diff --git a/cmd/msa-keygen/main.go b/cmd/msa-keygen/main.go
index caed954..197f570 100644
--- a/cmd/msa-keygen/main.go
+++ b/cmd/msa-keygen/main.go
@@ -39,7 +39,7 @@ func main() {
 	flag.Parse()
 
 	// The signing key is Ed25519 for challenge-response at the relay and for signing responses.
-	_, signingKey, err := ed25519.GenerateKey(rand.Reader)
+	signingPublic, signingKey, err := ed25519.GenerateKey(rand.Reader)
 	check(err)
 	// The key-agreement key is raw X25519: clamping is the curve library's job, and a stored key
 	// that had already been clamped would be a second, non-standard encoding to keep in sync across
@@ -88,13 +88,25 @@ func main() {
 	check(err)
 	encoded = append(encoded, '\n')
 
+	// The relay registration carries the agent's *public* signing key as well as the bearer token.
+	// Both are required: the token is only an abuse-control handle, and the signature over the relay's
+	// challenge is what proves the caller holds the node's private key. A registration without the
+	// key makes the relay refuse to start rather than start and reject every node, which is the
+	// failure mode that shipped when the key was omitted.
+	registration, err := json.Marshal(map[string]string{
+		"nodeID":  id,
+		"token":   token,
+		"signKey": base64.StdEncoding.EncodeToString(signingPublic),
+	})
+	check(err)
+
 	if *write == "" {
 		// The relay's own registration is printed alongside, because the two files have to agree on
 		// the node id and token and copying them by hand is where that agreement breaks.
 		fmt.Fprintf(os.Stderr, "# agent config (paste into %s, then add \"nodePassword\" if the node is protected)\n", "/etc/msa-agent/config.json")
 		os.Stdout.Write(encoded)
 		fmt.Fprintf(os.Stderr, "\n# relay registration: add this entry to MSA_AGENTS\n")
-		fmt.Fprintf(os.Stderr, "{\"nodeID\":%q,\"token\":%q}\n", id, token)
+		fmt.Fprintf(os.Stderr, "%s\n", registration)
 		fmt.Fprintf(os.Stderr, "\n# pairing secret (unprotected nodes only; protected ones use nodePassword): %s\n", pairingSecret)
 		fmt.Fprintf(os.Stderr, "# next: run `msa-agent --pair` on the node once, then pair the phone from the app\n")
 		return
@@ -107,7 +119,7 @@ func main() {
 		check(err)
 	}
 	fmt.Printf("wrote %s (mode 0600)\n", *write)
-	fmt.Printf("relay registration: {\"nodeID\":%q,\"token\":%q}\n", id, token)
+	fmt.Printf("relay registration: %s\n", registration)
 }
 
 func randomHex(bytes int) string {