[client] Improve rosenpass support (#6136)

* Updates rosenpass version

go-rosenpass v0.4.0 → v0.5.42 bump — detailed findings

Change summary
cunicu.li/go-rosenpass  v0.4.0  → v0.5.42   (target)
cilium/ebpf             v0.15.0 → v0.19.0   (transitive)
gopacket/gopacket       v1.1.1  → v1.4.0    (transitive)
wireguard               2023-07 → 2023-12   (transitive)
wireguard/wgctrl        2023-04 → 2024-12   (transitive)

Wire interop

v0.4.0 (in v0.70.5) <-> v0.5.42 OK
v0.5.42 <-> v0.5.42 OK

Quantum resistance: true both ends

---
**Replay error eliminated.**

Before (on v0.4.0):

`ERROR Failed to handle message: failed to load biscuit (ICR1): detected replay`

Recurring every ~50ms for minutes at a time. Gone entirely after both ends upgraded to v0.5.42. Upstream fix in biscuit/replay handling between v0.4.x and v0.5.x series.

* Fixup [::]:port socket trying to send to v4

* Adds more tests on netbird<->rosenpass interactions

* Anticipates rp handler creation before generateConfig

* [client] Moves deterministic key gen into rosenpass

* go mod tidy

* Adds reminder to reason about rosenpass surface area

* Apply code rabbit suggestions

client/internal/peer/conn.go

@@ -23,6 +23,7 @@ import (
 	"github.com/netbirdio/netbird/client/internal/peer/id"
 	"github.com/netbirdio/netbird/client/internal/peer/worker"
 	"github.com/netbirdio/netbird/client/internal/portforward"
+	"github.com/netbirdio/netbird/client/internal/rosenpass"
 	"github.com/netbirdio/netbird/client/internal/stdnet"
 	"github.com/netbirdio/netbird/route"
 	relayClient "github.com/netbirdio/netbird/shared/relay/client"
@@ -899,7 +900,7 @@ func (conn *Conn) presharedKey(remoteRosenpassKey []byte) *wgtypes.Key {
 	}
 
 	// Fallback to deterministic key if no NetBird PSK is configured
-	determKey, err := conn.rosenpassDetermKey()
+	determKey, err := rosenpass.DeterministicSeedKey(conn.config.LocalKey, conn.config.Key)
 	if err != nil {
 		conn.Log.Errorf("failed to generate Rosenpass initial key: %v", err)
 		return nil
@@ -908,26 +909,6 @@ func (conn *Conn) presharedKey(remoteRosenpassKey []byte) *wgtypes.Key {
 	return determKey
 }
 
-// todo: move this logic into Rosenpass package
-func (conn *Conn) rosenpassDetermKey() (*wgtypes.Key, error) {
-	lk := []byte(conn.config.LocalKey)
-	rk := []byte(conn.config.Key) // remote key
-	var keyInput []byte
-	if string(lk) > string(rk) {
-		//nolint:gocritic
-		keyInput = append(lk[:16], rk[:16]...)
-	} else {
-		//nolint:gocritic
-		keyInput = append(rk[:16], lk[:16]...)
-	}
-
-	key, err := wgtypes.NewKey(keyInput)
-	if err != nil {
-		return nil, err
-	}
-	return &key, nil
-}
-
 func isController(config ConnConfig) bool {
 	return config.LocalKey > config.Key
 }

client/internal/rosenpass/manager.go

@@ -28,6 +28,15 @@ func hashRosenpassKey(key []byte) string {
 	return hex.EncodeToString(hasher.Sum(nil))
 }
 
+// rpServer is the subset of rp.Server used by Manager. Defined as an interface
+// so tests can substitute a mock without spinning up a real UDP server.
+type rpServer interface {
+	AddPeer(rp.PeerConfig) (rp.PeerID, error)
+	RemovePeer(rp.PeerID) error
+	Run() error
+	Close() error
+}
+
 type Manager struct {
 	ifaceName    string
 	spk          []byte
@@ -36,7 +45,7 @@ type Manager struct {
 	preSharedKey *[32]byte
 	rpPeerIDs    map[string]*rp.PeerID
 	rpWgHandler  *NetbirdHandler
-	server       *rp.Server
+	server       rpServer
 	lock         sync.Mutex
 	port         int
 	wgIface      PresharedKeySetter
@@ -51,7 +60,22 @@ func NewManager(preSharedKey *wgtypes.Key, wgIfaceName string) (*Manager, error)
 
 	rpKeyHash := hashRosenpassKey(public)
 	log.Tracef("generated new rosenpass key pair with public key %s", rpKeyHash)
-	return &Manager{ifaceName: wgIfaceName, rpKeyHash: rpKeyHash, spk: public, ssk: secret, preSharedKey: (*[32]byte)(preSharedKey), rpPeerIDs: make(map[string]*rp.PeerID), lock: sync.Mutex{}}, nil
+	return &Manager{
+		ifaceName:    wgIfaceName,
+		rpKeyHash:    rpKeyHash,
+		spk:          public,
+		ssk:          secret,
+		preSharedKey: (*[32]byte)(preSharedKey),
+		rpPeerIDs:    make(map[string]*rp.PeerID),
+		// rpWgHandler is created here (instead of only in generateConfig) so it
+		// is never nil between NewManager and Run(). Otherwise an early
+		// OnConnected call (race observed on Android, issue #4341) panics on
+		// nil receiver in addPeer -> m.rpWgHandler.AddPeer. generateConfig will
+		// replace it with a fresh handler on each Run() to clear stale peer
+		// state from previous engine sessions.
+		rpWgHandler: NewNetbirdHandler(),
+		lock:        sync.Mutex{},
+	}, nil
 }
 
 func (m *Manager) GetPubKey() []byte {
@@ -65,6 +89,16 @@ func (m *Manager) GetAddress() *net.UDPAddr {
 
 // addPeer adds a new peer to the Rosenpass server
 func (m *Manager) addPeer(rosenpassPubKey []byte, rosenpassAddr string, wireGuardIP string, wireGuardPubKey string) error {
+	// Defense in depth against issue #4341 (Android crash): if Run() has not
+	// completed yet, m.server / m.rpWgHandler may be nil. Return an explicit
+	// error instead of panicking on nil-receiver dereference.
+	if m.server == nil {
+		return fmt.Errorf("rosenpass server not initialized")
+	}
+	if m.rpWgHandler == nil {
+		return fmt.Errorf("rosenpass wg handler not initialized")
+	}
+
 	var err error
 	pcfg := rp.PeerConfig{PublicKey: rosenpassPubKey}
 	if m.preSharedKey != nil {
@@ -79,6 +113,16 @@ func (m *Manager) addPeer(rosenpassPubKey []byte, rosenpassAddr string, wireGuar
 		if pcfg.Endpoint, err = net.ResolveUDPAddr("udp", peerAddr); err != nil {
 			return fmt.Errorf("failed to resolve peer endpoint address: %w", err)
 		}
+		// Our local Rosenpass UDP server binds on the IPv6 wildcard ([::]) — see
+		// GetAddress(). The remote peer's endpoint (pcfg.Endpoint) is the destination
+		// our server will sendto when initiating handshakes. ResolveUDPAddr returns a
+		// 4-byte IPv4 for IPv4 hosts, which the kernel rejects (EDESTADDRREQ) when
+		// sent from an AF_INET6 socket. Normalize the remote endpoint to IPv4-mapped
+		// IPv6 so its address family matches our listening socket.
+		// TODO: maybe bind the Rosenpass UDP server to the peer wg IP addr
+		if v4 := pcfg.Endpoint.IP.To4(); v4 != nil {
+			pcfg.Endpoint.IP = v4.To16()
+		}
 	}
 	peerID, err := m.server.AddPeer(pcfg)
 	if err != nil {
@@ -182,24 +226,31 @@ func (m *Manager) Run() error {
 		return err
 	}
 
-	m.server, err = rp.NewUDPServer(conf)
+	server, err := rp.NewUDPServer(conf)
 	if err != nil {
 		return err
 	}
 
+	m.lock.Lock()
+	m.server = server
+	m.lock.Unlock()
+
 	log.Infof("starting rosenpass server on port %d", m.port)
 
-	return m.server.Run()
+	return server.Run()
 }
 
 // Close closes the Rosenpass server
 func (m *Manager) Close() error {
-	if m.server != nil {
-		err := m.server.Close()
-		if err != nil {
-			log.Errorf("failed closing local rosenpass server")
-		}
-		m.server = nil
+	m.lock.Lock()
+	server := m.server
+	m.server = nil
+	m.lock.Unlock()
+	if server == nil {
+		return nil
+	}
+	if err := server.Close(); err != nil {
+		log.Errorf("failed closing local rosenpass server: %v", err)
 	}
 	return nil
 }

client/internal/rosenpass/manager_test.go

@@ -1,14 +1,412 @@
 package rosenpass
 
 import (
+	"errors"
+	"os"
+	"sync"
 	"testing"
 
+	rp "cunicu.li/go-rosenpass"
 	"github.com/stretchr/testify/require"
+	"golang.zx2c4.com/wireguard/wgctrl/wgtypes"
 )
 
+// --- test doubles -----------------------------------------------------------
+
+type addPeerCall struct {
+	cfg rp.PeerConfig
+}
+
+type removePeerCall struct {
+	id rp.PeerID
+}
+
+type mockServer struct {
+	mu         sync.Mutex
+	addCalls   []addPeerCall
+	removed    []removePeerCall
+	nextID     rp.PeerID
+	addErr     error
+	removeErr  error
+	closed     bool
+	ran        bool
+}
+
+func (m *mockServer) AddPeer(cfg rp.PeerConfig) (rp.PeerID, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.addCalls = append(m.addCalls, addPeerCall{cfg: cfg})
+	if m.addErr != nil {
+		return rp.PeerID{}, m.addErr
+	}
+	// Increment a byte in nextID so distinct peers get distinct IDs.
+	m.nextID[0]++
+	return m.nextID, nil
+}
+
+func (m *mockServer) RemovePeer(id rp.PeerID) error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.removed = append(m.removed, removePeerCall{id: id})
+	return m.removeErr
+}
+
+func (m *mockServer) Run() error  { m.ran = true; return nil }
+func (m *mockServer) Close() error { m.closed = true; return nil }
+
+type setPSKCall struct {
+	peerKey    string
+	psk        wgtypes.Key
+	updateOnly bool
+}
+
+type mockIface struct {
+	mu    sync.Mutex
+	calls []setPSKCall
+	err   error
+}
+
+func (m *mockIface) SetPresharedKey(peerKey string, psk wgtypes.Key, updateOnly bool) error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.calls = append(m.calls, setPSKCall{peerKey: peerKey, psk: psk, updateOnly: updateOnly})
+	return m.err
+}
+
+// newTestManager builds a Manager with deterministic spk so tie-break
+// against a peer pubkey is controllable from tests. The provided spk byte
+// becomes the first byte; remaining bytes are zero.
+func newTestManager(spkFirstByte byte, mock *mockServer) *Manager {
+	spk := make([]byte, 32)
+	spk[0] = spkFirstByte
+	return &Manager{
+		ifaceName:   "wt0",
+		spk:         spk,
+		ssk:         make([]byte, 32),
+		rpKeyHash:   "test-hash",
+		rpPeerIDs:   make(map[string]*rp.PeerID),
+		rpWgHandler: NewNetbirdHandler(),
+		server:      mock,
+	}
+}
+
+// validWGKey returns a deterministic 32-byte wireguard public key (base64).
+func validWGKey(t *testing.T, lastByte byte) string {
+	t.Helper()
+	var k wgtypes.Key
+	k[31] = lastByte
+	return k.String()
+}
+
+// --- pure helpers ----------------------------------------------------------
+
+func TestHashRosenpassKey_Deterministic(t *testing.T) {
+	key := []byte("hello-rosenpass")
+	require.Equal(t, hashRosenpassKey(key), hashRosenpassKey(key))
+	require.Len(t, hashRosenpassKey(key), 64) // sha256 hex
+}
+
+func TestHashRosenpassKey_DifferentInputsDifferOutputs(t *testing.T) {
+	require.NotEqual(t, hashRosenpassKey([]byte("a")), hashRosenpassKey([]byte("b")))
+}
+
+func TestGetLogLevel_DefaultWhenUnset(t *testing.T) {
+	// Snapshot + unset to exercise the LookupEnv ok=false branch. t.Setenv
+	// can only set, not delete, so do it manually with restore via t.Cleanup.
+	prev, hadPrev := os.LookupEnv(defaultLogLevelVar)
+	require.NoError(t, os.Unsetenv(defaultLogLevelVar))
+	t.Cleanup(func() {
+		if hadPrev {
+			_ = os.Setenv(defaultLogLevelVar, prev)
+		} else {
+			_ = os.Unsetenv(defaultLogLevelVar)
+		}
+	})
+	require.Equal(t, defaultLog.String(), getLogLevel().String())
+}
+
+func TestGetLogLevel_Cases(t *testing.T) {
+	cases := map[string]string{
+		"debug":   "DEBUG",
+		"info":    "INFO",
+		"warn":    "WARN",
+		"error":   "ERROR",
+		"unknown": "INFO", // default fallback
+	}
+	for input, wantStr := range cases {
+		input, wantStr := input, wantStr
+		t.Run(input, func(t *testing.T) {
+			t.Setenv(defaultLogLevelVar, input)
+			require.Equal(t, wantStr, getLogLevel().String())
+		})
+	}
+}
+
 func TestFindRandomAvailableUDPPort(t *testing.T) {
 	port, err := findRandomAvailableUDPPort()
 	require.NoError(t, err)
 	require.Greater(t, port, 0)
 	require.LessOrEqual(t, port, 65535)
 }
+
+// --- addPeer ---------------------------------------------------------------
+
+func TestAddPeer_HigherLocalPubkey_SetsEndpoint(t *testing.T) {
+	srv := &mockServer{}
+	m := newTestManager(0xFF, srv) // local spk lexicographically larger
+
+	remotePubKey := make([]byte, 32) // remote spk = all zeros (smaller)
+	err := m.addPeer(remotePubKey, "rosenpass-host:7000", "100.1.1.1", validWGKey(t, 1))
+	require.NoError(t, err)
+	require.Len(t, srv.addCalls, 1)
+
+	ep := srv.addCalls[0].cfg.Endpoint
+	require.NotNil(t, ep, "initiator side must set Endpoint")
+	require.Equal(t, 7000, ep.Port)
+	require.Equal(t, "100.1.1.1", ep.IP.String())
+}
+
+func TestAddPeer_HigherLocalPubkey_EndpointIPIsIPv4Mapped(t *testing.T) {
+	// Regression guard for the EDESTADDRREQ fix: Endpoint.IP must be 16-byte
+	// (IPv4-mapped IPv6) so it matches the AF_INET6 listening socket family.
+	srv := &mockServer{}
+	m := newTestManager(0xFF, srv)
+
+	err := m.addPeer(make([]byte, 32), "rp:5000", "100.1.1.1", validWGKey(t, 1))
+	require.NoError(t, err)
+
+	ep := srv.addCalls[0].cfg.Endpoint
+	require.NotNil(t, ep)
+	require.Len(t, ep.IP, 16, "IPv4 endpoint must be normalized to 16-byte v4-mapped form")
+	require.True(t, ep.IP.To4() != nil, "Endpoint must still be detected as IPv4")
+}
+
+func TestAddPeer_LowerLocalPubkey_LeavesEndpointNil(t *testing.T) {
+	srv := &mockServer{}
+	m := newTestManager(0x00, srv) // local spk smaller
+
+	remotePubKey := make([]byte, 32)
+	remotePubKey[0] = 0xFF
+	err := m.addPeer(remotePubKey, "rp:5000", "100.1.1.1", validWGKey(t, 2))
+	require.NoError(t, err)
+
+	require.Nil(t, srv.addCalls[0].cfg.Endpoint, "responder side must NOT set Endpoint")
+}
+
+func TestAddPeer_PresharedKeyPropagated(t *testing.T) {
+	srv := &mockServer{}
+	psk := &wgtypes.Key{0x42}
+	m := newTestManager(0xFF, srv)
+	m.preSharedKey = (*[32]byte)(psk)
+
+	err := m.addPeer(make([]byte, 32), "rp:5000", "100.1.1.1", validWGKey(t, 3))
+	require.NoError(t, err)
+	require.Equal(t, [32]byte(*psk), [32]byte(srv.addCalls[0].cfg.PresharedKey))
+}
+
+func TestAddPeer_InvalidRosenpassAddr_ReturnsError(t *testing.T) {
+	srv := &mockServer{}
+	m := newTestManager(0xFF, srv) // initiator path → parses rosenpassAddr
+
+	err := m.addPeer(make([]byte, 32), "not-a-host-port", "100.1.1.1", validWGKey(t, 1))
+	require.Error(t, err)
+	require.Empty(t, srv.addCalls, "server.AddPeer must not run when address parse fails")
+}
+
+func TestAddPeer_InvalidWireGuardPubKey_ReturnsError(t *testing.T) {
+	srv := &mockServer{}
+	m := newTestManager(0xFF, srv)
+
+	err := m.addPeer(make([]byte, 32), "rp:5000", "100.1.1.1", "not-a-valid-key")
+	require.Error(t, err)
+}
+
+func TestAddPeer_ServerError_Propagates(t *testing.T) {
+	srv := &mockServer{addErr: errors.New("boom")}
+	m := newTestManager(0xFF, srv)
+
+	err := m.addPeer(make([]byte, 32), "rp:5000", "100.1.1.1", validWGKey(t, 1))
+	require.Error(t, err)
+}
+
+// Regression guard for issue #4341 (Android crash). If Run() has not completed
+// before OnConnected fires, m.rpWgHandler or m.server may be nil. Without the
+// nil guards, m.rpWgHandler.AddPeer panics on nil receiver.
+func TestAddPeer_NilHandler_ReturnsErrorNoCrash(t *testing.T) {
+	srv := &mockServer{}
+	m := newTestManager(0xFF, srv)
+	m.rpWgHandler = nil // simulate Run() not yet completed
+
+	err := m.addPeer(make([]byte, 32), "rp:5000", "100.1.1.1", validWGKey(t, 1))
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "wg handler not initialized")
+}
+
+func TestAddPeer_NilServer_ReturnsErrorNoCrash(t *testing.T) {
+	m := newTestManager(0xFF, nil)
+	m.server = nil // simulate Run() not yet completed
+
+	err := m.addPeer(make([]byte, 32), "rp:5000", "100.1.1.1", validWGKey(t, 1))
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "server not initialized")
+}
+
+// NewManager must pre-initialize rpWgHandler so the nil-receiver crash from
+// issue #4341 cannot occur in the window between NewManager and Run().
+func TestNewManager_PreInitializesHandler(t *testing.T) {
+	psk := wgtypes.Key{}
+	m, err := NewManager(&psk, "wt0")
+	require.NoError(t, err)
+	require.NotNil(t, m.rpWgHandler, "rpWgHandler must be initialized in NewManager")
+}
+
+func TestAddPeer_RecordsPeerID(t *testing.T) {
+	srv := &mockServer{}
+	m := newTestManager(0xFF, srv)
+
+	wgKey := validWGKey(t, 5)
+	err := m.addPeer(make([]byte, 32), "rp:5000", "100.1.1.1", wgKey)
+	require.NoError(t, err)
+	require.Contains(t, m.rpPeerIDs, wgKey)
+}
+
+// --- OnConnected / OnDisconnected ------------------------------------------
+
+func TestOnConnected_NilRemotePubKey_NoAddPeer(t *testing.T) {
+	srv := &mockServer{}
+	m := newTestManager(0xFF, srv)
+
+	m.OnConnected(validWGKey(t, 1), nil, "100.1.1.1", "rp:5000")
+	require.Empty(t, srv.addCalls, "nil remote rosenpass pubkey must skip AddPeer")
+	require.Empty(t, m.rpPeerIDs)
+}
+
+func TestOnConnected_ValidPubKey_CallsAddPeer(t *testing.T) {
+	srv := &mockServer{}
+	m := newTestManager(0xFF, srv)
+
+	wgKey := validWGKey(t, 1)
+	m.OnConnected(wgKey, make([]byte, 32), "100.1.1.1", "rp:5000")
+	require.Len(t, srv.addCalls, 1)
+	require.Contains(t, m.rpPeerIDs, wgKey)
+}
+
+func TestOnDisconnected_UnknownPeer_NoOp(t *testing.T) {
+	srv := &mockServer{}
+	m := newTestManager(0xFF, srv)
+
+	m.OnDisconnected(validWGKey(t, 99))
+	require.Empty(t, srv.removed, "unknown peer key must not call RemovePeer")
+}
+
+func TestOnDisconnected_KnownPeer_CallsRemoveAndForgets(t *testing.T) {
+	srv := &mockServer{}
+	m := newTestManager(0xFF, srv)
+
+	wgKey := validWGKey(t, 1)
+	require.NoError(t, m.addPeer(make([]byte, 32), "rp:5000", "100.1.1.1", wgKey))
+	require.Contains(t, m.rpPeerIDs, wgKey)
+
+	m.OnDisconnected(wgKey)
+	require.Len(t, srv.removed, 1)
+	require.NotContains(t, m.rpPeerIDs, wgKey, "peer must be forgotten after disconnect")
+}
+
+// --- IsPresharedKeyInitialized ---------------------------------------------
+
+func TestIsPresharedKeyInitialized_UnknownPeer_ReturnsFalse(t *testing.T) {
+	srv := &mockServer{}
+	m := newTestManager(0xFF, srv)
+	require.False(t, m.IsPresharedKeyInitialized(validWGKey(t, 1)))
+}
+
+func TestIsPresharedKeyInitialized_AddedButNotHandshaken_ReturnsFalse(t *testing.T) {
+	srv := &mockServer{}
+	m := newTestManager(0xFF, srv)
+
+	wgKey := validWGKey(t, 2)
+	require.NoError(t, m.addPeer(make([]byte, 32), "rp:5000", "100.1.1.1", wgKey))
+	require.False(t, m.IsPresharedKeyInitialized(wgKey))
+}
+
+// --- NetbirdHandler.outputKey ----------------------------------------------
+
+func TestHandler_OutputKey_FirstCallUsesUpdateOnlyFalse(t *testing.T) {
+	h := NewNetbirdHandler()
+	iface := &mockIface{}
+	h.SetInterface(iface)
+
+	pid := rp.PeerID{0x01}
+	wgKey := wgtypes.Key{0xAA}
+	h.AddPeer(pid, "wt0", rp.Key(wgKey))
+
+	psk := rp.Key{0xBB}
+	h.HandshakeCompleted(pid, psk)
+
+	require.Len(t, iface.calls, 1)
+	require.False(t, iface.calls[0].updateOnly, "first PSK rotation must use updateOnly=false")
+	require.Equal(t, wgKey.String(), iface.calls[0].peerKey)
+}
+
+func TestHandler_OutputKey_SubsequentCallsUseUpdateOnlyTrue(t *testing.T) {
+	h := NewNetbirdHandler()
+	iface := &mockIface{}
+	h.SetInterface(iface)
+
+	pid := rp.PeerID{0x02}
+	h.AddPeer(pid, "wt0", rp.Key(wgtypes.Key{0xCC}))
+
+	h.HandshakeCompleted(pid, rp.Key{0x01}) // first
+	h.HandshakeCompleted(pid, rp.Key{0x02}) // second
+
+	require.Len(t, iface.calls, 2)
+	require.False(t, iface.calls[0].updateOnly)
+	require.True(t, iface.calls[1].updateOnly, "subsequent rotations must use updateOnly=true")
+}
+
+func TestHandler_OutputKey_NilInterface_NoCrashNoCall(t *testing.T) {
+	h := NewNetbirdHandler()
+	// no SetInterface — iface remains nil
+	pid := rp.PeerID{0x03}
+	h.AddPeer(pid, "wt0", rp.Key(wgtypes.Key{}))
+
+	// Must not panic.
+	h.HandshakeCompleted(pid, rp.Key{})
+}
+
+func TestHandler_OutputKey_UnknownPeer_NoCall(t *testing.T) {
+	h := NewNetbirdHandler()
+	iface := &mockIface{}
+	h.SetInterface(iface)
+
+	h.HandshakeCompleted(rp.PeerID{0xFF}, rp.Key{})
+	require.Empty(t, iface.calls, "unknown peer id must not trigger SetPresharedKey")
+}
+
+func TestHandler_RemovePeer_ClearsInitializedState(t *testing.T) {
+	h := NewNetbirdHandler()
+	iface := &mockIface{}
+	h.SetInterface(iface)
+
+	pid := rp.PeerID{0x04}
+	h.AddPeer(pid, "wt0", rp.Key(wgtypes.Key{0xDD}))
+	h.HandshakeCompleted(pid, rp.Key{0x01})
+	require.True(t, h.IsPeerInitialized(pid))
+
+	h.RemovePeer(pid)
+	require.False(t, h.IsPeerInitialized(pid), "RemovePeer must clear initialized flag")
+}
+
+func TestHandler_SetInterfaceAfterAddPeer_StillReceivesKey(t *testing.T) {
+	h := NewNetbirdHandler()
+	pid := rp.PeerID{0x05}
+	wgKey := wgtypes.Key{0xEE}
+	h.AddPeer(pid, "wt0", rp.Key(wgKey))
+
+	iface := &mockIface{}
+	h.SetInterface(iface) // set after AddPeer
+
+	h.HandshakeCompleted(pid, rp.Key{0x42})
+	require.Len(t, iface.calls, 1)
+	require.Equal(t, wgKey.String(), iface.calls[0].peerKey)
+}

client/internal/rosenpass/seed.go

@@ -0,0 +1,42 @@
+package rosenpass
+
+import (
+	"fmt"
+
+	"golang.zx2c4.com/wireguard/wgctrl/wgtypes"
+)
+
+// DeterministicSeedKey derives a 32-byte WireGuard preshared key from a pair
+// of peer public keys. Both peers, given the same key pair, produce the same
+// output regardless of which side runs the function: the inputs are ordered
+// lexicographically before concatenation.
+//
+// NetBird uses this value as the initial Rosenpass-side preshared key when no
+// explicit account-level PSK is configured, so both peers converge on the same
+// PSK before the first post-quantum handshake completes.
+//
+// The resulting key MUST NOT be treated as quantum-safe: it is deterministic
+// from public keys and exists only to seed WireGuard until Rosenpass rotates
+// in a real post-quantum PSK.
+func DeterministicSeedKey(localKey, remoteKey string) (*wgtypes.Key, error) {
+	lk := []byte(localKey)
+	rk := []byte(remoteKey)
+	if len(lk) < 16 || len(rk) < 16 {
+		return nil, fmt.Errorf("rosenpass: peer keys must be at least 16 bytes (got local=%d, remote=%d)", len(lk), len(rk))
+	}
+
+	var keyInput []byte
+	if localKey > remoteKey {
+		keyInput = append(keyInput, lk[:16]...)
+		keyInput = append(keyInput, rk[:16]...)
+	} else {
+		keyInput = append(keyInput, rk[:16]...)
+		keyInput = append(keyInput, lk[:16]...)
+	}
+
+	key, err := wgtypes.NewKey(keyInput)
+	if err != nil {
+		return nil, fmt.Errorf("rosenpass: deterministic seed key: %w", err)
+	}
+	return &key, nil
+}

client/internal/rosenpass/seed_test.go

@@ -0,0 +1,44 @@
+package rosenpass
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestDeterministicSeedKey_SameForBothSides(t *testing.T) {
+	// Peer A and peer B must derive the same PSK regardless of which side
+	// computes it: the function orders inputs internally.
+	a := strings.Repeat("a", 32)
+	b := strings.Repeat("b", 32)
+
+	keyAB, err := DeterministicSeedKey(a, b)
+	require.NoError(t, err)
+	keyBA, err := DeterministicSeedKey(b, a)
+	require.NoError(t, err)
+	require.Equal(t, keyAB.String(), keyBA.String(), "swapping arguments must yield identical key")
+}
+
+func TestDeterministicSeedKey_ChangesWithKeys(t *testing.T) {
+	a := strings.Repeat("a", 32)
+	b := strings.Repeat("b", 32)
+	c := strings.Repeat("c", 32)
+
+	keyAB, err := DeterministicSeedKey(a, b)
+	require.NoError(t, err)
+	keyAC, err := DeterministicSeedKey(a, c)
+	require.NoError(t, err)
+	require.NotEqual(t, keyAB.String(), keyAC.String(), "different peer pair must yield different key")
+}
+
+func TestDeterministicSeedKey_TooShortKey_ReturnsError(t *testing.T) {
+	short := "short" // < 16 bytes
+	long := strings.Repeat("x", 32)
+
+	_, err := DeterministicSeedKey(short, long)
+	require.Error(t, err)
+	_, err = DeterministicSeedKey(long, short)
+	require.Error(t, err)
+}
+