diff --git a/src/core/link.go b/src/core/link.go
index 9e0b15f..bc4f191 100644
--- a/src/core/link.go
+++ b/src/core/link.go
@@ -17,6 +17,7 @@ import (
 
 	"github.com/Arceliar/phony"
 	"github.com/yggdrasil-network/yggdrasil-go/src/address"
+	"golang.org/x/crypto/blake2b"
 )
 
 type linkType int
@@ -65,6 +66,7 @@ type linkOptions struct {
 	pinnedEd25519Keys map[keyArray]struct{}
 	priority          uint8
 	tlsSNI            string
+	password          []byte
 }
 
 type Listener struct {
@@ -129,6 +131,7 @@ func (e linkError) Error() string { return string(e) }
 const ErrLinkAlreadyConfigured = linkError("peer is already configured")
 const ErrLinkPriorityInvalid = linkError("priority value is invalid")
 const ErrLinkPinnedKeyInvalid = linkError("pinned public key is invalid")
+const ErrLinkPasswordInvalid = linkError("password is invalid")
 const ErrLinkUnrecognisedSchema = linkError("link schema unknown")
 
 func (l *links) add(u *url.URL, sintf string, linkType linkType) error {
@@ -166,6 +169,13 @@ func (l *links) add(u *url.URL, sintf string, linkType linkType) error {
 			}
 			options.priority = uint8(pi)
 		}
+		if p := u.Query().Get("password"); p != "" {
+			if len(p) > blake2b.Size {
+				retErr = ErrLinkPasswordInvalid
+				return
+			}
+			options.password = []byte(p)
+		}
 
 		// If we think we're already connected to this peer, load up
 		// the existing peer state. Try to kick the peer if possible,
@@ -351,6 +361,12 @@ func (l *links) listen(u *url.URL, sintf string) (*Listener, error) {
 		}
 		options.priority = uint8(pi)
 	}
+	if p := u.Query().Get("password"); p != "" {
+		if len(p) > blake2b.Size {
+			return nil, ErrLinkPasswordInvalid
+		}
+		options.password = []byte(p)
+	}
 
 	go func() {
 		l.core.log.Printf("%s listener started on %s", strings.ToUpper(u.Scheme), listener.Addr())
@@ -476,7 +492,10 @@ func (l *links) handler(linkType linkType, options linkOptions, conn net.Conn) e
 	meta := version_getBaseMetadata()
 	meta.publicKey = l.core.public
 	meta.priority = options.priority
-	metaBytes := meta.encode()
+	metaBytes, err := meta.encode(l.core.secret, options.password)
+	if err != nil {
+		return fmt.Errorf("failed to generate handshake: %w", err)
+	}
 	if err := conn.SetDeadline(time.Now().Add(time.Second * 6)); err != nil {
 		return fmt.Errorf("failed to set handshake deadline: %w", err)
 	}
@@ -489,7 +508,7 @@ func (l *links) handler(linkType linkType, options linkOptions, conn net.Conn) e
 	}
 	meta = version_metadata{}
 	base := version_getBaseMetadata()
-	if !meta.decode(conn) {
+	if !meta.decode(conn, options.password) {
 		return conn.Close()
 	}
 	if !meta.check() {
diff --git a/src/core/version.go b/src/core/version.go
index 0820fbd..e01fe10 100644
--- a/src/core/version.go
+++ b/src/core/version.go
@@ -8,7 +8,10 @@ import (
 	"bytes"
 	"crypto/ed25519"
 	"encoding/binary"
+	"fmt"
 	"io"
+
+	"golang.org/x/crypto/blake2b"
 )
 
 // This is the version-specific metadata exchanged at the start of a connection.
@@ -26,6 +29,8 @@ const (
 	ProtocolVersionMinor uint16 = 5
 )
 
+// Once a major/minor version is released, it is not safe to change any of these
+// (including their ordering), it is only safe to add new ones.
 const (
 	metaVersionMajor uint16 = iota // uint16
 	metaVersionMinor               // uint16
@@ -42,7 +47,7 @@ func version_getBaseMetadata() version_metadata {
 }
 
 // Encodes version metadata into its wire format.
-func (m *version_metadata) encode() []byte {
+func (m *version_metadata) encode(privateKey ed25519.PrivateKey, password []byte) ([]byte, error) {
 	bs := make([]byte, 0, 64)
 	bs = append(bs, 'm', 'e', 't', 'a')
 	bs = append(bs, 0, 0) // Remaining message length
@@ -63,12 +68,26 @@ func (m *version_metadata) encode() []byte {
 	bs = binary.BigEndian.AppendUint16(bs, 1)
 	bs = append(bs, m.priority)
 
+	hasher, err := blake2b.New512(password)
+	if err != nil {
+		return nil, err
+	}
+	n, err := hasher.Write(m.publicKey)
+	if err != nil {
+		return nil, err
+	}
+	if n != ed25519.PublicKeySize {
+		return nil, fmt.Errorf("hash writer only wrote %d bytes", n)
+	}
+	hash := hasher.Sum(nil)
+	bs = append(bs, ed25519.Sign(privateKey, hash)...)
+
 	binary.BigEndian.PutUint16(bs[4:6], uint16(len(bs)-6))
-	return bs
+	return bs, nil
 }
 
 // Decodes version metadata from its wire format into the struct.
-func (m *version_metadata) decode(r io.Reader) bool {
+func (m *version_metadata) decode(r io.Reader, password []byte) bool {
 	bh := [6]byte{}
 	if _, err := io.ReadFull(r, bh[:]); err != nil {
 		return false
@@ -81,6 +100,10 @@ func (m *version_metadata) decode(r io.Reader) bool {
 	if _, err := io.ReadFull(r, bs); err != nil {
 		return false
 	}
+
+	sig := bs[len(bs)-ed25519.SignatureSize:]
+	bs = bs[:len(bs)-ed25519.SignatureSize]
+
 	for len(bs) >= 4 {
 		op := binary.BigEndian.Uint16(bs[:2])
 		oplen := binary.BigEndian.Uint16(bs[2:4])
@@ -103,7 +126,17 @@ func (m *version_metadata) decode(r io.Reader) bool {
 		}
 		bs = bs[oplen:]
 	}
-	return true
+
+	hasher, err := blake2b.New512(password)
+	if err != nil {
+		return false
+	}
+	n, err := hasher.Write(m.publicKey)
+	if err != nil || n != ed25519.PublicKeySize {
+		return false
+	}
+	hash := hasher.Sum(nil)
+	return ed25519.Verify(m.publicKey, hash, sig)
 }
 
 // Checks that the "meta" bytes and the version numbers are the expected values.
diff --git a/src/core/version_test.go b/src/core/version_test.go
index 1c1f673..b71010f 100644
--- a/src/core/version_test.go
+++ b/src/core/version_test.go
@@ -3,33 +3,43 @@ package core
 import (
 	"bytes"
 	"crypto/ed25519"
-	"crypto/rand"
 	"reflect"
 	"testing"
 )
 
 func TestVersionRoundtrip(t *testing.T) {
-	for _, test := range []*version_metadata{
-		{majorVer: 1},
-		{majorVer: 256},
-		{majorVer: 2, minorVer: 4},
-		{majorVer: 2, minorVer: 257},
-		{majorVer: 258, minorVer: 259},
-		{majorVer: 3, minorVer: 5, priority: 6},
-		{majorVer: 260, minorVer: 261, priority: 7},
+	for _, password := range [][]byte{
+		nil, []byte(""), []byte("foo"),
 	} {
-		// Generate a random public key for each time, since it is
-		// a required field.
-		test.publicKey = make(ed25519.PublicKey, ed25519.PublicKeySize)
-		_, _ = rand.Read(test.publicKey)
+		for _, test := range []*version_metadata{
+			{majorVer: 1},
+			{majorVer: 256},
+			{majorVer: 2, minorVer: 4},
+			{majorVer: 2, minorVer: 257},
+			{majorVer: 258, minorVer: 259},
+			{majorVer: 3, minorVer: 5, priority: 6},
+			{majorVer: 260, minorVer: 261, priority: 7},
+		} {
+			// Generate a random public key for each time, since it is
+			// a required field.
+			pk, sk, err := ed25519.GenerateKey(nil)
+			if err != nil {
+				t.Fatal(err)
+			}
 
-		encoded := bytes.NewBuffer(test.encode())
-		decoded := &version_metadata{}
-		if !decoded.decode(encoded) {
-			t.Fatalf("failed to decode")
-		}
-		if !reflect.DeepEqual(test, decoded) {
-			t.Fatalf("round-trip failed\nwant: %+v\n got: %+v", test, decoded)
+			test.publicKey = pk
+			meta, err := test.encode(sk, password)
+			if err != nil {
+				t.Fatal(err)
+			}
+			encoded := bytes.NewBuffer(meta)
+			decoded := &version_metadata{}
+			if !decoded.decode(encoded, password) {
+				t.Fatalf("failed to decode")
+			}
+			if !reflect.DeepEqual(test, decoded) {
+				t.Fatalf("round-trip failed\nwant: %+v\n got: %+v", test, decoded)
+			}
 		}
 	}
 }