+	if initiator {
+		txKey = res.keyI2R
+		rxKey = res.keyR2I
+	} else {
+		txKey = res.keyR2I
+		rxKey = res.keyI2R
+	}
+	rx, err := chacha20poly1305.New(rxKey)
+	if err != nil {
+		return nil, err
+	}
+	tx, err := chacha20poly1305.New(txKey)
+	if err != nil {
+		return nil, err
+	}
+	c.readAEAD = rx
+	c.writeAEAD = tx
+	// Best-effort zeroing of the channel keys held by the handshake result
+	// once the AEADs have copied them internally.
+	zero(res.keyI2R)
+	zero(res.keyR2I)
+	return c, nil
+}
+
+// RemoteIdentity returns the verified remote IdentityPublic. Callers may
+// pin specific peers via Config.ExpectedRemote, but this getter lets
+// servers see who connected once the handshake succeeded.
+func (c *Conn) RemoteIdentity() *IdentityPublic { return c.remote }
+
+// Read reads decrypted plaintext into b. A Z-Wing record may be larger
+// than b, in which case the remainder is buffered for the next call.
+func (c *Conn) Read(b []byte) (int, error) {
+	c.readMu.Lock()
+	defer c.readMu.Unlock()
+
+	if len(c.readBuf) > 0 {
+		n := copy(b, c.readBuf)
+		c.readBuf = c.readBuf[n:]
+		if len(c.readBuf) == 0 {
+			c.readBuf = nil
+		}
+		return n, nil
+	}
+
+	frame, err := readFrame(c.raw)
+	if err != nil {
+		return 0, err
+	}
+	if c.readSeq == ^uint64(0) {
+		return 0, ErrSequenceExhausted
+	}
+	nonce := nonceFor(c.readSeq)
+	plaintext, err := c.readAEAD.Open(nil, nonce[:], frame, nil)
+	if err != nil {
+		return 0, ErrCiphertextCorrupted
+	}
+	c.readSeq++
+
+	n := copy(b, plaintext)
+	if n < len(plaintext) {
+		c.readBuf = plaintext[n:]
+	}
+	return n, nil
+}
+
+// Write encrypts b as a single Z-Wing record and writes it to the
+// underlying conn. Application payloads larger than MaxFrameSize-tag are
+// split.
+func (c *Conn) Write(b []byte) (int, error) {
+	c.writeMu.Lock()
+	defer c.writeMu.Unlock()
+
+	const maxPlain = MaxFrameSize - chacha20poly1305.Overhead
+	written := 0
+	for written < len(b) {
+		end := written + maxPlain
+		if end > len(b) {
+			end = len(b)
+		}
+		chunk := b[written:end]
+
+		if c.writeSeq == ^uint64(0) {
+			return written, ErrSequenceExhausted
+		}
+		nonce := nonceFor(c.writeSeq)
+		ciphertext := c.writeAEAD.Seal(nil, nonce[:], chunk, nil)
+		c.writeSeq++
+
+		if err := writeFrame(c.raw, ciphertext); err != nil {
+			return written, err
+		}
+		written += len(chunk)
+	}
+	return written, nil
+}
+
+// Close closes the underlying connection.
+func (c *Conn) Close() error {
+	if c.raw == nil {
+		return ErrChannelClosed
+	}
+	return c.raw.Close()
+}
+
+// LocalAddr returns the underlying local address.
+func (c *Conn) LocalAddr() net.Addr { return c.raw.LocalAddr() }
+
+// RemoteAddr returns the underlying remote address.
+func (c *Conn) RemoteAddr() net.Addr { return c.raw.RemoteAddr() }
+
+// SetDeadline sets read+write deadline on the underlying conn.
+func (c *Conn) SetDeadline(t time.Time) error { return c.raw.SetDeadline(t) }
+
+// SetReadDeadline sets the read deadline on the underlying conn.
+func (c *Conn) SetReadDeadline(t time.Time) error { return c.raw.SetReadDeadline(t) }
+
+// SetWriteDeadline sets the write deadline on the underlying conn.
+func (c *Conn) SetWriteDeadline(t time.Time) error { return c.raw.SetWriteDeadline(t) }
+
+// nonceFor builds a 12-byte ChaCha20-Poly1305 nonce from a 64-bit counter:
+// the high 4 bytes are zero, the low 8 are the big-endian counter.
+func nonceFor(seq uint64) [12]byte {
+	var n [12]byte
+	binary.BigEndian.PutUint64(n[4:], seq)
+	return n
+}
+
+// aeadSeal/aeadOpen are used during the handshake to protect the
+// responder identity payload. They use the X-Wing ciphertext as
+// associated data so the binding cannot be transplanted onto another
+// session.
+func aeadSeal(key, nonceLabel, aad, plaintext []byte) ([]byte, error) {
+	aead, err := chacha20poly1305.New(key)
+	if err != nil {
+		return nil, err
+	}
+	nonce := handshakeNonce(nonceLabel)
+	return aead.Seal(nil, nonce[:], plaintext, aad), nil
+}
+
+func aeadOpen(key, nonceLabel, aad, ciphertext []byte) ([]byte, error) {
+	aead, err := chacha20poly1305.New(key)
+	if err != nil {
+		return nil, err
+	}
+	nonce := handshakeNonce(nonceLabel)
+	pt, err := aead.Open(nil, nonce[:], ciphertext, aad)
+	if err != nil {
+		return nil, errors.New("zwing: handshake AEAD open failed")
+	}
+	return pt, nil
+}
+
+// handshakeNonce derives a 12-byte fixed nonce from a label. The key used
+// with this nonce is unique to a single handshake (HKDF over the X-Wing
+// shared secret with a session-specific label), so reusing the nonce is
+// safe.
+func handshakeNonce(label []byte) [12]byte {
+	var n [12]byte
+	copy(n[:], label)
+	return n
+}
@@ -0,0 +1,23 @@
+// Copyright (C) 2020-2026, Lux Industries Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package zwing
+
+import "time"
+
+// DefaultPort is the canonical Z-Wing TCP port.
+const DefaultPort = 9999
+
+// Config configures a Z-Wing dialer or listener.
+type Config struct {
+	// LocalIdentity is this endpoint's long-term identity. Required.
+	LocalIdentity *Identity
+
+	// ExpectedRemote pins the peer's expected public identity. If set, the
+	// handshake fails with ErrIdentityMismatch when the remote presents a
+	// different identity. Leave nil for "any peer with a valid identity".
+	ExpectedRemote *IdentityPublic
+
+	// HandshakeTimeout bounds the handshake itself. Zero means no timeout.
+	HandshakeTimeout time.Duration
+}
@@ -0,0 +1,61 @@
+// Copyright (C) 2020-2026, Lux Industries Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package zwing
+
+import (
+	"context"
+	"net"
+	"time"
+)
+
+// Dial connects to a Z-Wing listener at addr and runs the handshake.
+// The returned net.Conn is the post-handshake encrypted channel.
+func Dial(ctx context.Context, addr string, cfg *Config) (net.Conn, error) {
+	if cfg == nil || cfg.LocalIdentity == nil {
+		return nil, ErrConfigMissingID
+	}
+	d := net.Dialer{}
+	raw, err := d.DialContext(ctx, "tcp", addr)
+	if err != nil {
+		return nil, err
+	}
+	return clientHandshake(raw, cfg)
+}
+
+// Client wraps an existing net.Conn (e.g. a TLS conn, a Unix socket, a
+// pipe) and runs the Z-Wing handshake on top as the initiator.
+func Client(raw net.Conn, cfg *Config) (net.Conn, error) {
+	return clientHandshake(raw, cfg)
+}
+
+// Server wraps an existing net.Conn and runs the handshake as the responder.
+func Server(raw net.Conn, cfg *Config) (net.Conn, error) {
+	return serverHandshake(raw, cfg)
+}
+
+func clientHandshake(raw net.Conn, cfg *Config) (net.Conn, error) {
+	if cfg.HandshakeTimeout > 0 {
+		_ = raw.SetDeadline(time.Now().Add(cfg.HandshakeTimeout))
+		defer raw.SetDeadline(time.Time{})
+	}
+	res, err := runInitiator(raw, cfg)
+	if err != nil {
+		raw.Close()
+		return nil, err
+	}
+	return newConn(raw, res, true)
+}
+
+func serverHandshake(raw net.Conn, cfg *Config) (net.Conn, error) {
+	if cfg.HandshakeTimeout > 0 {
+		_ = raw.SetDeadline(time.Now().Add(cfg.HandshakeTimeout))
+		defer raw.SetDeadline(time.Time{})
+	}
+	res, err := runResponder(raw, cfg)
+	if err != nil {
+		raw.Close()
+		return nil, err
+	}
+	return newConn(raw, res, false)
+}
@@ -0,0 +1,30 @@
+// Copyright (C) 2020-2026, Lux Industries Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+// Package zwing implements Z-Wing, the canonical Lux post-quantum secure
+// channel. It provides an authenticated, forward-secret, hybrid PQ tunnel
+// that exposes a net.Conn so application protocols (e.g. luxfi/api/zap)
+// run unchanged on top.
+//
+// Layering:
+//
+//	Application: ZAP RPC (luxfi/api/zap)            <- unchanged
+//	Channel:     Z-Wing (this package)
+//	  KEM:       X-Wing  (X25519 + ML-KEM-768, IETF draft-connolly-cfrg-xwing-kem)
+//	  Identity:  Ed25519 + ML-DSA-65 hybrid signatures
+//	  AEAD:      ChaCha20-Poly1305, sequence-numbered nonces
+//	Routing:     Plain TCP (this version) or RNS (follow-up package)
+//
+// Z-Wing is one construction. There are no alternates, no build tags, no
+// cipher negotiation. The point of standardising is that two endpoints
+// either speak Z-Wing v1 or they don't talk.
+//
+// Public API:
+//
+//	id, _ := zwing.GenerateIdentity()
+//	ln, _ := zwing.Listen(":9999", &zwing.Config{LocalIdentity: id})
+//	conn, _ := zwing.Dial(ctx, "host:9999", &zwing.Config{LocalIdentity: clientID})
+//
+// `conn` and the result of `ln.Accept()` both implement net.Conn and can be
+// passed to zap.NewConn, http.Serve, or anything else that wants a stream.
+package zwing
@@ -0,0 +1,19 @@
+// Copyright (C) 2020-2026, Lux Industries Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package zwing
+
+import "errors"
+
+var (
+	ErrHandshakeFailed     = errors.New("zwing: handshake failed")
+	ErrIdentityMismatch    = errors.New("zwing: remote identity does not match expected")
+	ErrSignatureInvalid    = errors.New("zwing: signature verification failed")
+	ErrMessageTooLarge     = errors.New("zwing: message exceeds maximum size")
+	ErrShortRead           = errors.New("zwing: short read")
+	ErrInvalidWireFormat   = errors.New("zwing: invalid wire format")
+	ErrChannelClosed       = errors.New("zwing: channel closed")
+	ErrSequenceExhausted   = errors.New("zwing: AEAD sequence number exhausted")
+	ErrConfigMissingID     = errors.New("zwing: config missing LocalIdentity")
+	ErrCiphertextCorrupted = errors.New("zwing: AEAD authentication failed")
+)
@@ -0,0 +1,15 @@
+module github.com/luxfi/zwing
+
+go 1.26.2
+
+require (
+	github.com/luxfi/api v1.0.9
+	github.com/luxfi/crypto v1.18.3
+	golang.org/x/crypto v0.50.0
+)
+
+require (
+	github.com/cloudflare/circl v1.6.3 // indirect
+	github.com/luxfi/accel v1.0.7 // indirect
+	golang.org/x/sys v0.43.0 // indirect
+)
@@ -0,0 +1,12 @@
+github.com/cloudflare/circl v1.6.3 h1:9GPOhQGF9MCYUeXyMYlqTR6a5gTrgR/fBLXvUgtVcg8=
+github.com/cloudflare/circl v1.6.3/go.mod h1:2eXP6Qfat4O/Yhh8BznvKnJ+uzEoTQ6jVKJRn81BiS4=
+github.com/luxfi/accel v1.0.7 h1:ksHieAp50umwqxqgyHk9WiOmXM54kia3IEDb5H7FsM8=
+github.com/luxfi/accel v1.0.7/go.mod h1:iZD3oxffiMEIT/KvzD8bgwC/cBn4AYlMW3QJpbRa4RE=
+github.com/luxfi/api v1.0.9 h1:JuuKdJ6EaYCJSaZLB0xUWU470kbCnEklWcSOGIfl4Aw=
+github.com/luxfi/api v1.0.9/go.mod h1:5OFWvZF+PbyuvLCDyKKpXCA/xp+LxJ32yOhNEKwQFN0=
+github.com/luxfi/crypto v1.18.3 h1:f6mBUHNjZl9/9nXPSqjq+oJttrPl8slvcZ49Vi7jKw4=
+github.com/luxfi/crypto v1.18.3/go.mod h1:qBtCJDT6p6aNa2hMtPxYwC688Bnsb3Amso8q09GsMls=
+golang.org/x/crypto v0.50.0 h1:zO47/JPrL6vsNkINmLoo/PH1gcxpls50DNogFvB5ZGI=
+golang.org/x/crypto v0.50.0/go.mod h1:3muZ7vA7PBCE6xgPX7nkzzjiUq87kRItoJQM1Yo8S+Q=
+golang.org/x/sys v0.43.0 h1:Rlag2XtaFTxp19wS8MXlJwTvoh8ArU6ezoyFsMyCTNI=
+golang.org/x/sys v0.43.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
@@ -0,0 +1,366 @@
+// Copyright (C) 2020-2026, Lux Industries Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package zwing
+
+import (
+	"crypto/sha256"
+	"encoding/binary"
+	"io"
+
+	"golang.org/x/crypto/hkdf"
+)
+
+// Handshake is the Z-Wing 1-RTT mutual-auth handshake.
+//
+//	Initiator -> Responder : HandshakeInit
+//	    initiator IdentityPublic || ML-DSA+Ed25519 sig over (label || init pub)
+//
+//	Responder -> Initiator : HandshakeResponse
+//	    XWing ciphertext || encrypted{ responder IdentityPublic || sig }
+//
+// After both messages, both sides hold the same X-Wing shared secret
+// derived against initiator's static X-Wing key. Forward secrecy is
+// provided by the X25519 ephemeral inside X-Wing and by zeroing all
+// intermediate key material once channel keys are derived.
+//
+// Identity-binding: the responder signs a transcript hash that covers
+// the initiator's identity material AND the X-Wing ciphertext, so the
+// signature can't be replayed onto another session.
+
+const (
+	hsLabelInit     = "lux.zwing.v1/handshake-init"
+	hsLabelResponse = "lux.zwing.v1/handshake-response"
+
+	channelKeyLabelI2R = "lux.zwing.v1/i2r"
+	channelKeyLabelR2I = "lux.zwing.v1/r2i"
+
+	chacha20KeySize = 32
+)
+
+// HandshakeInit is the wire form of the initiator's first message.
+type HandshakeInit struct {
+	IdentityPub []byte // serialised IdentityPublic
+	Signature   []byte // identity signature over label || IdentityPub
+}
+
+// HandshakeResponse is the wire form of the responder's reply. The
+// identity payload is encrypted under a key derived from the X-Wing
+// shared secret so the responder identity is not revealed to passive
+// observers.
+type HandshakeResponse struct {
+	XWingCiphertext []byte // X-Wing ct (1088+32 bytes)
+	EncryptedID     []byte // AEAD-sealed responder identity + signature
+}
+
+// MarshalBinary encodes a HandshakeInit as
+//
+//	[2 bytes BE: idLen][id bytes][2 bytes BE: sigLen][sig bytes]
+func (h *HandshakeInit) MarshalBinary() []byte {
+	out := make([]byte, 0, 4+len(h.IdentityPub)+len(h.Signature))
+	out = appendU16(out, len(h.IdentityPub))
+	out = append(out, h.IdentityPub...)
+	out = appendU16(out, len(h.Signature))
+	out = append(out, h.Signature...)
+	return out
+}
+
+func parseHandshakeInit(data []byte) (*HandshakeInit, error) {
+	r := newSliceReader(data)
+	idLen, err := r.readU16()
+	if err != nil {
+		return nil, err
+	}
+	id, err := r.readN(int(idLen))
+	if err != nil {
+		return nil, err
+	}
+	sigLen, err := r.readU16()
+	if err != nil {
+		return nil, err
+	}
+	sig, err := r.readN(int(sigLen))
+	if err != nil {
+		return nil, err
+	}
+	if !r.empty() {
+		return nil, ErrInvalidWireFormat
+	}
+	return &HandshakeInit{IdentityPub: id, Signature: sig}, nil
+}
+
+// MarshalBinary encodes a HandshakeResponse as
+//
+//	[XWingCiphertextSize bytes][2 bytes BE: encLen][enc bytes]
+func (h *HandshakeResponse) MarshalBinary() []byte {
+	out := make([]byte, 0, XWingCiphertextSize+2+len(h.EncryptedID))
+	out = append(out, h.XWingCiphertext...)
+	out = appendU16(out, len(h.EncryptedID))
+	out = append(out, h.EncryptedID...)
+	return out
+}
+
+func parseHandshakeResponse(data []byte) (*HandshakeResponse, error) {
+	if len(data) < XWingCiphertextSize+2 {
+		return nil, ErrInvalidWireFormat
+	}
+	r := newSliceReader(data)
+	ct, err := r.readN(XWingCiphertextSize)
+	if err != nil {
+		return nil, err
+	}
+	encLen, err := r.readU16()
+	if err != nil {
+		return nil, err
+	}
+	enc, err := r.readN(int(encLen))
+	if err != nil {
+		return nil, err
+	}
+	if !r.empty() {
+		return nil, ErrInvalidWireFormat
+	}
+	return &HandshakeResponse{XWingCiphertext: ct, EncryptedID: enc}, nil
+}
+
+// handshakeResult holds the data both sides agree on after a successful run.
+type handshakeResult struct {
+	shared [XWingSharedSize]byte
+	remote *IdentityPublic
+	keyI2R []byte // 32 bytes, initiator->responder AEAD key
+	keyR2I []byte // 32 bytes, responder->initiator AEAD key
+}
+
+// runInitiator drives the initiator side of the handshake on conn.
+func runInitiator(conn io.ReadWriter, cfg *Config) (*handshakeResult, error) {
+	if cfg == nil || cfg.LocalIdentity == nil {
+		return nil, ErrConfigMissingID
+	}
+	local := cfg.LocalIdentity
+
+	// 1. Send HandshakeInit.
+	idPub := local.Public().MarshalBinary()
+	sig, err := local.Sign([]byte(hsLabelInit), idPub)
+	if err != nil {
+		return nil, err
+	}
+	init := &HandshakeInit{IdentityPub: idPub, Signature: sig}
+	if err := writeFrame(conn, init.MarshalBinary()); err != nil {
+		return nil, err
+	}
+
+	// 2. Receive HandshakeResponse.
+	respFrame, err := readFrame(conn)
+	if err != nil {
+		return nil, err
+	}
+	resp, err := parseHandshakeResponse(respFrame)
+	if err != nil {
+		return nil, err
+	}
+
+	// 3. Decapsulate X-Wing shared secret.
+	shared, err := XWingDecapsulate(local.XWing, resp.XWingCiphertext)
+	if err != nil {
+		return nil, err
+	}
+
+	// 4. Derive a temporary AEAD key for the responder-identity payload
+	//    and decrypt it. Then derive the channel keys from the same secret
+	//    via separate labels.
+	idKey := derive(shared[:], []byte("lux.zwing.v1/resp-id"), chacha20KeySize)
+	defer zero(idKey)
+	plaintext, err := aeadOpen(idKey, []byte("zwing-resp-id"), resp.XWingCiphertext, resp.EncryptedID)
+	if err != nil {
+		return nil, ErrCiphertextCorrupted
+	}
+
+	remoteID, remoteSig, err := splitRespIDPayload(plaintext)
+	if err != nil {
+		return nil, err
+	}
+	remote, err := ParseIdentityPublic(remoteID)
+	if err != nil {
+		return nil, err
+	}
+
+	// 5. Verify responder signature over transcript = init || ct.
+	transcript := transcriptHash(idPub, resp.XWingCiphertext)
+	if err := remote.Verify([]byte(hsLabelResponse), transcript, remoteSig); err != nil {
+		return nil, err
+	}
+
+	// 6. Optional pinning.
+	if cfg.ExpectedRemote != nil && !remote.Equal(cfg.ExpectedRemote) {
+		return nil, ErrIdentityMismatch
+	}
+
+	res := &handshakeResult{
+		shared: shared,
+		remote: remote,
+		keyI2R: derive(shared[:], []byte(channelKeyLabelI2R), chacha20KeySize),
+		keyR2I: derive(shared[:], []byte(channelKeyLabelR2I), chacha20KeySize),
+	}
+	return res, nil
+}
+
+// runResponder drives the responder side on conn.
+func runResponder(conn io.ReadWriter, cfg *Config) (*handshakeResult, error) {
+	if cfg == nil || cfg.LocalIdentity == nil {
+		return nil, ErrConfigMissingID
+	}
+	local := cfg.LocalIdentity
+
+	// 1. Read HandshakeInit.
+	initFrame, err := readFrame(conn)
+	if err != nil {
+		return nil, err
+	}
+	init, err := parseHandshakeInit(initFrame)
+	if err != nil {
+		return nil, err
+	}
+	remote, err := ParseIdentityPublic(init.IdentityPub)
+	if err != nil {
+		return nil, err
+	}
+	if err := remote.Verify([]byte(hsLabelInit), init.IdentityPub, init.Signature); err != nil {
+		return nil, err
+	}
+
+	if cfg.ExpectedRemote != nil && !remote.Equal(cfg.ExpectedRemote) {
+		return nil, ErrIdentityMismatch
+	}
+
+	// 2. Encapsulate X-Wing to initiator's static key.
+	ct, shared, err := XWingEncapsulate(nil, remote.XWingPub)
+	if err != nil {
+		return nil, err
+	}
+
+	// 3. Sign transcript and seal local identity.
+	idPub := local.Public().MarshalBinary()
+	transcript := transcriptHash(init.IdentityPub, ct)
+	sig, err := local.Sign([]byte(hsLabelResponse), transcript)
+	if err != nil {
+		return nil, err
+	}
+
+	plaintext := buildRespIDPayload(idPub, sig)
+	idKey := derive(shared[:], []byte("lux.zwing.v1/resp-id"), chacha20KeySize)
+	defer zero(idKey)
+	ciphertext, err := aeadSeal(idKey, []byte("zwing-resp-id"), ct, plaintext)
+	if err != nil {
+		return nil, err
+	}
+
+	resp := &HandshakeResponse{XWingCiphertext: ct, EncryptedID: ciphertext}
+	if err := writeFrame(conn, resp.MarshalBinary()); err != nil {
+		return nil, err
+	}
+
+	res := &handshakeResult{
+		shared: shared,
+		remote: remote,
+		keyI2R: derive(shared[:], []byte(channelKeyLabelI2R), chacha20KeySize),
+		keyR2I: derive(shared[:], []byte(channelKeyLabelR2I), chacha20KeySize),
+	}
+	return res, nil
+}
+
+// derive runs HKDF-SHA256 over the X-Wing shared secret to produce a key
+// for the requested label. We use SHA-256 (not SHA3) here to avoid pulling
+// a second hash construction into the critical path; the underlying secret
+// is already SHA3-256-derived by the X-Wing combiner.
+func derive(secret, label []byte, size int) []byte {
+	out := make([]byte, size)
+	r := hkdf.New(sha256.New, secret, nil, label)
+	if _, err := io.ReadFull(r, out); err != nil {
+		// HKDF over a fixed-length input never fails for reasonable sizes.
+		panic(err)
+	}
+	return out
+}
+
+// transcriptHash binds the initiator's identity payload and the X-Wing
+// ciphertext into a single 32-byte hash that the responder signs.
+func transcriptHash(initPub, ct []byte) []byte {
+	h := sha256.New()
+	h.Write([]byte("lux.zwing.v1/transcript"))
+	binary.Write(h, binary.BigEndian, uint32(len(initPub)))
+	h.Write(initPub)
+	binary.Write(h, binary.BigEndian, uint32(len(ct)))
+	h.Write(ct)
+	return h.Sum(nil)
+}
+
+// buildRespIDPayload encodes the responder identity + signature as
+//
+//	[2 BE idLen][id][2 BE sigLen][sig]
+func buildRespIDPayload(id, sig []byte) []byte {
+	out := make([]byte, 0, 4+len(id)+len(sig))
+	out = appendU16(out, len(id))
+	out = append(out, id...)
+	out = appendU16(out, len(sig))
+	out = append(out, sig...)
+	return out
+}
+
+func splitRespIDPayload(data []byte) (id, sig []byte, err error) {
+	r := newSliceReader(data)
+	idLen, err := r.readU16()
+	if err != nil {
+		return nil, nil, err
+	}
+	id, err = r.readN(int(idLen))
+	if err != nil {
+		return nil, nil, err
+	}
+	sigLen, err := r.readU16()
+	if err != nil {
+		return nil, nil, err
+	}
+	sig, err = r.readN(int(sigLen))
+	if err != nil {
+		return nil, nil, err
+	}
+	if !r.empty() {
+		return nil, nil, ErrInvalidWireFormat
+	}
+	return id, sig, nil
+}
+
+// ── small helpers ────────────────────────────────────────────────────
+
+func appendU16(b []byte, n int) []byte {
+	if n < 0 || n > 0xFFFF {
+		panic("zwing: u16 out of range")
+	}
+	return append(b, byte(n>>8), byte(n))
+}
+
+type sliceReader struct {
+	buf []byte
+}
+
+func newSliceReader(b []byte) *sliceReader { return &sliceReader{buf: b} }
+
+func (r *sliceReader) readU16() (uint16, error) {
+	if len(r.buf) < 2 {
+		return 0, ErrShortRead
+	}
+	v := binary.BigEndian.Uint16(r.buf[:2])
+	r.buf = r.buf[2:]
+	return v, nil
+}
+
+func (r *sliceReader) readN(n int) ([]byte, error) {
+	if n < 0 || len(r.buf) < n {
+		return nil, ErrShortRead
+	}
+	out := r.buf[:n]
+	r.buf = r.buf[n:]
+	return out, nil
+}
+
+func (r *sliceReader) empty() bool { return len(r.buf) == 0 }
@@ -0,0 +1,176 @@
+// Copyright (C) 2020-2026, Lux Industries Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package zwing
+
+import (
+	"crypto/rand"
+	"crypto/sha256"
+	"crypto/subtle"
+	"errors"
+	"io"
+
+	"github.com/luxfi/crypto/ed25519"
+	"github.com/luxfi/crypto/mldsa"
+)
+
+// Identity binds a peer to long-term Ed25519 + ML-DSA-65 keys plus an
+// X-Wing static keypair used as the KEM recipient material.
+type Identity struct {
+	EdPub  ed25519.PublicKey
+	EdPriv ed25519.PrivateKey
+
+	DSAPriv *mldsa.PrivateKey
+
+	XWing *XWingPrivateKey
+}
+
+// IdentityPublic is the wire-serialisable, secrets-stripped half of an
+// Identity. It is what peers exchange and verify against.
+type IdentityPublic struct {
+	EdPub    ed25519.PublicKey
+	DSAPub   *mldsa.PublicKey
+	XWingPub *XWingPublicKey
+}
+
+// GenerateIdentity creates a fresh Z-Wing identity using crypto/rand.
+func GenerateIdentity() (*Identity, error) {
+	return GenerateIdentityFrom(rand.Reader)
+}
+
+// GenerateIdentityFrom creates an identity from a custom entropy source.
+// Useful for deterministic key generation in tests.
+func GenerateIdentityFrom(r io.Reader) (*Identity, error) {
+	edPub, edPriv, err := ed25519.GenerateKey(r)
+	if err != nil {
+		return nil, err
+	}
+	dsaPriv, err := mldsa.GenerateKey(r, mldsa.MLDSA65)
+	if err != nil {
+		return nil, err
+	}
+	xwing, err := GenerateXWingKey(r)
+	if err != nil {
+		return nil, err
+	}
+	return &Identity{
+		EdPub:   edPub,
+		EdPriv:  edPriv,
+		DSAPriv: dsaPriv,
+		XWing:   xwing,
+	}, nil
+}
+
+// Public returns the public half of the identity.
+func (id *Identity) Public() *IdentityPublic {
+	return &IdentityPublic{
+		EdPub:    id.EdPub,
+		DSAPub:   id.DSAPriv.PublicKey,
+		XWingPub: id.XWing.Public(),
+	}
+}
+
+// Sign produces the Z-Wing identity signature: an Ed25519 signature over
+// SHA-256(ctx || message) concatenated with an ML-DSA-65 signature over
+// the same digest. ctx is a hard-coded protocol label so signatures are
+// not portable across protocols.
+func (id *Identity) Sign(ctx, message []byte) ([]byte, error) {
+	digest := identityDigest(ctx, message)
+	edSig := ed25519.Sign(id.EdPriv, digest)
+	dsaSig, err := id.DSAPriv.SignCtx(rand.Reader, digest, []byte(zwingDomain))
+	if err != nil {
+		return nil, err
+	}
+	out := make([]byte, 0, ed25519.SignatureSize+mldsa.MLDSA65SignatureSize)
+	out = append(out, edSig...)
+	out = append(out, dsaSig...)
+	return out, nil
+}
+
+// Verify checks an identity signature produced by Sign.
+func (pub *IdentityPublic) Verify(ctx, message, signature []byte) error {
+	if len(signature) != ed25519.SignatureSize+mldsa.MLDSA65SignatureSize {
+		return ErrSignatureInvalid
+	}
+	digest := identityDigest(ctx, message)
+	edSig := signature[:ed25519.SignatureSize]
+	dsaSig := signature[ed25519.SignatureSize:]
+	if !ed25519.Verify(pub.EdPub, digest, edSig) {
+		return ErrSignatureInvalid
+	}
+	if !pub.DSAPub.VerifySignatureCtx(digest, dsaSig, []byte(zwingDomain)) {
+		return ErrSignatureInvalid
+	}
+	return nil
+}
+
+// MarshalBinary serialises the public identity:
+//
+//	[Ed25519 pk: 32][ML-DSA-65 pk: 1952][X-Wing pk: 1216]
+func (pub *IdentityPublic) MarshalBinary() []byte {
+	out := make([]byte, 0, IdentityPublicSize)
+	out = append(out, pub.EdPub...)
+	out = append(out, pub.DSAPub.Bytes()...)
+	out = append(out, pub.XWingPub.MarshalBinary()...)
+	return out
+}
+
+// ParseIdentityPublic decodes the wire format produced by MarshalBinary.
+func ParseIdentityPublic(data []byte) (*IdentityPublic, error) {
+	if len(data) != IdentityPublicSize {
+		return nil, errors.New("zwing: invalid public identity size")
+	}
+	off := 0
+	edPub := make(ed25519.PublicKey, ed25519.PublicKeySize)
+	copy(edPub, data[off:off+ed25519.PublicKeySize])
+	off += ed25519.PublicKeySize
+
+	dsaPubBytes := data[off : off+mldsa.MLDSA65PublicKeySize]
+	off += mldsa.MLDSA65PublicKeySize
+	dsaPub, err := mldsa.PublicKeyFromBytes(dsaPubBytes, mldsa.MLDSA65)
+	if err != nil {
+		return nil, err
+	}
+
+	xwingPub, err := ParseXWingPublicKey(data[off : off+XWingPublicKeySize])
+	if err != nil {
+		return nil, err
+	}
+	return &IdentityPublic{EdPub: edPub, DSAPub: dsaPub, XWingPub: xwingPub}, nil
+}
+
+// Equal reports whether two public identities have byte-identical key material.
+func (pub *IdentityPublic) Equal(other *IdentityPublic) bool {
+	if pub == nil || other == nil {
+		return false
+	}
+	if subtle.ConstantTimeCompare(pub.EdPub, other.EdPub) != 1 {
+		return false
+	}
+	if subtle.ConstantTimeCompare(pub.DSAPub.Bytes(), other.DSAPub.Bytes()) != 1 {
+		return false
+	}
+	if subtle.ConstantTimeCompare(pub.XWingPub.MarshalBinary(), other.XWingPub.MarshalBinary()) != 1 {
+		return false
+	}
+	return true
+}
+
+// IdentityPublicSize is the fixed-size wire encoding of an IdentityPublic.
+const IdentityPublicSize = ed25519.PublicKeySize +
+	mldsa.MLDSA65PublicKeySize +
+	XWingPublicKeySize
+
+// zwingDomain is the protocol domain separator. It is bound into every
+// identity signature so Z-Wing signatures cannot be replayed onto another
+// Lux protocol that signs with the same identity keys.
+const zwingDomain = "lux.zwing.v1"
+
+func identityDigest(ctx, message []byte) []byte {
+	h := sha256.New()
+	h.Write([]byte(zwingDomain))
+	h.Write([]byte{byte(len(ctx))})
+	h.Write(ctx)
+	h.Write(message)
+	return h.Sum(nil)
+}
@@ -0,0 +1,185 @@
+// Copyright (C) 2020-2026, Lux Industries Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package zwing
+
+import (
+	"crypto/rand"
+	"errors"
+	"io"
+
+	"github.com/luxfi/crypto/mlkem"
+	"golang.org/x/crypto/curve25519"
+	"golang.org/x/crypto/sha3"
+)
+
+// X-Wing combiner constants per draft-connolly-cfrg-xwing-kem.
+//
+// shared_secret = SHA3-256( "\./" || "X-Wing" || ss_M || ss_X || ct_X || pk_X )
+//
+//	ss_M   ML-KEM-768 shared secret (32 bytes)
+//	ss_X   X25519 shared secret (32 bytes)
+//	ct_X   X25519 ephemeral public key sent by encapsulator (32 bytes)
+//	pk_X   X25519 static public key of recipient (32 bytes)
+var (
+	xwingLabelPrefix = []byte{'\\', '.', '/'} // 3 bytes: backslash, dot, slash
+	xwingLabelName   = []byte("X-Wing")       // 6 bytes ASCII
+)
+
+// X-Wing wire sizes.
+const (
+	XWingPublicKeySize  = mlkem.MLKEM768PublicKeySize + curve25519.PointSize  // 1184 + 32
+	XWingCiphertextSize = mlkem.MLKEM768CiphertextSize + curve25519.PointSize // 1088 + 32
+	XWingSharedSize     = 32
+)
+
+// XWingPublicKey is the recipient's X-Wing static public key.
+type XWingPublicKey struct {
+	MLKEM  *mlkem.PublicKey
+	X25519 [32]byte
+}
+
+// XWingPrivateKey is the recipient's X-Wing static secret key plus the
+// matching public material needed for the combiner.
+type XWingPrivateKey struct {
+	MLKEMPriv  *mlkem.PrivateKey
+	X25519Priv [32]byte
+	X25519Pub  [32]byte
+}
+
+// Public returns the X-Wing public key.
+func (sk *XWingPrivateKey) Public() *XWingPublicKey {
+	return &XWingPublicKey{
+		MLKEM:  sk.MLKEMPriv.PublicKey(),
+		X25519: sk.X25519Pub,
+	}
+}
+
+// MarshalBinary serialises the X-Wing public key as ML-KEM-768 || X25519.
+func (pk *XWingPublicKey) MarshalBinary() []byte {
+	out := make([]byte, 0, XWingPublicKeySize)
+	out = append(out, pk.MLKEM.Bytes()...)
+	out = append(out, pk.X25519[:]...)
+	return out
+}
+
+// ParseXWingPublicKey decodes the wire format produced by MarshalBinary.
+func ParseXWingPublicKey(data []byte) (*XWingPublicKey, error) {
+	if len(data) != XWingPublicKeySize {
+		return nil, errors.New("zwing: invalid X-Wing public key size")
+	}
+	mlkemPK, err := mlkem.PublicKeyFromBytes(data[:mlkem.MLKEM768PublicKeySize], mlkem.MLKEM768)
+	if err != nil {
+		return nil, err
+	}
+	pk := &XWingPublicKey{MLKEM: mlkemPK}
+	copy(pk.X25519[:], data[mlkem.MLKEM768PublicKeySize:])
+	return pk, nil
+}
+
+// GenerateXWingKey produces a fresh X-Wing static keypair.
+func GenerateXWingKey(reader io.Reader) (*XWingPrivateKey, error) {
+	if reader == nil {
+		reader = rand.Reader
+	}
+	_, mlkemPriv, err := mlkem.GenerateKeyPair(reader, mlkem.MLKEM768)
+	if err != nil {
+		return nil, err
+	}
+	sk := &XWingPrivateKey{MLKEMPriv: mlkemPriv}
+	if _, err := io.ReadFull(reader, sk.X25519Priv[:]); err != nil {
+		return nil, err
+	}
+	pub, err := curve25519.X25519(sk.X25519Priv[:], curve25519.Basepoint)
+	if err != nil {
+		return nil, err
+	}
+	copy(sk.X25519Pub[:], pub)
+	return sk, nil
+}
+
+// XWingEncapsulate runs the encapsulator side. Output is (ciphertext, shared).
+// The ciphertext is ML-KEM-768 ct || X25519 ephemeral pk.
+func XWingEncapsulate(reader io.Reader, recipient *XWingPublicKey) (ciphertext []byte, shared [XWingSharedSize]byte, err error) {
+	if reader == nil {
+		reader = rand.Reader
+	}
+
+	mlkemCT, ssM, err := recipient.MLKEM.Encapsulate(reader)
+	if err != nil {
+		return nil, shared, err
+	}
+
+	var ephPriv [32]byte
+	if _, err := io.ReadFull(reader, ephPriv[:]); err != nil {
+		return nil, shared, err
+	}
+	ephPub, err := curve25519.X25519(ephPriv[:], curve25519.Basepoint)
+	if err != nil {
+		return nil, shared, err
+	}
+	ssX, err := curve25519.X25519(ephPriv[:], recipient.X25519[:])
+	if err != nil {
+		return nil, shared, err
+	}
+
+	shared = combineXWing(ssM, ssX, ephPub, recipient.X25519[:])
+
+	ciphertext = make([]byte, 0, XWingCiphertextSize)
+	ciphertext = append(ciphertext, mlkemCT...)
+	ciphertext = append(ciphertext, ephPub...)
+
+	zero(ephPriv[:])
+	zero(ssM)
+	zero(ssX)
+	return ciphertext, shared, nil
+}
+
+// XWingDecapsulate runs the recipient side.
+func XWingDecapsulate(sk *XWingPrivateKey, ciphertext []byte) ([XWingSharedSize]byte, error) {
+	var shared [XWingSharedSize]byte
+	if len(ciphertext) != XWingCiphertextSize {
+		return shared, errors.New("zwing: invalid X-Wing ciphertext size")
+	}
+	mlkemCT := ciphertext[:mlkem.MLKEM768CiphertextSize]
+	ephPub := ciphertext[mlkem.MLKEM768CiphertextSize:]
+
+	ssM, err := sk.MLKEMPriv.Decapsulate(mlkemCT)
+	if err != nil {
+		return shared, err
+	}
+	ssX, err := curve25519.X25519(sk.X25519Priv[:], ephPub)
+	if err != nil {
+		return shared, err
+	}
+
+	shared = combineXWing(ssM, ssX, ephPub, sk.X25519Pub[:])
+	zero(ssM)
+	zero(ssX)
+	return shared, nil
+}
+
+// combineXWing implements the IETF X-Wing KDF combiner exactly:
+//
+//	SHA3-256( "\./" || "X-Wing" || ss_M || ss_X || ct_X || pk_X )
+//
+// All inputs are fixed-length so no separators are needed: ss_M=32,
+// ss_X=32, ct_X=32, pk_X=32.
+func combineXWing(ssM, ssX, ctX, pkX []byte) [XWingSharedSize]byte {
+	h := sha3.New256()
+	h.Write(xwingLabelPrefix)
+	h.Write(xwingLabelName)
+	h.Write(ssM)
+	h.Write(ssX)
+	h.Write(ctX)
+	h.Write(pkX)
+	var out [XWingSharedSize]byte
+	copy(out[:], h.Sum(nil))
+	return out
+}
+
+func zero(b []byte) {
+	for i := range b {
+		b[i] = 0
+	}
+}
@@ -0,0 +1,43 @@
+// Copyright (C) 2020-2026, Lux Industries Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package zwing
+
+import "net"
+
+// Listener is a Z-Wing listener. Accepted connections are post-handshake
+// net.Conns ready for application traffic.
+type Listener struct {
+	raw net.Listener
+	cfg *Config
+}
+
+// Listen binds a TCP listener at addr that performs Z-Wing handshakes
+// before yielding connections.
+func Listen(addr string, cfg *Config) (*Listener, error) {
+	if cfg == nil || cfg.LocalIdentity == nil {
+		return nil, ErrConfigMissingID
+	}
+	raw, err := net.Listen("tcp", addr)
+	if err != nil {
+		return nil, err
+	}
+	return &Listener{raw: raw, cfg: cfg}, nil
+}
+
+// Accept returns the next handshaken connection. If a handshake fails
+// the underlying conn is closed and Accept returns the error; callers
+// that want to keep listening should call Accept again.
+func (l *Listener) Accept() (net.Conn, error) {
+	raw, err := l.raw.Accept()
+	if err != nil {
+		return nil, err
+	}
+	return serverHandshake(raw, l.cfg)
+}
+
+// Close closes the underlying TCP listener.
+func (l *Listener) Close() error { return l.raw.Close() }
+
+// Addr returns the listener's TCP address.
+func (l *Listener) Addr() net.Addr { return l.raw.Addr() }
@@ -0,0 +1,54 @@
+// Copyright (C) 2020-2026, Lux Industries Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package zwing
+
+import (
+	"encoding/binary"
+	"io"
+)
+
+// MaxFrameSize is the largest single transport frame Z-Wing will read or
+// write. Application bytes larger than this are split by the channel.
+const MaxFrameSize = 1 << 20 // 1 MiB
+
+// frame layout:
+//
+//	[4 bytes BE length][payload]
+//
+// length covers the payload only. payload is either a handshake message
+// (raw bytes) or an AEAD-sealed transport record.
+
+func writeFrame(w io.Writer, payload []byte) error {
+	if len(payload) > MaxFrameSize {
+		return ErrMessageTooLarge
+	}
+	var hdr [4]byte
+	binary.BigEndian.PutUint32(hdr[:], uint32(len(payload)))
+	if _, err := w.Write(hdr[:]); err != nil {
+		return err
+	}
+	if _, err := w.Write(payload); err != nil {
+		return err
+	}
+	return nil
+}
+
+func readFrame(r io.Reader) ([]byte, error) {
+	var hdr [4]byte
+	if _, err := io.ReadFull(r, hdr[:]); err != nil {
+		return nil, err
+	}
+	n := binary.BigEndian.Uint32(hdr[:])
+	if n > MaxFrameSize {
+		return nil, ErrMessageTooLarge
+	}
+	if n == 0 {
+		return nil, ErrInvalidWireFormat
+	}
+	buf := make([]byte, n)
+	if _, err := io.ReadFull(r, buf); err != nil {
+		return nil, err
+	}
+	return buf, nil
+}
@@ -0,0 +1,116 @@
+// Copyright (C) 2020-2026, Lux Industries Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package zwing_test
+
+import (
+	"bytes"
+	"context"
+	"net"
+	"testing"
+	"time"
+
+	"github.com/luxfi/api/zap"
+	"github.com/luxfi/zwing"
+)
+
+// TestZAPOverZWing wires a luxfi/api/zap client through a Z-Wing channel,
+// runs one request/response, and verifies the application bytes survive
+// the encrypted transport unchanged.
+func TestZAPOverZWing(t *testing.T) {
+	clientID, err := zwing.GenerateIdentity()
+	if err != nil {
+		t.Fatalf("client id: %v", err)
+	}
+	serverID, err := zwing.GenerateIdentity()
+	if err != nil {
+		t.Fatalf("server id: %v", err)
+	}
+
+	ln, err := zwing.Listen("127.0.0.1:0", &zwing.Config{LocalIdentity: serverID})
+	if err != nil {
+		t.Fatalf("listen: %v", err)
+	}
+	defer ln.Close()
+
+	srvDone := make(chan error, 1)
+	go func() {
+		srvDone <- runZAPEchoServer(ln)
+	}()
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+	cConn, err := zwing.Dial(ctx, ln.Addr().String(), &zwing.Config{LocalIdentity: clientID})
+	if err != nil {
+		t.Fatalf("dial: %v", err)
+	}
+	defer cConn.Close()
+
+	zapConn := zap.NewConn(cConn, nil)
+	defer zapConn.Close()
+
+	payload := []byte("zap-over-zwing")
+	respType, respPayload, err := zapConn.Call(ctx, zap.MsgBuildBlock, payload)
+	if err != nil {
+		t.Fatalf("zap call: %v", err)
+	}
+	if respType&zap.MsgResponseFlag == 0 {
+		t.Fatalf("response missing MsgResponseFlag")
+	}
+	if !bytes.Equal(respPayload, payload) {
+		t.Fatalf("payload mismatch: got %q want %q", respPayload, payload)
+	}
+
+	// Close the client side first so the server's blocking ReadMessage
+	// returns EOF promptly, then close the listener.
+	zapConn.Close()
+	cConn.Close()
+	ln.Close()
+	select {
+	case err := <-srvDone:
+		if err != nil && err != net.ErrClosed {
+			t.Logf("server exited: %v", err)
+		}
+	case <-time.After(2 * time.Second):
+		t.Fatal("server did not exit after closing client and listener")
+	}
+}
+
+// runZAPEchoServer accepts one Z-Wing conn and runs a tiny ZAP echo loop
+// using the zap wire helpers directly so we don't need to construct a
+// full zap.Server (which would need a Listener built from a net.Listener,
+// not from zwing.Listener).
+func runZAPEchoServer(ln *zwing.Listener) error {
+	conn, err := ln.Accept()
+	if err != nil {
+		return err
+	}
+	defer conn.Close()
+
+	// Read one request frame, echo it back with the response flag set.
+	for {
+		msgType, payload, err := zap.ReadMessage(readerOf(conn))
+		if err != nil {
+			return err
+		}
+		if len(payload) < 4 {
+			return nil
+		}
+		// payload is [reqID:uint32][body...]; echo body back with reqID.
+		body := payload[4:]
+		respPayload := make([]byte, 4+len(body))
+		copy(respPayload[:4], payload[:4])
+		copy(respPayload[4:], body)
+		if err := zap.WriteMessage(writerOf(conn), msgType|zap.MsgResponseFlag, respPayload); err != nil {
+			return err
+		}
+	}
+}
+
+// readerOf / writerOf wrap a net.Conn so the zap wire helpers see plain
+// io.Reader / io.Writer (which they require).
+type readerOnly struct{ net.Conn }
+type writerOnly struct{ net.Conn }
+
+func readerOf(c net.Conn) readerOnly { return readerOnly{c} }
+func writerOf(c net.Conn) writerOnly { return writerOnly{c} }
@@ -0,0 +1,238 @@
+// Copyright (C) 2020-2026, Lux Industries Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package zwing
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"net"
+	"sync"
+	"testing"
+	"time"
+)
+
+func newPair(t *testing.T) (clientID, serverID *Identity) {
+	t.Helper()
+	c, err := GenerateIdentity()
+	if err != nil {
+		t.Fatalf("client identity: %v", err)
+	}
+	s, err := GenerateIdentity()
+	if err != nil {
+		t.Fatalf("server identity: %v", err)
+	}
+	return c, s
+}
+
+// pipeConn turns a net.Pipe end into a deadline-supporting conn. net.Pipe
+// already gives us net.Conns; we just plumb both ends.
+
+// runHandshakeOverPipe drives one initiator and one responder over a
+// memory pipe with the given configs and returns both Conns or the first
+// error.
+func runHandshakeOverPipe(t *testing.T, clientCfg, serverCfg *Config) (cConn, sConn net.Conn, cErr, sErr error) {
+	t.Helper()
+	left, right := net.Pipe()
+	var wg sync.WaitGroup
+	wg.Add(2)
+	go func() {
+		defer wg.Done()
+		c, err := Client(left, clientCfg)
+		cConn = c
+		cErr = err
+	}()
+	go func() {
+		defer wg.Done()
+		s, err := Server(right, serverCfg)
+		sConn = s
+		sErr = err
+	}()
+	wg.Wait()
+	return cConn, sConn, cErr, sErr
+}
+
+func TestHandshakeRoundTrip(t *testing.T) {
+	clientID, serverID := newPair(t)
+	cConn, sConn, cErr, sErr := runHandshakeOverPipe(t,
+		&Config{LocalIdentity: clientID},
+		&Config{LocalIdentity: serverID},
+	)
+	if cErr != nil || sErr != nil {
+		t.Fatalf("handshake errors: client=%v server=%v", cErr, sErr)
+	}
+	defer cConn.Close()
+	defer sConn.Close()
+
+	// The remote identities should be the peers'.
+	cRemote := cConn.(*Conn).RemoteIdentity()
+	sRemote := sConn.(*Conn).RemoteIdentity()
+	if !cRemote.Equal(serverID.Public()) {
+		t.Fatal("client did not see server identity")
+	}
+	if !sRemote.Equal(clientID.Public()) {
+		t.Fatal("server did not see client identity")
+	}
+
+	// Round-trip a payload in both directions.  net.Pipe is synchronous
+	// so writes must overlap with reads on the peer.
+	payload := []byte("z-wing flies")
+	wErr := make(chan error, 1)
+	go func() { _, e := cConn.Write(payload); wErr <- e }()
+	buf := make([]byte, len(payload))
+	if _, err := sConn.Read(buf); err != nil {
+		t.Fatalf("server read: %v", err)
+	}
+	if err := <-wErr; err != nil {
+		t.Fatalf("client write: %v", err)
+	}
+	if !bytes.Equal(buf, payload) {
+		t.Fatalf("c->s: got %q want %q", buf, payload)
+	}
+
+	go func() { _, _ = sConn.Write([]byte("ack")) }()
+	buf = make([]byte, 3)
+	if _, err := cConn.Read(buf); err != nil {
+		t.Fatalf("client read: %v", err)
+	}
+	if !bytes.Equal(buf, []byte("ack")) {
+		t.Fatalf("s->c: got %q want %q", buf, "ack")
+	}
+}
+
+func TestDialListen(t *testing.T) {
+	clientID, serverID := newPair(t)
+
+	ln, err := Listen("127.0.0.1:0", &Config{LocalIdentity: serverID})
+	if err != nil {
+		t.Fatalf("listen: %v", err)
+	}
+	defer ln.Close()
+
+	type accepted struct {
+		c   net.Conn
+		err error
+	}
+	acceptCh := make(chan accepted, 1)
+	go func() {
+		c, err := ln.Accept()
+		acceptCh <- accepted{c: c, err: err}
+	}()
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+	cConn, err := Dial(ctx, ln.Addr().String(), &Config{LocalIdentity: clientID})
+	if err != nil {
+		t.Fatalf("dial: %v", err)
+	}
+	defer cConn.Close()
+
+	a := <-acceptCh
+	if a.err != nil {
+		t.Fatalf("accept: %v", a.err)
+	}
+	defer a.c.Close()
+
+	msg := []byte("hello over tcp")
+	if _, err := cConn.Write(msg); err != nil {
+		t.Fatalf("write: %v", err)
+	}
+	buf := make([]byte, len(msg))
+	if _, err := a.c.Read(buf); err != nil {
+		t.Fatalf("read: %v", err)
+	}
+	if !bytes.Equal(buf, msg) {
+		t.Fatalf("got %q want %q", buf, msg)
+	}
+}
+
+func TestIdentityMismatch(t *testing.T) {
+	clientID, serverID := newPair(t)
+	_, otherID := newPair(t)
+
+	_, _, cErr, sErr := runHandshakeOverPipe(t,
+		// Client expects a server identity that does not match.
+		&Config{LocalIdentity: clientID, ExpectedRemote: otherID.Public()},
+		&Config{LocalIdentity: serverID},
+	)
+	if !errors.Is(cErr, ErrIdentityMismatch) {
+		t.Fatalf("client: want ErrIdentityMismatch, got %v", cErr)
+	}
+	// Server side may either succeed in writing then see the conn close,
+	// or fail with a pipe error - we don't pin the exact behaviour.
+	_ = sErr
+}
+
+func TestForwardSecrecy(t *testing.T) {
+	clientID, serverID := newPair(t)
+	cConn, sConn, cErr, sErr := runHandshakeOverPipe(t,
+		&Config{LocalIdentity: clientID},
+		&Config{LocalIdentity: serverID},
+	)
+	if cErr != nil || sErr != nil {
+		t.Fatalf("handshake: %v / %v", cErr, sErr)
+	}
+	defer cConn.Close()
+	defer sConn.Close()
+
+	// The post-handshake Conn must not retain any handshake-scoped raw
+	// key material in exported fields. The handshakeResult.keyI2R / keyR2I
+	// slices are zeroed after AEADs are constructed (see newConn). We can
+	// verify by introspecting the result via a fresh handshake and
+	// inspecting keys-after-zero.
+	res := &handshakeResult{
+		shared: [XWingSharedSize]byte{},
+		keyI2R: derive([]byte{1, 2, 3}, []byte("k1"), 32),
+		keyR2I: derive([]byte{1, 2, 3}, []byte("k2"), 32),
+	}
+	left, right := net.Pipe()
+	defer left.Close()
+	defer right.Close()
+	c, err := newConn(left, res, true)
+	if err != nil {
+		t.Fatalf("newConn: %v", err)
+	}
+	_ = c
+	// After newConn the slices fed in should be zeroed.
+	for i, b := range res.keyI2R {
+		if b != 0 {
+			t.Fatalf("keyI2R[%d] not zeroed: 0x%x", i, b)
+		}
+	}
+	for i, b := range res.keyR2I {
+		if b != 0 {
+			t.Fatalf("keyR2I[%d] not zeroed: 0x%x", i, b)
+		}
+	}
+}
+
+// TestSequencedNonces makes sure two messages in a row use distinct
+// nonces and decrypt independently.
+func TestSequencedNonces(t *testing.T) {
+	clientID, serverID := newPair(t)
+	cConn, sConn, cErr, sErr := runHandshakeOverPipe(t,
+		&Config{LocalIdentity: clientID},
+		&Config{LocalIdentity: serverID},
+	)
+	if cErr != nil || sErr != nil {
+		t.Fatalf("handshake: %v / %v", cErr, sErr)
+	}
+	defer cConn.Close()
+	defer sConn.Close()
+
+	for i, msg := range [][]byte{[]byte("one"), []byte("two"), []byte("three")} {
+		wErr := make(chan error, 1)
+		go func() { _, e := cConn.Write(msg); wErr <- e }()
+		buf := make([]byte, len(msg))
+		if _, err := sConn.Read(buf); err != nil {
+			t.Fatalf("read %d: %v", i, err)
+		}
+		if err := <-wErr; err != nil {
+			t.Fatalf("write %d: %v", i, err)
+		}
+		if !bytes.Equal(buf, msg) {
+			t.Fatalf("msg %d: got %q want %q", i, buf, msg)
+		}
+	}
+}